IRRADIATION TO ENSURE
THE SAFETY AND QUALITYOF PREPARED MEALSThe Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of
the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957.
The Headquarters of the Agency are situated in Vienna. Its principal objective is “to accelerate andenlarge the contribution of atomic energy to peace, health and prosperity throughout the world’’.

.

IRRADIATION TO ENSURE
THE SAFETY AND QUALITYOF PREPARED MEALSRESULTS OF THE COORDINATED RESEARCH PROJECTORGANIZED BY THE JOINT FAO/IAEA DIVISION OF
NUCLEAR TECHNIQUES IN FOOD AND AGRICULTURE (2002–2006)

INTERNATIONAL ATOMIC ENERGY AGENCY
VIENNA, 2009

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STI/PUB/1365

IAEA Library Cataloguing in Publication Data
Irradiation to ensure the safety and quality of prepared meals. — Vienna :International Atomic Energy Agency, 2009.
p. ; 24 cm.
STI/PUB/1365
ISBN 978–92–0–111108–1
Includes bibliographical references.
1. Radiation preservation of food.
I. International Atomic Energy Agency.
VICL

2. Food safety measures.
09–00560

FOREWORD
The consumption of prepared meals has increased enormously during thelast decade, not only in developed countries but also in developing countries
where many types of ethnic foods are now also prepared as convenience foods.
Consumer studies carried out on the consumption of these types of foods haveshown that perceived time pressures contribute positively to the purchase ofboth prepared meals and takeaway meals. Other reasons are also mentioned in
the literature, among them are the increasing proportion of working women
outside of the home, not enjoying cooking for oneself and the need of family
members to eat at different times.
Traditionally, prepared meals are retort processed, or, more recently,
stored frozen, whereas an increasing demand exists for chilled commodities,
partly due to their fresh appearance. However, the chilled prepared meals are
non-sterile and potential survival of some pathogenic microorganisms and/or
post-processing contamination before packaging creates microbiological risks
and a considerable limitation of shelf life. This is particularly important for
countries where the microbiological safety of many ethnic prepared meals isquestionable and their shelf life limited due to the conditions under which they
are produced, stored and distributed.
Food irradiation used on its own, or in combination with othertechnologies, could significantly enhance the microbial safety of such products
as well as extend their shelf life. Although extensive research has been carriedout on the microbiological, chemical, nutritional and sensorial effects ofirradiating individual uncooked food items, little work has been reported on
the irradiation of complex food systems such as prepared meals.
In 2002, the Joint FAO/IAEA Division of Nuclear Techniques in Foodand Agriculture initiated in a Coordinated Research Project on Irradiation to
Ensure the Safety and Quality of Prepared Meals. This project included thestudies of participants from different regions of the world. In total, more than
50 different prepared meals were investigated. This publication presents theresults of studies conducted over a five year period (2002–2006) on the safety,
shelf life and overall quality of the meals stored under ambient, chilled orfrozen conditions.
Special thanks are due to J. Farkas and C. Mohácsi-Farkas who assisted in
finalizing this manuscript for publication. The IAEA officer responsible forselecting the participants and organizing the first research coordination
meeting in Vienna was P. Loaharanu. The officer responsible for subsequent
follow-up of the project, as well as the preparation of this publication, wasT. Rubio-Cabello of the Joint FAO/IAEA Division of Nuclear Techniques inFood and Agriculture.

EDITORIAL NOTE
Although great care has been taken to maintain the accuracy of information
contained in this publication, neither the IAEA nor its Member States assume any
responsibility for consequences which may arise from its use.
The use of particular designations of countries or territories does not imply any
judgement by the publisher, the IAEA, as to the legal status of such countries or territories,of their authorities and institutions or of the delimitation of their boundaries.
The mention of names of specific companies or products (whether or not indicatedas registered) does not imply any intention to infringe proprietary rights, nor should it beconstrued as an endorsement or recommendation on the part of the IAEA.

CONTENTS
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Safer prepared meals for immunocompromised patients and the general
consumer by gamma irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
P. Narvaiz, C. Horak, M. Campos, P. Veronesi, E. Cossani,
L. Lound, A. Gasparovich, G. Liendo, J. Hovsepian, G. Mengoni
Irradiation of prepared meals for microbiological safety and shelf
life extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J. Nketsia-Tabiri, A. Adu-Gyamfi, F. Apea Bah
Part I: Improvement of the microbiological safety of two chilledsemi-prepared meals by gamma radiation . . . . . . . . . . . . . . . . . . . . . .
J. Farkas, É. Andrássy, L. Mészáros, K. Polyák-Fehér, J. Beczner,
Ö. Gaál, V.K. Lebovics, A. Lugasi
Part II: Effects of gamma irradiation on lipid and cholesterol oxidation
in mechanically deboned turkey meat . . . . . . . . . . . . . . . . . . . . . . . . . .
J. Farkas, É. Andrássy, L. Mészáros, K. Polyák-Fehér, J. Beczner,
Ö. Gaál, V.K. Lebovics, A. Lugasi

1

29

53

81

95

Part III: Comparing observed growth of selected test organisms in foodirradiation studies with growth predictions calculated by
ComBase softwares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
J. Farkas, É. Andrássy, L. Mészáros, K. Polyák-Fehér, J. Beczner,
Ö. Gaál, V.K. Lebovics, A. Lugasi
Radiation processing to ensure the safety and quality of ethnic
prepared meals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
A. Sharma, R. Chander, S.P. Chawla, S.R. Kanatt, V.S. Dhokne,
A.S. Bawa
Irradiation to ensure the safety and quality of some ethnic soups,
snacks and Yunan chicken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Z. Irawati, Harsojo, C.M. Nurcahya, F. Anas, L. Natalia
Part I: Hazard, sensorial and economic implications of applying thehazard analysis and critical control points to irradiated
ready-to-eat meals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Y.F. Haruvy

Part II: Utilization of the methodology for irradiation of ethnic
ready-to-eat meals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Y.F. Haruvy
Microbial inactivation and shelf life extension of Korean traditional
prepared meals by irradiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
C. Jo
Use of irradiation to improve the safety and quality of ethnic
South African foods
Part I: Combined edible coating and irradiation treatment on
sensory and microbiological quality of moist beef biltong . . . . . . . . . 219
A. Minnaar, K. Nortjé, A.M.A. Parry-Hanson, E.M. Buys
Use of irradiation to improve the safety and quality of ethnic
South African foods
Part II: Effect of gamma irradiation on the sensory andmicrobiological quality of ready-to-eat bovine tripe . . . . . . . . . . . . . . 231
A. Minnaar, K. Nortjé, A.M.A. Parry-Hanson, E.M. Buys
Effect of gamma irradiation on the microbial load and chemical andsensory properties of locally prepared fast meals . . . . . . . . . . . . . . . . 245
M. Al-Bachir
Use of irradiation to improve the safety and quality of Thai prepared
meals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
A. Noomhorm, T. Koomsanit, K. Pungsawat, T. Theamhong,W. Srisawas, P. Sirisoontaralak, P. Vongsawasdi, A. Vitittheeranon
Effect of gamma irradiation on the quality of ready meals and theirmeat components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
E.M. Stewart
Consumers’ willingness to pay for irradiated prepared ground beef . . . . . 343
R.M. Nayga, Jr., R. Woodward, W. Aiew
ANNEX I: BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
ANNEX II: ADDITIONAL READING . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
LIST OF PARTICIPANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

SUMMARY1.

INTRODUCTION

The prepared convenience foods sector has become a significant part ofthe economy of many developed countries, with a similar trend evolving indeveloping countries, where many types of ethnic foods are now also prepared
as convenience foods. For example, the prepared convenience foods sector in
Ireland is a significant part of the Irish economy. In 2001, just under half of thesector’s total output was exported for a value of €841 million, representing a
12% annual increase. The sector’s strong growth both in exports and in total
sales has made it one of the fastest growing sectors of the food industry in many
countries.
Consumer studies carried out on convenience foods have shown thatperceived time pressures contribute positively to the purchase of both preparedand takeaway meals. Other reasons found to contribute positively to thepurchase of prepared meals include the convenience of not cooking for oneself,
a value for money perception of convenience foods and different eating times
of family members. With rapid urbanization and change in socioeconomic
status, and an ever increasing proportion of working women, the tendencies are
similar in developing countries.
Traditionally, prepared meals are retort processed or, more recently,
stored frozen, whereas an increasing demand exists for chilled commodities,
partly due to their fresh appearance, which is more appealing to the consumer
than canned or frozen meals. Freezing and retort processing are also moreenergy demanding. Chilled prepared foods, however, are non-sterile andpotential survival of some pathogenic microorganisms and/or post-processing
contamination before packaging create microbiological risks and experience a
considerable shortening of shelf life. For example, in Germany, a survey of
prepared cooked meat products showed an incidence rate of 3.7% for Listeria
monocytogenes. In the ethnic Korean food, kimbab, Salmonella spp.1 is found insome instances, especially in the summer2.

1

NOACK, D.J., JOECKEL, J., Listeria monocytogenes: Occurrence and significance in meat and meat products and experience with recommendation for its detection
and assessment, Fleischwirtschaft 73 (1993) 581–584.
2
KANG, Y.S., et al., Prevalence of Staphylococcus aureus in kimbab, J. Food
Hygiene Safety 19 (2002) 35–44.

1SUMMARY

Even frozen foods are not necessarily safe if already contaminated bypathogenic bacteria. This safety problem is even more aggravated in the case ofchilled foods, which are more vulnerable to temperature abuse or instabilities
in the ‘cold chain’. This can result in the growth of psychrotrophic pathogens. In
addition to this problem, chilled prepared meals have a limited shelf life underchilling conditions, thereby limiting the geographical area in which they can bemarketed. Therefore, technologies that will improve their microbiologicalsafety, while extending the shelf life, are required.
As a consequence of the increased national and international interest in
the marketing of convenience and prepared foods, the food industry needs tofind new ways of producing safe and high quality prepared meals. One
technology with a particular potential to achieve these objectives is foodirradiation.
It is thought that research into the application of ionizing radiation to
products such as prepared meals could be of ultimate benefit to consumers,
industry and trade. This is particularly important for countries where the microbiological safety of many ethnic prepared meals is questionable and their shelf
life limited due to the conditions under which they are produced, stored anddistributed. Food irradiation used on its own or in combination with othertechnologies could significantly enhance the microbial safety of such products
as well as extending shelf life. This is of special importance for the mostvulnerable individuals in society, such as the immunocompromised. It isestimated that this group comprises 20% of the total world population,
whether they are hospitalized or not.
Although extensive research has been carried out on the microbiologicaland sensorial effects of irradiating individual uncooked food items, little work
has been reported on the irradiation of complex food systems such as prepared
meals. In this coordinated research project (CRP), the potential of using
irradiation technology for convenience foods has been investigated with regard
to safety, shelf life and overall quality, particularly in terms of sensory
acceptance. A wide range of ethnic meals, as well as meal components, were
investigated with the objective of meeting continual changes in consumer
demand worldwide.
Other aspects of the CRP included the adoption of a hazard analysis
critical control point (HACCP) system for prepared meals and research into
consumer willingness to purchase irradiated food at a premium price. The
scope of the CRP was therefore wide ranging.
The overall objective of this CRP was to evaluate the effectiveness ofirradiation as a method of ensuring the microbiological safety and extending
the shelf life of prepared meals, stored under ambient, chilled or frozen
conditions, and to evaluate the sensory quality of the treated products.

2

SUMMARY

The specific objective of the CRP was to use validated procedures forirradiation treatment and process control, and to use validated methods forassessing microbiological safety and quality as well as the sensory quality of
prepared meals, mainly of ethnic origin.

2.

ACHIEVEMENTS

2.1. General achievements
The participants carried out research into more than 50 different
prepared meals. Table 1 summarizes the dishes investigated as well theircomposition, intrinsic qualities and the analyses carried out in order todetermine their overall safety and quality.
2.1.1. Animal based prepared meals
The efficacy of radiation processing for the microbiological safety andquality of more than 30 prepared meals with beef, chicken, pork, mutton or
prawns as a major component was investigated (Table 1). The meals included
cannelloni, empanadas, sandwiches (ham and cheese), chicken pie, soups,
Yunan chicken, Thai spicy chicken, poached chicken, chicken chilli, chicken
masala, bulgogi, galbi, kubba, borak, sheesh tawoq, prawn pulao and khichadi.
The optimum gamma radiation doses were found to be in the range of 2–4 kGy
for a majority of the meals in order to achieve microbiological safety and thedesired sensory quality. Challenge studies with pathogens such as Escherichia
coli, L. monocytogenes, Staphylococcus aureus and Salmonella spp., revealed
that doses employed eliminated the test organisms, thus demonstrating
improvement in the microbiological safety of these products. In general, theshelf life of the meals was extended from one week to more than three weeks atchilled temperatures, depending upon the characteristics of the meals. No
significant changes were observed with regard to physical and chemical
properties such as pH, water activity and lipid peroxidation of the meals. There
was no significant difference in the overall acceptability of the meals at the
optimal doses of gamma radiation. In addition, it was found that using natural
antioxidants such as vitamin C, vitamin E and flavonoids (quercetin,
epicatechin and resveratrol) could enhance the quality of the meat componentof irradiated meals by successfully reducing the occurrence of oxidative
rancidity. Shelf life studies conducted at abuse temperatures emphasized theimportance of maintaining the ‘cold chain’ during production and storage ofirradiated prepared meals.

3SUMMARY

TABLE 1. PREPARED MEALS/MEAL COMPONENTS STUDIEDCountry

Animal based products

Vegetable/fruit based
products/miscellaneous

Argentina

Cannelloni
Empanadas
Sandwich (ham and cheese)
Chicken pie
Eggs (hard boiled)

Salad
Fruit salad
Custard
Bread pudding
Fruit based dessert

Ghana

Poached chicken meal
Beef tripe (with jollof rice)Fried fish (with waakye)

Jollof rice (rice cooked intomato sauce)
Waakye (co-boiled rice andcowpeas, and vegetable salad)

Hungary

Cordon bleu (reconstituted turkey
meat with cheese and ham)Filled pasta products (tortellini)

India

Prawn masala
Prawn pulao
Mutton shami kebabs
Chicken chilli
Chicken biryani
Prawn pulao

Poha (made from rice pressed
into flakes)
Upma (cooked semolina/
cracked wheat and spices)
Mixed vegetables
Rice
Vegetable pulao
Khichadi (cereal/legume gruel)Indonesia

Black soupOxtail soup
Chicken vegetable soup
Chicken sweetcorn soup
Yunan chicken

Croquette
RisolleSpring rolls

Republic of
Korea

Bulgogi (cooked beef withvegetables)
Galbi (marinated beef ribs)

Kimbab (cooked rice rolledin dried seaweed)
Kimchijumeokbab (cookedrice mixed with fermented
vegetables and fried pork)

South Africa

Beef biltong
Ready-to-eat bovine tripe

Syrian Arab
Republic

Kubba (spicy mince coated withground wheat)
Borak (lamb in dough/cheesein dough)
Sheesh tawoq (spicy, bonelesschicken)4

SUMMARY

TABLE 1. PREPARED MEALS/MEAL COMPONENTS STUDIED (cont.)
Country

Animal based products

ThailandThai spicy chicken basil rice(kao ka pao kai)Stir fried rice noodle with dried
shrimp (pad Thai)
Steamed sticky rice with roasted
chicken and papaya salad(kao neaw som tom)United Kingdom

Chicken masala
Minced beef patties
Salmon meat patties

Vegetable/fruit based
products/miscellaneous

2.1.2. Vegetable–fruit based prepared meals and miscellaneous meals
Radiation processing of two of the most popular vegetarian meals
consumed in India, namely vegetable pulao and mixed vegetables, was standardized. These samples were found to be contaminated by potentiallypathogenic bacteria such as S. aureus and spoiled within two weeks. Contrary tothis, no viable bacterial growth was observed in samples treated with gamma
radiation (2 kGy) up to 30 d in storage. It was concluded that these meals
treated with 2 kGy were microbiologically safe, with a shelf life of a month.
This would be a significant advantage to processors, retailers and consumers.
Studies carried out showed that some of the vegetable based preparations, including fruit salad, custard and bread pudding, could be decontaminated by radiation processing for immunocompromised patients. A dessert
composed of fresh apples and pear cubes mixed with strawberry flavoured
gelatine jelly and soft white cheese, packaged in polypropylene and refrigerated at 5°C, was successfully decontaminated by 1.5 kGy of gamma radiation,
attaining a 3 log cycle reduction in total bacteria counts (TBCs) with acceptablesensory quality throughout a week of storage, which doubled its shelf life. A
Salmonella enteritidis challenge test showed that this dose was sufficient to
reduce its counts by 6 log cycles, which ensured a good level of safety.
Gamma radiation of a carrot, hard boiled egg and tomato salad at a doseof 2 kGy, packaged in polypropylene, covered with PVC film and stored at 5°C
was sufficient to attain a 6 log cycle reduction in S. enteritidis counts. The TBCs
were reduced by 3 or 4 log cycles with few detrimental effects on sensory
quality.

5

SUMMARY

The sensory quality of cooked rice irradiated at more than 2 kGy was
found to be unacceptable in terms of texture and colour. For steamed sticky
rice, a dose of 3 kGy was enough to control L. monocytogenes and E. coli
during chilled storage when stored for more than 8 weeks. Doses of 4 kGy arerecommended for stir-fried rice noodles with sauces and dry shrimp. Similar
results were obtained for jollof rice, 3 kGy extended its shelf life under chilledstorage for 28 d without significant effects on its sensory quality.
Gamma irradiation with doses of 5–7 kGy of four frozen soups whichwere vacuum packaged within laminated pouches of polyester/aluminium foil/
LLDPE and made of different basic materials, having moisture contents
between 69 and 86%, could reduce microbial load by 2 or 3 log cycles andextend the shelf life to 3 months at 5 ± 2°C, without impairing sensory quality.
A challenge test result indicated that 5–7 kGy doses were sufficient to reduce
the population of Clostridium sporogenes by 6 or 7 log cycles.
2.2. Additional achievements
In addition to the general achievements, some participants carried out
studies on the following issues:• Predictive microbiological modelling;• HACCP;• Consumer studies;• Studies with immunocompromised patients.
2.2.1. Predictive microbiological modelling
As a result of intensive predictive microbiological modelling activities,
several computer programs and software became available recently for facilitating microbiological risk assessment. Among these tools, the establishment of
ComBase, an international database and its predictive modelling softwares of
the Pathogen Modelling Program (PMP) set up by the USDA Eastern
Regional Research Center and the Food Micromodel/Growth Predictor by theUnited Kingdom’s Institute of Food Research have been the most important.
Under the CRP, the PMP 6.0 software version of ComBase was used for apreliminary trial to compare observed growth of selected test organisms in
relation to irradiated food studied under previous FAO/IAEA coordinatedfood irradiation research projects (D6.10.23 and D6.20.07). The results ofchallenge tests with L. monocytogenes inoculum in untreated or irradiatedexperimental batches of semi-prepared breaded turkey meat steaks (cordon
bleu), sliced tomatoes, sliced watermelon, sliced cantaloupe and sous vide

6

SUMMARY

processed mixed vegetables, as well as S. aureus inoculum of a pasta product,
tortellini, were compared with their respective growth models under relevant
environmental conditions. This comparison showed good fits in the case of nonirradiated and high moisture food samples, whereas growth of radiation
survivors lagged behind the predicted values. Further progress in this CRP andincreasing efforts to invest in the automation of microbiological measurements
and the development of systematically organized databases for the collected
data would be of great interest.
2.2.2. HACCPThe objective of the work was to introduce a modified HACCP based
analysis for irradiated prepared meals that addresses potential safety hazards,
as well as sensorial failures, and economic risks, while pin-pointing failuremodes specific to the radiation pasteurization aspects. The analysis covered all
production inputs and stages, and all foreseen failure modes related to thephysical, chemical and biological hazards of the prepared meals: raw materials,
packaging and prepared meals. A practical 10 step approach to implement thesuggested modified HACCP plan, from comprehensive analysis to validated
protocol, was further provided. At the final stage of this study, a collaborative
HACCP was carried out on the ethnic foods of Indonesia as an example ofthese specific types of food. Approaching the industrial stage of safe prepared
meals was further assessed in this study. In view of the currently accelerating
consumer demand and industrial production of prepared meals andconvenience foods, the multistage approach to ingredient safety seems
preferred from safety, sensory, irradiation and economic perspectives. With
proper orchestration of the radiation stages within the production chain, it
would achieve better food quality and safety and at the same time use lessradiation, in two or more stages.
2.2.3. Consumer studies
The objective of the consumer studies was to assess and evaluate
consumers’ perceptions, acceptance and willingness to pay for irradiatedground beef patties. Determining consumers’ willingness to pay a premium forirradiated food products is important because this is a major factor that would
determine the potential marketability and success of the product. In addition,
food irradiation adds to the costs of production and these costs must be capableof being covered by the price premium before any food manufacturer orretailer will consider selling the irradiated product. Studies carried out using
both survey and experimental economics methodologies generally suggest that7

SUMMARY

information about the nature of food irradiation technology increases
consumer acceptance of irradiated prepared and processed ground beef. The
research findings also indicated that consumers are willing to pay a premiumfor irradiated ground beef. Most of the participants also conducted consumer
sensory evaluation tests to establish acceptability of these irradiated prepared
meals.
2.2.4. Study with immonocompromised patients
Regarding the experience with immunocompromised patients, it was
concluded that ionizing radiation, in combination with good manufacturing
practices and refrigeration, improve their feeding quality as more diversification is allowed, with both nutritional and psychological benefits. The level ofmicrobial decontamination attained would afford offering highly desired
unusual meals to these persons, without risk of foodborne diseases. Besides,
nutritionists were satisfied with the results obtained because the shelf life
extension due to irradiation would allow, in the future, a reasonable flow ofmeals provided to a hospital by a catering service, for instance, once a week,
without the food losing its fresh nutritive condition in consequence ofovercooking or freezing.
This was the first approach carried out in Argentina between immunocompromised patients and food irradiation. Much more work should beundertaken to widen meal variety and to publicize this method to other
patients, health institutes, catering services and supermarkets.

3.

SUMMARY OF RESULTS

A summary of the products studied, their composition, intrinsic qualities
and the results of analyses are given in Table 2, while an overall summary of theeffect of irradiation on the safety, shelf life and quality of the products listed inTables 1 and 2 is presented in Table 3.

8

Argentina

Country*

Wheat bread, butter, mayonaise,
ham and cheese
Wheat dough wrapping, chicken
and vegetable fillings

Sandwiches

Pies

S. typhimurium

L. monocytogenes

S. enteritidis

L. monocytogenes,
S. typhimurium

Fresh apples, pears, commercial
strawberry gelatine, soft cheese

Fruit salad ingelatine withwhite cheese

S. enteritidis

Bread pudding

Wheat dough wrapping (raw)Filling: boiled chicken breast,vegetables

Empanadas

S. enteritidis

L. innocua

Microbiological
Overall acceptability
using a 9 point
hedonic scale

Sensorial

Chemical/physical

Safety and quality parameters

S. typhimurium

Grated carrot
Whole cherry tomatoes,
hard boiled egg

Salad

pH,
water activity

Intrinsic
parameters

Custard

Wheat dough wrapping (raw)Filling: cooked spinach, veal meat,cheeseComposition of prepared meal(s)Cannelloni intomato sauce

Prepared meal(s)studiedTABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED

SUMMARY

9

10

Mechanicallydeboned turkey
meat

Pre-fried, irradiated slices/steaksof reconstituted turkey meat filledwith slices of ham and cheese

Cordon bleu

14 different commerciallyavailable airline meals

HACCP preparedready-to-eat
meals

Pasta filled with meat/vegetables

Co-boiled rice and cowpeas

WaakyeTortellini

Rice cooked in tomato sauce

Jollof rice

Hungary

Chicken, rice, carrots

Poached chicken
meat

Ghana

Composition of prepared meal(s)Prepared meal(s)studiedCountry

As abovepH,water activity

As above

As abovepH,water activity

Intrinsic
parameters

TBC,
enterobacteria
count

TBC, lactic acidbacteria,
L. monocytogenes,
Clostridia

TBC,
S. aureus

TBC, total
coliforms,
Salmonella/
Shigella,yeasts and moulds

TBC, total
coliforms, yeasts
and moulds

Total viable count,
Salmonella spp.,
S. aureus, E. coli,
yeasts and moulds,
Shigella

Total viable count,E. coli, S. aureus

Microbiological

As above

Hedonic scores,
ranking tests

Descriptive sensory
analyses

Triangle test, overall
acceptability using a
9 point hedonic scale

Sensorial

TBARS
Cholesteroloxidation products

TBARS

Thiamine

FFA
Peroxide value

FFA

Chemical/physical

Safety and quality parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARY

Beef, Pangium edule, shallot,
garlic, roasted coriander, red chilli,ginger, lemon leaf, roasted fish
paste, turmeric, ginger root, lemon
grass, Kaempferia galanga, salt,
palm sugar, bay leaf, palm oil,water
Oxtail, shallot, garlic, salt, palmoil, water, onion, nutmeg, cloves,white pepper, onion leaf, celery,margarineBlack soupOxtail soupIndonesia

Vegetables, chicken, rice, prawns,
garlic, ginger paste

Prawn masala
Prawn pulao
Mutton shami
kebabsChicken chilli
Chicken biryani
Prawn pulao
Khichadi (cereal/
legume gruel)
Poha
Upma
Mixed vegetables
Rice
Vegetable pulao

India

Composition of prepared meal(s)Prepared meal(s)studiedCountry
TBC,
S. aureus, B. cereus,
L. monocytogenes,
faecal coliforms,
yeasts and moulds,
aerobic spore
count

TBC,
yeasts and moulds,
coliforms, E. coli,
Salmonella spp.,
S. aureus,
C. perfringens

pH, fat,carbohydrate,
proteinMicrobiological

Overall acceptability
using a 5 point
hedonic scale

Overall acceptability
using a 10 point
hedonic scale

Sensorial
TBARS

Chemical/physical

Safety and quality parameterspH,water activity

Intrinsic
parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARY

11

12Country

Composition of prepared meal(s)Chicken, shallot, garlic, salt, water,
nutmeg, white pepper, onion leaf,
celery, margarine, sugar, carrot,
green beans, broccoli, sugar peas
Chicken, salt, water, nutmeg,
sweetcorn, chicken sausage,
carrot, egg, cornstarch
Wheat based sheet filled withcooked shrimps and chicken as
well as vegetables (including
young bamboo shoots)
Wheat based sheet filled withcooked chicken, vegetables
Potato based sheet filled with beefand vegetablesSpecially salted chicken,
marinated in herbs and spices(cooked in a steamer)

Prepared meal(s)studied

Chicken andvegetable soup

Chickensweetcorn soupSpring rolls

RisolleCroquette

Yunan chicken
As above plus
water activity

As above plus
water activity

As above plus
water activity

As above plus
water activity

Intrinsic
parameters
MicrobiologicalSensorial

Thiamine,
peroxide value

Chemical/physical

Safety and quality parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARYOxtail, shallot, garlic, salt, palmoil, water, onion, nutmeg, cloves,white pepper, onion leaf, celery,margarine
Chicken, shallot, garlic, salt, water,
nutmeg, white pepper, onion leaf,
celery, margarine, sugar, carrot,
green beans, broccoli, sugar peas
Chicken, salt, water, nutmeg,
sweetcorn, chicken sausage,
carrot, egg, cornstarch

Oxtail soup

Chicken andvegetable soup

Chickensweetcorn soup

Croquette

RisolleSpring rolls

Beef, football fruit (P. edule),
shallot, garlic, roasted coriander,
red chilli, ginger, lemon leaf,
roasted fish paste, turmeric, ginger
root, lemon grass, spice(K. galanga), salt, palm sugar,
bay leaf, palm oil, waterBlack soupIsraelComposition of prepared meal(s)Prepared meal(s)studiedCountry
HACCP
parameters

Intrinsic
parameters
HACCP
parameters

Microbiological
HACCP
parameters

Sensorial
HACCP
parameters

Chemical/physical

Safety and quality parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARY

13

14

Syrian Arab
Republic

Ground wheat, beef, spices, lamb,onion, fat, pistachio

Dough, eggs, lamb, onion, spices
Dough, eggs, cheese
Spicy, boneless chicken

Borak

Cheese borak

Sheesh tawoq

Beef tripe

Ready-to-eat
bovine tripe

Kubba

Salted, dried, intermediatemoisture meat productBiltong

Cooked rice mixed with fermented
vegetables and fried pork

Kimchijumeokbab

South Africa

Cooked rice rolled in dried laver(seaweed)

Bulgogi
Galbi
Kimbab

Republic of
Korea

Composition of prepared meal(s)Prepared meal(s)studiedCountry

Moisture, fat,ash, protein,water activity,
pH

Moisture,
NaCl, water
activity, fat,pH

pH, water
activity

Intrinsic
parameters

TBC, coliforms,
yeasts and moulds,
Salmonella spp.,
E. coliC. perfringens

S. aureus

TBC

Thermophilic
bacteria, coliforms,
S. aureus, E. coli,
S. typhimurium,
B. cereus,
Listeria ivanovii,
TBC

Microbiological

Overall acceptability
using a 5 point
hedonic scale

9 point hedonic scaleMultiple difference
testing
Overall acceptability
using a 9 point
hedonic scale

Overall acceptability
using a 9 point
hedonic scale

Sensorial

Lipid oxidation,
TVBN, total acidity
Proximateanalyses

TBARS

TBARS,
DPPH, proteaseactivity

Chemical/physical

Safety and quality parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARY

Salmon meat
patties

Beef patties

Chicken, onion, tomato, water,
yoghurt, coconut, red pepper,
tomato puree, rapeseed, oilmodified starch, coriander leaf,salt, ginger, cayenne pepper, malt
extract, turmeric

Sticky rice, roasted chicken andpapaya salad

Kao neaw som
tomChicken masalaStir-fried rice noodle with dried
shrimpPad Thai

UnitedKingdom

Cooked rice, chicken, vegetableoil, chilli, fish sauce, water, basil
leavesKao ka pau kai

ThailandComposition of prepared meal(s)Prepared meal(s)studiedCountry
Moisture, pH

Intrinsic
parameters

TBC,
Pseudomonas spp.,
psychrotrophs,
anaerobic spores

TBC,
Pseudomonas spp.,
psychrotrophos,
lactic acid bacteria,
coliforms

L. monocytogenes,
E. coli

L. monocytogenes,
E. coli

L. monocytogenes,
E. coli,S. typhimurium

Microbiological
Overall acceptability
using a 9 point
hedonic scale

Sensorial

CIELAB colour
measurements
Addition ofnaturalantioxidants

TBARS
CIELAB colour
measurements
Addition ofnaturalantioxidants

TBARS,
vitamins B1 and E,
cyclobutanone(EN1786)

Instrumental
texture analyses
Laboratory colour
measurements

Chemical/physical

Safety and quality parameters

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARY15

16

Ground beef
patties

UnitedStates ofAmerica

Beef

Composition of prepared meal(s)Consumerdemand andacceptanceparameters

Intrinsic
parameters

Chemical/physical323Prepared meal(s)studiedCannelloni intomato sauce

Salad

Empanadas

Country

Argentina

Effective
irradiation dose(kGy)

Aerobic

Aerobic

Aerobic

Packagingconditions

5±2

5±2

5±2

Temperatureof storage(ºC)

L. innocua(S. enteritidis)

L. innocua(S. enteritidis)

L. innocua(S. enteritidis)

Inoculated pathogens(surrogates)

The irradiation treatment rendered a
microbiologically safe and sensoriallyacceptable prepared meals studied atleast 8 storage days at refrigeration
temperatures (shelf life extended atleast threefold).

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED

Consumer demand
and acceptanceparameters

Sensorial

Safety and quality parameters
Microbiological

Additional to TBC, mould and yeast counts, spore forms, anaerobes, Salmonella spp., S. aureus, coliforms.
POV: total volatile basic nitrogen, DPPH: 1,1-diphenyl-2-picrylhydrazyl, FFA: free fatty acids.

*

Prepared meal(s)studiedCountry

TABLE 2. SUMMARY OF SAFETY AND QUALITY PARAMETERS STUDIED (cont.)

SUMMARYGhanaCountry

4

Bread pudding

3

3

Custard

Jollof rice withbeef tripe and
sauce

3.5

Pies

3

2.5

Sandwiches

Poached chicken

1.5

Effective
irradiation dose
(kGy)

Fruit salad ingelatine withwhite cheese

Prepared meal(s)studiedAerobic

Aerobic

Aerobic

Aerobic

Aerobic

Aerobic

Packagingconditions

3–5

3–5

5±2

5±2

5±2

5±2

5±2

Temperatureof storage(ºC)

E. coli(D10 = 0.17 kGy)
S. aureus(D10 = 0.26 kGy)
Salmonella spp.
(D10 = 0.29 kGy)

E. coli(D10 = 0.19 kGy)
S. aureus(D10 = 0.27 kGy)

L. monocytogenes
ATCC 15313(S. enteritidis
ATCC 13076)(S. typhimurium)

L. monocytogenes
ATCC 15313

L. monocytogenes
ATCC 15313(S. enteritidis)

Inoculated pathogens(surrogates)

Eliminated test pathogens
From 7 d (control) to 21 d at 3–5ºC

Eliminated test pathogens
From 7 d (control) to 21 d at 3–5ºC

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

17

18

India

HungaryCountry2

3

Cordon bleu
(water activity =0.96, pH = 6.2–6.3)

Tortellini(water activity =0.96, pH = 5.5–6.1)

L. monocytogenes 4ab
No.10(D10 ~ 0.80 kGy)
S. aureus ATCC 6538
(D10 < 0.80 kGy)

5–9

15

S. aureus ATCC 6538P(D10 = 0.37 kGy)
B. cereus MTCC 470(D10 = 0.47 kGy)

Mutton shami
kebabs0–3

E. coli(D10 = 0.27 kGy)
S. aureus(D10 = 0.33 kGy)
Salmonella spp.
(D10 = 0.44 kGy)

Inoculated pathogens(surrogates)

27–32

Temperatureof storage(ºC)

S. aureus ATCC 6538P(D10 = 0.37 kGy)
B. cereus MTCC 470(D10 = 0.47 kGy)

Aerobic

MAP (20%
CO2 + 80% N2)

MAP (20%
CO2 + 80% N2)

Packagingconditions

Chicken chilli

33

Waakye with fried
fish, vegetablesalad and tomato
sauce

Prawn masala

Effective
irradiation dose(kGy)

Prepared meal(s)studiedShelf life extended to at least 2 weeks
at 0–3ºC

Pathogens eliminated(L. monocytogenes, S. aureus, E. coli,
Salmonella)Less than 2 weeks (control) to 4 weeks
at 15ºC

From 1 week (control) to 2 weeks at 9ºC

From 2 weeks (control) to 4 weeks
at 5ºC

Shelf life studies not conducted

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

Indonesia

Country

Chickensweetcorn soup

Chicken andvegetable soupOxtail soup

Black soup

Vegetable pulao

Rice

Mixed vegetables

Upma

Poha

Khichadi (cereal/
legume gruel)

Chicken biryani

Prawn pulao

Prepared meal(s)studied

5–7(irradiatedunder cryogenic
conditions)2

Effective
irradiation dose(kGy)

Vacuumpackaged inlaminatedpouch(anaerobic)

Aerobic

Packagingconditions

5±2

0–3

Temperatureof storage(ºC)
Inoculated pathogens(surrogates)

Pathogens eliminated (E coli,
Staphylococcus spp., C. perfringens)
Irradiation extended the shelf life up to
3 months at 5 ± 2ºC

Pathogens eliminated(L. monocytogenes, S. aureus, E. coli,
Salmonella)
Shelf life extended to at least 4 weeks
at 0–3ºC

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

19

20Country

3–7

5–7

3–5

Croquette

Yunan chicken

7

Effective
irradiation dose(kGy)

RisolleSpring rolls

Prepared meal(s)studiedPackagingconditions

Temperatureof storage(ºC)(S. typhimurium)(D10 = 0.28 kGy)
Pseudomonas aeruginosa(D10 = 0.17 kGy)
E. coli 0157
(D10 = 0.12 kGy)
Campylobacter spp.
(D10 = 0.09 kGy)
L. monocytogenes(D10 = 0.66 kGy)

Inoculated pathogens(surrogates)

Test pathogens eliminated byirradiation
From 6 weeks (control) to 9 weeks(3 and 5 kGy) at 5 ± 2ºC

Pathogens eliminated (E coli,
Staphylococcus spp., C. perfringens)
Irradiation extended the shelf life up to
3 months at 5 ± 2ºC

Pathogens eliminated (E. coli,
Staphylococcus spp., C. perfringens)
Irradiation extended the shelf life up to
3 months at 5 ± 2ºC

Pathogens eliminated (E. coli,
Staphylococcus spp., C. perfringens)
Microbiological shelf life: 1 month at
5 ± 2ºC
Sensory quality not acceptable after
irradiation due to textural defect inyoung bamboo shootImprovement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

3

Kimchijumeokbab

Galbi

1

2.5–5

Bulgogi

Republic of
Korea

Kimbab2.5

Prepared meal(s)studiedCountry

Effective
irradiation dose(kGy)

Aerobic

Aerobic

Aerobic(but vacuum
recommended)

Aerobic

Packagingconditions

10

10

0–5

0–5

Temperatureof storage(ºC)

S. aureus KCTC 1916
(D10 = 0.31 kGy)
E. coli KCTC 1682
(D10 = 0.42 kGy)
(S. typhimurium) KCTC
(D10 = 0.44 kGy)
L. ivanovii KCTC 3444
(D10 = 0.43 kGy)

B. cereus KCTC 1012
(D10 = 0.66 kGy)
S. aureus KCTC 1916
(D10 = 0.59 kGy)
E. coli KCTC 1682
(D10 = 0.54 kGy)
(S. typhimurium) KCTC
(D10 = 0.63 kGy)

Inoculated pathogens(surrogates)

From 12 h (control) to 36 h (3 kGy)
at 10ºC

Eliminated all tested pathogens
From 12 h (control) to 36 h (1.0 kGy)
at 10ºC

Eliminated all inoculated pathogens
From 2 weeks (control) to 4 weeks(2.5 kGy) at 0–5ºC

Eliminated B. cereus, coliforms
From 2 weeks (control) to 4 weeks(2.5 kGy)

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

21

22
4–6
4–6

Kubba

Borak

Anaerobic(boil before
vacuumpackaging)

9

Syrian Arab
Republic

Aerobic(boil after
packaging)

9

Ready-to-eat
bovine tripe

Aerobic

Aerobic

Vacuum4

Biltong(water activity =0.979, pH = 5.32)

South
AfricaPackagingconditions

Prepared meal(s)studiedCountry

Effective
irradiation dose
(kGy)

0–4

0–4

5
15

5
15

Ambient

Temperatureof storage(ºC)

Salmonella spp.
(D10 = 0.47 kGy)
E. coli(D10 = 0.51 kGy)

C. perfringens ATCC 13124

S. aureus ATCC 9441

Inoculated pathogens(surrogates)

Elimination of pathogens
From less than 1 week (control)
to 3 weeks at 4 kGy and at least 5 weeks
at 6 kGy

From less than 1 week (control)
to 3 weeks at 4 or 6 kGy

Shelf life of irradiated samples at least
7 d at both 5 and 15ºC
Control sample spoils after 4 d at 15ºC

No C. perfringens after irradiation but
survival of heat and irradiation resistantaerobic spore formers
Extends shelf life to at least 2 weeks atboth 5 and 15ºC
Control sample spoils after 3 days at
15ºC
Elimination of test pathogen

Eliminated test pathogen

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARYThailand

Country2
1
4

3– cooked chicken– basil leaves

Pad Thai– cooked rice
noodle– sauce and dry
shrimp– cooked rice2

4–6

Sheesh tawoq

Kao ka pau kai

4–6

Effective
irradiation dose
(kGy)

Cheese borak

Prepared meal(s)studiedAerobic

Aerobic

Aerobic

Packagingconditions

5

0–4

0–4

Temperatureof storage(ºC)

L. monocytogenes(D10 = 0.49 kGy)
E. coli(D10 = 0.68 kGy)

L. monocytogenes(D10 = 0.29 kGy)
E. coli(D10 = 0.69 kGy)

L. monocytogenes
S. typhimurium

L. monocytogenes
E. coli

Salmonella spp.
(D10 = 0.30 kGy)
E. coli(D10 = 0.50 kGy)

Inoculated pathogens(surrogates)

From 2 weeks (control) to at least
4 weeks

Up to 2 weeks at 5ºC after irradiation

Cooked rice: from 2 weeks (control) to
atleast 4 weeks at 5ºC

Cooked rice: from 2 weeks (control) toat least 4 weeks at 5ºC

From 12 weeks (control) to at least
20 weeks (4 and 6 kGy)

Elimination of pathogens
From less than 1 week (control)
to 2 weeks at 4 kGy to at least 6 weeks
at 6 kGy

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

23

24

UK

Country

Chicken masala

L. monocytogenes(D10 = 0.23 kGy)
E. coli(D10 = 0.44 kGy)

L. monocytogenes(D10 = 0.33 kGy)
E. coli(D10 = 0.15 kGy)

Inoculated pathogens(surrogates)– papaya salad3

Temperatureof storage(ºC)

L. monocytogenes(D10 = 0.51 kGy)
E. coli(D10 = 0.52 kGy)

Aerobic

Packagingconditions– roasted chicken

2–3

4

Kao neaw som tom– sticky rice

Effective
irradiation dose(kGy)

Prepared meal(s)studiedShelf life of 14 d achieved with noadverse effect on vitamins B1 or E.
Irradiation easily detectable using
2-alkylcyclobutanone method(EN1786)

From 2 weeks (control) to at least
8 weeks

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

Country

Salmon meat
patties

Beef patties

Prepared meal(s)studiedOverwrapped

Overwrappedwith cling film

2.5

2.5

Vacuumpacked inpolyethylene
bags

Packagingconditions

2.5

Effective
irradiation dose
(kGy)

3

3

Temperatureof storage(ºC)
Inoculated pathogens(surrogates)

Addition of the flavonoid antioxidants
quercetin, epicatechin and reveratrol
can reduce oxidative rancidity
throughout shelf life.

Addition of the flavonoid antioxidants
quercetin, epicatechin and reveratrol
can reduce oxidative rancidity
throughout shelf life.

Total viable counts reduced to below
limit of detection by irradiation over
21 d storage period. Oxidative rancidity
increased with storage but maintainedat acceptable levels for sensory quality
by 2.5 kGy up to 21 d.

During the 21 d post-irradiation, total
viable counts were reduced/maintained
at low levels in vacuum packs.
Oxidative rancidity maintained at
acceptable levels for sensory quality
although appearance is poor until
patties allowed to ‘bloom up’ in anoxygen atmosphere prior to use.

Improvement in safety/shelf life

TABLE 3. SUMMARY OF THE EFFECTS OF IRRADIATION ON THE SAFETY, SHELF LIFE AND QUALITY OF
PRODUCTS STUDIED (cont.)

SUMMARY

25

SUMMARY

4.

CONCLUSIONSThe CRP demonstrated that radiation processing of prepared meals
results in safer food by eliminating pathogens and extending the shelf life bydecreasing the number of spoilage organisms without significantly jeopardizing
the overall quality. However, the work also highlighted the complexity andtechnological challenges of using radiation processing for multicomponent
food systems such as prepared meals.
The safety of radiation processed products was demonstrated using
challenge tests/inoculated pack studies using various pathogenic test organisms
or their surrogates. Such products could satisfy or fulfil several niche markets.
However, the proper storage temperature and maintenance of the cold chain
are crucial factors for food safety and stability. Oxidative changes are
sometimes enhanced by radiation treatment but it has been demonstrated thatsuch changes can be counteracted by employing proper packaging conditions
and using efficient antioxidant additives.
The implementation of a HACCP substantially reduced microbial counts,
although some potential pathogens survived. Although the HACCP planrequires that the ready meals were held at 0 to –5ºC in order to suppress growthof survivors, the latter could proliferate during temperature abuse when power
outages occur.
Strict hygiene practices during the manufacture of prepared meals are a
prerequisite for the successful application of irradiation in order to ensure
product safety, quality and extended shelf life.
In view of the insight gained about the quality changes that occur in theirradiated foods investigated under this CRP and the emerging needs ofconsumers (e.g. functional qualities of foods in relation to nutrition and health)further research activities are necessary.
In view of the increasing trend in consumer demand for safe preparedfoods, the importance in the use of radiation pasteurization is likely to increasein the future. This was confirmed by the consumer studies carried out in theUSA, the results of which were reported during the course of this CRP.
Provision of information about the nature of food irradiation increases
consumer acceptance and willingness to pay a premium for enhanced productsafety and quality.
As a result of extensive predictive microbiological modelling activities
during the last two decades, several computer programs and software became
available recently for facilitating microbiological risk assessment. After
validation of their satisfactory predictability, such softwares would be
worthwhile to use because they offer efficient tools for risk estimation for

26

SUMMARY

selected marketing scenarios and microbiological ecological parameters/stressfactors in foods, thereby decreasing the necessity for very costly challenge tests.
This technology could potentially be advantageous for consumers, food
manufacturers and traders worldwide as the foods are safer, have extended
shelf lives and are high quality. The use of this technology would also make itpossible to give a safer and wider variety of meals to specific target groups suchas immunocompromised patients, as was shown by one of the participants.
Radiation treatment thereby offers the opportunity for a wider utilizationand marketing of such high quality meals, including many ethnic food products.

5.

RECOMMENDATIONSWhen using any new food processing technology for complex foodsystems such as prepared meals, it is important to consider the requirements interms of both product and process parameters to obtain the desired safety andquality effects. The oversimplified attitude of employing ionizing radiation as atechnology to pasteurize an existing industrial meal product is often inadequate
to meet the goals of extended shelf life and improved safety. The meal should
be modified, first to extend its sensorial shelf life (e.g. texture) regardless ofbacterial growth, and then pasteurized by irradiation. In particular, shelf lifechanges relating to conversion of bound water into free water adversely affectthe sensorial quality of high moisture foods (e.g. dumplings). These ageing
effects should be minimized by the use of appropriate additives for that
purpose.
Radiation pasteurization is particularly advantageous as the final
processing step, applied to the packed and sealed prepared meal. Nonetheless,the ‘bioburden’ of the ingredients in the early stages of meal preparation canmost often be reduced by alternative methods, which may be advantageous to
specific foods. This attitude includes a pretreatment of radiation disinfection of
specific ingredients of high bioburden. Thus, the radiation dose at the final
stage, which affects all the ingredients, can be substantially lowered, resulting in
improved sensorial quality and, just as important, economic profitability.
The efficacy of radiation treatment should be tested/validated under
actual commercial conditions, since microbial growth might be greatly
facilitated under more or less abusive temperature conditions which may
frequently occur in the food chain and during home storage prior toconsumption.
Suitable packaging material and processes, as well as adequate storage
conditions, are prerequisites for successful deployment of this technology.

27

SUMMARY

Regulatory approval for new radiation pasteurized prepared meal
products is critical, both legally and economically, since it is crucial to allow
their market testing and consequent marketing as soon as their development iscomplete. Hence, it is strongly recommended that care be taken of all legal
aspects of the petitions for new products as soon as completion of theirdevelopment seems viable. New concepts, such as multistage irradiation (rawmaterial decontamination and end product treatment), should receive properconsideration by the regulatory authorities.
In conjunction with technological development, market and economic
studies are crucial to successful commercialization of irradiated prepared
meals.
Alongside the continuing research and development in this field, relevant
agencies should disseminate information and assist technology transfer tofacilitate the proper utilization of the knowledge gathered during CRPs such as
this one. They could also offer neutral and precompetitive support of suchknowledge for the common good of all the relevant stakeholders, including
regulators of food irradiation. In such meaningful technology transfer,comparisons of relative advantages and/or disadvantages of alternativetechnologies should always be considered.
It is essential to provide a solid scientific foundation for a wider
application of the knowledge gained from this CRP. Hence international
cooperative research efforts are needed for further implementing thetechnology.

6.

PUBLICATIONS

A list of the publications to date resulting from the research work carriedout under this CRP is given in Annex I.

28

SAFER PREPARED MEALS FORIMMUNOCOMPROMISED PATIENTSAND THE GENERAL CONSUMERBY GAMMA IRRADIATION
P. NARVAIZ, C. HORAK, M. CAMPOSNational Atomic Energy Commission (CNEA),
Buenos Aires Province
P. VERONESI, E. COSSANI, L. LOUND, A. GASPAROVICHNational Entre Ríos University, Gualeguaychú,
Entre Ríos Province
G. LIENDO, J. HOVSEPIAN
Belgrano University, Buenos Aires
G. MENGONI
Lister Laboratory,
La Plata, Buenos Aires Province
Argentina

Abstract
Ready-to-eat meals are commonplace nowadays in urban life. Many of them,minimally processed, could convey foodborne pathogens likely to cause diseases in the
consumer, which is of concern to the normal population and even more so to immunocompromised patients. The feasibility of attaining microbiological decontamination at
pasteurization levels of such foods by gamma irradiation was studied. Typical Argentine
dishes were chosen after market surveys: cannelloni in tomato sauce, tomato and carrot
salad with boiled egg, empanada, fruit salad in gelatin jelly with white cheese, ham andcheese sandwich, chicken and vegetable pie, custard, and bread pudding, in different
packaging. Microbiological profiles of the meals were obtained and challenge tests with
Listeria innocua or Salmonella enteritidis were performed to determine the minimum
radiation dose to be applied in each food so as to attain a 6 log cycle reduction ofpathogen counts. Preliminary sensory evaluations, out of panel, were carried out todetermine possible evident sensory alterations due to the irradiation treatment. Then, agreater number of samples were irradiated at the minimum radiation dose and at a
maximum dose equal to or less than twice the minimum, at the 60Co semi-industrial
facility of the Ezeiza Atomic Center. Microbiological and sensory analyses by aconsumer panel were performed on control and irradiated samples throughout storage

29

NARVAIZ et al.

life at refrigeration temperatures. A whole irradiated lunch, composed of salad,empanadas and fruit salad, was sampled by 44 immunocompromised patients at a
hospital. The composition and adequacy of this lunch was designed by nutritionists.
Results showed that it was feasible to attain the proposed decontamination goal without
significantly impairing the sensory quality. Shelf life was almost tripled in irradiatedsamples. Immunocompromised patients enjoyed the irradiated lunch and requested it
and other dishes to be made commercially available.

1.

INTRODUCTION

The present lifestyle in cities leads to little time for cooking, so many
ready-to-eat meals are available in supermarkets. Among them, canned foods
do not fulfil the present preference for freshness and nutritional value which
the consumers demand. Others are stored under frozen or refrigerated
conditions, most of them being minimally processed, which enhances theprobability of conveying foodborne pathogens. This is of particular importanceto the immunocompromised patients, whose natural defences against diseases
are low.
Data from the Regional System of Epidemiologic Watchfulness(SIRVETA), developed by the Panamerican Institute for Food Protection andZoonoses (Pan American Health Organization), indicate 152 foodborne
disease outbreaks in Argentina between 1993 and 2002, representing 3309 ill
persons and four deaths. The corresponding figures for the whole region (Latin
America and the Caribbean) are 6324 of such outbreaks, 228 579 ill persons,314 deaths. It must also be recalled that only a few per cent of cases are
generally reported.
In Argentina, the National System of Epidemiological Watchfulness(SINAVE) [1] reported 67 outbreaks during 2001, with 1237 ill persons
involved. These outbreaks corresponded to 15 geographical regions, out of a
total of 35. Homes were the places with the biggest prevalence for theseoutbreaks to take place (63.3%). The remaining 36.7% of outbreaks happened
at collective places (institutions, restaurants, community canteens). The agents
responsible were, in most cases, Salmonella spp. and Escherichia coli, followed,
not very closely, by Staphylococcus aureus and Clostridia. The main foods
causing this were, in decreasing order, various meats, prepared meals, water,
milk products, filled pasta and eggs.
Few data are available to demonstrate the effectiveness of irradiation to
improve the microbiological safety and quality of many types of prepared
meals currently being marketed either under ambient, chilled or frozen
conditions. A previous study in Argentina [2] showed promising results for30

NARVAIZ et al.

some irradiated ready-to-eat meals for immunocompromised patients, which
would allow their diets to be enriched with fresh produce or minimallyprocessed foods, more nutritious and palatable but usually forbidden becauseof the risk of foodborne diseases. Some conclusions of that work were that thetested variety of meals should be widened. Also, and as an example, somestudies carried out at the Clinical Hospital José de San Martín in Buenos Aires[3] indicate that because of the slow distribution of lunch or supper within theinstitution, the meals arrive at the patient’s bed lukewarm or even cold, which
enhances the probability of microbial growth.
The response of some ready-to-eat meals, widely consumed by theArgentine population, under ionizing radiation processing was studied in thiswork. Their usual commercial manufacture includes several steps in which
original or cross-contamination with pathogenic microorganisms, provided
either by the raw food materials, the environment or the personnel, can occur[4, 5]. Ionizing radiation has proven effective in controlling pathogen risk,
which both protects the consumer and benefits the producer owing to shelf life
extension [6–18]. This is especially important for the immunocompromised
population [19–27].
Among the list of known non-spore pathogenic microorganisms likely tocontaminate these ready-to-eat foods, Listeria was generally chosen forchallenge tests because of its being widespread, feasible of growing at refrigeration temperatures, and because it is possibly the most radiation resistant inthis group. In some other cases and according to the food product, Salmonella
was chosen instead.
Besides the microbiological safety, the chemical quality of these irradiated
ready-to-eat meals had to be evaluated. According to the literature, nutritional
stability at these radiation doses was considered to be fairly well established [28–33], but as organoleptic changes could take place sensory analyses were
performed to indicate potential consumer acceptability in the future.

2.

MATERIALS AND METHODS

The main brand supermarkets in Argentina, along with various foodchains and retailers, were visited in order to find the most popular meals
offered which could benefit from irradiation treatment. At least four varietiesof each product, sourced from different suppliers, were initially sampled by apanel of six persons in order to choose the best manufacturer. Selection was
carried out on the basis of parameters such as food quality, packaging andradiation dose, so as to minimize sensory damage after treatment. Selected
meals and their characteristics are summarized in Table 1.

31

32

Water, wheat flour, cooked
veal, fresh spinach, grated
Provolone cheese,pasteurized egg, sodium
chloride, sodium glutamate,ground nutmeg
Sauce: canned tomato puree,
fried onion, dehydrated
marjoram

Raw grated carrot, raw
whole cherry tomatoes, hardboiled egg

Fresh apples, pears, orange
juice, gelatin powder,strawberry flavour, Punzo
Red colourant, water, whitecheeseSalad

Fruit salad

Ingredients

Cannelloni

Meal

Polystyrene
containers withlid

Polypropylene
trays, covered
with PVC film

Polystyrene
containers withlid

Packaging

Manufacturer

Nutrition students at thelaboratory
High quality commercial
brand

Nutrition students at thelaboratory

Factory of a national goodquality brand which
distributes its products
widely in Argentina. They
were specially manufactured
for this experience without
the addition of potassium
sorbate as a preservative

TABLE 1. CHARACTERISTICS OF SELECTED MEALSRaw Granny Smith apples
and Packam pears, peeledand cut into cubes, were
soaked in fresh orange juice

Good manufacturing
practices were performed

Samples were cooked insidetheir closed packaging in a
General Electric microwave
oven (model Je 1831) for
6 min at level 4

Comments on
manufacturing
and cooking

3d

2d

5d
(commercial
presentation,
without sauce)

Estimated
shelf life
under
refrigeration

NARVAIZ et al.

Water, wheat flour,
margarine, vegetable oil, egg
yolk, cooked ham, EdamcheesePasta discs: water, wheat
flour, margarine
Filling: onion, tomato, milk,
chicken broth, chicken
breast, fresh capsicum,
sodium chloride, sodium
propionate

Pie

Ingredients

Sandwich

Meal

Pie portions were
packaged into
aluminium foil
recipes with lid

Polystyrene tray
covered with
PVC film

Packaging

Supermarket

Supermarket

Manufacturer

TABLE 1. CHARACTERISTICS OF SELECTED MEALS (cont.)

Filling placed between two
thin, wheat flour pasta discs,
25 cm diameter, one at thebase and the other on the
top. The wrapping of thesediscs, to avoid filling losses, ishandmade. They are usuallysold already cooked
Reheated in gas oven at
220°C for 6 min, lid half
openedThree thin, spongy, flat white
wheat bread layers, which
had been covered on one
side with a fat mixture madeof mayonnaise andmargarine, and contained aslice of cooked ham andanother of Edam cheese
between layers

Comments on
manufacturing
and cooking

2d

2d

Estimated
shelf life
under
refrigeration

NARVAIZ et al.

33

34

Milk, sugar, egg, vanillaessence

Bread (preferably one dayold), milk, sugar, egg, grated
lemon peel, vanilla essenceBreadpudding

Ingredients

Custard

Meal

Portions were
packaged intopolystyrene
container with lid

Aluminium foil
covered with
PVC film

Packaging

Pastry commercial chain

Supermarket

Manufacturer

TABLE 1. CHARACTERISTICS OF SELECTED MEALS (cont.)
Comments on
manufacturing
and cooking

4d

2d

Estimated
shelf life
under
refrigeration

NARVAIZ et al.

NARVAIZ et al.

Irradiation was carried out on one-day-old samples, at the semi-industrial
Co facility of the Ezeiza Atomic Center, using 1.1 × 1010 MBq of activity, at adose rate of 0.15 kGy/min. Doses were measured with silver dichromate [34].
Samples were placed into polystyrene boxes containing cooling bags to ensure
maintaining refrigeration temperature during treatment. These boxes wererotated after half the irradiation time to ensure a homogenous dose distribution. Some other samples were kept as controls and not irradiated. Every
sample was stored at 5 ± 2°C and 60 ± 8% RH along storage time.
The microbiological profile of the selected meals was evaluated on atleast two production batches; results are the average of ten replicates. For every
meal, 100 samples were investigated to evaluate survival of a specificinoculated microbial pathogen at increasing radiation doses (0, 1, 2, 2.5, 3 and4 kGy), and to detect obvious differences attributable to the treatment by apreliminary sensory evaluation of samples irradiated at the estimated minimum(3 kGy) and maximum doses (6 kGy). The inoculated microorganisms in thesechallenge tests were:60• Listeria innocua (for Listeria monocytogenes) in cannelloni, according toNotermans et al. [35].
• Salmonella enteritidis in salad, empanadas and fruit salad. An inoculum of
108 S. enteritidis cells/mL was prepared according to the McFarland scale.
Turbidity was adjusted to 0.5 and the suspension diluted to 106 cells/mL.
One millilitre of the suspension was inoculated into each meal with asterile syringe and another millilitre was spread on plate count agar tocheck inoculum recovery [36, 37].
• L. monocytogenes ATCC 7973 in sandwiches and chicken pie. Single path
Listeria was used as a screening method, according to the FDA [38] andalso the ELISA LISVIA Tecra® test, according to the USDA [39, 40].
• Salmonella typhimurium in custards, according to FIL standards [41]. A
batch of concentration with 107 cells/mL was inoculated with a syringe
into the middle of each sample.
• L. monocytogenes ATCC 15313 and S. enteritidis ATCC 13076 in breadpudding. In this case, a single colony was used to inoculate fresh tryptic
soy broth (Difco) for each experiment, which was incubated for 18 h at
32°C with rotational agitation. Cell density was typically 108 CFU/mL.
One millilitre of this solution was used to inoculate about 100 g of the
product with a syringe. The inoculated products were stabilized in arefrigerator (4°C) for 18 h before irradiation.
Replicates of microbiological analysis ranged between 3 and 10, and themeal sampling for these tests ranged between 5 and 10. A second experiment35

NARVAIZ et al.

consisted of irradiating new samples at the lowest dose used in the firstexperiment in order to obtain a 6 log cycle reduction in pathogen counts (Dmin),and at twice that dose (Dmax). Non-irradiated samples were kept as controls.
About 300 samples were analysed at this stage for each meal. Microbiologicalanalysis required by the Argentine Alimentary Code was performed on control
and irradiated samples during storage, including assessment of total bacterial
counts, moulds and yeasts, spore-forming anaerobes (required only for filled
pasta such as cannelloni), Salmonella spp., S. aureus, coliforms and faecal
coliforms, according to ICMSF, USDA, FSIS, FDA and FIL methods [36–43].
These samples were sensorially evaluated by a ~50 member ‘healthy’
consumer panel twice during their estimated shelf life. Panellists comprised
about 40% men and 60% women, with ages ranging from 25 to 65 years, 60%
university educated, 40% secondary school education, working at the Ezeiza
Atomic Center. The evaluated attributes were, in general, aroma, aspect,colour, flavour, texture and general acceptability, with a nine point hedonic
scale ranging from ‘like extremely’ to ‘dislike extremely’. Results were statistically analysed by the Dunnet test, p < 0.05 [44].
Forty-four immunocompromised patients also tasted a whole irradiatedlunch, consisting of salad, empanadas and fruit salad in gelatin. These patients
were: 70% women, 30% men, ages ranging between 18 and 75 years, theirconditions being: pregnancy: 30%, cancer 25%, high dose corticoid treatment
16%, blood albumin <3.5 g/dL 16%, neutropenia 11%, HIV+ 2% [45, 46].
Meals comprising the immunocompromised patients’ lunch were selected after
a survey at the hospital; there was a definite desire for colourful, juicy, fresh,
raw products, or for others with some kind of filling such as empanadas, usually
not allowed them owing to the risk of undercooking. Meals usually served toimmunocompromised patients in this hospital, as in many others in Argentina,
do not come from an external catering service but are prepared in the hospital
kitchen.
Sensory evaluation by the consumer panel was performed on days 2 and
15 for cannelloni, and for the rest of the meals, on days 2 and 8 after irradiation.
Control samples were only evaluated on the first analysis date so as to avoid
microbiological risk. Immunocompromised patients evaluated the meals ondays 2 and 8, and then only samples irradiated at Dmin.

3.

RESULTS AND DISCUSSION

Microbiological profiles of the selected meals are shown in Table 2. Total
bacterial counts were high in empanada, salad, sandwich and chicken pie, evensoon after their being manufactured. Moulds and yeasts were very high in the36

3 × 10

Fruit salad<50

5Custard

Bread pudding

5.1 × 102

3 × 10
7 × 1036

1.7 × 103

2.2 × 1010

9

5 × 1027

6

4

3 × 10

Salad

Empanada

Fruit salad

Sandwich

Chicken pie

Bread pudding

1 × 104

1.5 × 10

2.9 × 10

3.7 × 10

5 × 10

1.5 × 103

4

8

Custard

1.8 × 105

Cannelloni

1.4 × 106

5 × 10Faecalcoliforms

<10

<0.3

<0.3

2.7 × 10

<103

7.3 × 102

1.9 × 104

40

2

<10

<0.3

<0.3

3.1 × 10

<10

4.6 × 102

Storage time under refrigeration: 1–2 d

Total
coliforms

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentSalmonella spp.
(in 25 g)

<10

<0.3

<0.3

3.5 × 10

<10

3.2 × 10

2.9 × 10

60

3

3

5

2

<10

<0.3

<0.3

1.4 × 10

<10

4.2 × 102

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentStorage time under refrigeration: 8 d (15 d for cannelloni)

30

4

3.8 × 10

<10

6.3 × 10
3.4 × 106

Sandwich

Chicken pie

1.9 × 106

10 8

Empanada
2 × 1030

7 × 106

Salad

7

7.7 × 103

7 × 10Cannelloni

2

7.1 × 10

5

4

3

Mould
and
yeastsMeal

Totalbacterial
countsTABLE 2. MICROBIOLOGICAL PROFILE OF MEALS (CFU/g)

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentS. aureus(in 100 g)

<10

<10

Sulphitereducing
Clostridia

NARVAIZ et al.

37

NARVAIZ et al.

sandwich, high in cannelloni and salad at the beginning of the storage period
and very high at the end of it in almost every meal with the exception ofcustard. Pathogens were generally absent, although faecal coliforms were
found in salad and sandwiches. Coliform counts were high in sandwich, salad
and empanada. These results are similar to others reported in the literature[47, 48].
According to the results of survival of the pathogen after inoculation,some radiation doses were chosen as the minimum needed to attain a 6 log
cycle reduction (see Table 3). The Argentine Food Code [49] allows a dose
dispersion (Dmax/Dmin) of up to 2 for radiation doses higher than 1 kGy, butaccording to results of the preliminary sensory evaluation, in some of thestudied meals this had to be lowered due to product sensitivity. The main
observed changes were off odours and off flavours in fat-containing meals such

TABLE 3. DOSIMETRIC RESULTS
Radiation dose
(required)(kGy)

Minimum
radiation dose(delivered)(kGy)Maximum
radiation dose(delivered)(kGy)Maximum dose/
minimum dose

Cannelloni

3
6

2.89
6.31

4.57
8.98

1.58
1.42

Salad

2
3

2.44
3.07

3.65
4.43

1.5
1.44

Empanada

3
6

3.40
7.02

4.83
9.16

1.42
1.30

Fruit salad

1.5
2.5

1.52
2.64

2.20
3.72

1.45
1.43

Sandwich

2.5
4

2.50
4.03

2.91
4.65

1.16
1.15

Chicken pie

3.5
5

3.60
5.12

4.45
6.70

1.23
1.30

Custard

3
4.5

3.76
5.75

5.38
7.81

1.43
1.36

Bread
pudding

3
5

3.01
4.84

3.73
6.33

1.24
1.31

Meal

38

NARVAIZ et al.

as sandwich, chicken pie and egg yolk (salad), and also in custard; texture losses
in salad and fruit salad; browning in fruit salad; colour loss in carrot and egg
yolk (salad), and in custard.
Microbiological data of control and irradiated meals can be seen in
Table 4. Pathogens were generally absent in every sample. Coliforms were
present in salad, empanada and sandwich control samples, and they were sufficiently reduced after the irradiation treatment. The same was observed withmoulds and yeasts, which showed high counts in the control sandwich, salad
and cannelloni throughout the storage period, and in fruit salad in gelatin at theend of it. Total bacterial counts were reduced by 2–3 log cycles in cannelloni
and fruit salad in gelatin, by 3–4 log cycles in salad and custard, and by 4–6 log
cycles in sandwich, chicken pie, empanada and bread pudding. These results
are in agreement with others reported in the literature [50, 51].
Some microbiological requirements of the Argentine Food Code are, forinstance, for filled pasta: S. aureus: less than 10 per gram; Salmonella spp.:
absence in 25 g; sulphite reducing Clostridia: less than 10 per gram; moulds andyeasts: less than 100 per gram.
The meals’ sensory evaluations by the ‘healthy panel’ are shown in
Table 5. No significant differences due to the irradiation treament wereobserved in cannelloni, empanada, chicken pie and bread pudding. Instead,significant differences were found in irradiated salad (in texture and general
acceptability, and also in flavour in the Dmax sample), fruit salad in gelatin(texture and general acceptability in the Dmax sample), sandwich (in flavourand general acceptability, and in moisture and aroma in the Dmax sample), andcustard (in aroma, flavour, texture, general acceptability). Though thesedifferences were statistically different, they were small and scores never fell
below the threshold line of 5: ‘neither like nor dislike’. It is curious to see that
irradiated samples generally received better qualifications at the end of thestorage period, probably because by then the panellists had no control sample
with which to compare, and also perhaps due to the so-called ‘irradiation aftereffect’ which is more noticeable soon after the treatment, decreasing withstorage time.
In irradiated sandwiches, ham darkening was observed, especially in low
quality products, as has been also reported in the literature [52, 53]. Sandwiches
made at the authors’ laboratory, and those purchased at high standard bakeries,
gave higher sensory scores. However, as one of the objectives of the present
work was to transfer results to the food industry, in spite of having obtained
better preliminary sensory scores on high standard quality sandwiches, which
are in fact consumed only by a small part of the Argentine population, the best
one of those manufactured in supermarkets was chosen for irradiation.

39

40

Empanadas

Salad

Cannelloni(Note: sulphitereducing Clostridia
absent in every sample.)Food

1.8 × 1052

7.5 × 106
3

0
3

<100

2

10

3
0
3

3 × 102

2 × 1082

4 × 100

73

3.3 × 10

2.1 × 107

0

<3

60

<10

1.9 × 104<10

4.6 × 102<10

2.9 × 105<10

4.2 × 102<10

5 × 102

AbsentAbsent<10

1.1 × 102<10

1.1 × 103

AbsentAbsentStorage day under refrigeration: 8

<10

20

Storage day under refrigeration: 2<10

5.1 × 104

Storage day under refrigeration: 8<10

1.4 × 103

2

7.7 × 103

3.6 × 10<343Storage day under refrigeration: 2

7 × 106

0E. coli(CFU/g)Storage day under refrigeration: 15

1.7 × 103

3

7.1 × 103

2 × 10

5 × 10Coliform
bacteria(CFU/g)Storage day under refrigeration: 2

Mouldsand yeasts(CFU/g)5

Totalbacterial counts(CFU/g)0

Radiation
dose
(kGy)

TABLE 4. MICROBIOLOGICAL QUALITY OF CONTROL AND IRRADIATED MEALS

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentSalmonella(in 25 g)

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentS. aureus(in 100 g)

NARVAIZ et al.

Chicken pie

Sandwich

Fruit salad

Food

10

3

2.9 × 10
<10

3.5

6

0

2

<10

<10
AbsentAbsent<10

104

AbsentAbsent<10

7 × 103

AbsentAbsent<0.3<0.3

Absent<10

2.2 × 103

<0.3

<0.3

AbsentAbsentStorage day under refrigeration: 8

<10

<10

Storage day under refrigeration: 2

8 × 101.1 × 107<10

2 × 102.5

AbsentAbsentStorage day under refrigeration: 2

7 × 102

2 × 106

3

3.5

3 × 1001010Storage day under refrigeration: 2

7

2 × 104

6 × 10

2.5

0

107

0
2

3.7 × 103

2 × 103010

E. coli(CFU/g)Storage day under refrigeration: 8

30

40

90

1.5

1.5

Coliform
bacteria(CFU/g)Storage day under refrigeration: 2

Mouldsand yeasts(CFU/g)2 × 104

Totalbacterial counts(CFU/g)0

Radiation
dose
(kGy)

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentSalmonella(in 25 g)

TABLE 4. MICROBIOLOGICAL QUALITY OF CONTROL AND IRRADIATED MEALS (cont.)

AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentS. aureus(in 100 g)

NARVAIZ et al.

41

42

Bread pudding

CustardFood

4.7 × 106040
5 × 106

30
3

4 × 10

0

10
5

10

3

3

2

2

3 × 102

Totalbacterial counts(CFU/g)0

Radiation
dose
(kGy)

Coliform
bacteria(CFU/g)E. coli(CFU/g)<0.3<0.3
AbsentAbsent<0.3

10AbsentAbsent<50<50

AbsentAbsent

<50

<50

<50

<50

AbsentAbsentStorage day under refrigeration:

<50

<50

Storage day under refrigeration: 2

<10

10

Storage day under refrigeration: 11

<10

10

Storage day under refrigeration: 2

Mouldsand yeasts(CFU/g)AbsentAbsentAbsentAbsentAbsentAbsentAbsentAbsentSalmonella(in 25 g)

TABLE 4. MICROBIOLOGICAL QUALITY OF CONTROL AND IRRADIATED MEALS (cont.)

AbsentAbsentAbsentAbsentS. aureus(in 100 g)

NARVAIZ et al.

NARVAIZ et al.

TABLE 5. SENSORY ANALYSIS RESULTS (‘HEALTHY’ CONSUMERPANEL)
Food

Radiation
dose
Aroma Aspect Texture Juiciness Flavour Acceptability(kGy)

Cannelloni

Storage day under refrigeration: 6
0

7.1

7.1

7.3

7.2

7.1

7.0

3

6.4

7.0

7.1

7.0

6.8

6.9

6

6.3

7.2

7.4

7.2

6.5

6.8

Storage day under refrigeration: 15
3

7.0

7.1

7.4

6.9

7.1

7.2

6

6.4

7.1

7.6

7.1

7.0

7.0

0

7.0

7.0

7.0

6.6

7.0

7.0

3

7.2

7.3

7.0

6.5

7.1

7.2

6

7.1

7.2

7.0

6.8

7.1

7.1

3

6.9

7.0

7.1

6.6

7.2

7.1

6

7.0

6.9

7.1

6.4

7.3

7.2

Empanada

Storage day under refrigeration: 2

Storage day under refrigeration: 9

Chickenpie

Storage day under refrigeration: 4
0

7.2

7.6

7.1

6.2

7.3

7.3

3.5

7.0

7.3

7.0

6.3

7.1

7.0

5

6.9

7.3

6.9

6.2

7.1

7.0

Storage day under refrigeration: 9
3.5

7.3

7.3

7.3

6.7

7.5

7.4

5

6.9

7.2

7.0

6.4

7.3

7.1

Sandwich

Storage day under refrigeration: 4
0

6.9

7.2

7.2

7.0

7.7

7.5
a

6.7
6.5a

2.5

6.8

7.0

7.0

6.7

6.8

4

6.4a

7.0

6.8

6.7

6.8a

Storage day under refrigeration: 7
2.5

7.0

7.0

7.1

6.7

7.0

7.2

4

6.9

7.1

7.2

6.7

6.9

7.0

43

NARVAIZ et al.

TABLE 5. SENSORY ANALYSIS RESULTS (‘HEALTHY’ CONSUMERPANEL) (cont.)
Food

Radiation
dose
Aroma Aspect Texture Juiciness Flavour Acceptability
(kGy)

Salad

Storage day under refrigeration: 2
0

6.6

7.4

7.4

7.4

7.3

7.3

2

6.5

7.2

6.9a

7.4

6.5a

6.8a

3

6.6

7.5

6.8a

7.4

6.8

6.8a

Storage day under refrigeration: 7
2

6.8

7.2

7.2

7.4

7.0

7.2

3

6.8

7.1

7.0

7.3

6.9

6.9

0

7.2

7.4

7.5

7.6

1.5

7.2

7.5

7.5

7.3

Fruit salad

Storage day under refrigeration: 2

7.2

7.4

7.2

a

7.3

7.6

7.5

7.5

7.2

7.2a

2.5

7.2

1.5

7.3

7.4

7.4

7.1

7.4

7.3

2.5

7.3

7.2

7.3

7.0

7.4

7.2

Storage day under refrigeration: 8

CustardStorage day under refrigeration: 3
0

6.3

6.6

3.8

a

5.6

5.8

5.6a

7.0

7.1

7.0

6.1

5.7

a

a

6.0

5.8a

6.0

5.8a

6.4a

6.2a

Storage day under refrigeration: 11

Breadpudding

3.8

6.4

6.0

6.4

7.0

6.6

5.8

6.3

5.8

6.4

6.9

6.7

Storage day under refrigeration: 4
0

6.9

6.7

5.7

6.5

6.1

3

7.1

6.9

5.9

6.7

6.4

5

6.8

6.8

6.1

6.6

6.3

Storage day under refrigeration: 10

a

44

3

7.1

6.8

6.0

6.9

6.7

5

7.0

6.8

6.5

6.8

6.8

Significantly different from control, p < 0.05.

NARVAIZ et al.

It is interesting to compare the different behaviours of custard and breadpudding, their compositions fairly similar except for the wheat flour in thepudding, which lowered water content significantly. A higher water content,
which allows more radiolytic reactions through the secondary irradiation
effect; a higher fat content; the presence of radiosensitive chemical groups suchas sulphur compounds in egg and milk, among other characteristics, could havecontributed to acceptability differences between these two products. Other
aspects to be noticed are that the more sensorially radioresistant meals were in
general those which had been previously cooked, probably because texture
losses due to irradiation were lower than those previously caused by heat.
In every case, the close correlation between results obtained through theconsumer ‘healthy panel’ (50 members) and the preliminary sensory evaluation
panel (6 members) suggested that the latter is a useful, simpler tool for
screening coarse sensory effects on irradiated foods.
Sensory evaluation of the meals tasted as an irradiated lunch by the
immunocompromised patients can be seen in Fig. 1. Scores were very good, andhigher than those afforded by the consumer ‘healthy’ panel, probably due tothe fact that these patients usually long for meals such as these, with or without
fillings, which are forbidden to them owing to the risk of foodborne diseases. It
should also be mentioned that changes in ‘taste’ these patients sometimes
suffered due to mouth and gastric mucosa damage did not impair theirevaluation of these irradiated meals.
Most patients showed enthusiasm about this experience. One of them, aman who had suffered a kidney transplant, delayed his discharge from thehospital in order to be able to taste the irradiated meals. A woman accepted thetrial immediately as she was very fond of salads and had been denied them forthe previous three months.

SALAD

EMPANADAFRUIT IN GELATIN

9HEDONIC SCALE

8
7
6
5
4
3
2
1
AROMA

ASPECTFLAVOURJUICINESSTEXTURECOLOURACCEPTABILITY

FIG. 1. Sensory evaluation used for irradiated meals, as assessed by immunocompromisedl
patients.

45

NARVAIZ et al.

Some of these patients’ comments after eating the irradiated lunch were:“This is a very important meal, moreover because it relates to ill people. I
hope this chance will always exist… and that this food could be available all over
the world and especially in every Argentine region.”“It lacks quantity. It tastes good; I do not perceive differences with nonirradiated products.”“Very good and very tasty.”“Thank you for informing us of this kind of food preservation method.”“Great. Thank you for looking for solutions to improve our health. Fruits
keep [their] typical odour and flavour. Everything was tasty.”“This should be the true food for the ill.”“These are very well presented meals.”“The dessert has the natural fruit flavour.”“At first sight this lunch created a good impression. This new way of[treating] food with ionizing energy seems to me a fantastic idea, and I wish it
could be economically feasible, and available to all the community.”“Everthing [was] very tasty.”“I like it because it looks fresh.”“It was very interesting to me that food exposure to gamma irradiation did
not change their aspect or taste.”“The packaging kept empanadas still hot, which is very important for ill
people, because many times food [is served] cold. Very colourful and agreeable.”“Portions are very generous, presentation is very good, the young ladies
who invited (us) to try it showed great courtesy in informing us. Thank you andcontinue with this work.”“I think this is a good experience for neutropenic persons, and to be able toincorporate more and more foods. They neither lose taste nor colour; I like it tohave them available in supermarkets or food services.”
Some nutritional aspects of this lunch were evaluated, as well as
estimated vitamin losses due to the irradiation treatment, which turned out tobe small and similar to those caused by other preservation treatments, such asheat, or even storage [54, 55].
A great amount of discussion of this work was performed in scientificmeetings, conferences, expositions, and press and television releases. The
informative activities were very valuable in highlighting the whole foodirradiation issue, particularly in a country such as Argentina where regulatory
authorities appear reluctant to go ahead with further clearances, andsometimes still doubt its wholesomeness. These results are reported in various
theses [56–59] and publications [45, 46].

46

NARVAIZ et al.

The patients’ attitude towards the irradiated lunch deserves special
mention. They not only afforded the highest sensory qualifications to the meals,
but were also extremely receptive to food irradiation and very grateful to theyoung nutritionists who cared for their welfare.

4.

CONCLUSIONS

Gamma irradiation of the studied ready-to-eat meals rendered microbiologically safe and sensorially acceptable products for at least 8 storage days at
refrigeration temperatures, which implies a tripling of shelf life. In cannelloni,
shelf life was extended at least to 15 d. Therefore, it was shown that ionizing
radiation can be applied not only to simple food systems such as single
commodities but also to complex ones such as some whole ready-to-eat meals.
The applied radiation doses were sufficient to reduce 6 log cycles of themost radioresistant microbial pathogens (excluding spore forming bacteria andviruses) that could be present and which cause diseases in the consumer.
A 6 log cycle reduction is considered to be an overestimation of the
security margin, as the natural incidence of these microorganisms in food ismuch lower.
The minimum radiation dose (Dmin) should in this case not only beenough to fulfil the microbiological goal but also not to exceed the sensory
threshold of the most radiosensitive ingredient in the meal. In some cases, aproduct reformulation or separate irradiation of the meal components might beadvisable. This also applies to the maximum dose (Dmax) that the productwould absorb in an industrial treatment, which is generally accepted in mostcountries’ regulations as being up to twice the Dmin value. Under the experimental conditions of this study, it seemed preferable to lower the Dmax/Dminratio to protect sensory quality, and so it was chosen to be between 1.4 and 1.6
for most of the meals studied.
Regarding the experience with immunocompromised patients, it was
concluded that ionizing radiation, in combination with good manufacturing
practices and refrigeration, improves the food quality as more diversification isallowed, with both nutritional and psychological benefits. The level ofmicrobial decontamination attained would enable the offering of longed-for,unusual meals to those persons, without foodborne disease risk. Besides, nutritionists were satisfied with the results because the shelf life extension due toirradiation would allow, in the future, a reasonable flow of meals to be provided
to a hospital by a catering service, for instance, once a week, without the foodlosing its fresh nutritive condition as a consequence of overcooking or freezing.

47

NARVAIZ et al.

This was the first approach carried out in Argentina with respect toimmunocompromised patients and food irradiation. Much more work should
be undertaken to widen the meal variety and to explain this method to other
patients, health institutes, catering services and supermarkets. It should be
noted that many immunocompromised persons lead a fairly ‘normal’ life whenout of hospitals. The collaboration between food irradiation researchers andnutritionists is considered essential. It would also be desirable to advance
regulatory aspects related to this activity.

ACKNOWLEDGEMENTS
The authors express their gratitude to the Hospital de Clínicas ‘José deSan Martín’ staff and the immunocompromised patients who participated inthis study and to the IAEA Food and Environmental Preservation Section,
whose financial support, organization and encouragement made it possible.
Also to scientific colleagues of this CRP, who contributed their knowledge andprovided criticism and advice, as well as the 22 nutrition and food technology
students for their help in the development of experimental work during theirpractices. The contributions of the Ezeiza Atomic Center staff: laboratory
assistant, chemical dosimetry section, irradiation facility and ‘healthy’ panel
members are gratefully acknowledged.

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Buenos Aires, Argentina, 148 pages, (2005).

IRRADIATION OF PREPARED MEALSFOR MICROBIOLOGICAL SAFETY
AND SHELF LIFE EXTENSION
J. NKETSIA-TABIRI, A. ADU-GYAMFI, F. APEA BAH
Biotechnology & Nuclear Agriculture Research Institute,
Ghana Atomic Energy Commission,
Ghana

Abstract
Fourteen international ready meals prepared under the approved hazard analysis
critical control point (HACCP) plan and two Ghanaian ready meals, waakye (co-boiled
rice and cowpeas served with gravy, minimally processed vegetable salad, hydrated gari,fried fish and macaroni) and jollof rice (rice cooked in tomato sauce and served withgravy and beef tripe), were investigated with the view to enhancing microbiologicalsafety and extending shelf life under chilled conditions. The microbiological count of thecomplete waakye meal exceeded the microbiological standard. The microbiologicalcounts on meals prepared under the HACCP plan and the jollof rice meals were within
the microbiological standards. The D10 values for potential pathogens on waakye were0.271 kGy for Escherichia coli, 0.325 kGy for Salmonella aureus and 0.440 kGy for
Salmonella spp. while the D10 values on jollof rice meal were 0.173 kGy, 0.260 kGy and0.285 kGy, respectively. Challenge tests with the pathogens on one of the HACCP meals(poached chicken) or jollof rice suggested that the 3 kGy dose was sufficient for theelimination of the pathogens to ensure the microbiological safety of the meals andextended their shelf life under chilled storage for 28 days without significant effects on
their sensory quality. Doses of 1 and 2 kGy did not affect the sensory quality of the riceand chicken/gravy but boiled carrots were unable to withstand a dose of more than
1 kGy.

1.

INTRODUCTION

Current trends, in developed countries in particular, suggest an increasing
demand for convenience foods such as ready meals and those that require
minimum preparation before consumption. In Ghana, the trend is the samewith ‘street foods’ (ready-to-eat meals sold in the informal sector), which play amajor role in meeting the nutritional needs of the people [1, 2]. In mostdeveloping countries, including Ghana, these ready meals are prepared on adaily basis. Challenges facing ready meals are largely related to shelf stability
and microbiological safety. Over 90% of ready-to-eat meals prepared in Ghana

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are marketed under ambient conditions and have a shelf life of less than 12 h.
The hygienic limitations of street foods in Ghana and elsewhere have beenrecognized and reported [3–7]. Food service outlets have been reported toharbour varying levels of indicator organisms, sometimes as high as 109 CFU/g[5, 8, 9]. Microorganisms of public health concern isolated from these foods
included faecal Streptococci, coagulase-positive Staphylococcus aureus andfaecal coliforms, notably Escherichia coli and Shigella flexneri. Investigations
have demonstrated that these cook–chill meals are potential sources ofpathogenic bacteria and have been implicated in foodborne disease outbreaks[3–7].
The preparation of meals based on the hazard analysis critical control
point (HACCP) approach has the potential to enhance microbiological safety
provided the recommended post-processing handling instructions are also
complied with to control the multiplication of surviving pathogens. The use of
combination treatments involving irradiation in order to eliminate pathogens is
critical to ensure the microbiological safety of ready meals. The efficacy ofirradiation in controlling pathogens and enhancing food safety has long been
established. However, there is a need to develop irradiation protocols for
specific ready-to-eat meals in order to ensure not only their microbiologicalsafety but also their acceptability from an organoleptic viewpoint.
The overall objective of this research was to evaluate the effectiveness ofirradiation as a method to ensure microbiological safety and extend the shelf
life of prepared meals, stored either under chilled or frozen conditions, and toevaluate the sensory quality of the treated products.

2.

MATERIALS AND METHODS

2.1. Ready meals and their major components
The following meals were studied:
(a)
(b)
(c)
(d)

54

Fourteen ready meals prepared under the HACCP plan;
Waakye (co-boiled rice and cowpeas served with gravy, minimallyprocessed vegetable salad, hydrated gari, fried fish and macaroni);
Poached chicken meal (poached chicken, boiled rice, gravy and carrots);
Jollof rice (rice cooked in tomato sauce and served with gravy and beef
tripe).

NKETSIA-TABIRI et al.

2.2. Physicochemical analysis
The pH, water activity, peroxide value, percentage of free fatty acids were
determined using standard methods [10].
2.3. Microbiological analysis
2.3.1. Preparation of meal substrate portions
Meal portions of 20 g were prepared by homogenizing for 1 min using a
stomacher homogenizer (Mix2, AES Laboratoire, France).
2.3.2. Enumeration and identification tests
A 10 g homogenized meal sample was added to 90 mL peptone water(1% peptone water plus 0.5% NaCl) and stirred on a mechanical shaker(Junior Orbit Shaker, Lab-Line Instruments, United States of America) for
30 min. Standard methods [11] were used in determining the microbiologicalindices: for total bacteria count (TBC), plate count agar (Oxoid, United
Kingdom), incubated at 36°C/48 h; for general coliform count, eosin methylene
blue agar (Difco, USA) or violet red bile agar incubated at 36°C/48 h; forE. coli count, eosin methylene blue agar (Difco) at 37°C/48 h; for S. aureus
count, Baird Parker agar (Difco) at 37°C/48 h; for Salmonella count, xylose
lysine deoxycholate agar (Difco) at 37°C/48 h; for Salmonella/Shigella,
selective agar (Oxoid) incubated at 37°C/48 h; and for mould and yeast count,
Oxytetracycline (0.01%) glucose yeast agar (Merck, Germany) at 28°C/72 h.
The enumeration of survivors was done using a colony counter (Stuart
Scientific, UK).
Representative colonies from the plate counts were purified by
subculturing and identified using morphological characteristics and standard
biochemical tests. The tests used were Gram stain, catalase, oxidase, motility,
nitrate, carbohydrate fermentations, triple sugar iron and the IMViC tests withreference to Biochemical Tests for Identification of Medical Bacteria [12].
2.3.3. Preparation of inoculum of test pathogens
Cultures of test pathogens, E. coli, S. aureus and Salmonella spp. used forthe study were isolated from some locally prepared ready meals. The cultures
were stored on eosin methylene blue agar (Difco), Baird Parker agar (Difco) or
xylose lysine deoxycholate agar (Difco) at 3–5°C, before they were reactivatedby incubation at 37°C for 24 h and used for preparation of inocula. The inocula

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NKETSIA-TABIRI et al.

were standardized to a concentration of 107 CFU/mL by the methods of serial
dilution, pour plate and the use of a haemocytometer.
2.3.4. Radiation sensitivity tests
A 5 mL suspension of each test pathogen (population of 107 CFU/mL)
was added to 25 g portions of the homogenized meals in polythene bags andsealed. The inoculated samples were stored at 3–5°C for 24 h to allow test
pathogens to adjust and then treated with irradiation doses of 0.10, 0.30, 0.45,
0.60, 0.75 and 0.85 kGy. Both the controls and irradiated meals were analysed
for surviving test pathogens. Three independent experiments were conducted.
2.3.5. Challenge testing experiments
A 5 mL suspension of each test pathogen was added to 25 g of thehomogenized meal in a polythene bag and sealed. The inoculated meal samples
were stored at 3–5°C for 24 h to allow the test organism to adjust to thesubstrates (meals). The inoculated meal samples were subsequently treatedwith irradiation doses of 2 and 3 kGy. After irradiation, both the control andirradiated meals were stored in a refrigerator for 28 d (3–5°C). Enumeration ofsurviving cells of E. coli and S. aureus was carried out at 0, 7, 14, 21, 28 d ofchilled storage. Three independent experiments of two replicates each wereconducted.
2.4. Sensory tests
Irradiated and non-irradiated meals were stored at 3–5°C and at predetermined intervals the meals were subjected to sensory tests using trained
panellists. For the poached chicken, the meals were treated with 1.0 or 2.0 kGy
and at the appropriate intervals during storage, 24 consumer panellists used
triangle, hedonic and acceptability tests for the detection of differences
between, and preference for, the sensory quality of irradiated and nonirradiated meals. In the case of the jollof rice, the meals were irradiated with 1.5
or 3.0 kGy and, using descriptive tests, 15 trained panellists determined theeffect of irradiation and storage on selected sensory indices of the threecomponents: rice (colour, texture, taste), gravy (flavour, aroma) and beef tripe(chewiness, fibrousness). For each attribute, judgement was made by placing a
distinct vertical line across a given horizontal line. In all instances, the meals
were heated in a microwave oven (600 W) before presenting them to thepanellists.

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2.5. Irradiation
Irradiation of the meals was carried out at the semi-commercial 60Co
gamma irradiation facility of the Ghana Atomic Energy Commission at a dose
rate of 2.31 kGy/h in air.
2.6. Statistical analysis
Statistical analysis was done using the statistical analysis package ofMicrosoft ExcelTM (Microsoft Corp., USA). The microbial counts (CFU/g)
were transformed into logarithms (lg) and the data subjected to regression
analysis. The surviving fractions, lg (N/N0), of E. coli, S. aureus and Salmonella
spp. were calculated and used as relative changes of their actual viable cellcounts. The D10 values (the dose required to inactivate 90% of a population)
were calculated by plotting lg (N/N0) against dose (D) according to theequation [13]:D10 = D/(lg N – lg N0)
where
N0
N
D

is the initial viable count;is the viable count after irradiation with dose D;
is the radiation dose.

The linear correlation coefficient (r2) and the regression equations were
calculated.
Panellists’ scores were statistically analysed using Triangle, Paired
Comparison Tables of Significance or two-factor ANOVA with replication(Microsoft Excel).

3.

RESULTS AND DISCUSSION

3.1. Ready meals prepared under the HACCP plan
The meals were held at temperatures between –5 and 0°C for periods
ranging up to 5 d (Table 1). The TBCs did not exceed 3.95 lg CFU/g whilst thecoliform count did not exceed 2.7 lg CFU/g. For the meal coded HAP-3, no
coliform colonies were observed after the stipulated incubation period. The
presence of Salmonellae spp. and Shigellae spp. could not be established on any

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NKETSIA-TABIRI et al.

of the meals as there was no growth of microbes on the selective SS agar. The
results of the microbiological tests suggested that for all 14 HACCP guided
prepared meals, the counts obtained did not exceed the microbiologicalstandards for such short shelf life foods (TBC <105 CFU/g at 36°C/48 h andcoliforms <104 CFU/g at 36°C/48 h). These results demonstrated the important
contribution that effective implementation of an HACCP plan in the foodindustry can make towards improving hygiene quality and enhancing foodsafety.
Additional information in Table 1 which deserves mention is theobserved effects on the microbiological quality of holding the meals at 0 to
–5°C. The meals are strictly supplied to clients within 24 h of preparation.
However, it was considered relevant to investigate the microbiological qualityof some of the meals should they be held for periods longer than 24 h. Meals
HAP-10 and HAP-11 are the same, although the latter, which was analysed
after holding for 2 d, had lower aerobic mesophilic bacteria counts but higher
coliforms than HAP-10, which was analysed without holding. It is noteworthy
that the counts obtained for meals which were held for up to 5 d were also
within the microbiological standards. Potential pathogens isolated from themeals prepared under the HACCP plan included enterotoxigenic bacteria such
as E. coli, Serratia spp. and Klebsiella spp. The last two species were also
isolated from the complete waakye meals. Isolates of such potential pathogens
on ready meals have been reported. The results suggested that the implementation of an HACCP substantially reduced microbial counts, although somepotential pathogens survived. Although the HACCP plan requires that theready meals be held at 0 to –5°C in order to suppress growth of survivors, thelatter could proliferate during temperature abuse when power outages occur.
There is the need to adopt processes/technologies which have thepotential to eliminate potential pathogens from prepared meals and improvetheir microbiological safety. The potential of irradiation to enhance food safety
has long been recognized. However, the effectiveness of the treatment is,among other factors, dependent on the dose applied.
Table 2 shows the radiation sensitivity of three potential pathogens,
E. coli, S. aureus and Salmonella spp. The D10 values suggested that while
271 Gy was required to reduce a population of E. coli by 90%, a higher dose of
440 Gy was required to reduce a population of the Salmonella spp. by the sameamount. The higher radiation sensitivity of E. coli compared with S. aureus andSalmonellae spp. has been reported. This trend, as well as the fact that radiation
sensitivity is dependent on the test medium, have been reported.

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TABLE 1.
MICROBIOLOGICAL QUALITY OF READY MEALSPREPARED UNDER THE HACCP PLAN
Days held at
0 to –5°C

TBCb(lg CFU/g)

Coliform count(lg CFU/g)

HAP-1

2

3.95 ± 0.03

1.92 ± 0.02

Pseudomonas spp.,
Alkaligenes spp.

HAP-2

3

3.84 ± 0.04

0.39 ± 0.12

E. coli, Enterobacter spp.

HAP-3

4

1.33 ± 0.04

Not detected

E. coli, Enterobacter spp.

Meal codea

Isolates

HAP-4

2

1.70 ± 0.02

0.15 ± 0.21

Acinetobacter spp.

HAP-5

3

3.06 ± 0.03

2.70 ± 0.32

Acinetobacter spp.,
Serratia spp.

HAP-6

4

1.54 ± 0.05

1.34 ± 0.11

Acinetobacter spp.

HAP-7

4

3.91 ± 0.03

1.78 ± 0.16

Enterobacter spp.

HAP-8

4

2.71 ± 0.03

1.63 ± 0.04

Serratia spp.,
Enterobacter spp.

HAP-9

5

2.76 ± 0.02

2.11 ± 0.05

E. coli, Klebsiella spp.,
Acinetobacter spp.

HAP-1002.73 ± 0.01

0.69 ± 0.12

Acinetobacter spp.,
Serratia spp.

HAP-112

1.50 ± 0.71

1.42 ± 0.02

Acinetobacter spp.,
Serratia spp.

HAP-122

1.25 ± 0.10

0.39 ± 0.13

Acinetobacter spp.

HAP-134

3.45 ± 0.43

0.69 ± 0.13

Enterobacter spp.,
Klebsiella spp.

HAP-142

2.06 ± 0.03

0.30 ± 0.43

Enterobacter spp.,
Acinetobacter spp.

aMeal ingredients:
HAP-1: Fish fillet, cheese, sauce, oil, potato, spices, vegetables
HAP-2: Deboned chicken, spices, oil, plain rice, potato
HAP-3: Chicken, spices, sauce, oil, steamed rice, potato
HAP-4: Beef steak, spices, oil, potato, tomato, peppers
HAP-5: Beef steak, spices, sauce, oil, steamed rice
HAP-6 Chicken breast, spices, oil, boiled rice, sauce
HAP-7 Fish fillet, spices, oil, sauce, potato
HAP-8: Chicken, peppers, curry, oil, steamed rice
HAP-9: Fish, spices, oil, potato, sauce
HAP-10: Eggs, salt, oil
HAP-11: Eggs, salt, oil
HAP-12: Lamb, spices, oil
HAP-13: Chicken, spices, oil, vegetables, rice
HAP-14: Biscuit, fruits, cheese, cream.
b
Mean counts ± SD.

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NKETSIA-TABIRI et al.

TABLE 2. RADIOSENSITIVITIES OF E. coli, S. aureus AND Salmonella
spp. ON COMPLETE WAAKYE
PathogenRegression equationr2

D10 value(kGy)

E. coli

Y = –0.560X + 0.167

0.889

0.271 ± 0.060a

S. aureus

Y = –0.462X + 0.475

0.988

0.325 ± 0.048

Salmonella spp.

Y = –0.344X + 0.238

0.985

0.440 ± 0.064

aMean ± SD of three independent experiments of three replicates each.

TABLE 3. WATER ACTIVITY AND pH OF WAAKYE AND ITSACCOMPANIMENTS
SampleWater activity

pH

Completea waakye

0.939 ± 0.001b5.60 ± 0.02

Waakye only

0.936 ± 0.001

7.83 ± 0.01

Fried fish

0.887 ± 0.004

5.80 ± 0.10

Hydrated gari

0.931 ± 0.001

4.35 ± 0.03

Cooked macaroni

0.943 ± 0.001

6.48 ± 0.71

Vegetable salad

0.948 ± 0.001

4.85 ± 0.01

Gravy

0.897 ± 05.11 ± 0.01

ab

Waakye, gravy, fried fish, hydrated gari, macaroni and vegetable salad.
Mean ± SD.

3.2. Waakye and other ready meals
3.2.1. Waakye and its accompaniments
The vegetable salad had the highest water activity (0.943) while fried fish
had the lowest (0.887) (Table 3). Complete waakye, which consisted of waakye
and all its accompaniments, had a water activity of 0.939.
With respect to pH, hydrated gari (4.35) and the vegetable salad (4.85)
had relatively lower values than the other meals. It is important to note thesignificant reduction in the pH of waakye alone from 7.83 to 5.60 when theaccompaniments are added. Water activity and pH greatly influence the microbiological quality and shelf life of foods.

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TABLE 4. MICROBIOLOGICAL COUNT (lg CFU/g) OF WAAKYE AND
ITS ACCOMPANIMENTS
SampleTBC
aColiform countc

Moulds and yeasts

Complete waakyeb

7.01 ± 0.15

5.88 ± 0.16

3.58 ± 1.47

Waakye only

3.93 ± 0.47

1.19 ± 0.48

Not detectedFried fish

5.00 ± 1.53

1.27 ± 1.79

1.12 ± 0.66

Hydrated gari2.34 ± 1.29

1.27 ± 1.79

0.48 ± 0.68

Cooked macaroni

7.49 ± 0.72

6.48 ± 0.71

1.12 ± 0.66

Vegetable salad

7.24 ± 0.69

6.37 ± 0.63

3.26 ± 0.73

aWaakye, gravy, fried fish, hydrated gari, macaroni and vegetable salad.
Mean ± SD.
c
Positive coliform plates of complete waakye indicated the presence of Klebsiella spp.,
Enterobacter spp. and Citrobacter freundii.

b

The TBC for complete waakye meals was 7.01 lg CFU/g whilst coliform
count 5.88 lg CFU/g. These values are comparable to the counts obtained formacaroni (TBC: 7.49 lg CFU/g, coliform count: 6.48 lg CFU/g) and salad (TBC:
7.24 lg CFU/g and coliform count: 6.37 lg CFU/g). Relatively lower TBC(3.93 lg CFU/g) and coliform count (1.19 lg CFU/g) were obtained for waakye
only. The fried fish also had a high coliform count (4.67 lg CFU/g) (Table 4).
Mould and yeast counts were present on complete waakye (3.58 lg CFU/g)
and the raw vegetable salad (3.26 lg CFU/g) but could not be detected on
waakye alone. From these results, the raw vegetable salad appeared to be thesource of moulds and yeasts in the complete waakye meal. Salmonellae spp.
and Shigellae spp. could not be detected on any of the samples. However, thefact that the coliform count (5.88 lg CFU/g) exceeded the microbiologicalstandards for such short shelf life foods (TBC <105 CFU/g at 36°C/48 h andcoliforms <104 CFU/g at 36°C/48 h) has serious implications on the microbiological safety of the complete waakye meal.
The high coliform count on the meals in Table 4 is noteworthy. Isolates
from positive plates for the complete waakye included Klebsiella spp., Enterobacter spp. and C. freundii. The observed high count on the vegetable salad andmacaroni (Table 4) and the fact that they reflected the high count for complete
waakye deserve further investigation. Uncooked vegetable salads naturally
have a high microbial load unless strict procedures, including thorough washingand sanitization, are followed to reduce microbial load, while subsequent refrigeration or chilling is a requirement to control microbial growth. Discussions
with, and observation of, waakye processors revealed that the vegetable salads

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NKETSIA-TABIRI et al.

were washed with potable water, comminuted and displayed together withother accompaniments of waakye, during marketing. There is, therefore, noeffective sanitization treatment for the salads. Earlier studies also indicatedthat accompaniments of waakye, such as salads and pepper sauce, which areminimally processed, had high counts (aerobic mesophilic count >4 × 103 CFU/g,
S. aureus >3 × 104 CFU/g and Bacillus cereus >2 × 105 CFU/g).
A direct observation of waakye sellers also suggested cross-contamination resulting from the use of fingers or the same ladle to serve the salads,
cooked macaroni and waakye. Although the use of different ladles would
largely prevent cross-contamination among the meal components, this would
not prevent the contamination of the complete waakye meal as the results ofthe current study indicate (Table 4). Isolates from the positive coliform platesof complete waakye included C. freundii, Klebsiella spp. and Enterobacter spp.,
which have public health implications. The results suggested that the poor
microbiological quality of many street foods might result from the combined
impact of ineffective sanitary procedures during the preparation of the foods,
post-processing contamination and long holding under conditions which
enhance proliferation of microorganisms. Improving sanitary conditions underwhich street foods are prepared and marketed and assisting stakeholders to
adopt effective preventive procedures based on the HACCP approach, toconvert the raw food ingredients into ready-to-eat meals, are critical towards
ensuring food safety and good public health.
3.3. Poached chicken meal
The changes in physicochemical properties during storage of the various
components in non-irradiated and irradiated meals are shown in Table 5. The
high water activity and the pH range of the meals make them suitable formicrobial proliferation. With respect to free fatty acids, the component of mostinterest is the chicken and gravy because of their relatively higher fat content.
The results suggested that the irradiation treatment and chilled storage did not
induce fat hydrolysis.
3.3.1. Microbiological quality of poached chicken meal
The TBC of the various meal components is presented in Table 6. Counts
obtained for both the irradiated and control meal components on the first day(0) did not exceed 2.53 lg CFU/g. Although counts increased during storage,
TBCs for the irradiated meals were lower than the non-irradiated samples. On
day 14, only the irradiated rice and irradiated chicken/gravy had TBC which
did not exceed the microbiological standard for such ready meals; the62NKETSIA-TABIRI et al.

TABLE 5. CHANGES IN pH, FREE FATTY ACIDS AND WATERACTIVITY OF POACHED CHICKEN MEAL DURING CHILLED
STORAGE
Meal component

Treatment
(kGy)

Rice:
Control0

Irradiated1

Carrots:
Control0

Irradiated1

Chicken and gravy:
Control0

Irradiated2aStorage time(d)pHFree fatty acid
(%)

Water
activity

0
9
14
22

5.8
5.8
6.0
6.2

<0.01
<0.01
<0.01
<0.01

0.937
0.938
0.938
0.942

0
9
14
22

5.9
6.0
6.1
6.1

<0.01
<0.01
<0.01
<0.01

0.940
0.940
0.940
0.946

0
9
14
22

6.3
4.7
5.3
n.a.a

<0.01
<0.01
<0.01
n.a.

0.943
0.938
0.953
n.a.

0
9
14
22

6.3
6.3
6.4
n.a.

<0.01
<0.01
<0.01
n.a.

0.946
0.946
0.944
n.a.

0
9
14
22

5.7
5.3
5.7
n.a.

0.03
0.03
0.03
n.a.

0.943
0.934
0.939
n.a.

0
9
14
22

5.4
5.7
5.4
5.2

0.03
0.03
0.03
0.03

0.944
0.941
0.936
0.939

n.a.: not analysed.

irradiated carrots had deteriorated. At the end of the storage period of 21 d,
only irradiated rice had counts (2.18 lg CFU/g) which did not exceed the microbiological standard. These results indicated that irradiation improved themicrobiological quality and extended the shelf life of the meals to 14 d.
The sensory quality of control and irradiated poached chicken samples isshown in Table 7.
No significant difference (p > 0.05) was observed between the irradiatedand non-irradiated meal components (rice, chicken and gravy) on days 0 and 3
during chilled storage. On the 15th day, panellists also detected significant

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TABLE 6. EFFECT OF IRRADIATION ON THE TBC IN COMPONENTS
OF POACHED CHICKEN MEAL DURING STORAGE AT 3–5°C
Components
Rice

Dose
(kGy)
0

Storage time (d)0a2.24 ± 0.26
b

9

14

21

3.17 ± 1.28

3.53 ± 0.78

5.56 ± 0.62

1.50 ± 0.44

n.d.

2.18 ± 0.55
n.a.c

Rice

1

n.d.

Carrots02.53 ± 0.18

1.87 ± 0.45

5.58 ± 0.05

Carrots

1

1.05 ± 0.10

1.43 ± 0.61

n.a.

n.a.

Chicken & Gravy

01.68 ± 0.37

3.72 ± 0.54

ud

n.a.

Chicken & Gravy

2

1.35 ± 0.15

3.60 ± 0.35aMean count: lg CFU/g ± SD (n = 3).
n.d.: not detected.
cn.a.: not analysed owing to poor state and offensive odour.
du: uncountable, in excess of 6.00.
bdifferences between the irradiated and non-irradiated chicken/gravy; only theirradiated chicken/gravy was acceptable to the panellists. The irradiated rice
and irradiated chicken and gravy were acceptable to the panellists on the 22ndday but the non-irradiated equivalents were rejected. The rejection of the nonirradiated chicken/gravy on the 15th day may be attributed to the highmicrobial population (Table 6) and the related bad odour. It has been reported
that irradiated spicy chicken basil was rejected by panellists after 7 d storage
even though TBC did not exceed 103 CFU/g. They attributed the rejection of
the spicy chicken to objectionable changes in the aroma of irradiated basil.
Clearly sensory rejection of foods may not only be due to microbial activity but
also to chemical changes.
The results have shown that irradiation doses of 1 kGy for rice and 2 kGy
for chicken/gravy effectively controlled microflora, sensory quality andextended shelf life up to 14 d under chilled storage. The observed extension in
the shelf life of irradiated poached chicken/gravy and rice is very significant
since the recommended maximum shelf life of ready meals at 0–3°C is 5 d. The
positive impact of combinations of low dose irradiation and chilled storage on
the microbiological quality and shelf life of ready meals has also been reported.
Survival curves of E. coli and S. aureus were studied as a function ofirradiation dose. Figures 1 and 2 show that surviving E. coli and S. aureus cells
decreased with increasing irradiation dose.

64

0
1
0
2

Rice

Rice

Chicken and gravy

Chicken and gravy

Meal portion

Dose
(kGy)

7.4

7.1

7.6

7.2

Taste

7.6

7.5

7.3

7.4

Colour

9

6.9

6.8

6.6

6.5

Texture

7.2

3.9

7.3

7.4

Taste

6.4

5.3

7.0

7.4

Colour

15

6.6

5.8

7.3

7.4

TextureStorage time (d)6.5

Rejected

7.3

Rejected

Taste

7.3

Rejected

7.2

Rejected

Colour22

7.5

Rejected

7.1

Rejected

TextureTABLE 7. SENSORY SCORES FOR IRRADIATED AND NON-IRRADIATED POACHED CHICKEN AND RICESTORED AT 4 ± 1ºC FOR 22 DAYSNKETSIA-TABIRI et al.

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NKETSIA-TABIRI et al.

1

Dose (kGy)0

Log10 of surviving fraction (N/No)

0

0.1

0.3

0.45

0.6

0.75

0.85

-1
y = -0.582x + 0.320
r2 = 0.982
D10 = 0.255 kGy-2

E. coli - MealE. coli - Chicken-3y = -0.803x + 0.871-4

r2 = 0.989
D10 = 0.182 kGy-5-6

FIG. 1. Radioresistance curves of E. coli.

1

Dose (kGy)
Log10 of surviving fraction (N/No)

0
0

0.1

0.3

0.6

0.75

0.85

y = -0.519x + 0.647

-1

-2

0.45

R2 = 0.976
D10 = 0.287 kGy

y = -0.550x + 0.490
R2 = 0.987
D10 = 0.271 kGy-3-4

FIG. 2. Radioresistance curves of S. aureus.

66

S. aureus - MealS. aureus - Chicken

NKETSIA-TABIRI et al.

TABLE 8. RADIOSENSITIVITY OF E. coli AND S. aureus ON POACHEDCHICKEN MEAL AND MINCED CHICKEN SUBSTRATE
Meal/substrate

Test organism

Regression equationr2

D10 value

Poached chicken meal

E. coli

Y = –0.803X + 0.871

0.989

0.182 ± 0.019a

S. aureus

Y = –0.550X + 0.490

0.987

0.271 ± 0.004

E. coli

Y = –0.582X + 0.320

0.982

0.255 ± 0.003

S. aureus

Y = –0.519X + 0.647

0.976

0.287 ± 0.009

Minced chicken
substrateaMean ± SD (n = 2).

As can be seen in Table 8, the calculated D10 values of E. coli on poachedchicken meal and minced chicken substrate were 0.182 kGy and 0.255 kGy,
respectively; and those of S. aureus were 0.271 kGy and 0.287 kGy, respectively.
The linear correlation coefficients of the regression lines were all greater than
0.970 and highly significant (p < 0.01), indicating a strong negative linear correlation. The D10 values were lower on the poached chicken meal than theminced chicken substrate and values for S. aureus were higher than E. coli. The
calculated D10 values of E. coli compare well with the reported range of 0.16–
0.39 kGy on beef, chicken and other poultry meat by other studies. The
calculated D10 of S. aureus reported in this work also compares well with thereported range of 0.22–0.58 kGy on meat and poultry. The reported D10 valuesof the pathogens on the minced chicken substrate were higher than those on
the poached chicken meal.
Viable cells of E. coli and S. aureus in the non-irradiated poached chicken
meal stored at 3–5°C decreased by 1 and 2 log cycles respectively over the 28 d
storage period (Table 9, Fig. 3). Though viable cells of S. aureus increasedslightly by the 7th day, both viable cells of E. coli and S. aureus decreased
gradually to the 28th day (Fig. 3). A dose of 2 kGy reduced viable cells ofE. coli by almost 8 log cycles such that no surviving viable cells were detected in
the 28 d storage period.
A dose of 3 kGy eliminated the viable cells of S. aureus (Table 9, Fig. 3).
The results showed that populations of E. coli and S. aureus inoculated into thepoached chicken meal remained fairly stable for 7 d, after which period thenumbers declined by almost 2 log cycles to between 6.0 and 7.0 lg CFU/g after
a 28 d storage period. Other researchers have reported that pathogenic E. coli
generally survived well in foods at refrigeration temperatures (3–7°C) with a
100.5–101.5 CFU/g reduction over 1–5 weeks storage. Similarly, reports have also
indicated that though S. aureus has a long lag time at temperatures around
7–10°C, it survives and grows very slowly at lower temperatures. A dose of67

NKETSIA-TABIRI et al.

TABLE 9. EFFECT OF IRRADIATION ON THE GROWTH OF S. aureus
AND E. coli ON POACHED CHICKEN MEAL STORED AT 3–5°C
Microorganism

Storage time (d)

Dose
(kGy)

0

7

14

21

28

a

E. coli08.00 ± 1.05

7.91 ± 1.30

7.77 ± 1.35

7.22 ± 0.94

6.63 ± 1.00

S. aureus

08.30 ± 1.03

8.48 ± 0.78

8.21 ± 0.50

7.17 ± 0.82

6.47 ± 1.59

E. coli

2

0

0

0

0

0

S. aureus2

3.10 ± 0.27

2.27 ± 0.05

1.91 ± 0.63

1.56 ± 0.58

0.62 ± 0.72

E. coli

3

0

0

0

0

0

S. aureus

3

0

0

0

0

0

a

Mean count (lg CFU/g) of two independent experiments of two replicates each.
Mean ± SD (n = 4).

6

Log. of surviving fraction (N/No)

4

2

0
0

7

14

21

28

-2

-4

E. coli: 0 kGy
S. aureus: 0 kGy
E. coli: 2 kGy-6

S. aureus: 2 kGy
E. coli: 3 kGy
S. aureus: 3 kGy

-8

-10

Storage time (days)

FIG. 3. Survival of E. coli and S. aureus cells in irradiated and unirradiated poachedchicken meal stored at 3–5°C.

68

NKETSIA-TABIRI et al.

2 kGy reduced viable cells by 8 log cycles and completely eliminated E. colifrom the inoculated poached chicken meals. This finding is clearly supported by
the calculated D10 value of 0.18 kGy, which indicated that a dose of 2 kGy wasadequate enough to render inactivate an initial pathogen population of
108 CFU/g. It has also been reported that a dose of 2 kGy reduced viable cellsof E. coli by 7 log cycles and extended the shelf life of minced beef at 4°C threeto fivefold. The high susceptibility of E. coli to gamma radiation observed inthis study has also been reported elsewhere. In the case of S. aureus, a dose of
2 kGy reduced the initial viable cells by 5 log cycles to 3.10 lg CFU/g in the
inoculated poached chicken meal; and this residual population decreased overthe 28 d to <1.0 lg CFU/g. This finding is supported by other studies which haveindicated that though S. aureus is very susceptible to ionizing radiation, staphylococcal enterotoxin is very resistant to irradiation and will not be destroyed by
the approved dose used for the treatment of food. In addition, it has been
established that S. aureus is very resistant to heat and therefore survives
cooking in most instances. These facts are very significant since 104 CFU/g are
sufficient to produce food poisoning toxins. These findings emphasize the need
to use methods such as irradiation to eliminate S. aureus and therefore prevent
proliferation in foods.
In this study, 2 kGy completely eliminated E. coli while 3 kGy was
required to eliminate S. aureus (108 CFU/g) and prevent their growththroughout the 28 d storage period. However, considering the fact that both E.
coli and S. aureus are likely to be present in chilled ready meals, 3 kGy is therecommended dose to guarantee the hygienic safety of chilled poached chickenmeal.
3.4. Jollof rice
The moisture content of the jollof rice meal was 64.7 ± 2.0%, water
activity of 0.942 ± 0.002, pH6.11 ± 0.26, free fatty acids 0.06% and peroxide
value less than 0.01 Meq/kg. From the results, the jollof rice meal has ideal
conditions to support the growth of a wide range of spoilage and pathogenic
microbes unless preventative measures are taken. For example, the reported
minimum pH to support the growth of Salmonella spp. is 3.8 although the
optimum is 7–7.5; for the same organism, the minimum water activity for
growth is 0.94 and the optimum 0.99.
The TBC of the meal was between lg 2.9 ± 0.83 CFU/g and within the
microbiological standard for such ready meals. The general coliform count waslow (lg 1.70 ± 1.94 CFU/g) and also within the standard for such ready meals.
Faecal coliforms, Salmonellae and Staphylococci, were not detected. It is,however, noteworthy that isolates obtained from the general coliform plates

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NKETSIA-TABIRI et al.

included Klebsiella spp., Serratia marcescens and Salmonella spp. The
preliminary identification of Salmonella spp. among the general coliform
colonies but not detected on the xilose lysine desoxycholate agar for
Salmonellae count is noteworthy. Whilst this observation may infer very low
levels, the fact is that very low levels of Salmonellae can cause illness and it isimportant to ensure their absence from ready meals such as jollof rice. There isa need for the use of rapid identification techniques to facilitate theexamination of a wider range of colonies on all selective media.
Survival curves of E. coli, S. aureus and Salmonella spp. were studied as afunction of irradiation dose. The linear regression equations obtained for thepathogens in the jollof rice meal are presented in Table 10. The results
indicated that the number of surviving pathogens decreased linearly as theirradiation dose increased. The calculated D10 value of E. coli on the jollof rice
meal substrate was 0.173 ± 0.01 kGy; values obtained for S. aureus andSalmonella spp. were 0.260 ± 0.04 kGy and 0.285 ± 0.04 kGy, respectively. The
linear correlation coefficients of the regression lines were highly significant(p < 0.01), indicating a strong negative linear correlation. These results
suggested that E. coli in jollof rice was the most sensitive to ionizing radiationcompared with S. aureus and Salmonella spp. The ability of Salmonellae to growat temperatures of <5˚C has been reported, likewise the observation that they
are less sensitive to ionizing radiation at chilling temperatures.
The relatively lower D10 for E. coli in jollof rice compared with values
obtained for the poached chicken meal (0.182 kGy) and waakye meal
(0.248 kGy) in this study is attributed to the different compositions of themeals. The D10 values for S. aureus were also higher in the poached chicken
meal (0.271 kGy) and waakye meal (0.359 kGy). These results suggest that a
relatively lower radiation dose may be required to enhance the microbiologicalsafety of the jollof rice meal.

TABLE 10. RADIOSENSITIVITY OF PATHOGENS ON JOLLOF RICE
MEAL
PathogenRegression equationr2

D10 value(kGy)

E. coli

Y = –0.885X + 0.680

0.947

0.173 ± 0.010a

S. aureus

Y = –0.589X + 0.541

0.997

0.260 ± 0.051

Salmonella spp.

Y = –0.545X + 0.361

0.912

0.285 ± 0.044

aMean ± SD, of three independent experiments of two replicates each.

70

NKETSIA-TABIRI et al.

The results in Table 11 show that for the non-irradiated samples, there
was an initial increase in the population of all the three pathogens, but by the
14th day, a general decrease was observed; this trend continued to day 28. For
the irradiated samples, however, the population of the pathogens decreased
consistently. The observed data of this report are supported by other authors.
The results in Table 11 showed that 3 kGy is needed to ensure the microbiological safety of the jollof rice meal complete with gravy and beef tripe. It must
be emphasized that refrigeration temperature is very critical in the storage ofcook–chill meals, whether irradiated or not. It has been reported that proliferation of surviving microbes occurred rapidly at 10°C compared with 3°C at
equivalent doses of irradiation. This, therefore, highlights the need for good
refrigeration (0–3°C) of irradiated meals in order to achieve the maximum
benefits from irradiation.
Table 12 indicates that irradiation and storage had no significant effect on
the sensory quality of the gravy and beef tripe with respect to the attributes
tested. The results further indicated that all the attributes of the rice weresignificantly affected by either the irradiation dose and/or the storage time.
These observations support those reported for the poached chicken meal in thisTABLE 11.
EFFECT OF IRRADIATION ON GROWTH OF
PATHOGENS ON JOLLOF RICE MEAL DURING STORAGE AT 3–5°C
Pathogen

Dose
(kGy)

Storage time (d)
0

7

14

21

28

a

7.97 ± 0.23 7.65 ± 0.23 5.63 ± 0.65 5.37 ± 1.09

E. coli

08.04 ± 0.12

S. aureus

07.97 ± 0.69

8.41 ± 0.72 8.09 ± 0.51 7.45 ± 0.17 7.15 ± 0.16

Salmonella spp.

0

7.99 ± 0.49

8.42 ± 0.81 6.56 ± 0.31 6.79 ± 0.13 6.11 ± 0.30

E. coli21.61 ± 1.41a 1.26 ± 1.09

S. aureus2

4.02 ± 0.64

1.37 ± 1.19 1.28 ± 1.11

Salmonella spp.

2

3.56 ± 0.13

2.13 ± 0.46 1.44 ± 0.76 1.30 ± 1.12

E. coli

3

0

0

0

0

0

S. aureus

3

0

0

0

0

0

Salmonella spp.

3

0

0

0

0

0

0

0

0

0

0
0

a
Mean count (lg CFU/g) of three independent experiments of two replicates each.
Mean ± SD.

71

NKETSIA-TABIRI et al.

TABLE 12. SUMMARY OF 2-FACTOR ANALYSIS OF VARIANCE(ANOVA) WITH REPLICATION
Dose
Attribute

F value

Storage time (d)P value

F value

P value

Rice:
Colour

1.823

0.163

10.94

7E-07
(3.42, 4.13,
4.28, 6.16)

Grittiness

7.848

5E-04
(6.87, 6.41,
5.70)a

2.105

0.099

Hardness

13.46

2E-06
(6.77, 5.87, 5.19)

1.071

0.361

Taste

12.18

8E-06
(7.0, 6.54, 5.59)

2.935

0.033
(7.12, 6.67,
6.72, 6.90)

Aftertaste

13.59

2E-06
(6.9, 6.10, 5.83)

0.493

0.687

Aroma rancidity

0.646

0.586

1.304

0.273

Aroma sharpness

1.012

0.364

0.292

0.831

Flavour
sharpness

1.486

0.228

0.505

0.679

Flavour peppery

2.110

0.12

1.78

0.15

Chewiness

0.35

0.705

0.956

0.414

Fibrousness

0.578

0.562

1.351

0.258

Gravy:

Beef tripe:aMean scores for 0, 1.5, 3.0 kGy, respectively, or 0, 7, 14, 21 d storage time, respectively,in brackets.

study (Section 7.2.3) in that irradiation dose and storage time had a greater
impact on the sensory quality of the rice component than the chicken and gravy
component. In fact, the storage time did have a highly significant effect (p <0.001) on the rice (it became relatively lighter, finer and softer) as theirradiation dose increased. On the other hand the jollof rice aftertaste became
more appealing and the taste improved as the irradiation dose increased(Appendix). Furthermore, the taste of jollof rice improved as the storage time72

NKETSIA-TABIRI et al.

increased. These sensory data suggested that the treatment of jollof rice, gravy
and beef tripe with up to 3 kGy and chilled for 21 d did not seem to have anegative impact on the sensory quality of the meal.

4.

CONCLUSIONSThe pH and water activity of the prepared meals investigated weresuitable for the proliferation of spoilage microorganisms, coliforms andpotential pathogens.
The microbiological count of market samples of a complete waakye meal
exceeded the microbiological standards for such short shelf life foods; potential
pathogens were also present on the meals.
The microbiological counts on meals prepared under the HACCP plan aswell as jollof rice were within the microbiological standards for such short shelf
life foods. Some of the isolates of potential pathogens from waakye and its
accompaniments were also present on some of the meals prepared under the
HACCP. From these results, it could be concluded that although the adoptionof the HACCP improved the microbiological quality of prepared meals, it did
not eliminate potential pathogens. Consequently, there is a need tocomplement the HACCP with other processes that can eliminate pathogens inorder to enhance the microbiological safety of prepared meals.
From the radiosensitivity tests, it could be concluded that complete
waakye exerted protective effects on E. coli, S. aureus and Salmonella spp. suchthat their D10 values were higher than values obtained for the poached chicken
meal and jollof rice.
From the challenge tests using E. coli, S. aureus and Salmonella spp. on
the poached chicken meal or jollof rice, a 3 kGy dose was found to be sufficientfor the elimination of a mixture of the potential pathogens in order to ensure
the microbiological safety of the meals. In view of the relatively higher D10
values in complete waakye, more than a 3 kGy dose will be required to ensure
the microbiological safety of this meal if all the three potential pathogens were
present.
From the sensory tests, it could be concluded that vegetables such as
boiled carrots are unable to withstand more than a 1 kGy dose, consequently,
these should be packaged and treated separately or prepared fresh and servedwith the meal.
Treatment of poached chicken and gravy with 2 kGy or beef tripe andgravy in the jollof rice meal with up to 3 kGy did not have significant effects on
their sensory quality. Although the 1–3 kGy doses had significant effects on the73NKETSIA-TABIRI et al.

texture but not the colour of the rice components of the poached chicken mealand jollof rice, they were acceptable to the panellists.
From the foregoing, the microbiological safety and shelf life of a poachedchicken meal or jollof rice under chilled storage can be enhanced when treatedwith a 3 kGy dose. Such a treatment can extend the shelf life of the meals fromthe recommended 5 d to 28 d under chilled storage. It must be emphasized that
irradiation is not a replacement for good manufacturing practices and therefore
strict adherence to recommended storage temperature (0–3°C) is imperative inorder to achieve maximum benefits from irradiation.

ACKNOWLEDGEMENTS
The authors gratefully acknowledge the financial support and guidance
provided by the IAEA and the technical assistance of R. Banu, E. Akolmolga,
T. Mahami, D. Datohe, C. Owulah and J.-B.A. Mensah.

74

NKETSIA-TABIRI et al.

Appendix
DESCRIPTIVE PROFILE OF PREPARED MEAL

Name:

Date:

Dept.:

Product: Jollof rice

Please evaluate the intensity of the various named attributes of the jollof rice
samples provided. For each attribute, judge by placing a distinct vertical line on
the horizontal line given. Label each vertical line with its sample code.

437

249

572

681

Colour
Deep__________________________________________________________ Light

Texture (grittiness)
Fine__________________________________________________________Coarse

Texture (hardness)
Soft ___________________________________________________________ Hard

Flavour (aftertaste)
Appealing ____________________________________________________ Rancid

Taste
Nice __________________________________________________________ Awful75

NKETSIA-TABIRI et al.

DESCRIPTIVE PROFILE OF PREPARED MEAL

Name:

Date:

Dept.:

Product: Gravy

Please evaluate the intensity of the various named attributes of the gravy
samples provided. For each attribute, judge by placing a distinct vertical line on
the horizontal line given. Label each vertical line with its sample code.

437

249

572

681

Aroma (rancid/stale)
Fresh_________________________________________________________Rancid

Aroma (sharpness)
Savory ______________________________________________________ Pungent

Flavour (acid/sharpness)
Mild _________________________________________________________ Acidic

Flavour (peppery)
Mild____________________________________________________________ Hot76

NKETSIA-TABIRI et al.

DESCRIPTIVE PROFILE OF PREPARED MEAL

Name:

Date:

Dept.:

Product: Beef tripe

Please evaluate the intensity of the various named attributes of the samples ofbeef tripe provided. For each attribute, judge by placing a distinct vertical lineon the horizontal line given. Label each vertical line with its sample code.

437

249

572

681

Texture (chewiness)
Brittle________________________________________________________ Chewy

Texture (fibrousness)
Fine__________________________________________________________Coarse

77NKETSIA-TABIRI et al.

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TATINI, S.R., Thermal stability of enterotoxins in foods, Journal of Milk andFood Technology 39 (1976) 432–8.
PATTERSON, M.F., “Role of irradiation in a multiple-hurdle approach to foodsafety”, Ensuring the Safety and Quality of Food through Radiation Processing(Proc. FAO/IAEA/WHO Int. Conf. Antalya, 1999), Technomic Publishing
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PATTERSON, M.F., STEWART, E.M., “Effect of gamma irradiation on the shelflife and nutritional quality of ready made meals”, Radiation Processing for Safe,
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PART I: IMPROVEMENT OF THE
MICROBIOLOGICAL SAFETY OF
TWO CHILLED SEMI-PREPARED MEALSBY GAMMA IRRADIATION
J. FARKAS*, É. ANDRÁSSY*, L. MÉSZÁROS**,K. POLYÁK-FEHÉRCorvinus University of Budapest
J. BECZNER
Central Food Research InstituteÖ. GAÁL, V.K. LEBOVICS, A. LUGASINational Institute of Food Safety and Nutrition
Budapest, Hungary

Abstract
Experimental batches of a stuffed pasta product, tortellini and slightly pre-friedbreaded reconstituted turkey meat steaks with cheese and ham filling, cordon bleu, wereprepared according to commercial recipes, then inoculated to 104 CFU/g with Staphylococcus aureus (in the case of tortellini) and to 106 CFU/g with Listeria monocytogenes (inthe case of cordon bleu) prior to packaging in plastic pouches under a gas atmosphere of
20% CO2 and 80% N2. The inoculated packages were irradiated at 3 kGy (tortellini) and2 kGy (cordon bleu) by a 60Co source. The applied radiation doses were sensoriallyacceptable with these products. The experimental batches of tortellini were stored at 15oC,
while the cordon bleu samples were stored at 5 and 9°C, respectively. Non-irradiatedsamples were kept together with the respective irradiated ones. Storage was continued for
4 weeks and microbiological tests were performed before and after irradiation, and subsequently after every 7 d. Besides selective estimation of the counts of the test organisms,
total aerobic counts, and in the case of cordon bleu, colony counts of lactic acid bacteria,Enterobacteriaceae, sulphite reducing Clostridia, yeasts and moulds were also selectively
estimated. The 3 kGy dose reduced the S. aureus count in tortellini below the detection
limit (lg CFU = 0.26), and it remained undetectably low in the irradiated samples during
the whole 28 d of storage, while the S. aureus count in the non-irradiated samples
increased up to 108 CFU/g by the 8th day. The Listeria count in the cordon bleu was
reduced by irradiation from the initial lg CFU/g = 6.1 to lg CFU/g = 3.5. At 5oC storage,* Central Food Research Institute, Budapest, Hungary.
** National Institute of Food Safety and Nutrition, Budapest, Hungary.

81

FARKAS et al.

this residual count remained stagnant up to 3–4 weeks, but started to increase at 9°C after
one week. In the non-irradiated samples, the Listeria count increased hundredfold over
4 weeks at 5oC, and over 2 weeks at 9oC. Sulphite reducing Clostridia were, and remained,
undetectable (lg CFU/g < 0.48) in all samples even at 9°C. The limiting factor of the shelf
life of the non-irradiated poultry product was the growth of lactic acid bacteria at 9oC,
whereas enhanced lipid oxidation was an unwanted side-effect of radiation treatment. The
conclusion drawn from these studies is that the potential risk posed by the investigatednon-spore-forming pathogenic bacteria could be considerably reduced by gamma irradiation. However, storage temperature remains a crucial factor for safety and methods
should be developed to counteract the lipid oxidative effect of the radiation processing.

1.

INTRODUCTION

There is a growing interest in marketing semi-prepared and prepared
meals contained in modified atmosphere packages and distributed underchilled conditions instead of in the frozen state. Such products are less energy
demanding and more attractive for the consumers than frozen meals. However,they are non-sterile and potential survival of some pathogenic microorganisms
and/or post-processing contamination before packaging create microbiologicalrisks and place a considerable limitation on shelf life, especially under abusive
temperature conditions which may frequently occur during the retail display
period and during home storage before consumption.
Irradiation is an effective way to eliminate non-spore-forming pathogens
without changing the physical state of foods [1]. Therefore, the objective of theauthors’ work was to investigate the feasibility of diminishing the above risk by
gamma irradiation of two types of chilled semi-prepared meal: a filled pasta
product, tortellini, and slightly pre-fried reconstituted breaded turkey meatsteaks containing cheese and ham filling (cordon bleu). For challenge tests [2],experimental batches of the tortellini and cordon bleu were inoculated with
Staphylococcus aureus and Listeria monocytogenes, respectively.

2.

MATERIALS AND METHODS

2.1. Test organisms and preparation of inocula
The S. aureus strain ATCC 6538, obtained with a code number of B01462
as a liophylized culture from the National Collection of Agricultural andIndustrial Microorganisms, Budapest, was used as inoculum for tortellini.

82

FARKAS et al.

Resuscitation of the stock culture was made in brain–heart infusion broth(Merck, 1.10493). Its growth was checked by a Staphylococcus enrichment
broth and formation of typical colonies on Baird Parker agar (Merck, 1.07809),
as well as positive catalase and coagulase tests. Storage and subculturing weredone on brain heart infusion and plate count agar slopes.
For preparation of the inoculum, the bacterium was cultivated by shaking
in brain–heart infusion broth at 37°C for 24 h. The cells were harvested in arefrigeration centrifuge after 15 min at rcf 27 200 (15 000 rpm), andresuspended in Sörensen’s phosphate buffer of pH7.0.
Listeria monocytogenes 4ab strain No. 10, obtained from the culturecollection of Dr. B. Ralovich (National Meat Research Institute, Budapest),
was used as the test organism for cordon bleu. A 24 h culture produced at 30°C
in brain–heart infusion broth in a shaker bath was centrifuged as above for
15 min, and the sedimented cells were resuspended in sterile water.
2.2. Test materials
A commercially prepared tortellini pasta product and cordon bleu
composed of breaded and mildly pre-fried reconstituted turkey meat steaks
containing a slice of ham and a slice of cheese were used as test materials.
Cordon bleu is marketed presently as an aerobically packaged quick frozen
food.
The tortellini dumplings were made from durum wheat flour, egg andwater, and the stuffing was prepared from bread crumbs, smoked ham, cheese,salt, pepper and sodium glutamate. The pasta:filling ratio was 25:9. Water
activity of the product was approximately 0.96 at 25°C, and the pH ranged
between 5.5 and 6.1.
The water activity of cordon bleu was also approximately 0.96 at 25°C,
and the pH of the homogenized samples was in the range of 6.24–6.30.
2.3. Inoculation and packaging of samples
Tortellini dumplings were inoculated individually to approximately
10 CFU/g level with 10 μL aliquots of the S. aureus suspension prepared asabove, and the inoculated pasta (10 dumplings per pouch) were packaged by a
MULTIVAC Victus packaging machine with the packaging foil of thecommercial pasta producer under a gas atmosphere of approximately 20% CO2
and 80% N2. The residual O2 content was 0.23%.
Individual ‘steaks’ of cordon bleu were inoculated with 120 µL of
L. monocytogenes suspension, distributing it in 10 µL aliquots on the surface ofthe lightly pre-fried steaks, in order to obtain a Listeria contamination of
483

FARKAS et al.

approximately 106 CFU/g of the test material. The steaks were then vacuum
packed (10 bar residual pressure) into multibarrier-4 laminated foil pouches
which were then refilled to 750 bar pressure with a gas mixture of approximately 20% CO2 and 80% N2.
2.4. Radiation processing
Numerous replicate packages of the inoculated products were irradiatedby an RHγ-30 type self-shielded 60Co gamma irradiator at a dose rate of
2.4 kGy/h. Processing doses were 3 kGy for tortellini and 2 kGy for cordon
bleu, sensorially acceptable doses selected by preliminary experiments
reported elsewhere [3]. Non-irradiated packages were kept together with theirradiated samples as controls.
2.5. Storage and microbiological testing
The experimental batches of tortellini were stored at 15°C, representing astrongly abusive but not infrequent temperature condition, while cordon bleu
samples were stored at both 5 and 9oC. Storage was continued for 4 weeks andmicrobiological tests were performed before and after irradiation, andsubsequently after every 7 d of storage.
Besides selective estimation of the counts of the test organisms, total
aerobic viable cell counts, and, in the case of cordon bleu, also colony counts oflactic acid bacteria, Enterobacteriaceae, sulphite reducing Clostridia, as well as
yeasts and moulds were selectively estimated from appropriate dilution levels
prepared from duplicate packages per treatment.
Estimation of S. aureus was performed both by direct spread plating on
Baird Parker agar + tellurite egg yolk emulsion (Merck, 1.03785) at 37°C
(incubation for 48 h), and by Staphylococcus enrichment broth tubes (Merck,
1.07899), with K2TeO3 (Merck, 1.05164).
Selective estimation of L. monocytogenes was done both in Oxford agar
(Merck, 1.07004) with Listeria supplement (Merck, 1.07006), counting after 24
and 48 h at 30°C, and by the MPN technique as well, in triplicate liquid culturesusing Listeria enrichment broth (Merck, 1.10259) and incubation at 30°C for up
to 5 d. Listeria positive tubes were verified by subculturing them onto Oxoid
agar plates.
Total bacteria counts (TBCs) were estimated in casein-pepton-dextroseyeast agar (Merck, 1.05463) at 30°C with incubation for 2–3 d.
The counts of bacterial spores were determined by plating as the total
aerobic counts after 10 min heat treatment at 80oC of the first dilution level.

84

FARKAS et al.

Lactic acid bacteria were counted by plating into MRS medium (Merck
1.10661) with 1.5% agar, covered after inoculation with a surface layer of thesame medium, and incubated at 30°C for 3 d.
Enterobacteriaceae counts were estimated by plating in violet red bile
glucose agar (Oxoid, CM485), overlayered with the same medium, andincubated at 37°C for 24 h.
Sulphite reducing clostridia were investigated by plating into differential
clostridial agar according to Wenk (Merck, 1.10259) supplemented with ferricammonium citrate (1 g/L) and Na2SO3 (0.75 g/L), incubated in Oxoid HP11
anaerobic jars containing Oxoid Anaerogen AN35 oxygen adsorbent.
Yeasts and moulds were estimated in thin layers of DRBC agar (Oxoid
CM 727) with chloramphenicol and supplement (Oxoid SR 078E), incubatedfor 6 d at room temperature.
2.6. Measurement of head space gas composition
The head space of the modified atmosphere packaged samples waschecked by a SERVOMEX infrared gas analyser PA 404 for CO2 and by a
SERVOMEX oxygen analyser 574 for O2 content.
2.7. Measurement of pH and water activity
The pH was measured by a Physitemp electric pH meter and water
activity was estimated by the crystal liquefaction method.
2.8. Thiamine content
Thiamine (vitamin B1) content was estimated by a microbiologicalmethod [4]. This specific and sensitive method is based on the extent of growthof a Lactobacillus test organism, which has a requirement for thiamine, on athiamine-free basal medium when aliquots of extracts of a thiamine containing
food are added to it. The growth response is measured turbidimetrically after
an incubation period at 30°C and the optical density is compared to a standard
curve.
2.9. Lipid oxidation
Lipid oxidation was investigated by determination of thiobarbituric acidreactive substances (TBARS values) according to Newburg and Concon [5],expressed in malonaldehyde concentrations. Malonaldehyde is an oxidative
breakdown product formed mainly from peroxidized polyunsaturated fatty acids.

85

FARKAS et al.

3.

RESULTS3.1. Radiation processing of modified atmosphere package chilled tortellini
3.1.1. Microbiological effects
Results of the microbiological tests are summarized in Table 1.
The initial total aerobic viable cell counts of the inoculated samples were
determined by the S. aureus inoculum, because the original total aerobic cellcount of the non-irradiated samples was 2 log cycles less, approximately lg CFU= 2.3/g, composed mainly of aerobic bacterial spores.
As a result of irradiation, the S. aureus count was reduced to below thedetection limit (which was lower in the case of the MPN technique), i.e. lessthan lg CFU = 0.26. Thus, the radiation treatment resulted in a more than 3 log
cycle reduction of the test organism in the pasta product.
Considering the initial TBCs of the irradiated samples at the beginning of
the storage (lg CFU ≈ 1.5/g), the aerobic spores of the ‘native’ microbiota was
reduced by somewhat less than one log cycle by the 3 kGy dose. The surviving
spore formers were unable to grow in the irradiated samples under the experimental conditions.
The S. aureus inoculum grew up to the 108 CFU/g level in the nonirradiated samples within 8 d, although no S. aureus cells were found in theirradiated batch during 28 d storage at 15°C.

TABLE 1. LOGARITHM OF VIABLE CELL COUNTS IN DUPLICATESAMPLES OF TORTELLINI STORED AT 15°C
Storage time (d)Viablecell counts

0
0 kGy

8
3 kGy

0 kGy

14
3 kGy

0 kGy

28
3 kGy

0 kGy

3 kGy

a

TBCs

4.32
4.28

1.48
1.54

7.99
7.91

4.52
4.18

8.11
8.04

4.81
4.70

n.i.
n.i.

5.75
7.43

S. aureus(Baird Parker)

4.08

<1.70

7.98

<1.70

8.04

<1.70

n.i.

<1.70

4.04

<1.70

7.95

<1.70

8.04

<1.70

n.i.

<1.70

4.08

<0.26

7.88

<0.26

7.36

<0.26

n.i.

<0.26

4.67

<0.26

8.36

<0.26

7.36

<0.26

n.i.

<0.26

S. aureus(enriched broth)an.i. = not investigated.

86

FARKAS et al.

The aerobic total bacteria cell counts started to increase in the irradiatedsamples only after 8 d storage, and their slow increase afterwards was due tosome yeasts and micrococci forming white colonies distinctly different fromthose of the test organism.
3.1.2. Thiamine content
The thiamine content of the untreated samples was found to be 34 μg/100 g,
with an accuracy of +/–10%, and it was not changed by the radiation dose
applied.
3.2. Radiation processing of the modified atmosphere packaged
chilled cordon bleu
3.2.1. Microbiological effects
In order to determine how much microbial loads have been carried by the
pre-fried cordon bleu, individual components of uninoculated and nonirradiated steaks were investigated for TBCs, bacterial spores (cells surviving at
80°C for 10 min) and viable cell counts of lactobacilli, at the beginning of thestorage experiment. The results are shown in Table 2.
These results show that, although in relatively low numbers, not only
bacterial spores but also vegetative bacterial cells can be recovered from eachcomponent of the product. Therefore, in principle, there is an opportunity thateventual pathogenic contamination might occur in such product.

TABLE 2. MICROBIAL LOAD OF INDIVIDUAL COMPONENTS OF
THE UNINOCULATED AND NON-IRRADIATED CORDON BLEU
(lg CFU/g VALUES OF DUPLICATE SAMPLES)
Component

TBC

Spore countLactobacilli

Crumb

2.30
1.84

0.95
0.78

<0.48
<0.48

Turkey meat

2.15
2.73

0.48
0.48

1.48
1.89

Ham

1.32
1.71

1.48
<0.48

<0.48
<0.48

Cheese

2.36
2.32

1.89
1.82

0.78
0.78

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FARKAS et al.

TABLE 3. MICROBIOLOGICAL CHANGES OF INOCULATED NONIRRADIATED AND INOCULATED IRRADIATED (2 kGy) MODIFIEDATMOSPHERE PACKAGED CORDON BLEU AT 5°C STORAGE
TEMPERATURE (lg CFU/g VALUES OF DUPLICATE SAMPLES)
Untreated (d)Irradiated (d)Parameter
1

7

14

21

28

1

7

14

21

28

Listeria
counts

6.08
6.15

6.18
6.15

6.73
6.66

7.48
7.28

8.08
7.56

3.53
3.57

3.30
3.26

2.92
2.89

2.62
2.68

5.15
3.52

Lactobacilli

<0.48
<0.48

<0.48
<0.48

1.26
<0.48

4.00
6.11

6.41 <0.48
6.23 <0.48

<0.48
<0.48

<0.48
<0.48

<0.48
<0.48

<0.48
<0.48

pH

6.17
6.16

6.14
6.12

6.02
6.04

6.02
6.00

5.73
5.87

6.14
6.13

6.03
6.04

6.08
6.07

6.03
6.02

6.15
6.14

TABLE 4. MICROBIOLOGICAL CHANGES OF INOCULATED NONIRRADIATED AND INOCULATED IRRADIATED (2 kGy) MODIFIEDATMOSPHERE PACKAGED CORDON BLEU AT 9°C STORAGE
TEMPERATURE (lg CFU/g VALUES OF DUPLICATE SAMPLES)
Untreated (d)Irradiated (d)Parameter
1

7

14

21

28

1

7

14

21

28

Listeria
counts

6.08
6.15

6.98
7.43

8.15
8.04

8.90
8.46

8.51
8.41

3.53
3.57

3.74
3.46

6.52
6.46

7.71
7.79

8.11
8.15

Lactobacilli<0.48 <0.48<0.48 <0.48

1.62
<0.48

4.15
6.36

7.41
8.04

<0.48
<0.48

<0.48
<0.48

<0.48
<0.48

<0.48
<0.48

<0.48
<0.48

pH

6.17
6.16

6.07
6.06

5.74
5.72

5.74
5.63

5.56
5.58

6.15
6.14

6.13
6.14

6.04
6.05

5.94
5.92

5.72
5.75

The Listeria counts and the counts of lactobacilli of the inoculated
samples are shown together with the pH values in Tables 3 and 4 as a functionof irradiation and storage time.
Owing to the heavy inoculation and the low number of the native
microbiota, the total viable cell counts are not shown, because they were equalwith the Listeria counts. Other types of microorganism (spore counts, Enterobacteriaceae, yeasts and moulds) selectively investigated were and remained
under the detection level of lg CFU/g = 0.48.

88

FARKAS et al.

The Listeria count in cordon bleu was reduced by irradiation from theinitial lg CFU/g = 6.1 to lg CFU/g = 3.5. During storage at 5°C (Table 3), thisresidual count remained stagnant up to 3–4 weeks, but at 9°C (Table 4) it
started to increase after the first week. In the non-irradiated samples, theListeria counts increased hundredfold over the 4 weeks at 5°C, and over the
first 2 weeks at 9°C. The limiting factor of the microbiological shelf life of the
non-irradiated product was the growth of lactic acid bacteria at 9°C, although
they were in undetectably low numbers during the first two weeks of storage.
They apparently survived the pre-frying process heterogeneously distributed
and in very low counts inside the product.
The radiation treatment was effective in eliminating this low number oflactic acid bacteria. In spite of the buffer capacity of the samples, the decreasein the pH of the non-irradiated samples reflected the growth of lactic acidbacteria. However, a slight decrease of the pH was also noted in the irradiatedsamples during the course of storage, when an extensive growth of thesurviving Listeria was observed.
3.2.2. Gas composition of the head space of the experimental product
The CO2 and O2 contents of the head space of the packages as a functionof the storage time and temperature are given in Table 5.

TABLE 5. THE CO2 AND O2 CONTENTS OF THE HEAD SPACE OF
MODIFIED ATMOSPHERE PACKAGED CORDON BLEU AS A
FUNCTIONOFSTORAGETIME
AND
TEMPERATURE(MEASUREMENTS OF DUPLICATE PACKAGES)
Treatment
0 kGy

CO2 (%)
O2 (%)
Temperature(°C)
Initial 1 d 7 d 14 d 21 d 28 d Initial 1 d 7 d 14 d 21 d 28 d
5
9

2 kGy

19
20

10 12

10

12

12

12

11

8

12

12 14

10

20

18

12

11

17

18

9

11

10

10

5

20

11

12

12

11

11

9

18

11 12

15

14

16

10

12

13

14

1.4

2.0 2.0 1.6

1.8

1.9

1.8 1.5

1.8

1.8

1.8 1.7 1.5

1.7

1.7

1.4 1.4

1.7

1.7

1.5

1.7 1.8 1.3

2.0

2.0

1.7 1.0

2.0

2.0

1.4

1.7 1.3 0.8

1.9

2.0

1.7 0.4

1.9

1.9

1.4

89

FARKAS et al.

These measurements revealed that a considerable part of the CO2
introduced during packaging was soon dissolved in the high moisture product.
Thus, the equilibrium CO2 concentration in the head space became 10–12% in
those packages which have been stored at 5°C, while at 9°C the head spaceconcentration of CO2 increased again when bacterial growth became intense.
The O2 contents were most frequently between 1.5 and 2.0%, irrespective of
the storage temperature and time.
3.2.3. Appearance of the samples and lipid oxidation
The radiation treatment did not change the appearance of the samples
and no ‘off’ odour was noted at the opening of the pouches in the first half ofthe storage period. However, after 2 weeks of refrigerated storage, thebreadcrumb coating of the steaks started to develop a less freshly fried, moist
appearance, independent of the radiation treatment and the cheese slice inside
the non-irradiated samples started to liquefy, more intensely at 9°C than at 5°C.
Over the last two weeks of storage, the samples gradually lost their fresh,
attractive appearance and produced some oily exudation. The untreatedsamples developed a stale odour, while in the irradiated samples a rancid odour
was noted when they were prepared with an homogenizer for microbiologicaltesting.
The TBARS values of cordon bleu samples measured directly after
irradiation and after 4 weeks storage are given in Table 6. The increased TBAR
values showed that lipid oxidation progressed during storage and it wasenhanced by the radiation treatment.

TABLE 6. TBARS VALUES OF CORDON BLEU SAMPLES AS A
FUNCTION OF IRRADIATION AND STORAGETBARS (malonaldehyde mg/kg)
Radiation dose(kGy)

Directly after
irradiation

After 4 weeks
storage at 5°C

9°C

Mean

S.D.

Mean

S.D.

Mean

S.D.

0

0.38

0.04

0.85

0.03

1.00

0.24

2

0.51

0.03

1.58

0.20

1.86

0.25

90

FARKAS et al.

4.

DISCUSSION

The international literature on filled pasta products shows that theincidence of contamination with S. aureus is not infrequent [6–10]. The water
activity level of the product investigated in the authors’ experiments would not
exclude either the opportunity for growth and enterotoxin formation of
S. aureus if the pathogen would contaminate this type of product. Owing to thehigh heat resistance of Staphylococcus enterotoxins, the final cooking of thesestuffed pastas cannot inactivate pre-formed toxins. Therefore, inoculated packstudies were undertaken. The authors’ experiments showed that S. aureus was
growing readily at 15°C in the inoculated tortellini (water activity = 0.96), but
the 104/g artificial contamination level of the pathogen could be eliminatedfrom the experimental samples by 3 kGy of gamma radiation, a sensoriallyacceptable dose level, which did not decrease the thiamine content of the
product.
The present commercial production technology cannot fully ensure thesafety of the poultry product cordon bleu for non-frozen storage even undermodified atmosphere packaging, because even some vegetative bacteria mightsurvive the mild pre-frying of the product. Survival and growth of lactic acidbacteria in the non-irradiated experimental batches make it probable that
L. monocytogenes, a ubiquitous environmental contaminant, might eventually
be present too, and this is able to multiply during refrigerated storage. The
Listeria count in cordon bleu was reduced by 2.6 lg units by the sensoriallyacceptable 2 kGy gamma radiation dose. This extent of lethality is close to theresult of Thayer et al. [11] who found that the D-value of L. monocytogenes was
0.63 ± 0.06 kGy in ground cooked turkey meat. The observed reduction in
L. monocytogenes, the most radiation resistant non-spore former [12], could
result in a Listeria-free product, if the contamination level of this pathogen is
not higher than 102 CFU/g. In the authors’ heavily contaminated experimental
batch, the surviving level of the test organism remained stagnant at 5°C for up
to 3–4 weeks in the irradiated samples, while the Listeria counts of the nonirradiated samples increased a hundredfold over 4 weeks at 5°C, and over
2 weeks at 9°C. In irradiated samples stored at 9°C, the surviving Listeria also
started to grow after one week. This slow recovery of the radiation survivors isin agreement with the observation of Patterson et al. [13] who irradiated raw
and cooked poultry meat inoculated with L. monocytogenes with doses of 1.0
and 2.5 kGy and found that irradiation resulted in significantly increased lagtimes for this pathogen. Regarding psychrotrophic spore forming pathogens, it
is reassuring that sulphite reducing Clostridia were, and remained, undetectable during the entire period of the experiments, even in the non-irradiatedsamples. The results can be compared with those of Hashim et al. [14] who

91

FARKAS et al.

irradiated chicken meat with doses of 1.66–2.86 kGy to determine the effects ofradiation processing on the sensory attributes of both raw and cooked meat,but did not find significant effects upon the appearance or taste of cookedbreast meat. Kanatt et al. [15] irradiated minced chicken with 2.5 kGy andstored it at 0–3°C for up to 4 weeks. The irradiated meat was microbiologicallysafe and sensorially acceptable in the unfrozen state up to the end of thisstorage; the non-irradiated minced chicken had a shelf life of less than 2 weeks.

5.

CONCLUSIONSOne can conclude from these studies that the potential microbiologicalrisk in the experimental products posed by the investigated non-spore forming
pathogenic bacteria could be considerably reduced by sensorially acceptableradiation doses. However, storage temperature remains a crucial factor ofsafety, and increased lipid oxidation is a limiting factor of the shelf life of theirradiated poultry product even under the low O2 concentration of modified
atmosphere packaging. The possibility of counteracting lipid oxidation by
efficient use of antioxidative additives will be the subject of further studies.

ACKNOWLEDGEMENTS
The authors acknowledge, with gratitude, the estimation of the thiaminecontent of the tortellini samples made by M. Kontraszti of the National
Institute of Nutrition and Food Hygiene, Budapest.

REFERENCES
[1]
[2]

[3]

[4]
[5]

92

MOLINS, R.A., (ed.), Food Irradiation: Principles and Applications, Wiley
Interscience, NewYork (2001).
FOLEY, D.M., et al., Elimination of Listeria monocytogenes and changes inphysical and sensory qualities of a prepared meal following gamma irradiation,
Food Microbiol. 18 (2001) 193.
FARKAS, J., Improvement of the Microbiological Safety and Shelf-Life of
Selected Chilled Meals by Gamma Irradiation, Progress Report to the IAEA,
Contract No. 11905/R0, Szent István University, Budapest (2002).
GYÖRGY, P., PEASON, W.N., The Vitamins, Academic Press, New York (1967)
80-83, 130.
NEWBURG, D.S., CONCON, J.M., Malonaldehyde concentrations in food are
affected by cooking conitions, J. Food Sci. 45 (1980) 1681-1683.

FARKAS et al.

[6]
[7]
[8]

[9]
[10]
[11]
[12]

[13]

[14]
[15]

OSTOVAR, K., WARD, K., Detection of Staphylococcus aureus from frozen andthawed convenience pasta products, Lebensm.-Wiss. u.-Technol. 9 (1976) 218-219.
TROVATELLI, L.D., et al., Microbiological quality of fresh pasta dumplings soldin Bologna and the surounding district, Int. J. Food Microbiol. 7 (1988) 19-24.
PARK, C.E., et al., A survey of wet pasta packaged under a CO2:N2 (20:80)
mixture staphylococci and their enterotoxins, Can. Inst. Food Sci. Technol. 21(1988) 109-111.
FARBER, J.M., et al., Modified-atmosphere packaged pasta: a microbiologicalquality assessment, Ital. J. Food Sci. 2 (1993) 157-166.
ALTIERI, C., et al., Presence of Staphylococcus aureus in fresh pasta and freshegg pasta, Advances in Food Sciences 24 (2002) 37-39.
THAYER, D.W., et al., Fate of gamma irradiated Listeria monocytogenes on raw
or cooked turkey breast meat, J. Food Prot. 61 (1998) 979-987.
FARKAS, J., “Eliminating of Foodborne Pathogens by Ionising Radiation”, Food
Safety Assurance and Veterinary Public Health, Vol.2, Safety Assurance during
Food Processing, (SMULDERS, F.J.M., COLLINS, J.D. (Eds.), Wageningen
Academic Publishers, The Netherlands (2004) 157-176.
PATTERSON, M.F., et al., Effects of irradiation dose and storage temperature on
growth of Listeria monocytogenes on poultry meat, Food Microbiol. 10 (1993)
197-203.
HASHIM, I.B., et al., Descriptive sensory analysis of irradiated frozen and refrigerated chicken, J. Food Sci. 60 (1995) 664-666.
KANATT, S.R., et al., Effect of gamma irradiation on the lipid peroxidation inchicken, lamb and buffalo meat during chilled storage, J. Food Safety, 17 (1997)
283-294.

93.

PART II: EFFECTS OF GAMMA IRRADIATIONON LIPID AND CHOLESTEROL OXIDATIONIN MECHANICALLY DEBONED TURKEY MEAT
J. FARKAS*, É. ANDRÁSSY*, L. MÉSZÁROS**,K. POLYÁK-FEHÉRCorvinus University of Budapest
J. BECZNER
Central Food Research InstituteÖ. GAÁL, V.K. LEBOVICS, A. LUGASINational Institute of Food Safety and Nutrition
Budapest, Hungary

Abstract
The pasteurizing effect of a 2 kGy radiation dose on non-frozen mechanicallydeboned turkey meat was achieved without increase in cholesterol oxidation products
or increases in thiobarbituric acid reactive substance values during 15 d of chilledstorage following the treatments, while untreated samples were spoiled. The addition ofantioxidants, such as thyme oil or α-tocopherol plus ascorbic acid, significantly inhibitedthe oxidative changes of cholesterol and lipids during 3 kGy treatment.

1.

INTRODUCTION

The authors’ earlier work (see Part I and Refs [1, 2]), and other work in
the literature [3–7], showed that gamma irradiation accelerates the formationof cholesterol oxidation products (COPs) and increases the thiobarbituric acidreactive substance (TBARS) values. All of these studies showed that thepresence of oxygen, which depends on packaging and treatment conditions, is
one of the most important factors in the formation of COPs and lipid oxidation.
Certain cholesterol oxidation compounds have potentially undesirable
biological activities such as atherogenicity, atherosclerosis, cytotoxicity,
mutagenicity and carcinogenicity, and furthermore may cause cell membrane* Central Food Research Institute, Budapest, Hungary.
** National Institute of Food Safety and Nutrition, Budapest, Hungary.

95

FARKAS et al.

damage as well as inhibiting cholesterol biosynthesis. Current knowledge ofcholesterol oxidation and its biological effects has been reviewed in detail byGuardiola et al. [8]. Cholesterol oxides are present in certain foodstuffs inconcentrations of a few milligrams per kilogram. Cholesterol and lipidoxidation are affected by various factors, such as light, heat, radiation, oxygen,moisture, pH, certain pro-oxidizing agents, processing procedures and storage
conditions. In the authors’ studies, the effects of gamma irradiation on the
microbiological status, as well as on the oxidation of cholesterol and otherlipids, were compared. The efficiency of natural antioxidants in suppressing theundesirable oxidative changes during the treatments in fresh and chill stored
samples was also studied.

2.

MATERIALS AND METHODS

2.1. Test material and packaging
Numerous portions of 25–40 g of commercial, mechanically deboned
turkey meat were packaged into small plastic pouches formed from multibarrier 4 PE-PA laminated foil of 100 µm thickness (produced by WIPAK,
Finland), oxygen transmittance: 5 mL·m–2·24 h–1atm at 23°C and 50% relative
humidity, and sealed without evacuation by a MULTIVAC model 300 machine(Haggenmüller, Walfertschwerden, Germany).
2.2. Ionizing radiation
The MDM samples were treated with dosage levels of 2 and 3 kGy in a
Co self-shielded radiation source, type RH-g-30, at a dose rate of 3.9 kGy/h atapproximately 5°C in the presence of antioxidant additives, then stored
together with non-irradiated samples at 4°C for 15 d.

60

2.3. Addition of antioxidants
For assessing the effects of antioxidants, before packaging and radiation
treatment, the mechanically deboned turkey meat was divided into threeexperimental batches: (1) without antioxidants, (2) with addition of 250 mg
thyme oil/100 g and (3) with addition of 12 mg α-tocopherol plus 25 mg
ascorbic acid/100 g sample.

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FARKAS et al.

2.4. Analyses
2.4.1. Microbiological status
Total bacteria counts (TBCs) in tryptone glucose extract (TGE) agar
plates (Merck 1.05463) and Enterobacteriaceae counts on violet red bile glucose(VRBG) agar (Oxoid CM485) were estimated after incubation at 30°C for
48 h.
2.4.2. Measurement of thiobarbituric acid reactive substances (TBARS values)
The TBARS values were estimated according to Ramanathan and Das [9]and expressed as malondialdehyde.
2.4.3. Determination of cholesterol oxides
Approximately 50 g samples of meat or 100 g of chicken liver wereextracted with chloroform/methanol (2:1, v) according to Folch et al. [10]. Afterevaporation of solvents, the lipid extract was dissolved in 200 mL 1M potassiumhydroxide in methanol and saponified by refluxing for 60 min under a stream ofnitrogen. A 200 mL volume of distilled water was added to the saponified
mixture and the non-saponified organic layer was extracted three times with
100 mL of di-isopropyl-ether (Fluka AG, puriss) and the combined fractions
were washed three times with 200 mL distilled water and dried with anhydrous
sodium sulphate [11]. The filtrate was evaporated to dryness under vacuum.
The residue was dissolved in chloroform/methanol (2:1, v) to make aconcentration of 0.1 g/mL [1].
2.4.4. Separation and identification of cholesterol oxidation derivatives
The non-saponifiable extract was analysed by HPTLC using pre-coated
HPTLC Sil G 60F254 thin layer 10 cm × 10 cm glass plates, purchased from E.
Merck (Darmstadt, Germany). The chromato plates were developed twice in
heptane-ethylacetate (1:1, v). The plates were examined under UV light(254 nm) and sprayed with 100 g/L of CuSO4·5H2O dissolved in 85 mL/L
phosporic acid and heated to 110°C for several minutes for colour development. The identity of spots was confirmed by comparison with authentic
standards of known colour and Rf values [1].

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FARKAS et al.

2.4.5. Quantitation
The spots of silica gel adsorbents containing oxysterols were scraped andeluted. The determination of oxycholesterols was performed by the test systemcholesterol enzymatique PAP 250 ref 61225 which is based on the effect ofcholesterol oxidase [12].

3.

RESULTS3.1. Effects of 2 kGy irradiation and 15 d chilled storage
The effects of irradiation and chilled storage on the total aerobic bacteriacell count are shown in Table 1.
The radiation treatment resulted in a one log cycle reduction of the viable
cell count and no further changes were observed during 15 d storage of treatedsamples, while the untreated samples were spoiled.
3.1.1. Sensory changes
The radiation treatment did not generate an off odour or colour changes.
3.1.2. Cholesterol oxidation
Table 2 presents the results of COPs measurements in untreated andirradiated samples, respectively.

TABLE 1. TOTAL BACTERIA COUNTS IN MECHANICALLYDEBONED TURKEY MEAT (lg CFU/g) AFTER 2 kGy TREATMENT
AND 15 d CHILLED STORAGE
Chilled storage (+4°C)
0d

15 d

Control

7 × 103

8 × 107a

2 kGy

8 × 102

7 × 102a

The samples were spoiled.

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FARKAS et al.

TABLE 2. CONCENTRATION OF TOTAL COPs (mg/kg) IN
UNTREATED SAMPLES OF MECHANICALLY DEBONED TURKEY
MEAT AND THOSE TREATED WITH 2 kGy, FOLLOWED BY
REFRIGERATED STORAGE FOR 15 dControl

Total COPs

2 kGy

0d

15 d

0d

15 d

0.18

Samples spoiled

0.19

0.67

There were measurable initial levels of total COPs in the non-irradiatedmaterial, although no significant increase was noted directly after the relatively
low dose. After 15 d storage, a measurable increase of COPS was observed in
the non-spoiled, irradiated samples. The low initial TBARs value(0.035 malonaldehyde eqv·mg/kg) remained unchanged.
3.2. Effect of natural antioxidants on the microbial status and undesirable
oxidative changes in 3 kGy irradiated mechanically deboned turkey meat
stored chilled for 15 d
The aim of this experiment was to reduce the undesirable oxidativechanges during the 3 kGy irradiation and refrigerated storage.
3.2.1. Microbiological status
The 3 kGy radiation treatment reduced the TBC by 3.5 lg units (fromlg CFU/g = 4.75 to lg CFU/g = 1.20) and the Enterobacteriaceae count fromlg CFU/g = 4.1 to below the detection limit (lg CFU/g < 1.0) as estimateddirectly after treatment (0 d) in the antioxidant free samples. In the thyme oil
containing samples, the residual TBC at 0 d was lg CFU/g = 1.6 whereas it waslg CFU/g = 2.0 in the tocopherol ascorbic acid containing samples. After 15 d ofchilled storage, non-irradiated samples reached a spoilage level of TBCs
(lg CFU/g = 8.75).
3.2.2. Cholesterol oxidation and TBARSResults of COPs and TBARS measurements are presented in Tables 3
and 4, respectively.
It can be seen from Table 3 that several COPs were found even in the
non-irradiated samples, before irradiation and storage. Gamma irradiation
enhanced the cholesterol and lipid oxidation (causing an approximately 20%

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FARKAS et al.

TABLE 3. CONCENTRATION OF COPs (mg/kg) IN NON-IRRADIATED
AND GAMMA IRRADIATED MECHANICALLY DEBONED TURKEY
MEATa (AVERAGE OF DUPLICATED SAMPLES IN TWO PARALLEL
EXPERIMENTS)
Day 0(non-irradiated)

COPs

Day 0
( 3 kGy)

Day 15 at 4°C(3 kGy)

Cb

AOc

Td

C

AO

T

C

AO

T

7α-OH

2.04

1.11

0.89

3.06

1.40

1.34

3.63

1.73

1.78

7β-OH

2.12

1.04

0.79

2.02

1.58

0.92

2.14

1.64

2.54

7-keto

2.50

e

n.d.

n.d.

2.70

n.d.

n.d.

2.39

1.67

0.97

5α,6α-epoxide

2.30

n.d.

n.d.

2.28

n.d.

n.d.

2.37

n.d.

n.d.

Total

8.96

2.15

1.68

10.06

2.98

2.26

10.53

5.04

5.29

a

Cholesterol content: 668.6 mg/kg.
C: antioxidant-free control.
c
AO: α-tocopherol plus ascorbic acid.
d
T: thyme oil.
en.d.: <0.3 mg/kg; 7α-OH: 7α-hydroxycholesterol; 7β-OH: 7β-hydroxycholesterol;
7-keto: 7-ketocholesterol; 5α,6α-epoxide: cholesterol-5α,6α epoxide.
b

TABLE 4. TBARS (malonaldehyde mg/kg) IN NON-IRRADIATED AND
GAMMA IRRADIATED MECHANICALLY DEBONED TURKEY
MEAT
Day 0 (non-irradiated)
a

b

C

AO

4.42

1.64

Day 0 ( 3 kGy)

Day 15 at 4°C (3 kGy)

c

T

C

AO

T

C

AO

T

1.35

7.43

2.31

1.61

5.35

2.47

2.06

a

C: antioxidant-free control.
AO: α-tocopherol plus ascorbic acid.
c
T: thyme oil.
b

increase in the COPs level and a 50% increase in TBARS values) at 0 d in theantioxidant free samples. The presence of antioxidants reduced significantly
both the COPs and TBARS values (Table 4).
The addition of thyme oil caused favourable changes in colour, the slightly
brownish colour becoming the pink–red characteristic of fresh products. The
antioxidants in this experiment were highly effective in preventing oxidativechanges.

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FARKAS et al.

4.

DISCUSSION AND CONCLUSION

Turkey meat with a low endogenous level of tocopherols is rather
susceptible to oxidation of cholesterol and other lipids. Irradiation increased
the microbiological stability during chilled storage without sensory changes.
The pasteurizing 3 kGy dose enhanced, under aerobic storage conditions, theconcentration of COPs and TBARs. The COPs formed in the MDM samples
were mainly 7α-hydroxycholesterol, 7β-hydroxycholesterol (early and sensitive
indicators of oxidation of cholesterol), 7-ketocholesterol and cholesterol-5α,6α-epoxide. These observations confirmed literature data [13]. The antioxidants were highly effective in preventing oxidative changes. The mechanism
behind the decrease in the concentrations of preformed oxidation products dueto the addition of antioxidants is not yet clear and will be investigated. The
reduction/destruction of the intermediate peroxides might be involved in thisprocess.

REFERENCES
[1]
[2]

[3]

[4]

[5]
[6]

[7]

[8]

LEBOVICS, V.K., et al., Cholesterol oxides in γ-irradiated spray dried egg
powder, J. Sci. Food Agric. 60 (1992) 251-254.
LEBOVICS, V.K., et al., Influence of packaging atmosphere on the formation ofcholesterol oxides in gamma irradiated egg powder, J. Sci. Food Agric. 66 (1994)
71-73.
HWANG, K.T., MAERKER, G., Quantitation of cholesterol oxidation production in unirrdiated and irradiated chicken meats, J. Amer. Oil Chem. Soc. 70(1993) 371-375.
AHN, D.U., et al., Effect of irradiation and packaging conditions after cooking on
the formation of cholesterol and lipid oxidation products in meats during storage,
Meat Sci. 57 (2001) 413-418.
NAM, K.C., et al., Cholesterol oxidation products in irradiated raw meat withdifferent packaging and storage time, Meat Sci. 58 (2001) 431-435.
NAM, K.C., AHN, D.U., Combinations of aerobic and vacuum packaging tocontrol lipid oxidation and off-odour volatiles of irradiated turkey breast, Meat
Sci. 63 (2003) 389-395.
GOMES, H.A., SILVA, E.N., Effect of gamma radiation on the microbiologicalquality and lipid oxidation of mechanically deboned chicken meat stored underrefrigeration, Proc. 49th Int. Congr. Meat Sci. and Technol., Campinas, Brazil(2003) 289-290.
GUARDIOLA, F., DUTTA, P.C., CODONY, R., SAVAGE, G.P. (Eds), Cholesterol and Phytosterol Oxidation Products, Analysis, Occurrence, and Biological
Effects, AOCS Press, Champaign, Illinois, USA (2002).

101

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[9]

[10]
[11]
[12]
[13]

102

RAMANATHAN, L., DAS, N.P., Studies on the control of lipid oxidation in
ground fish by some polyphenolic natural products, J. of Agric., Food Chem. 40(1992) 17-21.
FOLCH, J., et al., A simple method for the isolation and purification of total lipids
from animal tissues, J. Biol. Chem. 726 (1957) 497-509.
MISSLER, S.R., et al., Separation and identification of cholsterol oxidation
products in dried egg preparations, J. Food Sci. 50 (1985) 595-598.
LEBOVICS, V.K., et al., Enzymatic determination of cholesterol oxides, J. Sci.
Food Agric. 71 (1996) 22-26.
CHEN, X., et al., Lipid oxidation, volatiles, and colour changes of irradiatedturkey patties as affected by antioxidants, J. of Food Sci. 64 (1999) 16-19.

PART III: COMPARING OBSERVED GROWTH
OF SELECTED TEST ORGANISMS
IN FOOD IRRADIATION STUDIESWITH GROWTH PREDICTIONS CALCULATEDBY COMBASE SOFTWARES
J. FARKAS*, É. ANDRÁSSY*, L. MÉSZÁROS**,K. POLYÁK-FEHÉRCorvinus University of Budapest
J. BECZNER
Central Food Research InstituteÖ. GAÁL, V.K. LEBOVICS, A. LUGASINational Institute of Food Safety and Nutrition
Budapest, Hungary
Abstract
As a result of intensive predictive microbiological modelling activities, several
computer programs and softwares became available recently for facilitating microbiological risk assessment. Among these tools, the establishment of the ComBase, an international database and its predictive modelling softwares of the Pathogen Modelling
Program (PMP) set up by the USDA Eastern Regional Research Center, Wyndmore,
PA, and the Food Micromodel/Growth Predictor by the United Kingdom’s Institute ofFood Research, Norwich, are most important. The authors have used the PMP 6.1
software version of ComBase as a preliminary trial to compare observed growth of
selected test organisms in relation to their food irradiation work during recent years
within the FAO/IAEA Coordinated Food Irradiation Research Projects (D6.10.23 andD6.20.07) with the predicted growth on the basis of growth models available in
ComBase for the same species as those of the authors’ test organisms. The results ofchallenge tests with Listeria monocytogenes inoculum in untreated or irradiated experimental batches of semi-prepared breaded turkey meat steaks (cordon bleu), sliced
tomato, sliced watermelon, sliced cantaloupe and sous vide processed mixed vegetables,
as well as Staphylococcus aureus inoculum of a pasta product, tortellini, were comparedwith their respective growth models under relevant environmental conditions. This
comparison showed good fits in the case of non-irradiated and high moisture foodsamples, but growth of radiation survivors lagged behind the predicted values.

* Central Food Research Institute, Budapest, Hungary.
** National Institute of Food Safety and Nutrition, Budapest, Hungary.

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FARKAS et al.

1.

INTRODUCTION

As a result of intensive predictive microbiological modelling activities,
several computer programs and softwares recently became available for facilitating microbiological risk assessment. Among these tools, the establishment of
ComBase, an international database and computer program, is the mostimportant. The authors obtained permission to use it now for teaching andresearch purposes. ComBase is the result of extensive cooperative efforts and it
combines information and predictive modelling softwares of the Pathogen
Modelling Program (PMP) set up by the USDA Eastern Regional ResearchCentre, Wyndmore, PA, and the Food Micromodel/Growth Predictor program
created by the United Kingdom’s Institute of Food Research, Norwich [1].

2.

METHODS

Regarding growth prediction of pathogenic bacteria, the authors haveused the PMP 6.1 software version in a preliminary trial to compare observed
growth of selected test organisms in relation to their food irradiation workwithin the FAO/IAEA Coordinated Food Irradiation Research Projects
D6.10.23 (Testing the efficiency and uncertainty of sample processing foranalysis of food contaminants) and D6.20.07 (Irradiation to ensure the safety
and quality of prepared meals) in recent years with the predicted growthprovided by growth models available for the same species of test organisms.
Figure 1 shows one example of the screen of PMP 6.1, displaying query
panels for selection of model and input factors (culture conditions) as well as
output panels illustrating predicted data points, lag phase duration, generation
time and a graphical representation of the prediction.

3.

RESULTS AND DISCUSSION

Figures 2–4 show microbiological ecological conditions and observed
growth data from the authors’ experiments in comparison with predictedvalues of the PMP software for reasonably similar or identical microbiologicalecological conditions. It should be emphasised, however, that the predictivemodels of PMP are based only on output from laboratory experiments withcomplex laboratory media. Thus, the PMP represents a sort of worst casescenario, which does not necessarily exist in specific foods, therefore, its data
are products of safe (conservative) predictions.

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FARKAS et al.

FIG. 1. Screen of the PMP 6.1 software.

109Predicted Growth (log10 CFU/g)

8
7

0 kGy
1 kGy

6
5

Sliced tomato
aerobic;
pH 4,3;aw >0,99

4
3
2
1
0
0

1

2

3

4

5

6

7

8

9

10

Observed Growth (log10 CFU/g)

FIG. 2. Relation of observed and predicted growth of Listeria monocytogenes in
untreated and irradiated samples of sliced tomato.

105

FARKAS et al.

10
0 kGy
9
1 kGy

Predicted Growth (log 10 CFU/g)

8

Tortellini, Stahp.
aureus, ph 7;
aw>0,96;
MAP 20 % CO2,
0 kGy

7
6
5

Sliced melons
pH 5,5-6,5; aw>0,99

4

Sous-vide mixed
vegetables
pH 7,1; aw>0,99

3
2
1
0
0

1

2

3

4

5

6

7

8

9

10

Observed Growth (log 10 CFU/g)

FIG. 3. Relation of observed and predicted growth of L. monocytogenes in untreated andirradiated samples of sliced melon and sous vide mixed vegetables.

109Predicted Growth (log 10 CFU/g)

8
7

0 kGy
1 kGy

6
Cordon Bleu
pH 6,2;aw=0,96;
MAP 20 %
CO2

5
4
3
2
1
0
0

1

2

3

4

5

6

7

8

9

10

Observed Growth (log 10 CFU/g)

FIG. 4. Relation of observed and predicted growth of L. monocytogenes in untreated andirradiated samples of cordon bleu.

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FARKAS et al.

For L. monocytogenes growth predictions, the source of the predictivemodel is the work of Buchanan et al. [2]. They applied triptose phosphate brothfor sound L. monocytognes Scott A inocula, the growth data were analysed byregression analysis to generate best fit Gompertz equations [3], and developed
a multivariant response surface model for predicting the growth. For Staphylococcus aureus growth predictions, the source of data is Buchanan et al. [4], who
generated growth curves by fitting the data obtained for S. aureus 196E in brain
heart infusion broth, and quadratic response surface models for growth
kinetics.

4.

CONCLUSIONS

Evaluation of the information illustrated in Figs 2–4 allows the following
conclusions to be drawn.
In high water activity sliced vegetable products such as sliced tomato,sliced water melon and cantaloupe as well as in the sous-vide mixed vegetables,
the L. monocytogenes propagated at least as well as the PMP culture, thus theobserved and predicted values were close to or in overlapping ranges of eachother.
The S. aureus in the filled pasta (tortellini) also grew as well in thismodified atmosphere packaged product as in the anaerobic PMP culture,
resulting in a validated prediction.
Regarding cordon bleu inoculated with the authors’ L. monocytogenes
strain, the predictive counts are always higher (as for the authors’ irradiatedsamples, they are much higher) than the observed counts. The overall
difference may be due to the fact that the PMP data are based on anaerobic
conditions, whereas the authors’ challenge tests have been performed undermodified atmosphere packaged conditions, and the increased CO2 concentration in the packaged samples was probably affecting growth of L. monocytogenes more than the simple anoxic condition of the model. In addition, in
the food system, competition from the native microbiota might result in lessgrowth than in the pure culture of the PMP experiments.
Comparing the differences between predicted and observed growth in thecase of radiation survivors in food samples, the Δ values were always considerably higher than those observed with non-irradiated samples, which probably
means that the surviving populations in the irradiated foods, owing to theirradiation injury, had longer lag phases, i.e. had less ability to start regrowth than
non-irradiated populations under the same environmental conditions (see also
Ref. [5]).

107FARKAS et al.

The authors’ initial experience with the computer modelling of thegrowth of specific foodborne pathogens is reassuring. Therefore, further workwith additional ComBase softwares would be worthwhile, offering an efficient
tool for risk estimation for selected marketing scenarios. It is planned to use, in
addition to the latest version of PMP, the Growth Predictor software, which isbased on a dynamic growth model developed by Baranyi et al. [6, 7], since it ispromising to understand and recognize better the role of physiological status of
the critical organisms and thereby their lag time (i.e. no-growth) periods beingof crucial importance to the safety or shelf life of the prepared and processed
foods.

REFERENCES
[1]
[2]

[3]

[4]

[5]

[6]
[7]

108

BARANYI, J., TAMPLIN, M.L., ComBase: a common database on microbial
responses to food environments, J. Food Protect. 67(2004)1967-1971.
BUCHANAN, R.L., et al., Effects and interactions of temperature, pH, atmosphere, sodium chloride, and sodium nitrite on the growth of Listeria monocytogenes, J. Food Prot. 52 (1989) 844-851.
GIBSON, A.M., et al., Predicting microbial growth: Growth responses of salmonellae in a laboratory medium as affected by pH, sodium chloride, and storage
temperature, Int. J. Food Microbiol., 6 (1988)155-178.
BUCHANAN, R.L., et al., Response surface models for the effects of temperature, pH, sodium chloride, and sodium nitrite on the aerobic and anaerobic
growth of Staphylococcus aureus 196E, J. Food Safety 13 (1993) 159-175.
PATTERSON, M.F., et al., Effects of irradiation dose and storage temperatureon growth of Listeria monocytognes on poultry meat, Food Microbiol. 10 (1993)
197-203.
BARANYI, J., et al., A non-autonomous differential equation to model bacterial
growth, Food Microbiol. 10 (1993) 43-59.
BARANYI, J., ROBERTS, T.A., A dynamic approach to predicting bacterial
growth in food, Int. J. Food Microbiol. 23 (1994) 377-394.

RADIATION PROCESSINGTO ENSURE THE SAFETY AND QUALITY
OF ETHNIC PREPARED MEALS
A. SHARMA, R. CHANDER, S.P. CHAWLA,
S.R. KANATT, V.S. DHOKNE
Food Technology Division,
Bhabha Atomic Research Centre,
MumbaiA.S. BAWA
Defence Food Research Laboratory,
MysoreIndia

Abstract
The effect of gamma radiation on microbiological, chemical and sensory qualities
of some Indian ethnic dishes, including items from a breakfast menu, meal components
and complete meals, as well as some commercially available traditional Indian ready-toeat meat products, were investigated. Initial total bacteria counts (TBCs) were in therange of 1–3 lg CFU/g in the case of samples prepared in the laboratory, while the counts
were higher (3.5–5 lg CFU/g) in the commercial meat products. The TBC increased
rapidly during storage at 0–3°C in non-irradiated samples. Radiation processing resulted
in a dose dependent reduction in the total bacterial counts. Staphylococcus spp. wascompletely eliminated by irradiation (1–2 kGy). A dose of 3 kGy was found to be
optimal for extending the shelf life of the commercial products by more than 2 weeks at
0–3°C compared with the corresponding non-irradiated controls. Lipid peroxidation
monitored in terms of thiobarbituric acid reactive substances content increased marginally on irradiation and with storage. However, the sensory attributes of products were
not significantly affected. The safety of irradiated chilled products was demonstrated byinoculated pack studies with Staphylococcus aureus and Bacillus cereus. The radiation
sensitivity of S. aureus and B. cereus in the commercial meat products was initiallyinvestigated. The D10 values of S. aureus in mutton shami kebabs and chicken chilli were0.33 ± 0.03 and 0.37 ± 0.03 kGy, respectively. The D10 values of B. cereus in mutton shami
kebabs and chicken chilli were 0.47 ± 0.07 and 0.47 ± 0.08 kGy, respectively. S. aureus(inoculated 106 CFU/g) was eliminated at a dose of 2.5 kGy in both products, whereas
B. cereus was eliminated at 3 kGy. The growth of both the test organisms inoculated into
these products during storage at chilled temperatures (0–3°C and 10°C) was studied. No

109

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growth of the test organisms was observed at 0–3°C. However, at higher temperatures
such as 10°C, the organisms could multiply. These results indicated that temperature
abuse during the storage of irradiated products should not be allowed. Radiation
processing in combination with low temperature (0–3°C) storage thus resulted in microbiologically safe ready-to-eat products with extended shelf life.

1.

INTRODUCTION

With rapid urbanization and change in socioeconomic status, there has
been an increase in demand for convenience/ready-to-cook/ready-to-eat foods.
Ready cooked meals, which are stored frozen at –18°C or below, are available
in developed countries. These foods are not always safe, due to contamination
by pathogenic bacteria such as Staphylococcus aureus, Salmonella spp., Campylobacter spp., Listeria monocytogenes, Aeromonas hydrophila and Escherichia
coli O157:H7 [1]. In India, meals are consumed within a short period after
cooking. However, a number of ready-to-eat meal components such as lentils(dals) and vegetables with retort processing have started appearing in Indian
markets. A retort process, such as freezing, is high in energy consumption andtherefore costly. The ready-to-eat meal market is becoming increasingly
popular among consumers looking for high quality and safe products. A
developing country such as India can ill afford high energy consumption
storage technology as it is not economically viable. Consumers prefer chilled
foods over frozen as these are perceived to be fresh and more convenient.
Freezing facilities are expensive. Also, freezing affects the texture of food andis not always safe as it does not eliminate pathogens. Ready-to-eat chilled meals
are therefore of particular interest to India and other developing countries.
However, cook–chill ready meals have a short shelf life of 7 d maximum at 4°C,
thereby limiting the geographical area in which they can be marketed.
Furthermore, there are significant concerns about their microbiological safety[2]. Cooking eliminates vegetative pathogens but sometimes undercooking
may allow some of them to survive. In addition, there is always a risk of recontamination after cooking. L. monocytogenes is of particular concern being
psychrotrophic and can grow at chilled temperatures. Technologies that allow aseveral fold extension of shelf life are therefore required. Radiation processing(1–2.5 kGy) of cook–chill meals at the end of the manufacturing process will
result in safer food. The advantages of the process are that it makes these foods
not only safe by eliminating non-sporulating pathogens but also extends theshelf life by decreasing the number of spoilage bacteria. Radiation processing
has the potential to ensure microbiological safety of ready-to-eat foods without
jeopardizing their taste or nutritive value.

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SHARMA et al.

There are ample data to show that irradiation at 2–5 kGy could significantly reduce the level of contaminants, thus improving the safety of individual
food commodities. However, data are scanty on the effect of radiation
processing of complex ready-to-eat meals, especially with regard to ethnic
preparations. Irradiation could be useful for the safety of ready meals provided
appropriate components are selected as ingredients, as some of the ingredients
may show undesirable changes upon irradiation. Therefore, the present studies
were undertaken to examine the effectiveness of irradiation for extending shelf
life and improving the microbiological safety of some of the ethnic preparations that include items of a breakfast menu, meal components and complete
meals.
In urban Indian markets several ready-to-eat meat products such chicken
chilli, chicken tikka, mutton shami kebabs and mutton shish kebabs aremarketed only in the frozen state. Storage of these products in a chilled state
would be advantageous. The effect of radiation processing on the microbiological, chemical and sensory attributes of two popular ethnic Indian meatproducts (chicken chilli and mutton shami kebabs) commercially available inIndia was evaluated to ascertain their ultimate keeping quality.
The radiation doses required to render inactivate 90% of the CFU of thecommon foodborne pathogens associated with meat and meat products are in
the range 1–4 kGy [3]. There are several reports on the radiation processing ofmeat products such as bacon, ham [4], sausages [5] and beefburgers [6]. The
presence of bacteria of public health significance in ready-to-eat meat products
is a known hazard to consumers as these products are sometimes consumed
without thorough cooking. The safety of radiation processed products was also
demonstrated using inoculated pack studies with S. aureus and B. cereus.

2.

MATERIALS AND METHODS

2.1. Preparation of ready-to-eat meals
Ready-to-eat meals and meal components were prepared with theingredients listed in Table 1. Commercially available chicken chilli and mutton
shami kebabs were purchased from a local meat processor and brought to thelaboratory in ice. For each product, a 100 g sample was packed in a sterile, lowdensity polyethylene bag (700 gauge; WVTR 0.4 g·m–2·d–1; OTR 1800 mL·m–2·d-1).
For sensory evaluation, a 200 g sample was packed separately. Three sets ofexperiments were carried out for each product.

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SHARMA et al.

TABLE 1. DESCRIPTION OF READY-TO-EAT MEALS
Item

Ingredients

Remarks

Poha

Dried pounded rice, onion, spices,
vegetable oil

Warm and serve, a few drops offresh lime juice enhance its taste

Upma

Semolina, onion, spices, vegetableoilWarm and serve with coconut
chutney

Mixed vegetables

Peas, beans, carrots, onion,
ginger–garlic paste, spices,
vegetable oil

To be consumed with rice/roti(Indian bread) after heating

Prawn masala

Deveined prawns, ginger–garlicpaste, spices, vegetable oil

Warm and serve with rice

Rice

Rice

Serve with mixed vegetables/
chicken or prawn curry

Vegetable pulao

Rice, peas, French beans, carrots,
onion, ginger–garlic paste, spices,
vegetable oil

Serve hot with curd

Chicken biryani

Rice, chicken drumsticks, ginger–
garlic paste, spices, vegetable oil

Serve hot with curd

Prawn pulao

Rice, deveined prawns, ginger–
garlic paste, spices, vegetable oil

Serve hot and garnish withcoconut flakes

Khichadi

Rice, lentils, spices, vegetable oil

A good meal for patients andthose with stomach upset

Breakfast:

Meal components:

Complete meals:

Commercial samples:
Chicken chilli

Chicken cubes, ginger, garlic,capsicum, spices, vegetable oil

Serve hot as a side dishMutton shami
kebabsMutton mince, semolina, onion,
chillies, ginger–garlic paste andspicesServe hot after frying as a side
dish

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SHARMA et al.

2.2. Irradiation
Irradiation of prepackaged products was carried out at melting ice
temperatures (1–3°C) in a food package irradiator with a 60Co source at a dose
rate of 3 kGy/h. The samples received minimal doses of 1, 2 or 3 kGy with an
overdose ratio of 1.3. Dosimetry was performed by a cerric–cerrous dosimeter
calibrated against Fricke’s dosimeter. Dosimetry comparison was carried out
with national standards established by the Radiological Physics and Advisory
Division of the Bhabha Atomic Research Centre. A non-irradiated sample
served as control. Until irradiation was complete, the control samples were
kept in ice. All samples were then stored at 0–3°C.
2.3. Microbiological analysis
The sample (25 g) in duplicate from the irradiated and the corresponding
control were aseptically homogenized for 1 min with sterile saline in a
Stomacher (Seward, United Kingdom). Appropriate serial dilutions of thehomogenate were carried out. Media used for the microbiological analyses
were purchased from HiMedia, India. The TBC was determined using plate
count agar incubated at 30°C for 48 h. Selective and differential media usedwere Baird Parker’s agar (37°C for 24 h) for enumeration of Staphylococcus
spp., violet red bile agar (44°C for 24 h) for faecal coliforms, sulphite polymixinsulphadiazine agar (37°C for 24 h in an anaerobic jar) for enumeration ofsulphite reducing Clostridium spp., and potato dextrose agar (30°C for 5 d) for
yeast and moulds. The total aerobic spore count was also determined. For this,5 mL of the 10% homogenate was heated at 80°C for 10 min, cooled and thenserial dilutions plated on plate count agar (30°C for 48 h).
2.4. Measurement of lipid peroxidation
Thiobarbituric acid reactive substances (TBARS) produced from lipid
peroxidation were determined using the method of Alasnier et al. [7]. A 4 g
portion of each sample was blended with 16 mL of 5% trichloroacetic acid andBHT (10 µg BHT/g of lipids). It was then filtered through a Whatman filter(No. 4). An equal amount of filtrate and 0.02M thiobarbituric acid was heatedin a boiling water bath for 30 min, cooled and the absorbance measured at
532 nm. The amounts of TBARS were expressed as milligrams of malonaldehyde per kilogram of meat.

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2.5. Sensory evaluation
The sensory attributes evaluated were appearance, flavour, texture andoverall acceptability of the products using a 10 point numerical scale, where 10
corresponded to ‘components characteristic of the highest quality’, 9 to ‘loss inpart of fresh components but not distinguished by new characteristics’, 7–8 to‘first significant change; degree of component change slight but consistently
apparent’, 5–6 to ‘moderate degree of change; increased intensity (quantitativechange) and/or occurrence of additional components (qualitative change), but
normal characteristics still dominant’, 3–4 to ‘strong degree of change;
abnormal components dominant in contrast to normal components; loss inpalatability definite’, 1–2 corresponded to ‘intense degree of change’ and 0 to‘too poor to evaluate’. Scores from 9–6 were considered acceptable. The panel
consisted of 15–20 experienced members of staff who were familiar with thecharacteristics of the meals under test. Sensory analyses were carried out after
steaming the samples for 1–2 min.
2.6. Inoculated pack studies
2.6.1. Test organisms
S. aureus ATCC 6538P was maintained on nutrient agar slants at 4°C.
Cells were grown at 37°C for 16 h in brain heart infusion broth (HiMedia). The
samples were centrifuged in a refrigerated centrifuge (4°C) (Sorvall RC 2) at
12 100g for 10 min and washed twice with sterile normal saline. The pellet wassuspended in sterile saline to give a cell count of approximately 107 CFU/mL.
B. cereus MTCC 470 was grown in soybean casein broth (HiMedia) at
37°C for 16 h. The samples were centrifuged in a refrigerated centrifuge (4°C)(Sorvall RC 2) at 12 100g for 10 min and washed twice with sterile normal
saline. The cell pellet was suspended in sterile saline to give a cell count ofapproximately 106 CFU/mL.
2.6.2. Inoculation of meat products
Mutton shami kebabs and chicken chilli were irradiated (5 kGy) toeliminate the background flora. Aseptically, a suspension (0.5 mL) of test
culture was uniformly spread on the meat products (25 g). The samples were
kept in a sterile workstation for 30 min to allow it to be absorbed. These werethen packed in sterile stomacher bags.

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SHARMA et al.

2.6.3. Determination of D10 values of the test organisms
The inoculated packs were irradiated at various doses at melting ice
temperature. Two packs were irradiated at each dose. The maximum dose
employed for both the test organisms was 3.0 kGy. Non-irradiated samples
were also stored at the same temperature until irradiation was complete.
The number of survivors at each dose was determined by plating onto
appropriate agars. Media employed for determining counts of S. aureus andB. cereus were Baird-Parker agar and soybean casein digest agar (HiMedia),
respectively. The logarithm of the bacterial count was plotted against theradiation dose received to determine the death rate of each organism. The D10
values (the dose required to inactivate 90% of a population) for each of theorganisms were calculated as the reciprocal of the slope of the logarithmic
portion of the inactivation curve.
Survival of the test organisms in meat products during storage at chilledtemperatures was also determined. Meat packs inoculated with test organisms
were prepared as described above. The packs were subjected to gamma
irradiation at 0–3°C at a dose rate of 3.0 kGy/h. The samples received aminimum dose of 3.0 kGy. For experiments on storage studies, samples werestored at 0–3°C and 10–12°C. Samples from both irradiated and non-irradiatedlots were analysed immediately after irradiation and subsequently at regularintervals during storage at chilled temperatures.
2.7. Statistical analysis
All data are expressed as mean ± SD. Differences between variables were
tested for significance by one way ANOVA with Tukey’s post-test using
GraphPad InStat version 3.05 for Windows 95 (GraphPad software, San Diego,
United States of America). Differences at p < 0.05 were considered to besignificant and n = 3.

3.

RESULTS AND DISCUSSION

3.1. Microbiological quality
The TBCs of poha, upma, meals and meal components are depicted inTables 2 and 3. The initial total aerobic count in non-irradiated samples varied withthe product and increased by 2–3 log cycles in many products in less than 14 d
storage and the samples spoiled. In irradiated samples, there was a dose dependent
reduction and at 2 kGy TBC was significantly lower or non-detectable in some115

SHARMA et al.

TABLE 2. MICROBIOLOGICAL QUALITY OF BREAKFAST AND
MEAL ITEMS STORED AT 0–3°Ca
Control
Meal

Storageperiod (d)

0

1 kGy
15

30

2 kGy

0

15

30

0

15

30

4.1
2.2

4.4
2.7

2.3
2.3

2.1
2.1

4.0
2.2

lg CFU/g
Pohaa

TBCb
SCc

3.4
3.2

5.5
3.7

6.7
3.6

2.7
2.6

Upmaa

TBC
SC

1.9
1.3

3.5
1.3

5.6
1.7

n.v.c.d n.v.c n.v.c.
n.v.c. n.v.c. n.v.c.

n.v.c. n.v.c. n.v.c.
n.v.c. n.v.c. n.v.c.

Mixedvegetablea

TBC

1.0

n.v.c.

3.6

n.v.c.

n.v.c. n.v.c.

SC

n.v.c. n.v.c. n.v.c.

n.v.c.

n.v.c. n.v.c.

n.v.c. n.v.c. n.v.c.
n.v.c.
n.v.c. n.v.c. n.v.c.

Prawn
masalaa

TBC
SC

2.2
1.9

2.3
2.2

1.5
1.0

1.5
1.7
n.v.c. n.v.c.

n.v.c. n.v.c.
n.v.c. n.v.c.

n.v.c.
n.v.c.

Ricea

TBC
SC

1.0
2.6
5.6
n.v.c. n.v.c. n.v.c.

n.v.c.
n.v.c.

n.v.c. n.v.c.
n.v.c. n.v.c.

n.v.c. n.v.c.
n.v.c. n.v.c.

n.v.c.
n.v.c.

2.3
2.2

aStaphylococcus spp., fungus and faecal coliforms not detected.
TBC: total bacteria count.
c
SC: spore count.
dn.v.c.: no organisms detected by the method employed.
bsamples, even after 28 d storage. Fungal growth was detected in some of the nonirradiated samples during chilled storage. The enhanced safety of radiation
processed products was evident from the complete elimination of potentiallypathogenic Staphylococcus spp. Microbial load, in particular aerobic spore counts
in poha, was fairly high and not completely eliminated with a dose of 2 kGy.
Non-irradiated vegetable pulao had an initial TBC and aerobic spore
count of about 2–3 lg CFU/g. The effect of irradiation treatment on the microbiological quality was a reduction in total viable count, as well as levels of
spores. Potentially pathogenic Staphylococcus spp. was absent in both
irradiated as well as non-irradiated samples. During storage at 0–3°C for 30 d,
total bacteria, Staphylococcus and aerobic spore counts gradually increased to
7.8, 3.9 and 4.37 lg CFU/g, respectively. Irradiated samples were microbiologically superior to their non-irradiated counterparts throughout the storage
period. A TBC of 1.3 lg CFU/g was observed in a 1 kGy irradiated sample after
storage for 30 d. No viable organisms were detected in samples treated with
2 kGy dose.

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TABLE 3. MICROBIOLOGICAL QUALITY OF COMPLETE MEALSSTORED AT 0–3°Ca
Dose
Meal

Storageperiod (d)Control
0

15

1 kGy
30

0

15

2 kGy
30

0

15

30

lg CFU/g
Vegetable
pulaoa

TBCb
SCd

2.6
2.0

6.5
1.3

6.4
2.8

n.v.c.c n.v.c. n.v.c.
n.v.c. n.v.c. n.v.c.

n.v.c. n.v.c. n.v.c.
n.v.c. n.v.c. n.v.c.

Chickenbiryania

TBC
SC

2.9
1.5

3.0
2.7

4.3
2.4

2.4
2.0

2.3
1.3

2.3
2.1

Prawn
pulaoa

TBC
SC

2.7
1.7

3.7
n.v.c.

5.6
1.7

1.0
n.v.c.

1.5 n.v.c.
n.v.c. n.v.c.

n.v.c. 1.3 n.v.c.
n.v.c. n.v.c. n.v.c.

Khichadia

TBC
SC

1.6
1.8 n.d.en.v.c. n.v.c. n.d.

n.v.c.
n.v.c.

n.v.c. n.v.c.
n.v.c. n.v.c.

n.v.c. n.v.c. n.v.c.
n.v.c. n.v.c. n.v.c.

1.6
1.7

2.2
1.8

2.0
n.v.c.

aStaphylococcus spp., fungus and faecal coliforms not detected.
TBC: total bacteria count.
cn.v.c.: no organisms detected by the method employed.
d
SC: spore count.
en.d.: fungus visible and consequently sample not analysed.
bNon-irradiated chicken biryani had initial total bacteria and aerobic
spore counts of about 2.9 and 1.5 lg CFU/g, respectively. The immediate effectof irradiation treatment on the microbiological quality was a reduction in TBC
as well as levels of spores. Total bacteria, Staphylococcus and aerobic spore
counts gradually increased to 4.26, 3.48 and 2.88 lg CFU/g, respectively, duringstorage at 0–3°C for 30 d (Tables 2 and 3). In irradiated samples, the radiation
damaged organisms failed to multiply rapidly, hence the counts observed were
almost static. This could be attributed to a combination of radiation damage,
chilled storage and the presence of spices, which make the environment hostilefor multiplication of organisms.
The TBCs of chicken chilli and mutton shami kebab are shown in Figs 1
and 2, respectively. Results are the mean values of three independent
experiments.
Irradiation significantly (p < 0.05) improved the microbiological qualityof the products by reducing the TBC. Further, the decrease in TBC was dose
dependent in both of the products. The numbers increased with storage time
and there was a significant (p < 0.05) difference between the irradiation doses.
In less than 14 d, non-irradiated chicken chilli had counts greater than117

SHARMA et al.

Control
1 kGy
2 kGy
3 kGy

8

log cfu/g

6

4

2

0
0

7

14

21

Storage tim e (days)

28

FIG. 1. Effect of irradiation (up to 3 kGy) on the TBCs of chicken chilli during storage at
0–3°C. Vertical lines represent error bars.

6 lg CFU/g, while in irradiated samples (3 kGy) it did not reach this value evenafter 28 d. In the case of mutton shami kebabs, control samples spoiled in lessthan a week while in irradiated samples after 28 d storage at 0–3°C, the counts
were less than 4 lg CFU/g. The effect of low dose irradiation in reducing thebacterial load of meat and meat products has been reported earlier from theauthors’ laboratory [8, 9]. The decrease in total bacterial population as a resultof irradiation was in agreement with other studies [10]. Under aerobic
conditions, the dominant spoilage organisms are the strictly aerobic
Pseudomonads [11], which are very sensitive to irradiation [12]. The bacteriathat grow most rapidly under the storage conditions of the products usually
dominate the spoilage flora of meat products. The sensitivity of theseorganisms to radiation explains the decline caused in the total aerobic counts of
the irradiated products. The D10 value of 0.13 kGy at 5°C for P. fluorescens inbeef has been reported [13].
Radiation processing had a significant effect on the reduction/eliminationof pathogenic bacteria (Table 4).
In both products, irradiation at 2 and 3 kGy resulted in complete
elimination of aerobic spore counts and Staphylococcus spp.

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C ontrol1 kG y2 kG y3 kG y8log cfu/g

6

4

2

0
0

7

14

21

28

Storage tim e (days)
FIG. 2. Effect of irradiation (up to 3 kGy) on the TBCs of mutton shami kebab duringstorage at 0–3°C. Vertical lines represent error bars.

TABLE 4. TOTAL Staphylococcus spp. AND AEROBIC SPORE COUNTSOF MEAT PRODUCTS STORED AT 0–3°C
SampleStorage time (d)
0

7

14

21

28

Total Staphylococcus spp. counts (lg CFU/g):
Chicken chilli (control)

2.32

3.02

3.59

5.12

n.d.a

Chicken chilli (1 kGy)

n.v.c.bn.v.c.

n.v.c.

n.v.c.

n.v.c.

Mutton shami kebabs (control)

4.17

4.58

n.d.

n.d.

n.d.

Mutton shami kebabs (1 kGy)

1.43

1.43

1.51

1.52

1.6

Chicken chilli (control)

1.12

1.21

1.14

1.42

n.d.

Chicken chilli (1 kGy)

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

Mutton shami kebabs (control)

2

2

n.d.

n.d.

n.d.

Mutton shami kebabs (1 kGy)

1.6

2

2

2.2

2

Total aerobic spore counts (lg CFU/g):abn.d.: analysis not undertaken due to sample spoiling.
n.v.c.: no organisms detected by the method employed.

119SHARMA et al.

In chicken chilli, non-irradiated control samples had initial Staphylococcus spp. counts of 2.32 lg CFU/g, which increased to 5.12 lg CFU/g after
21 d. In all irradiated chicken chilli samples, Staphylococcus spp. was notdetected throughout the storage period. About 4 lg CFU/g of Staphylococcus
spp. was present in non-irradiated mutton shami kebabs and irradiation at
1 kGy reduced the Staphylococcus spp. counts by 2 log cycles. In samples
irradiated at 2 and 3 kGy, this organism was not detected throughout thestorage period. It has already been reported that 90% of S. aureus in mechanically deboned chicken meat is killed by a dose of 0.36 kGy [14]. The D10 values
in the range 0.40–0.46 kGy for S. aureus in different meat systems irradiated at
5°C have also been reported [15].
Faecal coliforms were detected in only one batch of non-irradiatedcontrol chicken chilli samples. Faecal coliforms were not detected in any of theirradiated samples. Similar findings have been reported earlier by Naik andothers [8]. They found that irradiated meat (2.5 kGy) was completely free ofEnterobacteriaceae for the entire storage period (0–3°C) of five weeks.
Irradiation of fresh pork had the maximum effect on Enterobacteriaceae [16]. A
minimum dose of 1.5 kGy would destroy at least 6 lg of E. coli O157:H7, which
has a D10 value of about 0.24 kGy [17].
Of concern in any processed meat product is the survival and growth ofspore formers. Sulphite reducing Clostridia were not detected in any of thesamples throughout the storage period. The aerobic spore count in nonirradiated chicken chilli was 1.12 lg CFU/g and these organisms were notdetected in any of the irradiated samples (Table 4). In the control mutton
kebabs a spore count of 2.7 lg CFU/g was measured and even after irradiationsome low counts were found in irradiated samples. Lambert et al. [16] have also
reported that aerobic spore formers were present at levels of 10–2.5 × 103/g insome fresh pork samples irradiated at 0.5 kGy and stored at 15°C. Yeast/
moulds were not detected in any of the samples throughout the storage period.
Among the most sensitive microorganisms to radiation are gram negative rods,
followed by gram positive cocci and rods, yeast, moulds, fungal spores, aerobic
and anaerobic spore formers [11]. Low dose irradiation kills microorganisms of
public health significance and extends the shelf life of meat products. This has
already been established in earlier studies [3, 4] and the present study further
confirms these findings for ethnic Indian meat products.
3.2. Lipid peroxidation
Lipid peroxidation was measured in terms of TBARS. Non-irradiatedcontrol samples showed lower TBARS values than irradiated samples. The

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C on tro l
1 kG y2 kG y2 .5

1.5

U pm aP o ha
2 .0

1.0

1 .5

TBARS (mg MDA/kg sample)

1 .0

0.5
0 .5

0

15

0

30

2.0

15

30

2 .0

4

P r aw n m a s a la

C hic k en b iry a ni

M ix v e g e ta b le

1.5

1 .5

3

1.0

1 .0

2

0.5

0 .5

1

0.0

0 .0
0

15

30

2.5

0
0

15

30

1 .5

0

15

30

15

30

1 .5

P ra w ns p ulao

V e g e ta b le p ula o

K hic ha d i

2.0
1 .0

1 .0

0 .5

0 .5

1.5

1.0

0.5

0.0

0 .0
0

15

30

0 .0
0

15

30

0

S to rag e perio d (d ays)

FIG. 3. Lipid peroxidation measured as TBARS value of radiation processed meals.
Vertical lines represent error bars.

increase in the TBARS value depended on the dose and on the period ofstorage (Fig. 3).
TBARS values of chicken chilli and the kebabs are shown in Figs 4 and 5.
Results are the mean values of three independent experiments.
Non-irradiated control samples showed lower TBARS values (p < 0.05)
than irradiated samples. In the case of chicken chilli, the increase in the
TBARS value of irradiated samples was not very significant (p > 0.05). This
may probably be due to the spices used in its preparation that are known tohave antioxidant activity. The increase in the TBARS value was dose
dependent. Several other workers have also reported the acceleration of lipidoxidation caused by radiation processing [18–20]. The presence of oxygen is themost critical factor influencing lipid oxidation during the storage of irradiatedmeat [21]. Lipid oxidation and discoloration of meat is enhanced in thepresence of oxygen while increasing the antimicrobial action of radiation.
Hence, irradiating meat in a frozen state or in modified atmosphere packing/vacuum packaging or by addition of antioxidants can minimize or avoid thedevelopment of rancidity.

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5

TBARS (mg MDA/kg meat)4

C o n tro l
1 kG y2 kG y3 kG y

3

2

1

0
0

7

14

21

28

S t o r a g e p e r io d ( d a y s )FIG. 4. TBARS values of chicken chilli during storage (0–3°C). Vertical lines represent
error bars.

5
C o n tro l
1 kG y2 kG y3 kG yTBARS (mg MDA/kg meat)

4

3

2

1

0
0

7

14

21

28

S to r a g e t im e ( d a y s )FIG. 5. TBARS values of mutton shammi kebab during storage (0–3°C). Vertical lines
represent error bars.

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Control
1 kGy
2 kGy

Sensory score (Hedonic scale)

10

5

0
10

Chicken biryani

Vegetable pulao

Prawns pulao

Khichadi

M ix vegetable

Prawns curry

50FIG. 6. Sensory evaluation of radiation processed meals. Vertical lines represent error
bars.

3.3. Sensory evaluation
The appearance, flavour and texture of irradiated samples were notdifferent from their non-irradiated controls, and all the samples were
acceptable (data not shown). The overall sensory scores of irradiated and nonirradiated samples were not significantly different (Fig. 6).
The results of the initial sensory evaluations carried out for the meatproducts are illustrated in Fig 7. Results are the mean values of three
independent experiments.
For safety reasons, the samples were not submitted to the panellists if
their microbiological examination revealed a count of 106 CFU/g or more. In
the case of chicken chilli it was found that immediately after irradiation theoverall sensory scores of irradiated and non-irradiated samples were not significantly (p < 0.05) different. Appearance, flavour and texture of irradiatedsamples were not different from their non-irradiated controls and all thesamples were acceptable. The same observation was made in the case of
mutton shami kebabs (Fig. 7). Though oxidative rancidity measured in terms of
the TBARS value increased on irradiation, there was no significant effect on

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10

O v e r a ll a c c e p t a b ilit y
A p p e a ra n c e
F la v o u r
T e x tu r e

A

8
6

Sensory scores

4
2
0
10

B

8
6
4
2
0

C o n tro l

1 kG y2 kG y3 kG yFIG. 7. Sensory evaluation of (A): mutton shami kebab and (B): chicken chilli. Verticallines represent error bars.

the sensory quality of the irradiated meat. For irradiation of the three meatproducts, the doses employed (1, 2 and 3 kGy) were either below or close to thethreshold level and hence no irradiation odour was detected. Irradiation with adose above the threshold level had been reported as producing irradiation
odour in various meats [22]. As the control samples spoiled in a week they were
not used for further sensory analysis. Irradiated (3 kGy) samples were found tobe acceptable even at the end of the storage period (Fig. 8).
Results are the mean values of three independent experiments.
The authors’ observation is in agreement with the earlier findings of Kiss
and Farkas [23] who reported that irradiation (2–5 kGy) extended the keeping
quality of chicken carcasses in cold storage by a factor of two to three (10–15 dlonger than the control), without noticeable deterioration in organoleptic
quality. Irradiated meat will be successful in the market place only if consumers
are satisfied with its sensory quality.
3.4. Inoculated pack studies
3.4.1. Radiation sensitivity of test microorganisms
The effect of radiation treatment on the survival of S. aureus and B. cereus
in mutton shami kebabs and chicken chilli is shown in Fig. 9.

124SHARMA et al.

10Overall acceptability
Appearance
Flavour
TextureA

Sensory scores

8
6
4
2
0
10

B

8
6
4
2
0

1 kGy

2 kGy

3 kGy

FIG. 8. Sensory evaluation of (A): mutton shami kebab and (B): chicken chilli after
storage for 4 weeks at 0–3°C. Vertical lines represent error bars.

The D10 values of S. aureus were 0.33 ± 0.03 and 0.37 ± 0.03 kGy in mutton
shami kebabs and chicken chilli, respectively. Similarly, in the case of B. cereus,
the D10 values were 0.47 ± 0.07 and 0.47 ± 0.08 kGy in mutton shami kebabs andchicken chilli, respectively.
The radiation sensitivity of bacteria is affected by a number of factors
such as the medium of suspension, water activity, composition, irradiation
temperature and the presence of oxygen [24]. In their previous studies, theauthors observed D10 values for S. aureus and B. cereus suspended in sterile
normal saline to be 0.14 kGy and 0.16 kGy, respectively [25]. The D10 values forbacteria are normally higher in the presence of food than in saline. In roast beef
meal components, D10 values in the range 0.25–0.37 kGy and 0.13–0.29 kGy forS. aureus and B. cereus, respectively, have been reported [26]. Thayer andothers [15] reported D10 values in the range 0.40–0.46 kGy for S. aureus indifferent meat systems irradiated at 5°C. In mutton kebabs, D10 values forS. aureus and B. cereus are reported as 0.36 kGy and 0.29 kGy, respectively [25].
Similarly, in Kwamegi (traditional Korean semi-dried fish), D10 values for S.
aureus and B. cereus were reported as 0.59 kGy and 0.64 kGy, respectively [27].
The authors’ results are comparable with these studies. Variations in D10 values
can be attributed to the difference in irradiation temperature and in thesuspension medium.

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SHARMA et al.

8

Mutton shami kebab S. aureus
Chicken chilli S.aureus
Mutton shami kebab B. cereus
Chicken chilli B. cereus

7
6

Log CFU/g

5
4
3
2
1
0
0

500

1000

1500

2000

2500

3000

Radiation dose (Gy)FIG. 9. Effect of gamma irradiation treatment on survival of S. aureus and B. cereus in
mutton shami kebabs and chicken chilli. Vertical lines represent error bars.

The higher resistance of bacteria in foods can be attributed to various
food components. As in complex food systems, some of the constituents such asproteins are believed to scavenge radiolytic free radicals, thereby reducing thenet effect of radiation damage and making the organism more resistant [28].
The viability patterns of S. aureus and B. cereus during chilled storage at
0–3°C and 10–12°C in mutton shami kebabs and chicken chilli are shown in
Tables 5 and 6, respectively.
It was observed that in the case of non-irradiated samples stored at 0–
3°C, viable counts of S. aureus and B. cereus remained stationary at about 106
CFU/g and 104 CFU/g, respectively, during the storage period of 4 weeks (Table5). In irradiated samples, no viable cells of either test organism were detectedduring the study period. However, when storage temperature was increased to
10–12°C in the case of non-irradiated samples, viable counts of S. aureus andB. cereus increased by 2–3 log cycles over the storage period of 4 weeks (Table 6).
In irradiated samples, no viable cells of the test organisms were detected during
the study period. The minimum growth temperature for S. aureus and B. cereus
is reported as 6°C [29] and 5°C [30], respectively. The results of the present
study confirm these findings and propose the importance of temperature

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SHARMA et al.

TABLE 5. VIABILITY OF S. aureus AND B. cereus IN MEAT PRODUCTS
STORED AT CHILLED TEMPERATURE (0–3°C)
Product

Initial1 week2 weeks

3 weeks

4 weeks

S. aureus counts (lg CFU/g)
Mutton shami kebab (control)
Mutton shami kebab (3 kGy)
Chicken chilli (control)
Chicken chilli (3 kGy)

6.1 ± 0.24 6.3 ± 0.29 6.2 ± 0.37 6.9 ± 0.29 6.9 ± 0.39
n.v.c.an.v.c.

n.v.c.

n.v.c.

n.v.c.

5.6 ± 0.14 5.7 ± 0.21 5.6 ± 0.10 5.9 ± 0.25 5.8 ± 0.52
n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

B. cereus counts (lg CFU/g)
Mutton shami kebab (control)
Mutton shami kebab (3 kGy)
Chicken chilli (control)
Chicken chilli (3 kGy)a

4.2 ± 0.64 4.3 ± 0.44 3.9 ± 0.36 3.8 ± 0.63 3.8 ± 0.46
n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

4.3 ± 0.25 4.0 ± 0.35 4.1 ± 0.41 3.9 ± 0.76 3.9 ± 0.66
n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.: no viable organisms detected by the method employed.

TABLE 6. VIABILITY OF S. aureus AND B. cereus IN MEAT PRODUCTS
STORED AT CHILLED TEMPERATURE (10–12°C)
Product/treatment

Initial1 week2 weeks

3 weeks 4 weeks

S. aureus counts (lg CFU/g)
Mutton shami kebab(control)Mutton shami kebab (3 kGy)
Chicken chilli (control)
Chicken chilli (3 kGy)

5.68 ± 0.78 6.01 ± 0.02 7.64 ± 0.65
n.v.c.bn.v.c.

n.v.c.

5.43 ± 0.95 6.02 ± 0.11 7.51 ± 0.38
n.v.c.

n.v.c.

n.v.c.

n.d.a

n.d.

n.v.c.

n.v.c.

n.d.

n.d.

n.v.c.

n.v.c.

B. cereus counts (lg CFU/g)
Mutton shami kebab(control)Mutton shami kebab (3 kGy)
Chicken chilli (control)
Chicken chilli (3 kGy)ab

5.02 ± 0.47 5.70 ± 0.43 7.89 ± 0.75
n.v.c.

n.v.c.

n.v.c.

5.05 ± 0.17 5.74 ± 0.49 7.23 ± 0.47
n.v.c.

n.v.c.

n.v.c.

n.d.

n.d.

n.v.c.

n.v.c.

n.d.

n.d.

n.v.c.

n.v.c.

n.d.: analysis not undertaken due to sample spoiling.
n.v.c.: no viable organisms detected by the method employed.

127

SHARMA et al.

control during storage and marketing of chilled ready-to-eat meat products, inensuring the efficacy of irradiation treatment for enhancing the microbiologicalsafety of ready-to-eat meat products.

4.

CONCLUSION

Radiation processing of ethnic Indian ready-to-eat products resulted in adose dependent decrease in the total viable counts and in the reduction/
elimination of pathogenic organisms. Irradiation at 2–3 kGy extended thechilled storage life of the ready-to-eat products by 2 weeks compared with nonirradiated samples. The results of packed inoculum study demonstrated that
irradiation in conjunction with chilled storage can enhance the microbiologicalsafety of ready-to-eat food products. Thus, radiation processing could be used
to the advantage of processors, retailers and consumers.

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IRRADIATION TO ENSURE THE SAFETY
AND QUALITY OF SOME ETHNIC SOUPS,SNACKS AND YUNAN CHICKEN
Z. IRAWATI, HARSOJO, C.M. NURCAHYA, F. ANAS
Centre for the Application of Isotope and Radiation Technology,
National Nuclear Energy Agency (BATAN),
Jakarta
L. NATALIA
Research Institute for Veterinary Science,
Bogor
Indonesia

Abstract
Semi-concentrated black, oxtail, chicken vegetable and chicken sweetcorn soups,
precooked spring roll, rissole and croquette snacks, and Yunan chicken were individually packed in a dry laminate pouch of PET 12 µm/LDPE adh.2 µm/Al foil 7 µm /LDPE
adh/LLDPE (C4) 50 µm under vacuum followed by freezing for 24 h at –18oC prior toirradiation with doses of 1, 3, 5 and 7 kGy at cryogenic conditions (–79oC). Both the
non-irradiated and irradiated prepared meals were then stored in a refrigerator at
5 ± 2oC. The non-irradiated samples and those samples irradiated at 1 kGy were mostly
damaged after a week in storage. Gamma irradiation at doses of 5–7 kGy for soups andsnacks, and doses of 3–5 kGy for Yunan chicken can reduce the microbial load by about
2–3 log cycles, respectively, without affecting the physicochemical parameters and palatability over 2–3 months. However, the irradiated spring roll was unable to withstandmore than 1 month storage. The D10 values for potential pathogens on Yunan chicken
were 0.28 kGy for Salmonella typhimurium, 0.17 kGy for Pseudomonas aeruginosa,
0.12 kGy for Escherichia coli O157, 0.66 kGy for Listeria monocytogenes and 0.09 kGy
for Campylobacter jejuni.

1.

INTRODUCTION

A successful experiment on the application of irradiation technology athigh doses in combination with storage under cryogenic conditions in theprocessing of some vacuum packed Indonesian ethnic dishes concluded that
gamma irradiation at the dose of 45 kGy could maintain the safety and quality
attributes for 1.5 years at 28–30°C [1, 2]. The purpose of radiation processing at

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such a high dose is that such meals are meant for consumption by a hospitalpatient, people engaging in outdoor activities and military personnel. Suchmeals would offer convenience and shorter preparation time, but conventionally stored, with limited shelf life under ambient temperatures, in a chilled
or frozen state for long term sale in supermarkets and intended for
microwaving prior to consumption.
Reportedly, irradiation at pasteurization doses also has a potential role in
improving the microbiological safety and shelf life of prepared meals [3–6]. The
prepared meals currently marketed under frozen conditions could possibly be
replaced through irradiation followed by storage under chilled conditions. This
would ensure safety, maintain quality, based on objective and subjective
parameters, and lengthen shelf life, thereby meeting market requirements andresulting in more practical and quick preparation, thereby saving energy andlowering operation cost.
The overall objective of this study was to evaluate the effectiveness of
medium irradiation doses in ensuring the microbiological safety and to extend
the shelf life within months of some ethnic prepared meals and functional foods
such as semi-concentrated soups, snacks, and Yunan chicken, being vacuum
packed in a laminate pouch and stored at 5 ± 2°C. The microbiological assessments, some physicochemical characteristics and their acceptability from theorganoleptic point of view as well as sensory attributes of the treated products
and determination of D10 values for some pathogenic bacteria in Yunan
chicken were also carried out.

2.

MATERIALS AND METHODS

2.1. Materials
Four selected frozen soups: black, oxtail, chicken vegetable and chicken
sweetcorn, were purchased from a supermarket, while precooked snacks:
spring rolls, rissole, croquette and Yunan chicken, were sourced locally.
Commercially, around 400 cm3 of each type of the soup was individuallywrapped in a high density polyethylene (HDPE) pouch. Snacks were divided
into groups, each group containing 6 pieces of each type of snack which werewrapped with the same type of plastic pouch. The waxy thin carton was selected
as a secondary packing for each product, then it was kept in frozen conditions,at –18°C, until it sold out. After arrival in the laboratory, the boxes of soups andsnacks were stored at –18°C prior to use for the research work. Similar types ofsoup, i.e. black, oxtail, chicken vegetable and chicken sweetcorn, were also
prepared and developed at the BATAN laboratory in parallel to provide a132

IRAWATI et al.

formulation for a standard operating procedure for irradiating soups. The
quantity of raw materials used in making the selected soups in the laboratory todevelop a standard operating procedure is listed in Annex I, and the quantity of
raw materials used by the food industry in making the selected snacks is listed
in Annex II.
2.2. Methods
2.2.1. Laboratory preparation of selected soups
The raw materials used in making the soups are listed in Annex I.
2.2.1.1. Rawon/black soup
Beef was boiled in 5 L of water for 1 h then removed and cut into 2 × 2 ×
2 cm cubes. Shallot, garlic, candlenut, coriander, red chilli and Pangium edule
were ground in a blender to form a mix of ingredients. Palm oil was heated andthen mixed with the ingredients, followed by addition of roasted fish paste,turmeric, lemon leaf, ginger root and lemon grass until the the aroma
manifested itself. The beef was added to the mixture and fried for 10 min. An
amount of broth, 50% taken from the total volume, was then poured into the
spicy cooked beef and added with some salt and sugar. The soup was readyafter cooking for 30 min.
2.2.1.2. Oxtail soupOxtail was boiled in water for 1 h. The oxtail was then removed from thebroth and cut into 2 cm thick pieces. The oxtail was then put into heated palm
oil for 5 min, removed, and put onto a separate plate. All the ingredients,
together with cut onion, onion leaf and celery, were fried in margarine. An
amount of broth, 50% from the total volume, was then poured onto the fried
ingredients and vegetables, then cooked together with the oxtail for 15 min.
Ground white pepper and nutmeg were finally added into the mixture 30 min
prior to cooking.
2.2.1.3. Chicken vegetable soup
Chicken was first boiled in 3 L of water, removed, and then cut into cubes.
Margarine was first heated in a pan, followed by the ground ingredients, celery
and onion leaf until an aroma arose. Chicken broth was boiled and added to thefried ingredients and boiled for 30 min. The broth, 50% from the total volume,

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was separated from the ingredients and boiled again. Carrot (0.5 cm slices),
green beans, broccoli, defrosted sugar peas, chopped chicken and ground white
pepper were added to the broth and boiled for 20 min.
2.2.1.4. Chicken sweetcorn soup
Chicken was first boiled in 3 L of water, removed, and then cut into cubes.
After removing the corn from the stalk, part of the corn was mixed with thechicken broth; some salt, sugar, ground white pepper, ground nutmeg werethen added and kept boiling for 15 min. Corn starch was added to the cooked
mixture, together with chicken meat, chicken sausage (0.5 cm thick slices),carrot and corn (not blended), and boiled again for 15 min. At the end, beaten
eggs were poured into the final cooked mixture and boiled for another 15 min.
2.2.2. Local preparation of selected precooked snacks and Yunan chicken
2.2.2.1. Spring roll
Filling: Both the sliced shallot and garlic were fried in vegetable oil until
the aroma arises. The rest of the filling materials as listed in Annex II wereadded, mixed thoroughly, decanted, and then split into 20 portions.
Sweet sauce and tauco sauce: All materials listed in Annex II were mixed
and allowed to boil in order to cook and raise the consistency. The sauce was
not irradiated but served separately.
Finally, the spring roll was prepared by spreading the cooked filling on
top of a spring roll sheet, folding it into a rectangular shape, and the edges withsealed with egg.
2.2.2.2. Rissole
Rissole sheet: Rissole was prepared by pouring the materials into a bowl,
whisking and mixing thoroughly. The mix was then fried in a pan and made intoa very thin sheet.
Filling: The procedure for cooking the filling was similar to that for springrolls, but the materials used in this preparation are different from those listed in
Annex II. As final preparation, the filling was poured onto a piece of sheet,folded into an envelope shape, and the edges sealed with egg. Finally, therissole was rolled on breadcrumbs until the surface was completely covered.

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2.2.2.3. Croquette
Mashed potato, together with the other ingredients, were prepared as acroquette wrapper (the ingredients are listed in Annex II). The rest of themethod of making croquettes was the same as that for making rissoles.
2.2.2.4. Yunan chicken
Yunan chicken was also selected and prepared by a local establishment,
but the general recipe for making the chicken was given by another source [7].
It was prepared from 200–225 g body weight of a 3 month-old hen (‘buras’).
The chicken was slaughtered, washed, then marinated for 40–60 min in various
spices such as ginger, garlic, pepper, Chinese ingredients which were preparedfrom dried plants and then ground, with sufficient water added. The wholemarinated chicken was then wrapped with salt paper and bound tightly
followed by addition of salt, then cooked in a stainless steel pan for 3 h at low
heat, removed and finally wrapped with HDPE sheet.
2.2.3. Packaging material and sample condition
The packing technique was confirmed by the quality assurance guidance
manual model for safe shelf-stable foods using high dose irradiation [8]. A typeof laminated pouch of PET 12 µm/LDPE as adh. 2 µm/Al foil 7 µm/LDPE as
adh./LLDPE 50 µm was selected similar to the previous work [1] as the primary
packaging of ‘warm fill’ soups, snacks and Yunan chicken prior to being
vacuum sealed. Styrofoam boxes (33.75 cm × 36.25 cm × 51.25 cm) were filledwith dry ice at –79°C, in order to maintain the cryogenic condition of the
prepared meals during the irradiation process [9].
2.2.4. Irradiation treatment and storage condition
All non-irradiated and irradiated prepared meals were kept at –20ºC for
48 h before removing to styrofoam boxes. Gamma irradiation was conducted at
the IRPASENA irradiator at the Centre for the Application of Isotope andRadiation Technology, National Nuclear Energy Agency, Pasar Jumat, Jakarta.
Cobalt-60 was used as the source of ionizing radiation (capacity of 20 kCi) at adose rate of 3 kGy/h. Perspex was used as the calibration dosimeter todetermine absorbed dose [10]. Soups and snacks were irradiated with absorbed
doses of 1, 3, 5, 7 kGy and doses of 3 and 5 kGy for Yunan chicken, respectively.
Following irradiation, all non-irradiated and irradiated prepared meals
were then stored at 5 ± 2ºC and tested for up to 3 months’ storage for soups and135

IRAWATI et al.

snacks and 9 weeks for Yunan chicken, in order to determine the effect of
gamma irradiation on objective parameters such as microbial safety andradiation sensitivity of some pathogenic bacteria and physicochemical
characteristics, and subjective quality parameters.
2.2.5. Methods of analysis and statistics
2.2.5.1. Microbiological safety of the prepared meals
The microbial load of the total bacteria plate count (TBC) (CFU/g) andtotal mould and yeast count (TMYC)(CFU/g) were assessed according toIndonesian National Standard methods [11] and Buckle [12], respectively.
Staphylococcus aureus was identified using the Indonesian National Standard
method [13]. The presence of Escherichia coli (E. coli) and coliforms wascalculated as the most probable number (MPN) [14], Clostridium perfringens
was identified according to the previous method [2] and Salmonella spp. wasdone according to Australian Standard [15]. These microbes are of particularimportance in the microbiological assessment of safe stable foods stored in arefrigerator [16].
2.2.5.2. Determination of D10 values for some pathogenic bacteriain Yunan chicken
The determination of D10 values for some potential pathogenic bacteriasuch as Salmonella typhimurium, Pseudomonas aeruginosa and E. coli O157 oncommercial Yunan chicken was developed from the method of Rashid et al.
[17]. Three local type strains of S. typhimurium, P. aeruginosa and E. coli O157
were used to determine the D10 value in the sterilized chicken meat. The microorganisms were propagated in nutrient agar medium (containing Bacto beef
extract 3 g, Bacto peptone 5 g and agar 15 g) and incubation was conducted at
37°C for 24–48 h. The cells were harvested and placed in sterilized distilledwater, then inoculated into the samples using a sterilized syringe. The
inoculated samples were then irradiated with doses of 0.1, 0.2, 0.3 and 0.4 kGy,
respectively. Fricke dosimetry was conducted [10] and the dose rate was
1.14 kGy/h. The irradiated samples were plated by serial dilutions and thenincubated at 37°C for 24–48 h.
Inoculation, enumeration and sample preparation to determine the D10
values for Listeria monocytogenes and Campylobacter jejuni were also
developed [12, 14]. The freeze-dried culture of L. monocytogenes was a local
isolate. It was initially grown on Listeria enrichment broth base (LEBB)(OXOID CM 862) for 48 h at 37ºC. The purity check of the isolate was done by136

IRAWATI et al.

growing the isolate on blood agar with 5% defibrinated sheep blood. The pureculture was then grown in LEBB. For preparing the inoculum of L. monocytogenes, the growth curve of L. monocytogenes in LEBB was determined firstby enumerating the bacterial concentration on blood agar plates and measuring
the optical density (at 550 nm) of the culture broth. The desired concentrationof L. monocytogenes (108 CFU/mL) was used as inoculum. Prior to inoculation,
Yunan chicken was cut into pieces and made into 100 g packages. The chicken
was first wrapped with aluminum foil, then packed in a sterile HDPE bag. The
chicken packages were then autoclaved to eliminate all microorganisms in thechicken. Chicken inoculations with L. monocytogenes were done in biohazard
class II cabinet at the Research Institute for Veterinary Science Laboratory in
Bogor. Each package of 100 g was inoculated with 1 mL of culture brothcontaining approximately 108 CFU L. monocytogenes. Therefore, theinoculation dose was 106 CFU/g. Inoculation was effected using a 1.0 mL
syringe and the dose was injected, sprayed and distributed throughout thewhole chicken meat. After inoculation, the chicken was wrapped, labelled andstored at ±4°C, ready for irradiation. Dosage levels for irradiation were: 0.5,
1.0, 1.5, 2.0, 2.5, 3.0, 4.0 and 5.0 kGy. For each dose of irradiation, samples wereprepared in triplicate.
Enumeration and determination of the surviving number of L. monocytogenes was made as follows:• Twenty-five grams of chicken was homogenated with the addition of
100 mL sterile 0.1% peptone diluent. Stomacher was used for obtaining
the homogenized suspension.
• Decimal dilutions were made from the sample with sterile 0.1% peptone
diluent.
• L. monocytogenes was determined from direct plating of 100 µL
suspension on blood agar base media (OXOID CM 55) and plated in
duplicate.
• The colonies on agar plates were examined, confirmed and counted. The
culture colonies’ identities were confirmed by morphology, Gram stain(+) and catalase reaction (+), and motility test (+).
The freeze-dried culture of C. jejuni obtained from a local isolate was
firstly grown on nutrient broth (with 5% blood), Campylobacter blood freeselective agar base (OXOID CM 739) or Campylobacter agar base (OXOID
CM 689), for 48 h at 37°C. Incubation was carried out using an anaerobic jar
with 5% oxygen, 10% carbon dioxide, 80% nitrogen and hydrogen (microaerophilic). The purity check of the isolate was done by growing the isolate on
blood agar with 5% defibrinated sheep blood. For preparing the inoculum of137

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C. jejuni, its growth curve in the nutrient broth was first determined. The
growth curve (log phase) of C. jejuni in nutrient broth was made byenumerating the bacterial concentration on blood agar plates and measuring
the optical density at 550 nm of the culture broth. The desired concentration,
108 CFU/mL of C. jejuni, was used as inoculum. Prior to inoculation, Yunan
chicken was cut into pieces and made into 100 g packages. The chicken wasthen wrapped with aluminum foil and placed in a sterile HDPE bag. The
chicken packages were then autoclaved to eliminate all the microorganisms.
Chicken inoculations with C. jejuni were carried out in a biohazard class II
cabinet. Each package (100 g) was inoculated with 1 mL of culture brothcontaining approximately 108 CFU of C. jejuni. Therefore, the inoculation dose
was 106 CFU/g. Inoculation was carried out using a 1.0 mL syringe and the dose
injected, sprayed and distributed throughout the chicken meat. After inoculation, the chicken was wrapped, labelled and stored at ±4°C, ready forirradiation with doses of 0.1, 0.2, 0.3 and 0.4 kGy, respectively. For each dose ofirradiation, samples were prepared in triplicate.
Enumeration and determination of the number of surviving C. jejuni wasmade as follows:• Twenty-five grams of chicken was homogenated with the addition of
100 mL sterile nutrient broth. Stomacher was used for obtaining thehomogenized suspension.
• Decimal dilutions were made from the sample with the nutrient broth asa diluter.
• C. jejuni was determined from direct plating of 100 µL suspension on
blood agar base media and plated in duplicate. Incubation was carried out
by using an anaerobic jar with 5% oxygen, 10% carbon dioxide, 80%
nitrogen and hydrogen.
• The colonies on agar plates were examined, confirmed and counted. The
culture colonies identities were confirmed by morphology, Gram stain (–)
and catalase reaction (+), oxidase (+) and motility test (+).
In addition, the MPN technique was used for estimating the number ofmicroorganisms L. monocytogenes and C. jejuni in the chicken sample [14].
Decimal dilutions in LEBB (broth tubes) for L. monocytogenes and in nutrient
broth (broth tubes) for C. jejuni, respectively, were used to recover injured
organisms. The manipulation and dilution of samples in LEBB for the MPN
method was essential to the procedure used in colony counts. Three tubes wereplanted for each dilution used. The generally accepted time allowable frompreparing the sample homogenate to planting in the last tube was 20 min.
Incubation was carried out for 48 h at 37°C for estimating the number of138

IRAWATI et al.

L. monocytogenes. For C. jejuni, incubation was effected by using an anaerobic
jar with 5% oxygen, 10% carbon dioxide, 80% nitrogen and hydrogen (microaerophilic) for 48 h at 37°C. MPN tables were used for determining MPN
estimates for the three tube series.
A flow diagram for counting L. monocytogenes/C. jejuni [14] in Yunan
chicken is illustrated in Fig. 1.
The determination of the D10 values (the dose required to inactivate 90%
of a population) for some pathogenic bacteria was calculated by plotting ln (N/N0) against dose (D) according to the equation: D10 = D/(ln N – ln N0) where N0
is the initial number of microorganisms and N is the number of microorganisms
surviving the radiation dose [17].
Physicochemical characteristics analysis
The following physicochemical characteristics of the prepared meals,soups, snacks and Yunan chicken were measured: water activity [18, 19],
moisture content (%), pH and total fat content (%) and carbohydrate content(%) [20]. Protein content (%) was determined using a combined method of
Lowry and biuret reaction [21]. Some other chemical parameter analyses suchas peroxide value (meq/kg) [22], fatty acids [23] and amino acid [24] contents(%), vitamin B1 (ppm) [25, 26], ash and salt contents (%) [27] were only carriedout for the Yunan chicken.
Design and analysis of experiments were undertaken statisticallyaccording to Steel and Torrie [28].
The nutritive values of raw materials used for each type of soup and snack
were calculated on the basis of the quantity of each of the materials according
to the following formula:
Nutritive value/serving size/pouch = (weight of material × nutritive
value)/100 [29].
2.2.5.3. Sensorial evaluation
Testing of sensory attributes was done by 10 experienced panellists usinga 5 point hedonic scale where 5 = excellent, 4 = good, 3 = fair, 2 = poor and
1 = extremely poor [30].

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25 g samples+ 100 mL sterile peptone water 0.1% (for L. monocytogenes)+ 100 mL nutrient broth (for C. jejuni)
Stomacher to homogenize

Decimal dilutions of sample suspension

Broth:(LEBB for L. monocytogenes,
nutrient broth for C. jejuni)

Blood agar base(plated in duplicate for each dilution)

Three tube series for each dilution

Incubation for 48 h at 37ºC
Use anaerobic jar, 5% O2, 10% CO2, 80% N2, 5% H2 (for C. jejuni)

Bacterial colonies on agar examined, counted and confirmed
L. monocytogenes:

C. jejuni:Colony morphology

Colony morphology

Gram’s stain (+)

Gram’s stain (–)

Catalase (+)
Motility (+)

Catalase (+)
Oxidase (+)
Motility (+)
Confirmation with MPN estimates

L. monocytogenes or C. jejuni counts in sample

FIG. 1. Flow diagram of procedure for counting L. monocytogenes/C. jejuni in Yunan
chicken.

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3.

RESULTS AND DISCUSSION

3.1. Microbiological assessments
3.1.1. Soups
Microbiological assessments (TBC and TMYC) are summarized inTable 1.
The results from Table 2 show that most raw materials used for laboratory
made soups, in particular beef and oxtail, contained high levels of bacteria.
However, Staphylococcus spp. and E. coli were not detected in any of the tested
samples. Contamination of the ingredients was high in some of them despite
the fact that strict selection was done.
The results showed that 5 kGy eliminated all bacteria, moulds and yeasts
in black soup. This dose was less effective in the other soups studied; however,
all of them presented a very low contamination. Pathogenic bacteria such as
E. coli, coliforms, Salmonella spp., Staphylococcus spp. and Clostridium spp.
were absent from both non-irradiated and irradiated soups.

TABLE 1. EFFECT OF GAMMA IRRADIATION ON MICROBIAL
LOADa OF SOUPS AT THE BEGINNING OF STORAGE

Parameter

TBC(CFU/g)

TMYC(CFU/g)aType of soup

Irradiation
dose
(kGy)

Black

0

3.7 × 103

1

2

Chickenvegetable

Chickensweetcorn

4.6 × 103

7.6 × 103

6.1 × 103

8.5 × 102

2.4 × 10

2.9 × 103

1.5 × 1033

1.4 × 102

1.7 × 102

1.4 × 102

1.6 × 102

50

6.0 × 101

7.0 × 101

4.0 × 101700

1.8 × 101

4.0 × 1020

1.9 × 103

3.0 × 103

4.1 × 103

3.4 × 1031

1.0 × 102

1.5 × 102

2.7 × 103

1.4 × 10330

1.3 × 102

1.5 × 102

1.2 × 103

501

5.0 × 10

6.0 × 101

5.0 × 101

700

2.0 × 100

Oxtail0

Average of three replications.

141

IRAWATI et al.

TABLE 2. MICROBIAL LOAD OF WATER AND RAW MATERIALS AT
EACH STEP IN PREPARATION OF LABORATORY SOUPS BEFOREIRRADIATION
Samples

TBC(CFU/g)

TMYC(CFU/g)S. aureus(CFU/g)E. coli(MPN/g)Tap water (not potable)

1.6 × 103

3.0 × 10200

Cooked water (potable)

2.6 × 10

2

0

0

0

8.5 × 10

7

0

0

0

5.3 × 10

7

0

0

0

2.1 × 10

3

0

0

0

Raw seasonings for blacksoup

1.5 × 107

3.9 × 1000

Raw seasonings for oxtail
soup

1.1 × 106000

Raw seasonings forchicken vegetable soup

5.1 × 104

3.6 × 10400

Raw seasonings forsweetcorn soup

8.5 × 103

1.0 × 10300

Raw mixed vegetables forchicken vegetable soup

1.0 × 103

3.0 × 10300

Raw mixed vegetables forsweetcorn soup

1.9 × 103

1.2 × 10300Meat broth for black soup

0

0

0

0

Broth for oxtail soup0

Raw beef
Raw oxtail
Raw chicken

3

0

0

0

Cooked seasonings forblack soup

8.0 × 10

4

0

0

0

Cooked seasonings for
oxtail soup

6.0 × 103000Black soup after cooking

3.6 × 103000

Oxtail soup after cooking

5.6 × 103

3

3.6 × 1000Chicken vegetable soup
after cooking

7.7 × 103

3

1.2 × 1000Chicken sweetcorn soup
after cooking

1.4 × 103

1.1 × 103

0

0

142

IRAWATI et al.

Warm soups poured into a laminate pouch of PET 12 µm/LDPE as adh.
2 µm/Al foil 7 µm/LDPE as adh./LLDPE 50 µm followed by vacuum sealing
gave better results than cold soups without vacuum treatment (preliminary
work data are not shown). Packages found during storage which showeddamage such as leakage, peeled laminates and swelling were separated andinvestigated microbiologically, then discarded. The results show that most of
the accidents were caused by mishandling during the preparation steps and thegrowth of Staphylococcus spp. found in the swollen packages. The soups werestill acceptable from the microbiological viewpoint, but they were not acceptedby the panellists owing to their general appearance.
Tables 3 and 4 show that all irradiated samples presented a low microbial
load and no pathogenic microorganisms were found except in two samples
treated with 1 kGy. Some control samples were positive to coliforms, S. aureus
and E. coli.
3.1.2. Precooked snacks
Table 5 shows the results on microbiological quality of raw mixed
vegetables and seasoning used in the preparation of spring roll, rissole andcroquette.
Results of the microbial assessment of spring roll are presented inTable 6. On the basis of the microbiological results, this item could be stored at
5 ± 2°C for about 3 months after irradiation with 7 kGy. However, from thesensory evaluation point of view, this product was acceptable only up to
1 month of storage. Pathogenic bacteria such as E. coli, coliforms,
Pseudomonas spp. and C. perfringens were not found in any of the samples.
After 1 month of storage, the filling of non-irradiated and irradiated (up to
5 kGy) spring rolls became moist and produced some gases. A strong
unpleasant odour escaped from the package through tiny pinholes in the sealed
area during the storage period. This was probably a result of fermentation due
to a biochemical process in the bamboo shoot, which was used as filler material
during the preparation of the spring roll. From the obtained results, irradiation
with 7 kGy could maintain the quality of the spring rolls vacuum packed in thelaminated pouch for 1 month at 5 ± 2°C.
Tables 7 and 8 show that the most effective radiation dose was 7 kGy forboth types of snack, i.e. rissole and croquette before and after storage of up to
3 months at refrigeration temperature. Doses of 5 kGy and temperatures 5 ±2°C can keep the product in good microbiological condition at least for one
month. Pathogenic bacteria, i.e. E. coli, coliforms, Pseudomonas spp. andC. perfringens, were negative in all tested samples.

143

IRAWATI et al.

TABLE 3. MICROBIOLOGICAL ASSESSMENTSa OF IRRADIATED
SOUPS PREPARED IN THE LABORATORY AND PACKED IN
VACUUM SEALED LAMINATE POUCHES BEFORE AND AFTER
STORAGE AT 5 ± 2°C FOR 3 MONTHS

Parameter

TBC (CFU/g)

TMYC (CFU/g)

Coliforms (MPN/g)

S. aureus (CFU/g)a

Radiation
dose
(kGy)

Black
0 months

Oxtail3 months0103

4.0 × 10

0

0

0

0

5

0

0

0

0

7

0

0

0

0

0

1.3 × 10

1

0

3

3

3

3 months
> 106

10

3

0 months
10

0

0

0

3.8 × 10

1

0

0

0

0

3

0

0

0

0

5

0

0

0

0

7

0

0

0

0

0

15

Negative

Negative

Negative

1

10

Negative

Negative

Negative

3

Negative

Negative

Negative

Negative

5

Negative

Negative

Negative

Negative

7

Negative

Negative

Negative

Negative

0

40

0

0

0

1

0

0

0

0

3

0

0

20

0

5

0

0

0

0

7

0

0

0

0

Average of three replications.

144

Type of soup and storage time

IRAWATI et al.

TABLE 4. MICROBIOLOGICAL ASSESSMENTSa OF IRRADIATED
SOUPS PREPARED IN THE LABORATORY AND PACKED IN
VACUUM SEALED LAMINATE POUCHES BEFORE AND AFTER
STORAGE AT 5 ± 2°C FOR 3 MONTHS

Parameter

TBC (CFU/g)

TMYC (CFU/g)

Coliforms (MPN/g)

E. coli (MPN/g)aType of soup and storage time

Radiation
dose
(kGy)

0 months

3 months

0 months

3 months0

3.3 × 104

1.7 × 105

1.0 × 106

2.5 × 1051

1.2 × 104

1.3 × 102

5.0 × 105

2.0 × 1023

2

5.4 × 100

1.1 × 10

5

0

0

0

0

7

0

0

0

Chicken vegetable

Chicken sweetcorn

3

4

0

0

0

3.3 × 100

2.4 × 103

1

0

0

0

0

3

0

0

0

0

5

0

0

0

0

7

0

0

0

0

0

Negative

1.1 × 102

Negative

Negative

1

Negative

Negative

Negative

Negative

3

Negative

Negative

Negative

Negative

5

Negative

Negative

Negative

Negative

7

Negative

Negative

Negative

Negative

Negative2

1.1 × 10

Negative

1

0

Negative

1

Negative

Negative

8.0 × 10

Negative

3

Negative

Negative

Negative

Negative

5

Negative

Negative

Negative

Negative

7

Negative

Negative

Negative

Negative

Average of three replications.

145

IRAWATI et al.

TABLE 5. MICROBIAL LOADa OF RAW MIXED VEGETABLES AND
UNCOOKED SEASONINGS OF SPRING ROLL, RISSOLE AND
CROQUETTEType of producta

Microbial load

Raw mixed
vegetables

Spring rollfillerRissolefillerCroquettefillerBreadcrumbsTBC (CFU/g)

1.2 × 104

1.9 × 103

3.3 × 104

3.1 × 104

1.7 × 103

TMYC (CFU/g)

1.1 × 105

1.3 × 105

1.2 × 104

1.3 × 103

1.2 × 103

E. coli (MPN/g)

Negative

Negative

Negative

Negative

Negative

Coliforms (MPN/g)

Negative

Negative

Negative

Negative

Negative

Pseudomonas spp.
(CFU/g)

0

0

0

0

0

Staphylococcus
spp. (CFU/g)

1.2 × 102

0.5 × 102

2.3 × 102

1.1 × 102

Negative

C. perfringens(MPN/g)Negative

Negative

Negative

Negative

Negativea

Average of three replications.

TABLE 6. MICROBIAL LOADa OF VACUUM PACKED NON-IRRADIATED AND IRRADIATED SPRING ROLL STORED UP TO 3 MONTHS
AT 5 ± 2°C
Microbial loada
TBC (CFU/g)

TMYC (CFU/g)

Staphylococcus spp.
(CFU/g)Average of three replications.

146

0

3

5

0

3

2.3 × 100

14

1.6 × 10

0

3

3

>10

4.2 × 10

4.5 × 10

0

0

0

0

0

0

0
3

3

7

3

1.2 × 10

0
3

0
0

0

0

1

1.4 × 10

3

3

>10

4.2 × 10

2.8 × 10

0

0

0

0

0

1

0

0

0

0

10

0

3
a

Irradiation dose (kGy)

Storage time(months)

3

>10

2

10

2

2

0

IRAWATI et al.

TABLE 7. MICROBIAL LOADa OF VACUUM PACKED NON-IRRADIATED AND IRRADIATED RISSOLE STORED UP TO 3 MONTHS AT
5 ± 2°C
Microbial loada
TBC (CFU/g)

0
1

TMYC (CFU/g)

Staphylococcus
spp. (CFU/g)0
2.7 × 10

3

5

7

3

0

0

0

3

0

4.0 × 10
3

0

3

>10

4.0 × 100

3.6 × 10301

1

3.9 × 103

1.4 × 10
4.1 × 101

2.3 × 10

0

0

0

0

0
1

0

0

0

0

102

10

0

0

0

0

0

1

0

0

>10

0
1

1.2 × 10

>10

3

2

1

3

3
a

Irradiation dose (kGy)

Storage time(month)Average of three replications.

TABLE 8. MICROBIAL LOADa OF VACUUM PACKED NON-IRRADIATED AND IRRADIATED CROQUETTE STORED UP TO 3 MONTHS
AT 5 ± 2°C
Microbial loada
TBC (CFU/g)

TMYC (CFU/g)

Staphylococcus
spp. (CFU/g)

0

0

3

5

7

9.45 × 102

6.05 × 102

0

0

1

3

1.38 × 10

4.37 × 102

0

0

3

3

6.37 × 10

2

3.35 × 10

0

0

0

2

2.45 × 10

21.71 × 10

0

0

1

3

1.56 × 10

21.60 × 10

003

2.54 × 103

1.40 × 102

0

0

2

0

0

0

0

0

0

0

0

0

0

1

0

3
a

Irradiation dose (kGy)

Storage time(month)

<10
3

>10

Average of three replications.

147

IRAWATI et al.

3.1.3. Yunan chicken
The control samples presented a high level of contamination since thebeginning of the storage period. Priadi et al. [32] concluded that the microbiological safety and quality of chicken and chicken products collected from thelocal market were poor and potential sources of foodborne disease outbreak inIndonesia. Ashari et al. [33] came to a similar conclusion for meatballconsumption, regarding its safety and convenience. Table 9 summarizes theresults of TBC (CFU/g) on commercially prepared Yunan chicken. It showsthat irradiation at doses of 3 and 5 kGy was sufficient to eliminate total bacteria
in the samples. The TBC (CFU/g) in control samples increased by 3 log cycles
after 6 months of storage. Neither E. coli nor coliforms were found in the nonirradiated and irradiated samples during storage. The absence of E. coli in thesamples may be viewed as an indication of good processing steps in the industry
or less possibility to grow at the storage temperature. Likewise, other types ofGram negative bacteria such as Pseudomonas spp., Vibrio spp., and Gram
positive bacteria such as Listeria spp., are the most critical microorganisms infoodstuffs stored at 5 ± 2°C [34]. Generally, coliforms are not good sanitary
indicators for poultry products because other bacteria such as Salmonellae may
exist in a flock prior to slaughter, and thus a positive faecal coliform test may beunrelated to post-slaughter contamination [35, 36].
Determination of D10 values for S. typhimurium, P. aeruginosa and E. coli
O157 were 0.28, 0.17 and 0.12 kGy, respectively. If the Yunan chicken iscontaminated with those three types of bacteria, the irradiation doses appliedshould not be less than their D values. The D10 value for L. monocytogenes was
0.66 kGy and for C. jejuni it was 0.09 kGy. It seems that the values of the two
types of bacteria in Yunan chicken were lower than those in fresh chicken
meat. This was probably due to the presence of some natural food additives
such as spices and salt added in making Yunan chicken [37].

TABLE 9.
MICROBIAL LOAD OF NON-IRRADIATED AND
IRRADIATED YUNAN CHICKENTBC (CFU/g)
Storage time (weeks)

Irradiation dose
(kGy)
0

3
6

6
8

9
9

7.5 × 1070

1.2 × 10

5.9 × 10

9.4 × 10

3

0

0

0

0

5

0

0

0

0

148

IRAWATI et al.

3.2. Physicochemical characteristics analysis
3.2.1. Soups
Irradiation (up to 7 kGy) did not affect the pH (6–7) of the soup studied.
However, fat and protein contents were affected by irradiation (5 and 7 kGy)and storage time. The moisture content of the soups was in the range 70–87%.
The carbohydrate content of the chicken soups varied between 27 and 35%. Fatcontent was between 10 and 32% and protein content was between 13 and25%. These values were higher than those for cream soups determined by theIndonesia National Standard [38], and also the carbohydrate contents werehigher than the USDA Nutrient Database for Standard Reference [27]. A
slight reduction was found in the fat and protein contents of certain irradiatedsoups during storage. The selected storage temperatures were not effective
enough to maintain the stability of either the fat or the protein contents in thesemi-liquid samples.
The purpose of calculating the nutritive values/serving size/pouch of thesoups was to assess the nutrition factor of each raw material prior to use, basedon some essential food components (Table 10).

TABLE 10.
STUDIED

Nutrient(unit)PROXIMATE NUTRITIVE VALUE OF THE SOUPS

Nutritive value/serving size/pouch of soup
(weight of material × nutritive value)/100
Black
OxtailChicken vegetable
300 g/pouch 300 g/pouch
300 g/pouch

Chicken sweetcorn
250 g/pouch

Energy (cal)

796

466

674

659

Protein (g)

26.6

19.5

32.8

32.3

Fat (g)

74.4

40.7

46.1

51.3

Carbohydrate (g)

54.4

3.99

26.2

17.8

Calcium (mg)

32.2

29.4

87.6

45.5

Phosphorus (mg)

249

190

493

353

Iron (mg)

4.17

3.46

5.47

3.35

Vitamin A (IU)

30.04515.128

4.702

2.841

Vitamin B1 (mg)

0.136

0.299

0.374

0.252

Vitamin C (mg)

5.77

3.98

24.2

4.87

149

IRAWATI et al.

3.2.2. Precooked snacks
The nutritive values of precooked snacks are shown in Table 11.
The results of water activity measurement of either non-irradiated or
irradiated spring roll samples were within the range of 0.80–0.90. Some otherquality parameters, i.e. pH value, moisture and protein contents in the springroll before and after irradiation at doses of 5–7 kGy without storage indicatethat the samples were stable after the treatment (pH4.6–4.8, moisture content
72–73% and protein content 3.64–3.76%), carbohydrate content slightly
increased at the dose of 7 kGy, but fat content slightly reduced at the dose of
5 kGy (from 3.9% to 2.99%).
The results of physicochemical characteristics of rissole and croquette(Tables 12 and 13) showed that pH values and fat content of the non-irradiatedand irradiated samples decreased during the 3 months storage. It was probably
caused by the biochemical degradation of some macrocomponents within the
products. On the basis of the overall results, rissole and croquette showed more
promising applications of irradiation than spring rolls.

TABLE 11. PROXIMATE NUTRITIVE VALUE OF PRECOOKEDSNACKS MADE IN HOME INDUSTRY

Nutrient(unit)

Nutritive value/serving size/pouch of snack(weight of material × nutritive value)/100
Spring roll/
100 g

Rissole/100 g

Croquette/
100 g

Energy (cal)141.80284.68131

Protein (g)

6.46

15.11

5.15

Fat (g)

4.76

16.99

7.39

Carbohydrate (g)

13.67

12.11

11.2

Calcium (mg)27.39

236.7621

Phosphorus (mg)85.45

244.83

81.7

Iron (mg)

1.47

2.228

156.91742.77

Vitamin B1 (mg)

0.068

0.165

0.086

Vitamin C (mg)

3.49

1.219

9.45

Vitamin A (IU)

150

1
206.3

IRAWATI et al.

TABLE 12.
RESULTS OF PHYSICOCHEMICAL ANALYSISa OFRISSOLE BEFORE AND AFTER IRRADIATION AT DOSES UP TO
7 kGy AND STORED AT 5 ± 2°C
Irradiation dose (kGy)

Storage time(months)

0

3

5

7

0

0.81 ± 0.00

0.85 ± 0.04

0.87 ± 0.01

0.92 ± 0.02

3

0.86 ± 0.01

0.86 ± 0.00

0.80 ± 0.00

0.90 ± 0.01

07.60 ± 0.02

7.35 ± 0.02

7.45 ± 0.04

7.45 ± 0.01

3

4.21 ± 0.02

4.40 ± 0.02

5.30 ± 0.08

5.90 ± 0.70

Moisturecontent (%)

038.04 ± 0.29

38.21 ± 0.22

37.96 ± 0.02

38.78 ± 0.21

338.75 ± 1.00

38.31 ± 0.89

41.82 ± 0.19

40.32 ± 0.75

Carbohydrate(%)

016.56 ± 0.48

17.47 ± 0.33

16.66 ± 0.31

16.52 ± 0.46

3

15.92 ± 1.71

17.35 ± 1.54

16.00 ± 0.44

15.65 ± 0.43

Fat (%)

06.50 ± 0.36

5.14 ± 0.25

6.86 ± 1.01

7.35 ± 1.11

3

5.16 ± 0.12

4.60 ± 0.19

4.07 ± 0.99

5.22 ± 0.21

00.13 ± 0.00

0.13 ± 0.01

0.13 ± 0.00

0.12 ± 0.01

30.08 ± 0.00

0.09 ± 0.00

0.10 ± 0.01

0.10 ± 0.00

Parameter
Water activity

pH

Protein (%)
a

Average of three replications.

3.2.3. Yunan chicken
There was no important effect of irradiation on the water activity (0.92–0.95), pH (6.0–6.4) and moisture content (59–60%) of Yunan chicken.
Irradiation treatment did not affect the fat content, which has also been
demonstrated by other authors [6, 9]. The effect of ionizing radiation on thefatty acids in poultry meat and its products strongly depends on the presenceof unsaturated fatty acids [39–41]. The results from irradiated Yunan chicken
during nine weeks of storage indicated that the most radiosensitive fatty acidcomponent to irradiation at 5 kGy was palmitic acid (C16:0) (from 21% to17%), followed by oleic acid (C18:1) (from 33% to 31%) and linoleic acid(from 19% to 15%). The percentage of palmitoleic (C16:1) (1.02–1.11%) andarachidic (C20:2) (0.15%) acids were relatively stable after the same
treatment.

151

IRAWATI et al.

TABLE 13.
PHYSICOCHEMICAL CHARACTERISTICSa OF
CROQUETTE BEFORE AND AFTER IRRADIATION OF UP TO 7 kGy
DURING STORAGE AT 5 ± 2°C
Parameter
Water activity
pH

Irradiation dose (kGy)

Storage time(months)

0

3

5

7

0

0.89 ± 0.00

0.87 ± 0.00

0.89 ± 0.00

0.90 ± 0.01

30.88 ± 0.00

0.88 ± 0.01

0.86 ± 0.00

0.85 ± 0.00

06.63 ± 0.01

6.64 ± 0.01

6.65 ± 0.00

6.66 ± 0.01

33.85 ± 0.02

4.30 ± 0.03

4.48 ± 0.02

5.88 ± 0.09

Moisturecontent (%)

036.37 ± 1.33

39.46 ± 0.54

39.09 ± 0.15

39.92 ± 0.22

340.34 ± 0.15

40.58 ± 0.22

41.82 ± 0.18

39.70 ± 0.39

Carbohydrate(%)

017.79 ± 0.17

17.73 ± 0.06

17.56 ± 0.06

17.45 ± 0.07

316.50 ± 0.30

16.84 ± 1.26

16.59 ± 1.13

15.92 ± 0.12

Fat (%)

0

10.09 ± 0.82

7.31 ± 1.15

8.06 ± 0.07

9.68 ± 0.66

3

6.45 ± 0.35

5.30 ± 0.25

7.46 ± 0.25

9.23 ± 1.03

Protein (%)
a00.10 ± 0.01

0.11 ± 0.01

0.12 ± 0.00

0.12 ± 0.11

3

0.10 ± 0.00

0.10 ± 0.00

0.10 ± 0.00

0.10 ± 0.01

Average of three replications.

Table 14 summarizes data on the measurement of peroxide value in
irradiated Yunan chicken. The values showed an increase with higher doses.
However, the values decreased during the storage time. Interaction between
irradiation and storage time could significantly reduce the peroxide value in thesamples. Unsaturated acyl lipids as well as acyl lipid constituents, which include
oleic, linoleic and linolenic acids, have one or more allyl groups within the fatty
acid molecules which are readily oxidized to hydroperoxide, and after
subsequent degradation induced by radiolysis might yield a great number ofother compounds. The degradation process either induced by auto-oxidation or
by lipid peroxidation of oleic, linoleic and linolenic acids might liberate some of
the numerous volatile and non-volatile compounds such as aldehydes andketones which might affect the aroma and flavour of the products. Postirradiation effects such as auto-oxidation of unsaturated acyl lipids in irradiatedYunan chicken could be retarded and suppressed through exclusion of oxygen
within the package prior to process, irradiation under cryogenic conditions andstorage of the irradiated products at low temperature (5 ± 2°C).

152

IRAWATI et al.

TABLE 14. EFFECT OF GAMMA IRRADIATION ON PEROXIDEVALUE (mek/kg) OF NON-IRRADIATED AND IRRADIATED YUNANCHICKEN STORED AT 5 ± 2°C
Peroxide value (mek/kg)
Irradiation dose(kGy)

Storage time (weeks)
0

3

6

9

0

237.72 ± 0.04a*

65.26 ± 0.32b33.32 ± 0.98c

36.92 ± 0.34d

3310.41 ± 0.03e

66.56 ± 0.89b

23.92 ± 0.44f

23.98 ± 0.64f

5586.04 ± 0.94g

98.00 ± 0.64h

96.91 ± 0.83h

57.54 ± 0.16i*

Means for each character followed by the same letter are not significantly different at
p < 0.05.

The determination of protein and major amino acid contents indicatedthat irradiation with doses up to 5 kGy did not have any significant effect onprotein content (33–34%) and neither did the major amino acids in thesamples. These results are supported by several authors [41]. It is reported thatin most experiments there were no significant changes in amino acidcomposition in the dose range below 50 kGy. If there was any effect of irradiation, it was within the range of biological variability. Likewise, the storage
time and the interaction between irradiation and storage time could slightly
influence the protein content as well as in the analysis of amino acids in theanalysed samples.
Chicken meat contains vitamin B1 which is very sensitive to radiation
exposure. It cannot be protected solely by the exclusion of oxygen from thepackage, but also requires the temperature during the radiation process to be
maintained. Yunan chicken was placed in vacuum packed laminate pouches
and irradiated under cryogenic conditions at doses of up to 5 kGy and thevitamin was slowly reduced by about 20–50% both before (from 0.11 mg/100 g
to 0.04 mg/100 g edible portion) and after storage (from 0.13 mg/100 g to
0.06 mg/100 g edible portion). Severe damage in vitamin B1 might occur if theradiation processing of Yunan chicken is conducted in the presence of oxygen
and at ambient temperature.
Previous studies on irradiated minerals and trace elements indicated that
irradiation does not affect some micronutrients and there is no evidence thatthe bioavailability of these elements might be adversely affected by irradiation[31, 40]. The effect of ionizing radiation on Yunan chicken resulted in somefluctuating values in ash content (3–4%) and this is probably caused by the153

IRAWATI et al.

processing step and types of seasoning used in its preparation. Ash content in
the processed meat was about 0.7–1.3% [42]. The increase in salt content in
irradiated Yunan chicken during storage was probably due to greater salt
absorption within the product with increasing length of storage. Unfortunately,
the quantity of salt added in the Yunan chicken during preparation was not well
documented by the food industry.
3.3. Sensory evaluation
3.3.1. Soups
The results obtained in sensory evaluations, i.e. appearance, aroma, taste
and texture/consistency of the products, indicated that the values of each
attribute remained high (3–4), but non-irradiated soups were mostly rejected(1–2) after 1 month of storage at 5 ± 2°C.
3.3.2. Precooked snacks
The results from treatment of spring roll indicate that irradiation at 7 kGy
followed by 1 month’s storage at 5 ± 2oC could maintain the score of sensory
attributes, i.e. general appearance (3.8), colour (3.5), texture (3.3), aroma (2.8)
and taste (2.4). However, after 1 month, all samples were rejected by thepanellists. Sensory tests of rissole and croquette showed that irradiation atdoses of 5 and 7 kGy and storage times of up to 3 months at 5 ± 2°C could
significantly maintain general appearance (3.3), aroma (3.8) and taste (3.3) ofrissole, but a dose of 5 kGy gave better sensory results for colour (4.0) and taste(3.0) than one of 7 kGy in the case of croquette under the same storage
conditions. The laminate packaging material used and the packing technique
may play an important role in maintaining the quality of these products duringstorage, but some samples remained attached to the inner layer and needed tobe slowly removed prior to analysis. It is suggested that an intermediate
package, as well as PET trays or HDPE film sheet as direct contact packing
material to the product, is needed. A polypropylene tray is not suitable for sucha purpose because it is not able to withstand irradiation at –79°C.
3.3.3. Yunan chicken
On the basis of the results of the overall sensory evaluation of irradiatedYunan chicken at doses of up to 5 kGy and storage periods of up to 9 months, theproduct was still accepted by the panellists within the score range of 3 to 4. There
was no effect on either flavour or aroma of fatty acid changes induced by radiation.

154

IRAWATI et al.

4.

CONCLUSIONS AND RECOMMENDATIONS

It can be concluded from the results that gamma irradiation at pasteurization doses of 5–7 kGy in combination with cryogenic conditions (–79°C)
could maintain the safety and quality of four types of home made soup
packaged in a laminate pouch under vacuum and stored for 3 months at
5 ± 2°C. Irradiation at doses of 5–7 kGy could also extend the shelf life of
rissole and croquette for 3 months at the same temperature without significantly affecting their general quality. Gamma irradiation as cold pasteurization
at doses of 3 and 5 kGy could maintain the overall quality of Yunan chicken for
up to 9 months with storage at 5 ± 2°C.
The use of direct contact as well as a flexible sheet and rigid packing
material inside the laminate pouch and the development of a packing
technique are needed in order to protect against the damage caused by vacuum
treatment.

ACKNOWLEDGEMENTS
The authors wish to thank the IAEA for funding this research work
under the Coordinated Research Project and would also like to express theirgratitude to P. Loaharanu and W.T. Rubio Cabello for their technical supportand encouragement. Special thanks are extended to colleagues at BATAN andat the Research Institute for Veterinary Science, for their technical assistanceand also to A. Purwanti and L.S. Andina and other staff at the Food
Preservation Section at BATAN for the technical assistance given during theexperimental work.

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IRAWATI et al.

Annex I
RAW MATERIALS, INGREDIENTS AND QUANTITIESFOR MAKING BLACK, OXTAIL, CHICKEN VEGETABLE AND
CHICKEN SWEETCORN SOUPS IN THE LABORATORY
Soup
Materials/
ingredients

Beef

Black
OxtailChicken vegetable Chicken sweetcorn
Quantities for Quantities for
Quantities for
Quantities for
20 packages
20 packages
18 packages
25 packages@ 300 g@ 300 g@ 200 g@ 250 g
(1)
(2)
(3)
(4)
2.5 kgOxtail2 kg

Chicken

3 kg

P. edule

275 g

Shallot

175 g

70 g

105 g

Garlic

35 g

35 g

30 g

Roastedcoriander

25 gRoastedcandlenut

100 g

Seedless red
chilli

50 g

Ginger

10 cm

Aromatic
lemon leaf

5g

Roasted fish
paste

6g

Turmeric

10 cm

Ginger root

10 cm

Lemon grass

100 g

Kaempferia
galanga

10 cm
25 g

25 g

Salt

20 g

Palm sugar

15 g

Bay leaf

10 g

Palm oil

1L

3 kg

75 g

500 mL159

IRAWATI et al.

RAW MATERIALS, INGREDIENTS AND QUANTITIESFOR MAKING BLACK, OXTAIL, CHICKEN VEGETABLE AND
CHICKEN SWEETCORN SOUPS IN THE LABORATORY
Soup
Materials/
ingredientsBlack
OxtailChicken vegetable Chicken sweetcorn
Quantities for Quantities for
Quantities for
Quantities for
20 packages
20 packages
18 packages
25 packages@ 300 g@ 300 g@ 200 g@ 250 g
(1)
(2)
(3)
(4)

Water

5L

5l

Onion

50 g

Groundnutmeg

20 g

3l

3l

12.5 g40 g

Cloves2g

Groundwhite pepper

25 g

20 g

Onion leaf

100 g

200 g

Celery

75 g

150 g

Margarine

30 g

75 g

Sugar (cane)

25 g

Young
sweetcorn

5 kg

Chickensausage1100 gCarrot

450 g

Eggs

400 g

Corn starch
Green beans

350 g

Broccoli

400 g

Frozen sugar peas

500 g

160

350 g

IRAWATI et al.

Annex II
RAW MATERIALS, INGREDIENTS AND QUANTITIESFOR MAKING SPRING ROLLS, RISSOLES AND CROQUETTES
Spring roll and filler
Ready preparedspring roll sheets

Rissole filler

Croquette filler

30 g

30 g

50 g

150 g

200 g

Margarine
Minced beef/chicken

250 g

Peeled shrimp

100 gYoung bamboo
shoot

300 g

Wheat flour

16 g

Chicken broth

100 mL

100 mL

20 g

20 g

Shallot
Garlic

120 g

Salt

16 g

Sago

5g

Sweet soya sauce

2.5 g

Green beans

15 g

20 g

50 g

Carrot100 g

Cheese100 g

Ground peppers,
salt

5g

Eggs

125 g

Wrapper

RissoleMilk

250 mL

Eggs

125 g

Wheat flour

20 g

Salt

4g

Croquette

125 g

Steamed potatoes

500 g

Chicken broth

100 mLGround nutmeg

7.5 g

Breadcrumbs

100 g

100 g

161

.

PART I: HAZARD, SENSORIAL AND ECONOMICIMPLICATIONS OF APPLYING THE HAZARDANALYSIS AND CRITICAL CONTROL POINTSTO IRRADIATED READY-TO-EAT MEALS
Y.F. HARUVY
Soreq Nuclear Research Centre,
Yavne, Israel

Abstract
The classical methodology of hazard analysis and critical control points focuses on
hazards and related implications. A new methodology is suggested here, one that
attempts at a systematic simultaneous assessment of safety hazards, sensorial failuresand economic risks, and the critical control points necessary for their early detection
and/or prevention of their potential outcomes. The new methodology also attempts tocombine the three parameters to form a qualitative prioritization of the numerous
control points and to screen those that can be cost effective for implementation. This isdemonstrated in this paper for a complex product, i.e. radiation sterilized ready-to-eat
meals. Hence, a fourth parameter specific to this product — the radiation specific pitfall— is also assessed. The advantages and drawbacks of the combined assessment methodology are described and their overall possible impact is discussed. Finally, the suggested
combined assessment and control system for ensuring the safety and quality of food canprovide a more structured and critical approach to control identified hazards, comparedwith that achievable by traditional inspection and quality control procedures. It has thepotential to identify areas of concern where failure has not yet been experienced,
making it particularly useful for new operations and products thereafter.

1.

INTRODUCTION

The classical methodology of hazard analysis and critical control points(HACCP) stems from regulations and liability aspects of production
operations and their corresponding commercial products. The classical
HACCP does not aim to be, nor does it provide, a means of assessing failuremodes that relate mainly to marketing or economic disasters. Nevertheless, it is
the potential commercial success that drives the producer to invest in theassessment, detection and prevention of failure modes. Thus, it seems
important to harness the HACCP in the drive for commercial success andincreased profits, via a new combined HACCP methodology, as discussed here.

163

HARUVY

In the food industry, the ready-to-eat sector is a fast growing one with
failure modes that may be concealed up to a point, in particular the failuremodes that correlate to the unskilled consumer and/or food preparercustomers. While success in this sector of the market may be highly beneficial,
failure may be disastrous for numerous reasons. In this already complex field,
radiation processing offers a unique opportunity for pasteurized or sterilized
foods.
Nevertheless, the use of irradiation technology to reduce/eliminate
bacteria necessitates skilful assessment of the radiation specific failure modes,
sensorial in principle, to ensure the anticipated economic success.

2.

METHODOLOGY

2.1. Assessment parameters
A systematic assessment of four parameters is discussed. The assessment
was carried out at each stage of food processing (Table 1), and in the sameorder. This systematic approach was found useful to ensure consideration ofeach cause of failure and the consequent failure mode. Regarding specifically
HACCP analysis of a ready-to-eat-meal, the primary concern, as in the classic
HACCP, is the concern of hazard implications stemming from the safety andhealth of the end consumer. In this respect, intermediate customers of theindustry (e.g. distributors) and food preparers are much less of a priority.
Next to the primary parameter in the combined HACCP assessment, thesafety/health hazard, the second one is the sensory quality of the food. Thisparameter is crucial for reaching the objective of a viable food business, rather
than an anecdotal research food. The third parameter is the economic impactof each and every failure mode of the food, also crucial for becoming a viablefood business. These last two parameters ought to indicate that the businessaspects of the food are well taken care of, thus leaving a sufficient profit margin
to finance an uncompromised care of the hazards per se.
Last but not least, the radiation specific nature of each and every failurecause and failure mode is assessed, aimed at bringing attention to the sensory
relevant and business relevant technological differences between radiation
processed food and food that is processed only by traditional means.

164

HARUVY

2.2. Assessment stages
In the following combined multiparameter assessment (Table 1), thestages of food processing aim to cover each distinct operation, ‘from farm tofork’, from harvesting crops through to assessing the hazard relevant quality of:(1) the ingredients, (2) processing the ingredients, (3) mixing and structuring of
the food, (4) heat treatments of the food (baking, frying, cooking), (5)packaging the food, (6) irradiation produced, (7) pasteurization or sterilization,(8) distributing the food, (9) preparing the food for the end consumer, and (10)actual consumption steps.
The special importance of consumer responsibility in preventing hazards
and complaints afterwards is further discussed, focusing on the importance ofappropriate consumer guidance.

3.

RESULTS AND DISCUSSION

3.1. HACCPThe comprehensive combined HACCP chart is exemplified in Table 1.
3.2. A retrospective hazard analysis: The Bamba story
The importance of the comprehensive HACCP shown in Table 1 isdemonstrated in the following anecdote. The fatal consequences could havebeen prevented ab initio if the HACCP had been adequately carried out.
About 15 years ago, a severe epidemic of Salmonella affecting children
was reported in London. There were two mortalities. A quick investigation
revealed that all the sick children were from the orthodox Jewish community.
The significance of this was that all the children used to consume special kosher
snacks that were all imported from Israel for the sole consumption of that
community. Their favorite snack was Bamba, a peanut flavoured puffed cornsnack which catered for toddlers and very young children, as it dissolved in themouth without requiring chewing.
Once the origin of the hazard was identified, all the imported snacks wererecalled and immediately sent for bacterial analysis. Not surprisingly, therecalled Bamba snacks were found to be highly contaminated with Salmonella.
A special investigator was appointed to inspect all Bamba ingredients andequipment, aiming at tracking down the origin of the bacteria.

165

166
Failure mode/hazard

Post-harvest contamination due
to injuries

Storage: Mould or bacterial
growth due to damp storage
conditions

Storage: Mould or bacterial
growth due to excessive
temperature storage conditions

Storage: Contamination by birds, Bird, rodent and insect control
rodents or insects
storage programme

Supplier: High microbial loading Selection of suppliers of hygiene Microbiologicalof unknown source
practices
smear testing

Bacterial

Bacterial

Bacterial

Bacterial

Inspection:
Microbiologicalsmear testing

Microbiologicalsmear testing

Microbiologicalsmear testing

Dry storage/humidity control
and moisture control in storage
warehouse
Temperature control in storage
warehouse

Inspection fordamagedvegetables

Discard of damaged vegetables

Inspection:
Microbiologicalsmear testing

Bacterial

Bird, rodent and insect control
field programme

Contamination in the field bybirds, rodents or insects

Bacterial

Microbiologicalsmear testing

Detectability

Bacterial contamination due toirrigation with sewage
contaminated water

Irrigation inspection

Preventive control measure

Bacterial

Raw materials: Vegetables

Control point

TABLE 1. THE COMBINED HACCP

9

9

99

99

99

9

99

Sens.

99

99

99

Haz.

9

Econ.

Rad.
specific

HARUVY

Excessively low temperature
upon intermediate storage,
resulting in damaged skin

Storage: Spoilage by exposure to Temperature control in storage
extreme temperatures
warehouse

Temperature

High concentration of hard fibres Inspection, sortingor grainy material
Set threshold for batch discard

Physical

Excessively high temperature
upon harvesting, resulting indamaged skin

Microbiologicalsmear testingContamination by foreign matter, Inspection, sieving and washinge.g. stones, metal objects, shells
Set threshold for lot discarding

PhysicalTemperature

Inspection,mechanical testing

Faulty texture, rigidity, stem cutor damaged skinInspection, sortingSet threshold for batch discard

Inspection, sortingSet threshold for batch discard

Harvesting quality protocols,monitoring and sorting

Inspection,mechanical testing

Inspection,mechanical testing

Inspection, sieving
and washing

Inspection

Pesticide smear
testing

PhysicalPost-detection: Discard batch

Contamination by pesticides

Biotoxins smear
testing

Detectability

Pesticides

Preventive control measure

Accumulation of biotoxins due to Post-detection: Discard batch
sustained exposure to bacteria
and/or moulds

Failure mode/hazard

Biotoxins

Control point

TABLE 1. THE COMBINED HACCP (cont.)

99

99

99

9

99

99

99

99

99

99

99

99

99

99

99

Econ.

99

Sens.

Haz.

99

Rad.
specific

HARUVY

167

168
Failure mode/hazard

Variation in concentration salt
and bacterial growth

Salt mixtures

Bacterial contamination fromburst intestines

Bacterial contamination fromcuts, bruises and abscesses

Bacterial contamination from
insect bites and larvae therein

Bacterial

Bacterial

Bacterial

Raw materials: Animal products

Discard parts contaminatedbeyond permitted level

Discard parts contaminatedbeyond permitted level

Discard parts contaminatedbeyond permitted level

Adjust recipe to maintain spicelevel within set limits

Inspection andmicrobiologicaltesting

Inspection andmicrobiologicaltesting

Inspection andmicrobiologicaltesting

Analysis of spices

Analysis of spices

Variation in concentration ofactive material and bacterial
growthFermentation
products

Adjust recipe to maintain spicelevel within set limits

Analysis of spices

Adjust recipe to maintain spice
Variation in concentration ofacid, e.g. lemon, vinegar, bacterial level within set limits
growthActive material Variation in concentration ofconcentration active material, e.g. capsicum,
ginger, bacterial growth

Acidityconcentration

Detectability

Analysis of spices

Preventive control measure

Adjust recipe to maintain spicelevel within set limits

Raw materials: Spices — all of the above as well as:Control point

TABLE 1. THE COMBINED HACCP (cont.)

9

9

9

99

9

9

99

9

9

99

9

9

99

Sens.

9

Haz.

Econ.

9

9

9

99

99

99

99

Rad.
specific

HARUVYPackaging batch
inspection

Contamination by dirt from
Bacterial(pre-packaging) machinery and workers

Packaged batch
inspection
Inspection of
packaging prior
and after
packagingContamination (external) by dirt Clean storage environment
Bacterial(post-packaging)

PackagingdamageContamination by penetration of Discard damaged packaging
insects and bacteria
materials

Packaged batch
inspection

Bacterial
Contamination by penetration of Bird, rodent and insect control(post-packaging) birds, rodents or insects
programme

Clean storage environment

Packaging batch
inspection

Inspection

Bacterial
Contamination by birds, rodents Bird, rodent and insect control(pre-packaging) or insects
programme

Raw materials: Packaging

Fat degradation during
Discard parts containing fat
irradiation and production of ‘off’ beyond a predetermined levelodoursFat content

Detectability

Discard parts physicallyInspection
contaminated beyond permitted
level

Preventive control measure

Bones, teeth, scale and theirfragments

Failure mode/hazard

PhysicalControl point

TABLE 1. THE COMBINED HACCP (cont.)

99
99
99
99

99
9
9
9

9

9

99

9

9

99

Sens.

Haz.

9

99

9

Econ.

99

99

9

Rad.
specific

HARUVY

169

170
Failure mode/hazard

Bacterial

As above plus inclusion ofbacteria from a specificingredient

Processing: Mixing
Discard any contaminatedingredient

Microbiologicalinspection of
mixed batches

99

99

99

Foreign objects Inclusion of foreign objects from Pre- and post-and processing
Pre- andcutting equipment and/or boards inspection of cutting equipment post-processing
inspection of
Discard suspicious batches
cutting equipment

999

Bacterial growth due toprocessing temperature

Bacterial

9

Inclusion of bacteria from
Inspection of pre-processed
Microbiological/
chopped insects or small rodents batches for insects or rodents or foreign particle
or their litter
litter (Bamba story)
inspection ofprocessed batches

Bacterial

Temperature control of cutting
equipment
Discard contaminated batches

Pre-cleaning and temperature
Inclusion of bacteria fromcontaminated cutting equipment control of cutting equipment
and/or boards
Discard contaminated batches

Bacterial

Microbiologicalinspection ofprocessed batches

Sens.

99

Haz.

9

Microbiologicalinspection of
cutting equipment
and processedbatches

Detectability

99

Preventive control measure

9

Processing: Cutting (or pressing)Control point

TABLE 1. THE COMBINED HACCP (cont.)

9

99

9

9

9

Econ.

99

99

99

99

Rad.
specific

HARUVY

Failure mode/hazard

Preventive control measure

99

9

99

9

Spoiled food from overcooking Discard spoiled batches
or defective stirring
Radiation enhancement of off taste

Spoilage of food texture by tools Discard spoiled batches
used for transfer or stirring

Overcooking

Texturespoilage

Monitor stirring
tools and process

Monitor stirring,temperature, time99

Inclusion of bacteria fromcookware or transfer tools

99

Bacterial

99

9

99

Foreign objects Inclusion of foreign objects from Pre- and post-cooking inspection Pre- andcookware or transfer toolsof cookware
post-processing
Discard suspicious batches
inspection of
cookware

99

99

Econ.

9

Sens.

Haz.

9

Discard batches contaminatedbeyond permitted level

Pre- andpost-processing
inspection of
mixing equipment

Detectability

Inspection andmicrobiologicaltesting of
cookware andfood

Processing: Cooking

Foreign objects Inclusion of foreign objects from Pre- and post-processing
cutting equipment and/or boards inspection of mixing equipment
Discard suspicious batches

Control point

TABLE 1. THE COMBINED HACCP (cont.)

99

9

Rad.
specific

HARUVY

171

172

Spoilage of food texture by tools Discard spoiled batches
used for transfer or stirring

Off taste due to use of spoiled oil Discard spoiled batches
Radiation enhancement of off
taste

Off taste due to oil spoilage on
overheating
Radiation enhancement of off
taste

Texturespoilage

Rancidization

Rancidization

Discard spoiled batches

Monitortemperature, time,stirring

Frying oil
packaging QA
Laboratory and/or
sensory inspection

Monitor stirring
tools and process

Monitor stirring,temperature, time

Discard spoiled batches

Inclusion of spoiled food fromoverfrying or defective stirring

Inspection andmicrobiologicaltesting of fry-wareand food

Detectability

Overfrying

Discard batches contaminatedbeyond permitted level

Preventive control measurePre- andpost-processing
inspection offry-wareInclusion of bacteria from fryware or transfer tools

Failure mode/hazard

Foreign objects Inclusion of foreign objects from Pre- and post-frying inspection
fry-ware or transfer toolsof fry-wareDiscard suspicious batches

Bacterial

Processing: Frying

Control point

TABLE 1. THE COMBINED HACCP (cont.)

99

99
9
99

99

99

99
9
99

99

99

9

Econ.

9

Sens.

9

Haz.

99

99

9

Rad.
specific

HARUVY

Excessive inclusion of oil in thefood due to underheating
Radiation enhancement of off
taste

Spoilage of food texture by
sticking onto fry-ware

Oil inclusion

Sticking

Monitor shear
forces on food
Monitor foodstructuring
operations

External
Spoilage of envelope food texture Discard spoiled batches
texture spoilage by processing tools

Inspection andmicrobiologicaltesting of tools
and foodInternal texture Spoilage of inner food texture by Discard spoiled batches
spoilageprocessing tools

Discard batches contaminatedbeyond permitted level

Monitor stirring
tools and process

Monitortemperature upon
introduction offood

Detectability

Pre- andpost-processing
inspection of tools

Inclusion of bacteria fromprocessing tools

Discard spoiled batches

Discard spoiled batches

Preventive control measure

Foreign objects Inclusion of foreign objects from Pre- and post-processing
processing tools
inspection of tools
Discard suspicious batches

Bacterial

Processing: Structuring and stuffing

Failure mode/hazard

Control point

TABLE 1. THE COMBINED HACCP (cont.)

99

99

99

99

99

99
99

9

99

99
9

99

9

Econ.

Sens.

9

Haz.

9

99

Rad.
specific

HARUVY

173

174

Bacterial

Distribution

Bacterial

Storage

Microbial growth in moist
products

Microbial growth in moist
products

Distribution chain of moist
products at 5 + 2oC
Limited shelf life

Storage of moist products at
5 + 2oC
Limited shelf life

Chill distribution
chain 5 + 2oC

Monitortemperature andfood spoilage

Pre- andpost-packaging
inspection offood texturePre- andpost-packaging
inspection of foodmicrobiologicallevel

Detectability

External
Spoilage of envelope food texture Discard spoiled batches
texture spoilage by packaging equipment

Discard contaminated batches

Preventive control measurePre- andpost-packaging
inspection of tools
and equipment

Inclusion of bacteria frompackaging equipment

Failure mode/hazard

Foreign objects Inclusion of foreign objects from Discard spoiled batches
packaging equipment

Bacterial

Processing: Packing

Control point

TABLE 1. THE COMBINED HACCP (cont.)

9

9

9

9

9

9

9

9

9

Sens.

9

Haz.

99

99

99

99

99

Econ.

99

99

99

Rad.
specific

HARUVYDate label and stock rotation
control

Preventive control measure

Cross-contamination from raw
material, germination andgrowing areas

Metal fragments in productBacterial(personnel)

Bacterial(personnel)

Use of metal detector

Enforcement of controlled
movement of staff andequipment
Discard contaminated batches

Contamination due to unsanitary Personnel hygiene enforcement
handling practices
Discard contaminated batches

Storage abuse of product leading Clear instructions to theto microbial growth
consumer on storage, shelf lifeand product preparation

Distribution of out of date
product

Failure mode/hazard

Bacterial(personnel)

All steps

Bacterial

Consumer

Bacterial

Control point

TABLE 1. THE COMBINED HACCP (cont.)

9

99

99

99

Controlled
movement of staff
and equipment
Use of metal
detector

9

99

9

9

9

9

Sens.

Haz.

Personnel hygiene
inspection

Clear instructions
to the consumer
on storage, shelf
life and productpreparation

Date, label andstock rotation
control

Detectability

9

99

99

999

99

Econ.

999

99

99

99

99

Rad.
specific

HARUVY175

HARUVY

The only ingredient carrying the bacteria was identified as peanut butter
imported from South Africa. Here, the contamination source was tracked tothe pre-pressed raw peanuts, which were detected as carrying a huge flora of
Salmonella, among other bacteria. A close inspection of the pile of raw peanuts
in the open shed farm storehouse revealed that the piles of peanuts included
significant amounts of rodent litter. The above ‘detective’ story is a mishap
chronology, typical of products with inadequate HACCP. In retrospect, it seems
rather trivial to carry out proper HACCP for food products. In reality,
numerous mishaps similar to the above take place all the time, probably
creating insufficient understanding of the trade-off between the HACCP
endeavour and cost, on the one hand, and possible mishaps, exertion anddamages on the other.
3.3. Pros and cons of carrying out a comprehensive HACCP
It is quite obvious that each HACCP has a price tag. The more comprehensive the HACCP and the consequential tests at numerous control points,
the higher this price tag becomes. The pros are obvious: the more comprehensive the HACCP, the smaller the risk of marketing an unsafe food, andfacing lawsuits, fines and compensations thereafter. The cons are trivial: themore expensive the HACCP becomes, the bigger the risk that the product will
fail, business-wise.
Hence, the crucial question stemming from the above displayed HACCP
methodology is how to reach an optimum balance between the value of
producing a safe food and the need to keep the costs at a reasonable level andto ensure reasonable profits for the producer and thereby, a sustained business.
The rationale leading to this optimum seems straightforward: critical control
points should be prioritized for implementation, on grounds of food safety andbusiness safety alike. As a matter of fact, this is what is so often practiced, intuitively. In this paper, this attitude is logically and systematically discussed, aimed
at allowing its broad implementation.
The salient advantage of such a systematic rationale is the resulting
documentation, which allows troubleshooting, in the short run, and skilful
improvement cycles in the long run, as mandated by the ISO 9000 standards.
3.4. Prevention versus detection: A strategy enigma
Prevention is apparently better than detection, yet cost effectivenessconsiderations make this strategic enigma slightly more complex. Prevention offoreseen hazards is typically more effective in ensuring the safety and quality of
the food products. It is of course much more expensive if investment is made in176

HARUVY

hazard prevention, most of which will rarely materialize. Business-wise,
nobody can afford to invest comprehensively in both the prevention anddetection routes.
Practicing prevention alone, without detection, is highly risky in view ofthe fact that detection aims not only at foreseen hazards but also at some
unexpected ones, which are difficult to cover by preplanned prevention
measures. Hence, one should preferably seek an optimal balance between theprevention and detection routes. Even then, covering the entire spectrum of
failure modes, many of which are redundant, is unrealistic for a viable foodbusiness. Hence, the salient question is how to prioritize the various hazards tobe taken care of and how to decide which of them should engage prevention,
which should preferably engage detection and which of them both prevention
and detection. The following rationale may assist in formulating the optimal
strategy:(1)(2)

Raw materials (Table 1): Detailed protocols of harvesting, storage andtransport can be highly cost effective in preventing most failure modes
and hazards relevant to raw materials. Such protocols will minimize thenumber of detection control points necessary for the food product.
Nevertheless, the applicability of such protocols is limited to wellestablished food products and processes. A newly developed productrequires both extensive and even somewhat excessive prevention
measures, as well as detection ones, aiming at discovering the actual
hazards/pitfalls related to that particular product and concurrent
processing, in particular the unexpected ones.
Once the knowledge base of possible mishaps sufficiently increases, one
may decrease the level of caution and the excessive portion of prevention
and detection measures. In particular, one may decrease the detection
measures related to foreseen hazards that do not materialize for a sufficiently long time under a wide variety of circumstances. Consequently,
one may also consider, with utmost care, whether the preventive
measures are just adequate, or constitute ‘overkill’.
Thermal processing (Table 1): Failure prevention in relation to thermal
processing is significantly less expensive when compared with possible
damage consequences. Hence, an extensive HACCP and the consequent
control measures of temperature distribution and stability seem vital. In
particular, measures should be taken to avoid the charring of food at the
typically hot bottom of the cookware.
A less straightforward branch of this failure prevention in thermal
processing relates to the spoilage of frying oil owing to its repeated use.
The long term hazard of carcinogen formation exceeds the short term one

177

HARUVY(3)(4)

of an off taste, yet both should be eliminated: both problems gravely
increase following the radiation processing and the consequent chemistry.
Routine sampling of the frying oil and off-line analysis seems onerous
and costly.
Nevertheless, on-line optical gauging of the oil colour may offer a highly
cost effective preventive measure. Once the process protocols are set tochange the spoiled frying oil, or to recycle it, for example by a charcoal
column or similar means, this problem may be cost effectively solved.
Mechanical processing (Table 1): Failures in this respect are subtle
changes in the food, and relate to undesired textural changes, leading tofood chunks that substantially differ in size and/or texture from what ispreferred by the customers. Prevention can be carried out by carefully
monitoring the food texture, a non-trivial task. Intriguingly, monitoring
the power consumption of the processing machines can give early
warnings about overprocessing or underprocessing, as well as about loose
metal parts that might have become detached from the machine!
Packaging: Materials and processes related to packaging are often
considered ‘out of the scope’ of the food per se. Nonetheless, packaging
failure modes may result in scenarios far more serious than food failures,for two simple reasons: (i) almost no monitoring of the food is carried out
once it is packaged and, (ii) handling of the packaged food is carried out
with much less care than before packaging. The axiom that packaged foodis no longer susceptible to contamination relays to an ideally fault freepackaging, which does not exist. Hence, comprehensive packaging QA is
a must when food is invlolved.
In particular, packaging integrity is important for irradiated food, forwhich an extended shelf life has been promised, and which cannot becompromised. In other words, the greater the promise, the greater theliability and QA requirements needed thereafter.

3.5. Why the special emphasis on radiation specific effects?
Radiation processing of food is nowadays well acknowledged as similar,
in many aspects, to thermal processing (e.g. cooking, frying, baking) and does
not imply any exceptional hazards. Nonetheless, radiation specific thinking isrequired for two major reasons:
(1)

178

Specific knowledge of radiation chemistry in general, and radiation
chemistry of foods in particular, is insufficiently disseminated. Thissituation necessitates that experts on radiation processing of food should

HARUVY(2)

carry out the combined HACCP and thus explicitly analyse the radiation
specific pitfalls, such as fat rancidization.
Specific knowledge of the bacterial safety of food, irradiated long shelf
life foods in particular, is also insufficiently disseminated.

Chemically preserved foods are only mildly sensitive to the opening of
the packaging, as the preserving agent is still present. Radiation disinfection offoods leaves no preserving agent behind and, hence, their safety may bejeopardized if, after opening the packaging, the sanitary care is compromised.
The unwary consumer, who is in the focus of the HACCP, must be made awareof this difference. This can only be achieved if the unwary producer is similarly
made sufficiently aware of the above difference, via the HACCP and theradiation specific analysis therein. Thus, the producer can skilfully relay proper
cautioning to its consumers, for their uncompromised safety, and for the
producer’s uncompromised business success.
3.6. A practical approach for optimizing HACCP implementation
The following eleven step methodology is suggested as a practical
approach to attain an optimal HACCP for a food product aiming at a sustained
business:(1)

Carry out a comprehensive HACCP analysis of the actual food to beprepared.
(2) Assess the most risky (less controlled) points in the process.
(3) Set the necessary QA system to minimize the need for control points.
(4) Set the necessary control measures, inspection points and inspection
frequency.
(5) Run a few experimental preparations, employing markers for bacteria,
foreign bodies and texture damage, etc., introduced at reasonable points.
(6) Analyse the effectiveness of the HACCP system.
(7) Improve the HACCP set, add missing control points and remove
redundancy.
(8) Run validation preparations as before.
(9) Write the protocol and manual for performing the HACCP.
(10) Train the HACCP personnel, verify their knowledge and certify
accordingly.
(11) Start production.

179

HARUVY

4.

CONCLUSIONSThe combined multi-risk HACCP assessment seems capable of providing
a broad and comprehensive picture of the potential failure modes and theirconsequent risks to food. Special emphasis on assessing the risks for radiation
pasteurized foods provided the key control points for minimizing thesehazards, as well as promoting adequate awareness of producers and consumers,
to the specifics of handling such processed foods.
A cost effectiveness driven critical review of the preventive versus
detection measures is crucial to obtain a cost effective safe product and thus asustained business. The pragmatic approach should back the theoreticalassessment with experimental controlled production, to verify which parts ofthe HACCP are necessary, which are missing, and which are redundant. Finally,
the HACCP, in common with the food production it accompanies, should
advance with time and experience gained, to provide both increased safety andreduced safety costs.

180

PART II: UTILIZATION OF THE METHODOLOGYFOR IRRADIATION OF
ETHNIC READY-TO-EAT MEALS
Y.F. HARUVY
Soreq Nuclear Research Centre,
Yavne, Israel

Abstract
A multiparameter hazard analysis and critical control point methodology forfoods under development has been described in Part I. It focused on a systematic
fourfold assessment of safety hazards, sensorial failures, economic adversities andradiation specific pitfalls, and the critical control points for their early detection and/or
mitigation. It attempted also at combining these four parameters to form a qualitative
prioritization of the numerous control points, to screen the most cost effective ones for
implementation. The further development of the methodology described in this reportdemonstrates its application for ethnic foods. These foods are often characterized withmulti-ingredient recipes and multiple preparation steps, subtle ensemble of specificflavours, as well as relatively high bacterial loads. A group treatment of these ingredients has been demonstrated on several ready-to-eat foods investigated by Indonesian
researchers. This approach has been found greatly effective in pinpointing the primarycontrol points of the prepared ethnic meals. The primary achievement resulting fromthis approach is the insight that a two stage irradiation is apparently the best solution toattain both bacteria eradication and taste/flavour conservation or, in other words, thedesired combination of high levels of safety and high quality.

1.

INTRODUCTION

The methodology of hazard analysis and critical control points (HACCP)
is employed in the food industry almost solely for foods under production,
typically following a regulatory demand. It is rarely carried out for foods under
R&D, since foods are still being considered ‘simple products’ despite their everincreasing complexity and innovation.
In contrast, in high-tech products, space systems in particular, thecontemporary practice is to start the risk assessment as soon as the first design
is complete, and develop the risk assessment hand in hand with the products’
evolution. The rationale behind this practice is to eliminate higher risk designs
as soon as possible, before undue time, effort and finance are invested. Food

181

HARUVY

products in general, and prepared meals in particular, are nowadays moving
ever closer to high-tech ones. Hence, the rationale of HACCP at the R&D
stage of innovative foods seems more viable in general, and for long shelf life
foods in particular. The adaptation of the HACCP from a single parameter
methodology, aimed at production only, into to a four parameter one, aimed at
R&D as well, has been demonstrated in Part A. In Part B, several ethnic
radiation pasteurized prepared meals, which have been studied in Indonesia,
were analysed by the modified HACCP.
The prepared meals of Indonesia, as well as numerous other ethnic foods,
are characterized with a very long list of ingredients and preparative processes.
This list seems too long for utilizing the detailed ingredient by ingredientassessment that has been done for more simple foods. Hence, a further
modified HACCP methodology, adapted for multi-ingredient prepared meals,
was apparently needed. The modification employed is demonstrated anddiscussed, and the conclusions and benefits derived thereby are assessed.

2.

METHODOLOGY

2.1. Ingredients grouping
Table 1, copied from Ref. [1], shows the numerous ingredients used inIndonesian ethnic soups. For these types of food, a group by group assessment
methodology seemed crucial and, hence, was developed. The primaryassessment groups are: animal source ingredients, of which the major hazard isbacterial and health compromising; fat-rich ingredients, including frying oils,
the primary hazard of which is rancidization and sensorial degradation; antibacterial ingredients/spices, the primary concern related to these being
uncontrolled concentration of active materials, and uncontrolled bacterial andsensorial quality. All other groups are of minor related hazards.
2.2. Combined HACCP of ingredient groups
The assessment of the various hazard elements was carried out by
employing the same methodology presented in Part I (see Table 1 in Part I).
Only the primary ones which justify inspection and/or preventive actions havebeen listed. The assessment is based on the assumption that the prepared meals
are being produced, whether by a food laboratory or a food industry, while
appropriately conforming with the fundamental prerequisites of good hygiene
and manufacturing practices, as well as good irradiation practice.

182

HARUVYTABLE 1. INGREDIENTS FOR PREPARING INDONESIAN ETHNICSOUPS ON A LABORATORY SCALE
Soup (quantity)
Ingredients

Beef

Black

Oxtail20 × 300 g

20 × 300 g

Chickenvegetable
18 × 200 g

Chickensweetcorn
25 × 250 g

3 kg

3 kg

2.5 kgOxtail2 kg

ChickenFootball fruit(Pangium edule)

25 nuts

Shallot

175 g

70 g

105 g

35 g

35 g

30 g

5 teaspoons

5 teaspoons

5 spoons

3L

3L

2.5 teaspoons

5 teaspoons

GarlicRoasted coriander

5 teaspoons

Roasted candlenut

25 pieces

Seedless red chilli

5 pieces

Ginger

10 cm

Small aromaticlemon leaf

10 pieces

Roasted fish paste

3 teaspoons

Turmeric

10 cm

Ginger root

10 cm

Lemon grass

5 pieces

Spice(Kaempferia galanga)

10 cm

Salt

4 teaspoons

Palm sugar

3 teaspoons

Bay leaf

10 pieces

Palm oil

1L

500 mL

Water

5L

5L

Onion

5 pieces

Ground nutmeg

4 teaspoons

Cloves

20 pieces

Ground white pepper

5 teaspoons

4 teaspoons

5 pieces

10 pieces

Onion leaf

183

HARUVYTABLE 1. INGREDIENTS FOR PREPARING INDONESIAN ETHNICSOUPS ON A LABORATORY SCALE (cont.)
Soup (quantity)
Black

Oxtail20 × 300 g

20 × 300 g

Chickenvegetable
18 × 200 g

Celery5 pieces

10 pieces

Margarine

2 spoons

Ingredients

Sugar (cane)

Chickensweetcorn
25 × 250 g

5 spoons
4 teaspoons

Young sweetcorn

20 pieces

Chicken sausage

1.1 kgCarrot

450 g

Eggs

7

Corn starch
Green beans

10 spoons
350 gBroccoli

400 g

Frozen sugar peas

500 g

3.

350 g

RESULTS AND DISCUSSION

Table 2 lists the primary ingredients of the group carrying the highest
bioburden, namely, ingredients from animal sources. Table 3 lists the primary
HACCP elements of these ingredients which, importantly, carry typicalbacterial loads of 107 CFU/g and over [1].
The foremost hazard, demonstrated in Table 3, is the high bacterial loadin the animal source ingredients, which poses a grave cross-contamination risk
to the manufacturing line. This assessment suggests that a pre-pasteurization
stage, used separately for animal source ingredients, may be advantageous. This
preventive measure can be achieved by the manufacturer of the prepared
meals implementing a two stage irradiation. In other words, pre-pasteurizationof all highly contaminated ingredients may be greatly beneficial in reducing thecross-contamination risk. Practically, the ingredients carrying high bacterialloads can be pasteurized by radiation as part of the production strategy
employed by their suppliers, e.g. packed frozen meats can be irradiated prior to
supplying them to the prepared meals factory.
Such a strategy may allow a much lower dose to be used for the
pasteurization of the whole prepared meal, at the last stage, and, possibly,184

HARUVYTABLE 2. ANIMAL SOURCE INGREDIENTS FOR PREPARING
INDONESIAN ETHNIC SOUPS
Soup (quantity)
Black

Oxtail20 × 300 g

20 × 300 g

Ingredients

Beef

Chickenvegetable
18 × 200 g

Chickensweetcorn
25 × 250 g

3 kg

3 kg

2.5 kgOxtail2 kg

Chicken
Chicken sausage
Roasted fish paste

1.1 kg3 teaspoons

Eggs

7

TABLE 3.
COMBINED HACCP FOR ANIMAL SOURCE SOUP
INGREDIENTS
Raw materials: Animal source
Control
point

Failure mode/
hazardPreventive
measures

Bacteria Very high loads

Microbial test
Two stageirradiation

OK

Fat

Fat loads andrancidization
upon irradiation

Fat removal

OK

Bones

Bone fragments: Bone removal Only of large
Internal wounds
fragments!
and bleeding

Detectability Haz. Sens. Econ.

Rad.
spec.

99

99

99

99

99

99

better preservation of the sensorial quality of the food. Nonetheless, any
initiative of two stage irradiation must be accompanied by adequate research,
to assess the possible formation of undesirable compounds. Further, a proper
regulation allowing two stage irradiation must be implemented, since all thecurrently existing regulations still abide by the now obsolete concept that reirradiation is harmful and hence has been banned. The ‘high dose’ committee[2] has established an overwhelming rationale that the sensorial quality ofirradiated foods will degrade at irradiation doses orders of magnitude lower

185

HARUVY

than those which may pose any radiation related health risk. Hence, once noncompromising bacterial safety and sensorial quality are targeted, the radiationdose and the number of irradiation stages are no longer issues of any specificconcern.
Another hazard shown in Table 3, the bone residuals, is non-radiation
specific, but rather soup specific: people tend to swallow the soup ‘as is’ andtherefore bone residuals pose a much higher risk than in solid meals that
require chewing and, hence, provide the consumer sufficient time and sensorial
experience to detect bone fragments before swallowing the food.
The fat hazard mentioned in Table 3 in relation to animal fat and rancidization is further addressed in Tables 4 and 5, which relate to all non-animal
source, fat-rich ingredients of the prepared meals.
The primary hazard related to the fat content in the food is the sensorial
one, rather than immediate health risk. Nonetheless, of particular economic
impact (Table 5) is the radiation induced long term development of rancidization products (last row in Table 5). Intermediate species formed during theirradiation gradually develop into oxidized products with the typical ‘off’ tasteof rancidization. The grave economic risk related to this long term sensorial
failure stems from the fact that the ‘price tag’ for this failure is the highest: theentire product costs, packaging and shipment costs, inventory costs and loss of
reputation, since this type of failure is a consumer detected one.
It is noteworthy that proper oxygen free packaging of the food can help
minimize the rancidization processes. Nevertheless, minimizing the radiationdose for the fat-rich ingredients can also help in minimizing the rancidization,
well in accord with the two stage irradiation rationale.

TABLE 4. FAT-RICH INGREDIENTS FOR PREPARING INDONESIANETHNIC SOUPS
Soup (quantity)
IngredientsBlack

Oxtail20 × 300 g

20 × 300 g

Chickenvegetable
18 × 200 g

2 spoons

5 spoons

Roasted coriander

5 teaspoons

Roasted candlenut

25 pieces

Margarine
Palm oil

186

1L

500 mL

Chickensweetcorn
25 × 250 g

HARUVYTABLE 5. COMBINED HACCP FOR FAT-RICH INGREDIENTS
Raw materials: Fats and oils
Control
point

Failure mode/
hazardPreventive
measuresDetectability Haz. Sens. Econ.

Degraded Oil oxidation of Temperature andfat
fried ingredients ‘ecycling’ control

Mainlysensorial

999

Degraded Oil charring of Temperature andfat
fried ingredients recycling control

Mainlysensorial

999

Degraded Radiationfat
inducedrancidization

Mainlysensorial

999

Minimize
quantity of fat
and frying fat

99

Rad.
spec.

99

The rancidization effected hazard seems economically alarming in view of
its manifestation in the final product at the end of storage, whereas thecapability to predict it is currently poor. Running the updated and modified
HACCP on the various ethnic foods investigated in this coordinated research
project demonstrated the complexity of this issue, and the insufficientknowledge of the interplay of radiation, oxygen and antioxidants on the final
level of rancidization and the resulting off flavours. Further importance of therancidization factor stems from the fact that fat rich parts of the meat are
typical of the diet of impoverished people. Hence, fat is typical in many ethnic
foods around the world and addressing rancidization properly should be a highpriority.
HACCP related to ingredients with potential antibacterial activity isdisplayed in Tables 6 and 7. While these ingredients per se may impede thegrowth of bacteria, during irradiation some of them can also impede the actual
killing of the bacteria by the radiation and, hence, necessitate higher doses toobtain the desired reduction in bacterial loads.
The principal objective is to lower the bacterial loads in the prepared
meals below a certain limit, at a constant dose, and to maintain a predictable
constant shelf life of the prepared meals thereafter. However, the seasonalvariance of active materials in the above ingredients may hamper this stability,
which depends on consumer acceptance. Hence, attempts should be made tocompensate for these seasonal variances in antibacterial activity and consequently flavour. Detecting concentrations of the active materials in the raw
materials is essential for that purpose, and compensation by quantity changes,
as needed, can solve the problem.

187

HARUVYTABLE 6. INGREDIENTS WITH ANTIBACTERIAL ACTIVITY IN
INDONESIAN ETHNIC SOUPS
Soup (quantity)
Black

Oxtail20 × 300g

20 × 300g

Chickenvegetable
18 × 200g

35 g

30 g

5
teaspoons4teaspoonsIngredients

Seedless red chilli

Chickensweetcorn
25 × 250g

5 pieces

Garlic

35 g

Ginger root

10 cm

Ground white pepper

TABLE 7. COMBINED HACCP FOR INGREDIENTS WITH POSSIBLE
ANTIBACTERIAL ACTIVITY
Raw materials: Ingredients with possible antibacterial activity
Control point

Failure mode/
hazardPreventive
measuresDetectability Haz. Sens. Econ.

Rad.
spec.

Antibacterial
agent

Seasonal
Testvariations in concentration
concentration of active agent
compensate

?

99

99

99

Antibacterial
agent

Radiation
destruction

?

99

99

99

Test
concentrationof active agent
compensate

The possible interference of these ingredients in bacteria eradication is aserious drawback. It suggests, once again, that the major bacteria eradication
exercise should take place before adding ingredients which may protect thebacteria, another rationale supporting the strategy of two stage irradiation.
This complexity is further demonstrated in Tables 8 and 9, which relate to alarge number and variety of herbs and flavouring vegetables.
The salient features of the list of ingredients in Table 8 are their numbers
and variance. Their ripening takes place at different seasons and, hence, fresh
products will exhibit great variance in taste from one season to another. This188

HARUVYTABLE 8. VEGETABLES AND HERBS USED IN INDONESIANETHNIC SOUPS
Soup (quantity)
IngredientsBlack

Oxtail20 × 300g

20 × 300g

Chickenvegetable
18 × 200g

70 g

105 g

Football fruit(P. edule)

25 nuts

Shallot

175 g

Lemon leaf

10 pieces

Lemon grass

5 pieces

K. galanga andturmeric

10 cm each

Bay leaf

10 piecesOnion

5 pieces

Cloves

20 pieces

Onion leaf

5 pieces

10 pieces

Celery5 pieces

10 pieces

Chickensweetcorn
25 × 250g

Young sweetcorn

20 pieces

Carrot450 g

Green beans

350 g

Broccoli

400 g

Frozen sugar peas

500 g

350 g

TABLE 9. COMBINED HACCP FOR VEGETABLES AND HERBS
Raw materials: Vegetables and herbs
Control
point

Failure mode/
hazardPreventive
measuresDetectability

Haz. Sens. Econ.

Microbial Contamination Microbial testing Microbial and99
by birds, rodents of many different aflatoxin testing
insects, etc.
ingredientsof the product

99

99

99

99

99

PhysicalForeign matter, Carefule.g. stones,
inspection andmetal, shells
sievingDifficult at theindustrial scale

Rad.
spec.
99

189

HARUVY

variance may hamper the sensorial stability which is important for consumer
acceptance, as well as the radiation effected changes. Of course, this variancecan be minimized by employing frozen ingredients, albeit at a severe increase incosts. These factors require thorough consideration by the respective industry
when planning their raw materials supply chain.
The large variety of vegetables and herbs, typical of ethnic foods, calls for
special care regarding the irradiation pasteurization. Ethnic foods are often
characterized by a very rich flavour, catering to the taste of the local consumers.
Hence, sensorial damage by overirradiation is a distinct risk and, hence, it isessential to try and lower the dose applied to these flavour producing ingredients. In view of the relatively large dose necessary for attaining theacceptable safety level of other ingredients, the two stage irradiation seems
advantageous.
As for the HACCP for each and every ingredient per se, it would be quite
a tedious task to monitor all of these, even on a laboratory scale, let alone anindustrial one. Nonetheless, nowadays, the supply chain of herbs andvegetables is becoming more and more industrial. Many of the ingredients inTable 8 can nowadays be ordered and purchased cut, cleaned, inspected andpacked under modified atmosphere, as well as under cooling conditions. Ifpurchased from a certified industrial producer of these intermediate products,
the manufacturer of the prepared meals can save much effort, expense and risk.
In the specific case of soups, water is a major constituent by weight, witha potentially strong effect on both the bacterial load and the sensorial quality.
Ordinary tap water in some places may not be sufficiently wholesome frombacterial, sediment and off taste considerations, to use it for preparing highquality and safe prepared meals. Nevertheless, on an industrial scale, a water
treatment facility is an acceptable requirement, rather a common one, in thisindustry. Hence, the water quality issue on the HACCP list can be answeredwith standard good manufacturing practice methods.
Likewise, most of the ingredients in Tables 10 and 11 can nowadays beordered and purchased from a certified industrial source and, hence, no longer
be a cause for concern. However, Table 12, which relates to all the ingredients,
draws attention to a fundamental difference between laboratory scale rationale
and an industrial scale one.
The key factor, often overlooked at the food laboratory scale of‘production’, is product reproducibility. Once consumer trust in a new producthas been gained, typically owing to sensorial attributes, changes to the productare risky. Changes to a product may result in consumers abandoning it, since it
may no longer meet their sensorial expectations and preferences. That is why it isessential, well before attempting to transfer the new prepared meals to industrial
production, to ‘seal’ all the quantity loopholes that remain in the food recipe.

190

HARUVYTABLE 10.
POWDERED INGREDIENTSINDONESIAN ETHNIC SOUPSAND

LIQUIDS

IN

Soup (quantity)
IngredientsBlack

Oxtail20 × 300 g

20 × 300 g

Chickenvegetable
18 × 200 g

Corn starch

Chickensweetcorn
25 × 250 g
10 spoons

Sugar (palm)

3 teaspoons

Sugar (cane)

4 teaspoonsSalt

4 teaspoons

5 teaspoons

5 teaspoons

5 spoons

Water

5L

5L

3L

3L

TABLE 11. COMBINED HACCP FOR POWDERED INGREDIENTSAND LIQUIDS
Raw materials: Powders and liquids
Control
point

Failure mode/
hazardPreventive
measuresMicrobial

Contamination
following
inadequate
storage

PhysicalForeign matter

Detectability

Haz.

Sens.

Econ.

Microbial
testing

OK

9

9

9

Carefulinspection
andsievingDifficult at
an industrial
scale

99

99

99

Rad.
spec.

TABLE 12. ALL INGREDIENTS IN INDONESIAN ETHNIC SOUPS
Soup (quantity)
Ingredients

All

Black

OxtailChickenvegetable

XX pieces

YY teaspoons

ZZ cm leaf

Chickensweetcorn

191

HARUVYTABLE 13. COMBINED HACCP FOR ALL INGREDIENTS
Raw materials: Fats
Controlpoint
XXpieces,YY cm

Failure mode/hazard

PreventiveRad.
Detectability Haz. Sens. Econ.
measuresspec.

Undefined weight candrastically alter thetaste, the bacterial loador the antibacterial
activity

Defineweightacceptable
limits,e.g. 15–18 g

OK

9

99

99

99

For radiation pasteurized foods, this aspect is of greater importance, inview of the recently established consumer acceptance. It is essential to remainalert to the risk that taste changes may be attributed to public perception of the‘bad effects of radiation’ and result in rumour, panic and long lasting damage toconsumers’ acceptance. In other words, product reproducibility and stability of
sensorial quality are ‘musts’ in relation to all so-called high-tech foods,
irradiated ones in particular.
As with the need to practice accurate quantity control in the foodpreparation so there is a need for accurate process control, as demonstrated inTables 14 and 15. Without the latter, the stability of the sensorial quality is atstake. It should be emphasized again that this industry related considerationneeds to be addressed at the R&D stage, rather than at a later stage.
Last, but not least, comes the prepared meal packaging and its related
hazards. If the food in question involves multistage industrial processing, intermediate packaging of the semi-processed ingredients and the final packaging of
the entire prepared meal should be carried out. The intermediate packaging
needs to eliminate contamination between process stages, as well as spoilage
due to loss of flavour, gradual oxidation, or changes in moisture levels.
The typical shelf life desired for intermediate packaging is a few days
unless an intermediate semi-processed ingredient is, by itself, a product which is
being transported from one industry to another. On the other hand, the final
packaging is required to allow a rather prolonged shelf life, under sales andconsumer handling, without compromising safety and quality.
3.1. The two stage irradiation strategy: Pros and cons
The potential strategy of two stage irradiation discussed so far is rather
new and, hence, insufficiently tested and assessed. In view of its great promise,
it is timely to discuss its possible drawbacks, as well as viable alternatives, as

192

HARUVYTABLE 14. ALL INGREDIENTS IN INDONESIAN ETHNIC SOUPS
Soup
IngredientsAll

TABLE 15.
PROCESSES

Black

OxtailChickenvegetable soup

Frying, cooking

Cutting

Rinsing

COMBINED

HACCP

FOR

ALL

Chickensweetcorn

PREPARATION

All ingredientsControl point

Failure mode/
hazardTemperature, Loss oftime,volatile
covering
ingredients

Preventive
measuresDetectability Haz. Sens. Econ.

Rad.
spec.

99

99

Needing to be
defined:Acceptable limitsof cooking/frying
temperature andduration
Cover technique(or pressure
cooking)
Rinsing protocols(must be welldefined)

OK

99

99

TABLE 16. PACKAGING OF INGREDIENTS AND PREPARED MEALSOF INDONESIAN ETHNIC SOUPS
Soup
IngredientsIntermediate
preparations,final prepared
meal

Black

OxtailChickenvegetable

Chickensweetcorn

Packaging

Packaging

Packaging

Packaging

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HARUVYTABLE 17. COMBINED HACCP FOR PACKAGING
Raw materials: Fats
Control
point

Failure mode/
hazardPreventive
Measures

Packaging Packaging
QA 1.2 QC
QA
failure:Microbial testing
Microbial
contamination

Detectability Haz. Sens. Econ.

Rad.
spec.

99

99

OK

99

Obtain COC
and COT fromthe packaging
producer on
oxygenpermeability

OK

99

Humidity loss As above
regardingwater vapour
permeability

OK

99

Oxygenpenetration

99

99

shown in Table 10. Essentially, the principle of two stage irradiation is that raw
materials which are bacterially contaminated beyond acceptable levels will beirradiated (under optimal conditions) before being admitted into the foodfactory. This is particularly important for animal source raw materials.
Nevertheless, the currently available ensemble of bacterial eradication
technologies, besides ionizing irradiation, includes heating, hydrostaticpressure and other alternatives. Hence, irradiation should preferably beconsidered as part of the ensemble of bacteria eradication technologies and notas the sole method, in order to prevent its misuse, overuse and abuse. Skilful
optimized orchestration of the various methods, at the right dose and sequence,
should be tailored for each raw material, intermediate preparation or prepared
meal. Such a scientifically based attitude should aim at the highest levels interms of safety, shelf life and quality, as well as at the most cost effective route.
A skilfully operated HACCP, one that accompanies the various alternatives
investigated, already at the R&D stages, can assist in decision making andresult in a cost effective R&D, and then yield the most cost effective productand production route specifications.
Approaching the industrial production stage of safe prepared meals was
further emphasized during this study of applying the modified HACCP to
ethnic foods. In view of the currently accelerating consumer demand and194

HARUVYTABLE 18. PROS, CONS AND ALTERNATIVES OF THE TWO STAGE
IRRADIATION OF PREPARED MEALS
Issue of concern

Pros

Cons

Alternatives

Cross-contaminationfrom contaminatedraw materials

Cross-contamination Additional costs ofrisks are reduced,
packaging, transport
prevention andand logistics
detection costs are
reducedCross-contamination
focused HACCP,
prevention anddetection

Increased final dose
due to protection ofbacteria by antioxidants

Overall lower doses
to achieve safe levelsof bacteria

Possible bacteria
recovery between
irradiation stages

Combination of heat,pressure andirradiation toeradicate bacteria

Increased off
flavours, e.g.
rancidization

Overall lower doses
minimize
rancidization

Possible
rancidization
between irradiation
stages, and strong off
flavour thereafter

Active charcoal
canisters to trap
volatile off flavour
molecules

Texture spoilage
Speciality flavour
loss

Overall lower doses Elapsed timeminimize texture and between irradiation
flavour damage
stages and extra
handling may
increase texture
damageUse of additives for
texture toughening
and flavour
enhancement

Costs

Lower weight × dose
costs

Contract stipulationof clean raw
materials from the
suppliers

Higher logisticalcosts

industrial production of prepared meals and convenience foods, the multistage
treatment approach to ensure ingredient safety seems favoured on the basis ofsafety, taste and smell, irradiation (or alternative methods) and economics.
Optimizing bacteria eradication along the production stages can achieve better
food quality and safety, while practically using less food treatment, but at two
or more sequential stages.

4.

CONCLUSIONSThe combined multirisk HACCP assessment, carried out through the
R&D of novel foods, is suitable not only for pinpointing the most critical195

HARUVY

control points, but also for identifying potentially advantageous production
pathways.
In view of the relative complexity and variety of ingredients in ethnic
foods, the combined HACCP is effective in pinpointing their specific criticalcontrol areas: (i) animal source ingredients (bacterial loads), (ii) fat richingredients (rancidization potential), (iii) antibacterial active ingredients(seasonal variations and microbial load impact) and (iv) flavour richingredients (radiation sensitivity and sensorial quality impact).
Two stage irradiation of ethnic foods, at the individual ingredient stage
and the final stage, was found to be a highly valuable approach. It deserves
further study and regulatory steps, as well as skilful orchestration with nonirradiative pasteurization methods, in order to attain the optimal food products
and their processing sequences.
Food R&D HACCP seems a novel way to direct food R&D progresseffectively. Nonetheless, the industrial scale considerations and rationale
should already be implemented, as well as the economic ones, customer
acceptance in particular. The HACCP should thus encompass all the facets offood R&D to ensure its safety, quality and marketability, particularly forcomplex and innovative foods such as prepared ethnic meals.

REFERENCES
[1]

[2]

196

IRAWATI, Z., NATALIA, L., NURCAHYA, C.M., ANAS, F., Irradiation to
Ensure the Safety and Quality of Home Style Frozen Foods, 1. Liquid based materials, The role of medium radiation dose on microbiological safety and shelf-life ofsome traditional soups, presented at International Meeting on Radiation
Processing (IMRP), Kuala Lumpur, Malaysia, to be published in International
Journal of Radiation and Physical Chemistry (2006).
WORLD HEALTH ORGANIZATION, “High Dose Irradiation: Wholesomeness of Food Irradiated with Doses Above 10 kGy”, WHO, Technical Report
Series 890 (1999) 127–149.

MICROBIAL INACTIVATION AND SHELF LIFE
EXTENSION OF KOREAN TRADITIONALPREPARED MEALS BY IRRADIATION
C. JO
Department of Animal Science and Biotechnology,
Chungnam National University,
Daejeon,Republic of Korea

Abstract
The effects of gamma irradiation on microbial inactivation and shelf life extensionof Korean traditional prepared meals, including bulgogi and its sauce, marinated beef
rib and Kimbab, were investigated. Raw vegetables, fruits and soy sauce used formaking bulgogi sauce were highly contaminated and most of them with Bacillus spp. andcoliform bacteria at the initial stage. Irradiation at 10 kGy eliminated coliforms in thebulgogi sauce and no growth was found during the 4 weeks of storage at 20°C. The
sensory evaluation of bulgogi and its sauce showed that the colour of irradiated samples
was better than that of non-irradiated controls or heat treated samples. The total
bacteria count and coliform of marinated beef ribs were 5.68 and 3.68 ln CFU/g, respectively. The effect of irradiation on the growth of the four test microorganisms inoculated(about 106–107 CFU/g) into the marinated beef ribs were dose dependent (a higher dose
produced a greater reduction). All the four pathogens inoculated on marinated beef ribs
were eliminated at 4 kGy. The D10 values of Bacillus cereus, Staphylococcus aureus,
Salmonella typhimurium and Escherichia coli on inoculated marinated beef ribs were0.66 ± 0.01, 0.59 ± 0.05, 0.64 ± 0.02 and 0.54 ± 0.01 kGy, respectively. Of these, E. coli was
the most radiation sensitive in the raw marinated beef ribs. The number of the four
pathogens inoculated into Kimbab decreased by 2–3 ln CFU/g for every 1 kGy
increment and were not detected after 3 kGy. The D10 values of pathogens inoculated
into the Kimbab were in the range 0.31–0.44 kGy. This study indicated that irradiation iseffective in ensuring the safety of Korean traditional prepared meals, including bulgogi
sauce, bulgogi, marinated beef ribs and Kimbab with acceptable sensory quality. For
Kimchijumeokbab, viable cells of the four pathogens inoculated increased slightly after
abusive storage condition (20°C), although under commercial condition (4°C), and after
2 weeks of storage, no viable cells were detected. A 3 kGy dose was the threshold dose
for this meal from the sensorial viewpoint. This dose must be applied with cold storage
in order to improve the safety and ensure a shelf life extention of Kimchijumeokbab.

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1.

INTRODUCTION

Owing to the expansion of the convenience food industry, mainly by thedevelopment of the catering services and distribution system, the importanceof the hygienic quality of prepared food during the preparation, processing,handling and storage has increased. Nowadays, prepared foods are widely
available on the market all around the world, but at the same time, they havebeen the cause of major outbreaks of foodborne diseases. In the United Statesof America, overall incidences of pathogens in cooked ready-to-eat meatproducts were 8.1% over the period 1993–1996 [1]. A survey of ready-to-eat
cooked meat products in Germany showed an incidence rate of 3.7% for
Listeria monocytogenes [2]. Mytle et al. [3] reported that illnesses have resulted
when supposedly ready-to-eat foods were not reheated before consumption. It
has also been reported that raw beef, soy sauce and raw vegetables may
harbour potential foodborne pathogens [3–5]In the Republic of Korea, Salmonella spp. in Kimbab was detected at
623 CFU/g on an average of about 214 samples and the frequency of detectionin the summer was higher than in the winter season [6].
The World Health Organization [7] reported that gamma irradiation
technology has positive effects in preventing decay thereby killing microorganisms and by improving the safety and shelf stability of food products. The
technology has been officially adopted for its wholesomeness and economic
benefits.
The objective of the present study was to demonstrate the efficacy ofirradiation treatment in eliminating the potential pathogens of public healthsignificance in typical Korean prepared meals, such as bulgogi and its sauce,
marinated beef ribs, Kimbab and Kimchijumeokbab, the popular types ofprepared product in the Republic of Korea, thereby ensuring the safety andextending the shelf life of the products.

2.

MATERIALS AND METHODS

2.1. Preparation of sample
Samples of bulgogi sauce, bulgogi, marinated beef ribs and Kimbab wereprepared immediately before the experiment. Freshly prepared marinated beef
ribs (deboned, uncooked Galbi), Kimbab (steamed rice rolled in dried laver)raw materials for bulgogi sauce (soy sauce, garlic, onion, green onion, sugar,
kiwi, sesame oil, black pepper and grain wine) and meat for making bulgogi
were purchased from a local store.

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A portion of the prepared bulgogi sauce was heated at 100°C for 30 min
and another portion was packaged separately in a polyethylene bag ready forirradiation. A non-irradiated and non-heat-treated sample was also prepared
as a control. The sauces that were treated by heat or irradiation (2.5, 5.0 and
10 kGy) were analysed for microbiological quality, pH and protease activity.
Sliced meat was marinated with each prepared sauce in a 2:1 ratio for 3 h in arefrigerator (4°C) and cooked for sensory analysis.
The marinated beef ribs and Kimbab were sliced (1 cm thickness) asepticallyand packaged (10 g) in oxygen impermeable nylon bags (2 mL O2·m–2·24 h–1 at 0°C,
0.09 mm thickness (Sunkyung Co. Ltd., Seoul). The samples were exposed to an
irradiation dose of 30 kGy (AECL, IR-79, MDS Nordion) at 12 ± 0.5°C to achieve
the complete inactivation of the indigenous microflora.
For artificial contamination, Kimchijumeokbab was prepared withsteamed rice, Kimchi, sugar, sesame oil, hot pepper powder and fried pork,
which was prepared with grain wine, green onion, garlic, sesame seed, ginger,
pepper, soy sauce, sugar and sesame oil.
2.2. Strains and culture condition
For the inoculation test, Staphylococcus aureus (KCTC 1916), Bacillus
cereus (KCTC 1012), Salmonella typhimurium (KCTC 1925), Escherichia coli
(KCTC 1682) and Listeria ivanovii were obtained from a Korean collection for
type culture (KCTC, Daejeon). Of these, E. coli, S. aureus and L. ivanovii weregrown in a tryptic soy broth (Difco Laboratories, Sparks, USA), andS. typhimurium in a nutrient broth (Difco Laboratories). The incubation
temperature for E. coli, S. aureus and S. typhimurium was 37°C, and for
L. ivanovii it was 30°C. The bacterial cultures were prepared for 24 h in asterilized broth medium from one colony from an agar slant, from which
0.1 mL was transferred to a new broth medium and grown for 18 h. The
cultures were centrifuged (2795g for 10 min at 4°C) in a refrigerated centrifuge(Vs-5500, Vision Scientific Co., Seoul). Cultures were washed twice with sterile
peptone water. The pellet was finally suspended in sterile peptone water toachieve a cell density above the 107~108 CFU/g levels.
2.3. Inoculation of samples with test organism
Packaged marinated beef ribs and Kimbab were inoculated with 106–107 CFU/g of the four pathogens and later stored. The test culture suspension(200 μL) was uniformly and aseptically spread and kept in a sterile workstationfor 10 min to allow it to be absorbed. The samples were then packed into sterile
stomacher bags and sealed.

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2.4. Irradiation
Packed marinated beef ribs and Kimbab inoculated with the test
organisms, bulgogi sauce and cooked bulgogi were treated in a 60Co irradiator(AECL, IR-79, MDS Nordion) at the Korea Atomic Energy Research Institutein Daejeon. An ice bag (1 cm thickness) covered the sample holder to avoid atemperature increase of the sample during irradiation. The source strength wasapproximately 100 kCi with a dose rate of 10 kGy/h at 12 ± 0.5°C. Dosimetry
was performed using 5 mm diameter alanine dosimeters (Bruker Instruments,
Rheinstetten, Germany) and the free radical signal was measured using a
Bruker EMS 104 EPR analyser. The dosimeters were calibrated against aninternational standard set by the IAEA. The doses applied in this study were 1,2, 2.5, 3, 4, 5 and 10 kGy for different prepared foods. After irradiation, themarinated beef ribs were stored under two different conditions: (i) commercial
refrigeration (4°C) and (ii) abusive temperature (20°C). The Kimbab samples
were stored at 10, 20 and 30°C for 24 h post-irradiation.
2.5. Microbiological analysis
The samples (10 g each) were aseptically homogenized for 2 min in asterile stomacher bag containing 90 mL of sterile peptone water using a
stomacher laboratory blender (Model 400, Tekmar Co., Cincinnati, USA). The
media used for enumeration of the coliform bacteria, Salmonella–Shigella spp.,
S. aureus, Bacillus spp., B. cereus, S. typhimurium and E. coli were prepared by
dextrose tryptone agar (Difco), SS agar, Baird Parker agar (Difco), cereus
selective agar (Oxoid, Basingstoke, United Kingdom), xylose lysine deoxycholate agar (Difco) and eosin methylene blue agar (Difco), respectively. The
incubation temperatures for Bacillus spp., L. ivanovii and the others were 50,
30 and 37°C, respectively, for 48–72 h. The colony forming units per gram werecounted and the D10 values determined. Experiments with each bacteria
culture were conducted independently, twice.
2.6. pH and relative neutral protease activity
The pH was measured using a pH meter (Model 520A, Orion ResearchInc., Boston, USA) by adding 9 parts of deionized distilled water (DDW) to
1 part of sample homogenate. Relative neutral protease activity was measured
by the method developed by Kim et al. [8] and modified. A 10 g portion of thebulgogi sauce was homogenized with 90 mL of DDW using a blender (Hanil,
FM680T, Seoul) for 60 s and left to stand for 30 min at 4°C, and then filteredwith filter paper (No. 3, Whatman International, UK). The filtrate was used for

200

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the protease activity. The substrate used was casein (0.5%, dissolved in 50mM
phosphate buffer, pH6.0) and the released tyrosine was determined. One unitof enzyme activity was defined as the amount of enzyme required to liberate
1 μmol tyrosine/min.
2.7. Sensory analysis
A consumer test (n = 33) was used to evaluate the sensory quality of thebulgogi sauce and the cooked bulgogi. For the sauce, the odour and the colour
were measured using a dish holding 50 mL of sauce. The cooked bulgogi wasmarinated with the sauce in a 2:1 ratio and the marinated beef was placed in apreheated pan at about 170°C and cooked for about 8.5 min to reach atemperature of approximately 78°C. After cooling for 2 min at room temperature, a 20 g sample was served to the panellists individually. A 9 point hedonic
scale was provided for the panellists to assess as follows: like extremely (9), likevery much (8), like moderately (7), like slightly (6), neither like nor dislike (5),dislike slightly (4), dislike moderately (3), dislike very much (2), and dislike
extremely (1). The sensory parameters for the cooked bulgogi were colour,
odour, taste and tenderness.
2.8. Statistical analysis
Each data represents the mean of two different experiments with threemeasurements in each experiment. Mean values and standard deviations were
calculated using a statistical analysis system [9] and recorded.

3.

RESULTS AND DISCUSSION

3.1. Bulgogi and bulgogi sauce
Raw vegetables and fruits used for making bulgogi sauce exhibited highlevels of bacterial contamination (Table 1). Bacillus spp. was detected in all
ingredients except for grain wine, in a range of 102–105 CFU/g, and coliform
and Salmonella–Shigella were also found in the garlic and onion samples. These
results indicated that the contamination of the raw materials was affecting thehygienic quality and the safety of the prepared bulgogi sauce.
The growth of Bacillus spp. in bulgogi sauce during one month of storage
at 20°C is shown in Fig. 1.
The control, which was not irradiated or heat treated, and heat treatedbulgogi sauce showed a rapid growth of Bacillus spp. No experiments were

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JO

TABLE 1.
MICROBIOLOGICAL CONTAMINATION OF RAW
MATERIALS USED IN THE PREPARATION OF BULGOGI SAUCEa
Microbes (CFU/g)
Raw materials
Bacillus spp.

Coliform

Salmonella–Shigella spp.

Soy sauce

3.77 × 103

n.g.b

n.g.

Grain wine

n.g.

n.g.

n.g.

Sugar

4.10 × 103

Garlic58.74 × 10

4.81 × 10

Kiwi

2.24 × 103

3.10 × 103

n.g.

Green onion

3.15 × 10

58.10 × 103

6.24 × 103

Onion

5.95 × 104

1.72 × 103

3.39 × 103

Sesame oil

3.20 × 103

n.g.

n.g.

4.10 × 10

Total

2.13 × 106

a

n.g.
4

2

Black pepper

b

n.g.

9.22 × 102

n.g.

n.g.

5.90 × 104

1.17 × 104

Detection limit was less than 101 (CFU/g).
n.g.: no growth on plate.

Heated80 kGy

Log CFU/g

2.5 kGy
5 kGy

6

10 kGy

4
2
0
0

1

2

3

4

Storage (week)
FIG. 1. Growth of Bacillus spp. in irradiated or heat treated bulgogi sauce samples.

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JO

Heated80 kGy

Log CFU/g

2.5 kGy

6

5 kGy
10 kGy

4
2
0
0

1

2

3

4

Storage (week)
FIG. 2. Growth of coliforms in irradiated or heat treated bulgogi sauce samples.

conducted with these samples after two weeks because of the excessive
microbial growth. Irradiation significantly reduced the level of Bacillus spp.
and this reduced level was maintained during storage.
Song et al. [10] reported that Bacillus spp. of Korean type fermented soy
sauce, Kanjang, and a Japanese type fermented soy sauce, Shoyu, were reducedby 3 log cycles with 10 kGy, with a D10 value for Bacillus spp. of 2.67 kGy.
The growth of coliforms in bulgogi sauce samples during the storage
period is shown in Fig. 2.
The control sample showed high contamination of coliforms (Fig. 2).
Heating at 100°C for 30 min eliminated the coliform bacteria. Sauce irradiatedat 2.5 kGy initially had coliforms but these were not found after 2 weeks ofstorage. Kim et al. [11] reported that the decrease in the microbial population
during storage after irradiation was due to the post-irradiation effect, where
surviving cells that had been damaged by gamma irradiation gradually died,not having adapted to their surrounding environment during storage.
Irradiation at 5 and 10 kGy eliminated coliforms in the bulgogi sauce and no
growth was found during storage at 20°C. Lee et al. [12] reported that coliform
bacteria were not detected in bulgogi sauce treated by heating the packaging
bag at 100°C for 20 min or by gamma irradiation, which is in a good agreementwith the present study.
The growth pattern of bacteria in selective media SS agar was similar to
coliforms but irradiation even at 2.5 kGy completely controlled the microbial
growth.

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TABLE 2. pH AND RELATIVE PROTEASE ACTIVITY IN BULGOGISAUCE IMMEDIATELY AFTER TREATMENT
Treatment

pH

Relative protease activity (%)*

Control**

5.72

100.0a

Heat

5.71

22.3b

2.5 kGy

5.76

102.1a

5.0 kGy

5.75

98.7a

10 kGy

5.76

99.2a

0.008

2.3

SEM

***

*

Different letters within a column differ significantly (p < 0.05).
Control not heated or irradiated.
***
Pooled standard errors of the mean (n = 15).
**

The pH of the sauce showed no difference between treatments
immediately after irradiation (Table 2). Jo et al. [13] reported that the pH ofsausage irradiated at 4.5 kGy did not change significantly while rapid reductionin pH was observed in the non-irradiated sausage. The authors interpreted the
pH decrease to be due to microbial change, because the acid producing
bacterial growth may result in pH reduction.
The relative neutral protease activity of the sauce was significantly
reduced by heat treatment, while irradiation had no effect. Heat treatment may
denature the proteolytic enzyme, resulting in lower protease activity.
Proteolytic enzymes, such as ficin, papain and bromelain, have been used in thetenderizing of meat and act preferentially against connective tissue fibres [14].
Kamphuis et al. [15] reported that actinidin is one of the plant thiol proteinases
and is present in kiwi fruit. The scanning electron microscopy of meat treatedwith crude actinidin showed that it was more fragile than that of the controls.
Research has shown that the irradiation of proteins and amino acids in foods
has little or no effect on the biological value of the proteins and enzymes aremostly unaffected by low dose irradiation (<1–10 kGy).
Raw bulgogi sauce was also sensorially evaluated (odour and colour)(Table 3). A significant difference was observed in colour at 2.5 kGy, thehighest score, while the heat treated sauce was the lowest. Heat treatment ofbulgogi sauce resulted in colour changes to the fresh vegetables in the sauce.
Major components of the soy sauce are different amino acids and some of thesecontain sulphur which could affect the odour [16] even though the odour of thesoy sauce itself is relatively strong. The sample of heat treated sauce lacked afresh odour.

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TABLE 3. SENSORY EVALUATION OF BULGOGI SAUCE AND
COOKED BULGOGI AFTER IRRADIATION* TREATMENT
Sensory
parameter

Irradiation dose (kGy)Heat
treated

0

2.5

5.0

10.0

4.8

6.3

6.4

6.1

5.2

0.52

3.0c

4.9b

7.2a

5.6b

4.9b

0.47

Tenderness

5.8

6.3

6.8

6.0

6.0

0.46

Taste

5.1

6.4

6.1

5.5

5.4

0.56

Acceptance

5.2

6.2

6.1

5.3

5.3

0.52

SEM**

Bulgogi sauce:
Odour
Colour***Cooked bulgogi:*

Odour and colour were evaluated using a 50 mL sample of sauce. Raw beef wasmarinated with the sauce at a 2:1 ratio and the marinated beef was placed in apreheated pan at about 170°C and cooked for about 8.5 min to reach approximately
80°C. After cooling for 2 min at room temperature, a 20 g sample was served to thepanellists (n = 33) individually. A 9 point hedonic scale was used: like extremely (9)to dislike extremely (1).
**Pooled standard errors of the mean (n = 33).
***
Different letters within the same row differ significantly (p < 0.05).

In cooked bulgogi, no statistically significant difference was found but
tenderness and taste might be affected by heat treatment of the sauce before
cooking.
3.2. Marinated beef ribs
Commercial marinated beef rib samples recorded contamination of
5.68 ln CFU/g of viable cells (Table 4). Pathogens B. cereus and S. aureus were
found at levels of 3.81 and 2.57 ln CFU/g, respectively. These results indicatedthat even if the marinated beef rib is cooked before consumption, theundercooked meat might pose a potential hazard.
The D10 values for bacteria in food are affected by a number of factors,
such as water activity, composition, irradiation temperature, presence ofoxygen and so on. In addition, some of the constituents of a complex foodsystem, such as proteins, are thought to compete with the cells for interaction
with radiolytic free radicals, thereby reducing the net effect of radiation
damage and making the organisms sometimes more radiation resistant [17].

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TABLE 4. MICROBIAL LOAD IN COMMERCIAL MARINATED BEEF
RIBS
Microorganism

Viable cell count (ln CFU/g)

Total aerobic bacteria

5.68 ± 0.03a

Coliform bacteria

3.68 ± 0.51

B. cereus

3.81 ± 0.13

S. aureus

2.57 ± 0.20

S. typhimurium

n.v.c.bE. colin.v.c.

ab

Mean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit was 101 CFU/g).

TABLE 5. D10 VALUES OF PATHOGENIC BACTERIA IN ARTIFICIALLYCONTAMINATED BEEF RIBS
D10 value (kGy) ± SDar2

B. cereus

0.66 ± 0.01

0.99

S. aureus

0.59 ± 0.05

0.99

S. typhimurium

0.64 ± 0.02

0.98

E. coli

0.54 ± 0.01

0.99

Microorganisma

SD: standard deviation.

Bhide et al. [18] reported that gamma irradiation is not very effective against
Gram positive spore forming bacteria such as B. cereus and Clostridium spp. In
fact, the D10 value of B. cereus in the current study was the highest among thefour pathogens.
The D10 values observed in marinated beef ribs for B. cereus, S. aureus,
S. typhimurium and E. coli were calculated to be 0.66 ± 0.01, 0.59 ± 0.05, 0.64 ±0.02 and 0.54 ± 0.01 kGy, respectively (Table 5). Grant et al. [19] have reported
in roast beef meal components D10 values in the range 0.252–0.316 kGy and
0.126–0.288 kGy for S. aureus and B. cereus, respectively, which are lower thanthe values found in the current study for marinated beef ribs. Thayer and Boyd[20] reported D10 values in the range 0.40–0.46 kGy for S. aureus in different
meat systems irradiated at 5°C.

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Viable cells in non-irradiated marinated beef ribs were initially 6 ln CFU/g
and doses of 4 kGy presented no viable cell growth of S. aureus, B. cereus,
S. typhimurium or E. coli. Viable cells of all the four pathogens increasedslightly during abusive storage at 20°C (Tables 6–9); E. coli was the mostradiation sensitive bacteria (Table 9).

TABLE 6. EFFECT OF IRRADIATION ON THE GROWTH OF S. aureus
IN MARINATED BEEF RIBS DURING STORAGE AT 20°Ca
Dose
(kGy)

Viable cell count (ln CFU/g)
0d

3d

6d

9d

0

6.51 ± 0.60

6.61 ± 0.07

6.22 ± 0.28

6.06 ± 0.04

1

4.99 ± 0.05

5.83 ± 0.18

5.51 ± 0.19

5.32 ± 0.25

22.83 ± 0.02

4.32 ± 0.02

4.14 ± 0.51

4.16 ± 0.06

3

1.20 ± 0.28

3.18 ± 0.03

3.88 ± 0.14

3.03 ± 0.01b4

n.v.c.

1.87 ± 0.12

2.25 ± 0.36

2.73 ± 0.09

5

n.v.c.

n.v.c.

1.47 ± 0.12

1.64 ± 0.31

abMean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

TABLE 7. EFFECT OF IRRADIATION ON THE GROWTH OF B. cereus
IN MARINATED BEEF RIBS DURING STORAGE AT 20°Ca
Dose
(kGy)

Viable cell count (ln CFU/g)
0d

3d

6d

9d

0

6.07 ± 0.06

6.90 ± 0.05

6.71 ± 0.15

6.34 ± 0.19

14.74 ± 0.06

5.80 ± 0.03

5.75 ± 0.04

5.70 ± 0.11

2

3.12 ± 0.07

4.28 ± 0.03

4.13 ± 0.01

4.05 ± 0.05

31.80 ± 0.07

3.27 ± 0.03

3.17 ± 0.12

3.08 ± 0.22b4

n.v.c.

2.13 ± 0.18

2.15 ± 0.07

2.05 ± 0.07

5n.v.c.

n.v.c.

1.79 ± 0.21

1.65 ± 0.01abMean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

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TABLE 8. EFFECT OF IRRADIATION ON THE GROWTH OF
S. typhimurium IN MARINATED BEEF RIBS DURING STORAGE AT
20°Ca
Dose
(kGy)

Viable cell count (ln CFU/g)
0d

3d

6d

9d

0

6.15 ± 0.15

6.21 ± 0.13

6.14 ± 0.09

6.32 ± 0.03

1

5.21 ± 0.06

5.44 ± 0.61

5.89 ± 0.04

5.42 ± 0.23

2

3.91 ± 0.12

4.10 ± 0.10

4.84 ± 0.29

4.34 ± 0.06

3

1.79 ± 0.04

2.43 ± 0.25

3.20 ± 0.08

3.92 ± 0.07

4n.v.c.b1.89 ± 0.16

2.48 ± 0.20

2.37 ± 0.16

5n.v.c.

n.v.c.

1.40 ± 0.11

1.35 ± 0.38abMean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

TABLE 9. EFFECT OF IRRADIATION ON THE GROWTH OF E. coli IN
MARINATED BEEF RIBS DURING STORAGE AT 20°Ca
Dose
(kGy)

Viable cell count (ln CFU/g)
0d

3d

6d

9d

0

7.16 ± 0.02

7.40 ± 0.14

6.39 ± 0.12

5.83 ± 0.24

15.73 ± 0.04

5.95 ± 0.18

5.27 ± 0.10

4.95 ± 0.07

2

3.12 ± 0.01

4.28 ± 0.19

3.98 ± 0.57

3.83 ± 0.35

31.45 ± 0.13

1.96 ± 0.26

2.83 ± 0.24

2.46 ± 0.54

4bn.v.c.

n.v.c.

1.88 ± 0.39

1.87 ± 0.19

5n.v.c.

n.v.c.

n.v.c.

n.v.c.

ab

Mean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

After irradiation at 3 kGy, the samples had contamination of about 1 ln
CFU/g of viable cells (Tables 10 and 11). However, during commercial
conditions (4°C), and after 2 weeks of storage, no viable cell was detected.
Sublethal damage to cells caused by irradiation is likely to increase their
sensitivity to the environmental stress factors [21]. Similarly, the failure of theradiation injured cells of S. typhimurium during refrigerated storage wasreported [22]. Patterson [23] pointed out that one of the most common

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TABLE 10. EFFECT OF IRRADIATION ON THE GROWTH OF B. cereus
AND S. aureus IN MARINATED BEEF RIBS DURING STORAGE AT
4°Ca
Dose
(kGy)

B. cereus (ln CFU/g)
Initial2 weekS. aureus (ln CFU/g)

4 weekInitial2 week

4 week0

6.07 ± 0.06 6.20 ± 0.17 5.25 ± 0.02

6.51 ± 0.60

6.90 ± 0.02

5.27 ± 0.06

14.74 ± 0.06 4.15 ± 0.06 3.55 ± 0.15

4.99 ± 0.05

4.50 ± 0.06

2.54 ± 0.09

2

2.94 ± 0.19 2.33 ± 0.21 1.90 ± 0.08

2.83 ± 0.02

2.17 ± 0.03

1.95 ± 0.07

31.52 ± 0.06

n.v.c.bn.v.c.

1.20 ± 0.28

n.v.c.

n.v.c.

4

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

5

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

ab

Mean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

TABLE 11. EFFECT OF IRRADIATION ON THE GROWTH OF E. coli
AND S. typhimurium IN MARINATED BEEF RIBS DURING STORAGE
AT 4°C a
Dose
(kGy)

E. coli (ln CFU/g)

S. typhimurium (ln CFU/g)

Initial2 week

4 weekInitial2 week

4 week0

7.16 ± 0.02

7.23 ± 0.13

4.83 ± 0.03

6.15 ± 0.15

6.69 ± 0.16

5.55 ± 0.33

15.73 ± 0.04

5.64 ± 0.18

2.57 ± 0.38

5.21 ± 0.06

4.53 ± 0.02

3.48 ± 0.15

2

3.12 ± 0.01

2.09 ± 0.12

1.04 ± 0.06

3.91 ± 0.12

2.48 ± 0.09

1.94 ± 0.13

31.45 ± 0.13

n.v.c.bn.v.c.

1.79 ± 0.04

n.v.c.

n.v.c.

4

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

5

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

n.v.c.

ab

Mean ± standard deviation (n = 2).
n.v.c.: no viable cell growth detected (detection limit of 101 CFU/g).

combination treatments to obtain a ‘hurdle’ effect is the use of irradiation withrefrigeration. Patterson indicated that a dose of 2.5–3.0 kGy is sufficient to
reduce significantly the vegetative pathogens in poultry meat. The combinationof storage under refrigeration conditions and 4 and 5 kGy of irradiation
eliminated the viable cells of the four pathogens studied (Tables 10 and 11). In
studies on the growth of B. cereus at 4°C, it has been reported that cells were

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unable to grow at pH5–7 and water activity in the range 0.99–0.95 [24]. Whenfish was inoculated with B. cereus and irradiated at 1 and 3 kGy, there was noincrease in the number of survivors for weeks at 2–4°C [25]. Recently, Chawla
et al. [26] reported that D10 values of B. cereus, S. aureus, S. typhimurium, E. coli
were 0.64, 0.59, 0.56 and 0.55 kGy, respectively, in semi-dried seafood productsin the water activity range of 0.90–0.95. In the current study, the raw marinatedbeef rib has a water activity of 0.99 ± 0.01. Thayer et al. [27] reported that a
reduced water content or increased NaCl level may result in the survival levelsof the foodborne pathogens of irradiated meat being greater than expected.
3.3. Kimbab
The inhibiting effect of irradiation on S. typhimurium, E. coli, S. aureus
and L. ivanovii, inoculated into ready-to-eat Kimbab, is illustrated inTables 12–15. The level of inocula of S. typhimurium into the Kimbab was
6.22 ln CFU/g at the initial stage. A dose of 2 kGy reduced the level to 2.29 ln
CFU/g and 3 kGy to an undetectable level (Table 12). In fact, Jo et al. [28] hadalready reported that 3 kGy of irradiation reduced the population of the microorganism in prepared foods (seasoned and cooked beef, fried egg and ham) toan undetectable level (lower than 102 CFU/g).
The effect of irradiation on E. coli inoculated into the ready-to-eat
Kimbab is shown in Table 13. Irradiation at 2 kGy decreased the E. coli level tobelow 4 ln CFU/g at the beginning of the storage period. These bacteria were
not detected after 3 kGy, although they recovered (3 ln CFU/g) after 8–24 h ofstorage at 20 and 30°C. Lee et al. [29] reported that combined use of irradiationand low temperature storage was effective in attaining microbiological safety ofKimbab and ready-to-use foods.
L. ivanovii inoculated into Kimbab decreased about 4 ln CFU/g with
2 kGy (Table 14), and and was not detected after 3 kGy regardless of thestorage temperatures [30, 31]. Kimbab showed a significant reduction with
2 kGy (Table 14). The effect of irradiation on S. aureus inoculated into theready-to-eat Kimbab is shown in Table 15. Kimbab showed a significant
reduction with 2 kGy.
Table 16 shows the D10 values for different pathogens in artificiallycontaminated Kimbab samples. The D10 values were in the range 0.31–0.44 kGy
for the four bacteria studied. Rajkowski et al. [34] found D10 values of E. coli
O157:H7 on broccoli seeds of 1.11–1.43 kGy. Clavero et al. [35] reported thatthe D10 values of Salmonella spp. were 0.621–0.624 and 0.618–0.661 on low fat
ground beef and high fat ground beef, respectively. The radiation D10 values of
L. monocytogenes on beef were 0.45 kGy at 0°C and 1.21 kGy at –20°C [20].
Lamb et al. [36] reported that two experiments on S. aureus in ready-to-eat

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TABLE 12. EFFECT OF IRRADIATION ON THE GROWTH OF
S. typhimurium IN KIMBAB DURING STORAGE AT DIFFERENT
STORAGE TEMPERATURESa
Storagetemperature
(°C)

Dose
(kGy)

S. typhimurium (ln CFU/g)
0h

8h

10

0
6.22 ± 0.25
5.88 ± 0.27
13.85 ± 0.15
3.88 ± 0.20
22.29 ± 0.16
2.09 ± 0.12
b
n.d.
3
n.d.
20
0
6.22 ± 0.25
5.80 ± 0.14
13.85 ± 0.15
3.63 ± 0.04
2
2.29 ± 0.16
2.44 ± 0.06
3
n.d.
n.d.
30
0
6.22 ± 0.25
5.98 ± 0.19
13.85 ± 0.15
4.93 ± 0.76
22.29 ± 0.16
3.00 ± 0.14
3
n.d.
n.d.
a
Mean ± standard deviation (n = 2).
bn.d.: no viable colony growth at detection limit <102 CFU/g.

24 h5.85 ± 0.21
3.52 ± 0.35
2.20 ± 0.28
n.d.
6.26 ± 0.04
4.06 ± 0.18
2.57 ± 0.12
n.d.
7.89 ± 0.08
4.55 ± 0.02
3.18 ± 0.11
n.d.

TABLE 13. EFFECT OF IRRADIATION ON THE GROWTH OF E. coli
IN KIMBAB DURING STORAGE AT DIFFERENT STORAGE
TEMPERATURESa
Storagetemperature
(°C)
10

Dose
(kGy)

E. coli (ln CFU/g)
0h

8h

0
7.36 ± 0.17
7.33 ± 0.22
15.79 ± 0.12
5.81 ± 0.10
23.36 ± 0.37
3.27 ± 0.38
n.d.
3
n.d.b
20
0
7.36 ± 0.17
7.40 ± 0.10
15.79 ± 0.12
6.83 ± 0.11
2
3.36 ± 0.37
5.15 ± 0.20
3n.d.
3.40 ± 0.3630
07.36 ± 0.17
8.59 ± 0.06
1
5.79 ± 0.12
7.71 ± 0.01
23.36 ± 0.37
4.52 ± 0.39
3n.d.
3.72 ± 0.18
aMean ± standard deviation (n = 2).
bn.d.: no viable colony growth at detection limit <102 CFU/g.

24 h
7.10 ± 0.11
5.76 ± 0.16
2.85 ± 0.21
n.d.
8.78 ± 0.09
6.93 ± 0.04
5.00 ± 0.02
3.84 ± 0.01
9.14 ± 0.07
7.80 ± 0.12
4.47 ± 0.04
3.64 ± 0.15

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TABLE 14. EFFECT OF IRRADIATION ON THE GROWTH OF
L. ivanovii IN KIMBAB DURING STORAGE AT DIFFERENT STORAGE
TEMPERATURESa
Storagetemperature
(°C)

Dose
(kGy)

L. ivanovii (ln CFU/g)
0h

8h

10

0
6.04 ± 0.12
6.94 ± 0.34
14.64 ± 0.32
4.46 ± 0.31
2
2.09 ± 0.12
2.09 ± 0.12
n.d.
3
n.d.b
20
0
6.04 ± 0.12
7.94 ± 0.18
14.64 ± 0.32
5.21 ± 0.19
2
2.09 ± 0.12
2.27 ± 0.04
3
n.d.
n.d.
30
0
6.04 ± 0.12
8.08 ± 0.01
14.64 ± 0.32
5.62 ± 0.29
2
2.09 ± 0.12
2.41 ± 0.09
3
n.d.
n.d.
a
Mean ± standard deviation (n = 2).
bn.d.: no viable colony growth at detection limit <102 CFU/g.

24 h7.61 ± 0.37
4.87 ± 0.06
2.21 ± 0.05
n.d.
8.61 ± 0.03
5.08 ± 0.03
2.46 ± 0.03
n.d.
8.06 ± 0.03
5.82 ± 0.01
3.51 ± 0.09
n.d.

TABLE 15. EFFECT OF IRRADIATION ON THE GROWTH OF S. aureus
IN KIMBAB DURING STORAGE AT DIFFERENT STORAGE
TEMPERATURESa
Storagetemperature
(°C)
10

Dose
(kGy)

S. aureus (ln CFU/g)
0h

8h

0
7.87 ± 0.05
7.63 ± 0.09
1
4.11 ± 0.05
4.87 ± 0.24
2
2.09 ± 0.12
2.59 ± 0.16
b
n.d.
3
n.d.
20
0
7.87 ± 0.05
7.65 ± 0.19
1
4.11 ± 0.05
5.81 ± 0.13
2
2.09 ± 0.12
3.80 ± 0.02
3n.d.
2.80 ± 0.1430
07.87 ± 0.05
8.88 ± 0.20
1
4.11 ± 0.05
5.85 ± 0.21
2
2.09 ± 0.12
3.95 ± 0.04
3n.d.
2.82 ± 0.23
aMean ± standard deviation (n = 2).
bn.d.: no viable colony growth at detection limit <102 CFU/g.

212

24 h
7.27 ± 0.37
3.77 ± 0.32
2.51 ± 0.05
n.d.
8.79 ± 0.01
5.74 ± 0.31
4.40 ± 0.11
2.50 ± 0.14
8.81 ± 0.56
6.26 ± 0.43
4.96 ± 0.02
3.09 ± 0.44

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TABLE 16. D10 VALUE OF PATHOGENS IN ARTIFICIALLY CONTAMINATED SAMPLES OF KIMBAB
PathogenD10 value

S. typhimurium KCTC 1925

0.44 ± 0.01a

E. coli KCTC 1682

0.42 ± 0.04

S. aureus KCTC 1916

0.31 ± 0.01

L. ivanovii KCTC 3444

0.43 ± 0.01

aMean ± standard deviation (n = 2).

ham and cheese sandwiches yielded D10 values of 0.62 and 0.63. The applicationof low dose gamma irradiation for the extension of the shelf life, microbiological safety and retention of quality in minimally processed vegetables andfruits has been gaining importance in the industry, including restaurants andinstitutional and airline catering [34].
Kimchijumeokbab
Kimchijumeokbab, steamed rice with fried kimchi and pork and otherfood materials, is one of the famous Korean traditional prepared foods taken
when people go on a picnic. It is similar to Kimbab. Higher water activity andstorage conditions (because of the retrogradation of rice starch) also make thisproduct vulnerable to contamination. The total aerobic bacterial numbers in
raw Kimchi mix and raw pork mix were 6.42 and 7.40 ln CFU/g, respectively.
The frying procedure presented significant reductions (Table 17). However,lactic acid bacteria must be largely responsible for the higher contamination of
raw Kimchi mix. A 10 kGy dose showed no viable cells at day 0 but 2.15 ln
CFU/g after 2 d storage at 30°C, which is an abusive temperature condition(Table 18). The viable cells in fried pork and prepared Kimchijumeokbab were
not detected in 5 kGy samples at day 0 but were detected at day 1 stored at
30°C.
Sensory evaluation indicated that 3 kGy was the threshhold dose for
Kimchijumeokbab (Table 19). It could be concluded that irradiation at 3 kGy
combined with low temperature storage improved the safety and ensured theshelf life extension of Kimchijumeokbab without any adverse changes inquality for consumption.

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TABLE 17. CONTAMINATION LEVELS IN THE INGREDIENTS FOR
KIMCHIJUMEOKBAB
Parameter
Total bacteria counts

Lactic acid bacteria

SampleMean

SEM

Fried Kimchi

4.50

0.05

Fried pork

2.48

0.01

Raw Kimchi mix

6.42

0.08

Raw pork mix

7.40

0.10

Fried Kimchi

3.97

0.07

Raw Kimchi mix

6.55

0.10

TABLE 18. EFFECT OF IRRADIATION ON GROWTH (ln CFU/g) OF
TOTAL BACTERIA COUNTS IN FOOD MATERIALS AND
KIMCHIJUMEOKBAB DURING STORAGE AT 30°C
Samples
Fried Kimchi

Fried pork

Kimchijumeokbab

0

1

2

0

4.50

5.99

8.81

5

2.56

2.10

4.69

n.v.c.

2.15

a

10

n.v.c.

0

2.48

7.44

7.30

5

n.v.c.

3.62

5.13

10

n.v.c.

5.09

5.90

0

3.94

7.78

8.80

5

n.v.c.

6.75

8.76

10
Cooked riceaStorage (day)Irradiation dose(kGy)n.v.c.

5.49

8.26

n.v.c.

n.v.c.

n.v.c.

n.v.c.: no viable cell growth detected.

4.

CONCLUSION

The results of these studies indicated that irradiation treatment canminimize the risk of the harmful pathogens in Korean traditional prepared
meals including bulgogi sauce, bulgogi, marinated beef ribs, Kimbab andKimchijumeokbab. Doses of 1–3 kGy were effective in ensuring the safety and

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TABLE 19.
SENSORYKIMCHIJUMEOKBABEVALUATION*OF

IRRADIATED

Irradiationdose (kGy)

Colour

Flavour

TextureTaste

Overall
acceptance

Odour

0

4.57a

5.36a

5.50a

5.36a

5.86a

2.00b

3

4.00ab

4.86a

4.71ab

4.50ab

5.14ab2.86b

5

3.86ab3.43b

3.71bc

3.57bc

3.36c

3.39ab7

4.36ab3.43b

4.36bc3.64bc4.00bc3.00ab

10

3.36b

2.93b

3.30c

2.93c

3.14c

4.25a

SEM

0.463

0.536

0.443

0.608

0.594

0.614

*

The 7 point hedonic scale was used (n = 25).

extending the shelf life of the prepared foods while maintaining acceptablesensory quality.

ACKNOWLEDGEMENT
This research was supported by a grant from the nuclear R&D
programme, of the Ministry of Science and Technology, Republic of Korea, andpartially supported by the IAEA (CRP project no. 11908).

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USE OF IRRADIATION TO IMPROVE
THE SAFETY AND QUALITY
OF ETHNIC SOUTH AFRICAN FOODSPart I: Combined edible coating and irradiation treatment
on sensory and microbiological quality of moist beef biltong
A. MINNAAR, K. NORTJÉ,
A.M.A. PARRY-HANSON, E.M. BUYS
Department of Food Science,
Faculty of Natural and Agricultural Sciences,
University of Pretoria,
Pretoria,
South Africa

Abstract
South Africa is a multicultural country with different eating habits and food preferences. Traditional African foods such as bovine tripe form a part of the diet of black South
Africans. These foods are laborious to prepare, not generally available commercially, andhave a limited shelf life. Other popular ethnic foods in South Africa include meat products
such as biltong, an intermediate moisture dried raw meat product. Moist beef biltong has
the potential to cause food poisoning. The application of irradiation alone or in combination with other technologies can help solve these problems. Lean moist beef biltong (47%moisture, 3.7% NaCl, 1.5% crude fat, water activity 0.92) can be irradiated with doses up
to 10 kGy without adversely affecting sensory acceptability, provided that the irradiationis performed under vacuum conditions and that the biltong is exposed to aerobic conditions after irradiation to dissipate off odour volatiles. However, low dose irradiation(£4 kGy) was perceived to be more acceptable and preferable by consumers. Gamma irradiation of moist beef biltong (53.6% moisture, 1.91% NaCl, water activity 0.979) at doses
between 4 and 5 kGy was adequate to ensure safety from Staphylococcus aureus even if
contamination levels as high as 107 CFU/g were initially present. However, doses up to
5 kGy were insufficient to prevent yeast and mould spoilage if initial fungal contaminationlevels were high (>103 CFU/g). Casein-whey protein edible coatings did not inhibit
microbial growth on moist beef biltong, probably owing to diminished oxygen barrier
properties resulting from the very high moisture content of the biltong. Ready-to-eat
bovine tripe can be irradiated up to 9.3 kGy without affecting the consumer acceptanceadversely. Gamma irradiation at a target dose of 9 kGy significantly reduced total bacteria
counts and aerobic spore counts and extended the shelf life of ready-to-eat bovine tripe toat least 14 d at both 5 and 15°C when aerobic conditions prevailed. However, this dose
may not be sufficient to assure safety of the product if surviving aerobic spores are pathogenic Bacillus cereus spores. When anaerobic conditions prevail during processing of219

MINNAAR et al.

ready-to-eat bovine tripe, the use of boiling in combination with gamma irradiation at adose of 9 kGy and chilling at 5°C can be used to produce ready-to-eat bovine tripe that issafe from a Clostridium sporogenes perspective with an extended shelf life.
South Africa is a multicultural country with different eating habits and food preferences. Traditional African foods such as bovine tripe form a part of the diet of black
South Africans. These foods are laborious to prepare, not generally available commercially, and have a limited shelf life. Other popular ethnic foods in South Africa include
meat products such as biltong, an intermediate moisture dried raw meat product. Moist
beef biltong has the potential to cause food poisoning. The application of irradiation
alone or in combination with other technologies can help solve these problems.
The overall objective of the study was to determine the effect of irradiation, alone
and in combination with other processing technologies, on the microbiological andsensory quality of moist beef biltong and ready-to-eat bovine tripe, respectively.

1.

INTRODUCTION

Beef biltong is nowadays often preferred to be moister than the salty, dryvariants of this traditional South African salted, dried, raw meat product. Moist
beef biltong (moisture content ≥40%, water activity ≥0.85) [1] can, however,support the growth of the enterotoxin producing pathogen Staphylococcus
aureus [2]. It also provides an ideal growth medium for spoilage yeasts andmoulds [3]. Should significant contamination with these organisms occur, thisproduct could potentially present a health risk and/or have a limited shelf life.
Since gamma irradiation is effective in inactivating microorganisms from raw
meat products [4] and since milk protein based edible coatings have been
proposed in combination with irradiation to inhibit aerobic growth of microbes
such as yeasts and mould surviving irradiation by acting as oxygen barriers [5],the effects of these treatments on the microbiological safety and quality ofmoist beef biltong were determined.
During this research, the effect of gamma irradiation on the sensory
perception of moist beef biltong was first established [6]. Thereafter, the effectof a protein based edible coating on inoculated S. aureus and the indigenous
microbiological flora of whole moist beef biltong was investigated [7].

2.

MATERIALS AND METHODS

Experimental designs for this research project are provided in Figs 1
and 2.
Prior to any sensory tests being conducted, representative samples ofmoist beef biltong were tested for the presence of S. aureus, Salmonella spp.,

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Vacuum packaged moist beef biltong (n = 2)

(47 % moisture, 3.7 % NaCl, 1.5 % crude fat, water activity = 0.92)

Irradiate (doses of 2, 4, 6 and 8 kGy) at ambient temperature (20–25°C)(actual measured absorbed doses for two replicates:

1.84/1.89, 4.00/4.31, 6.17/6.40, 9.69/10.05 kGy)

Analyses

Lipid oxidation products(Thiobarbituric acid reactive substances (TBARS) [8])Sensory multiple difference testing (n = 96)(Same/different/R index method) [9]Sensory acceptability/hedonic testing (n = 50)(conducted if significant differences are found between control and irradiated samples)

FIG. 1. Experimental design for determination of the effect of irradiation on the sensory
perception of moist beef biltong.

Escherichia coli and coliforms. No E. coli or Salmonella spp. were present.
Although total coagulase positive Staphylococcus (counts ranging between
7.0 × 102 and 1.4 × 103 CFU/g) were found on all control samples, this was notregarded as holding any health risk since toxin production only commences atcell densities of between 105 and 106 CFU/g. The samples were therefore
considered to be safe for consumption by the sensory panel [6].
An S. aureus ATCC 9441 culture was used for challenge testing. Biltong
strips were inoculated (106–107 CFU/g) by spraying 20–25 mL of the inoculum
onto each biltong strip with a sterile spray bottle. Control samples were
sprayed in the same way with sterile distilled deionized water. All samples wereleft to dry for 30 min [7].
An edible protein coating solution containing calcium caseinate and whey
protein isolate was applied to biltong strips using a spray procedure [7]. Before

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Analyses
Whole moist beef biltonga (n = 3)

Aerobic plate count(Petrifilm™: AOAC Method

No inoculation (control)

S. aureus inoculation(106–107 CFU/g)

990.12) [11]Yeast and mould count(Petrifilm™) [12]S. aureus count [9]No coating

Coating

No coating

Coating% moisture content(control)(control)(AOAC Method 24.002) [13]Irradiateb (4 kGy) vacuum packed% NaCl content(ambient temperature: 20–25°C)(AOAC Method 24.010) [13]Store unpackaged in incubator for 7 d (25°C)

water activity

pHa

Moist beef biltong: 54% moisture, 1.91% NaCl, pH5.32, water activity

0.979 [10].
bActual measured absorbed doses for three replicates: 4.19, 4.96 and 5.08

kGy, respectively [10].

FIG. 2. Experimental design [6, 7] for determination of the effect of irradiation and acasein-whey protein edible coating on the microbiological safety and quality of moist beef
biltong. Experiment repeated three times (samples tested in triplicate during individual
replicates). Results statistically analysed by ANOVA and Fisher’s LSD test.

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application, the solution was sterilized at 121°C for 15 min to induce thermal
cross-linking to improve water barrier properties [5].

3.

RESULTS AND DISCUSSION

3.1. Effect of irradiation on the sensory perception of moist beef biltong[6, 10]A dose dependent increase in TBARS values was observed (Table 1).
However, only biltong irradiated at a dose of approximately 10 kGy (target
dose of 8 kGy) had significantly higher levels of oxidation products thanuntreated biltong, probably due to higher levels of free radicals produced.
These results support the findings of other researchers [14–18]. The relatively
low TBARS values found in the biltong research were not unexpected given
the fact that irradiation processing was done under vacuum conditions and thatthe fat content of the moist beef biltong was relatively low (i.e. 1.53%).
Although Greene and Cumuze [19] found the TBARS threshold level at which
unacceptable oxidation flavours were first detected by inexperienced panellists
for precooked beef to be between 0.6 and 2 mg/kg, Caballero, Trugo andFinglas [20] stated that TBARS values do not consistently correspond to a
specific degree of rancidity in different products. Since a mean TBARS value ofapproximately 0.9 mg/kg was found for non-irradiated biltong samples, it could
be assumed that the threshold for detection of unacceptable flavours in moist
beef biltong is in excess of 1.0 mg/kg [6].
TABLE 1. EFFECT OF GAMMA IRRADIATION ON THE TBARSVALUES OF MOIST BEEF BILTONG (adapted from Ref. [6])Irradiation dose*(kGy)

Mean TBARS value (± standard deviation)**(mg malonaldehyde/kg biltong)

00.888 ± 0.054a

2

0.898 ± 0.041a

4

0.929 ± 0.055a

60.952 ± 0.062ab

8

1.010 ± 0.062b*

Actual measured absorbed doses for two replicates: 2 kGy: 1.84/1.89, 4 kGy: 4.00/4.31,
6 kGy: 6.17/6.40, 8 kGy: 9.69/10.05 kGy.
**
Mean TBARS values followed by different letters are significantly different(p < 0.05).

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In contrast to the TBARS analyses, it was found that all irradiated moist
beef biltong samples could be distinguished from untreated biltong whensensory difference ratings of an analytical panel were analysed using the
R-index method and the Wilcoxon–Mann–Whitney rank sums test. The degreeof difference between the irradiated samples was perceived to be rather small,since only ratings of 2 and 10 kGy (target dose of 8 kGy) samples differedsignificantly (p < 0.05) [6].
A consumer acceptability (hedonic) test performed to determine therelation of perceived differences between untreated and irradiated moist beef
biltong to the acceptability of the different samples revealed that none of theirradiated biltong samples were significantly less acceptable than the control(0 kGy) (Table 2). However, biltong irradiated at the lower target doses (2and 4 kGy) was preferred significantly to untreated biltong or biltong
irradiated at higher target doses (i.e. 6 and 8 kGy). The preference for low
dose irradiated biltong over untreated biltong was unexpected and may be
because the slight irradiation flavour that developed in these samples
contributed to a fuller, more meaty flavour, since moist beef biltong is usually
blander in flavour than drier biltong types due to the higher residual moisture
content. This is supported by findings from various researchers [14, 15, 21]
where irradiation flavour in beef irradiated at low doses under anaerobic
conditions was described as acceptable and meaty, roasted or barbeque-cornlike in nature.
It was therefore concluded that irradiation at a target dose of 4 kGy
would be the most suitable irradiation treatment for biltong, since this was theirradiation dose used for which the sensory quality of the biltong was deemedmost acceptable and preferable.

TABLE 2.
EFFECT OF IRRADIATION ON MEAN HEDONIC
RATINGS (± STANDARD DEVIATION) OF MOIST BEEF BILTONG(adapted from Ref. [6])Dose (kGy)

Overall likingof taste*
*

0

2

4

6

8

5.66
±2.26a**7.06±1.15b

7.00±1.58b

6.02±1.71a5.92±1.91aMean hedonic ratings where 1 = dislike extremely, 5 = neither like nor dislike, 9 = likeextremely.
**
Mean hedonic ratings with different letters are significantly different (p < 0.05).

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MINNAAR et al.

3.2. Effect of irradiation and a casein-whey protein based edible coating on
the microbiological safety and quality of moist beef biltong [7, 10]
The effect of irradiation and a casein-whey edible coating on the mean
S. aureus, aerobic plate, yeast and mould counts of inoculated and noninoculated moist beef biltong samples is summarized in Table 3.
From Table 3, it is clear that considerable variation occurs around themean microbial counts. Although it is expected that microbial counts would
differ somewhat when biltong is produced from different raw materials, andespecially during different production runs, as was the case for the three
replicates of this experimental work (results not shown but reported [7]), thedifferences between total bacteria plate, yeast and mould counts of thereplicates were highly significant (p < 0.05). The reason for this is believed to be

TABLE 3. EFFECT OF IRRADIATION AND A CASEIN-WHEY
PROTEIN EDIBLE COATING ON THE MEAN S. aureus, AEROBIC
PLATE, YEAST AND MOULD COUNTS OF NON-INOCULATED AND
INOCULATED MOIST BEEF BILTONG WITH S. aureus(adapted from Ref. [7])Innoculation
with S. aureus

Non-irradiated (0 kGy)
Non-coated

CoatedIrradiated (4 kGy)
Non-coated

CoatedMean S. aureus count* (ln CFU/g)**
Non-inoculated
Inoculated

1.37 ± 1.29b
7.21 ± 0.38b

1.84 ± 1.09b
6.96 ± 0.22b<1a0.73 ± 1.10a<1a0.67 ± 1.00a

Mean aerobic plate count (ln CFU/g)
Non-inoculated
Inoculated

6.06 ± 0.76b
7.21 ± 0.32b6.23 ± 0.85b6.99 ± 0.39b

1.44 ± 1.30a
2.04 ± 0.50a

1.01 ± 1.07a
1.76 ± 0.85a

Mean yeast count (ln CFU/g)
Non-inoculated
Inoculated

3.50 ± 1.91b
3.27 ± 1.82b

4.03 ± 1.53b
2.94 ± 2.08ab

2.14 ± 1.47a
2.15 ± 1.79ab

2.06 ± 1.81a
1.89 ± 1.62a

Mean mould count (ln CFU/g)
Non-inoculated
Inoculated

3.06 ± 2.10b
2.95 ± 1.77b

3.43 ± 1.92b
2.88 ± 2.15b

1.65 ± 1.39a
1.74 ± 1.69a

1.80 ± 1.63a
1.55 ± 1.43a*

Means (± standard deviation) with different letters in a row are significantly different(p < 0.05).
**
Minimum growth detection limit: 1 ln CFU/g.

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due to the implementation of new quality assurance measures by the manufacturer during the research. Strictness of microbiological raw material specifications was increased between production of the first and second biltong
replicates. Furthermore, improved drying room cleaning and sanitation
processes were implemented between production of the second and third
replicates.
Irradiation at a target dose of 4 kGy reduced inoculated S. aureus counts
by approximately 6 log cycles, irrespective of application of the edible coating.
This is not to be unexpected since S. aureus is rather sensitive to irradiation.
Gamma D10 values lower than 0.8 kGy have been reported in various meatproducts [23–29]. Since viable S. aureus counts found on non-inoculated biltong
samples never exceeded 103 CFU/g, it can be concluded that irradiation at thisdose would, under normal conditions, be very effective in rendering moist beef
biltong safe from this pathogen. Even in the event of unexpectedly highcontamination with S. aureus (as in the inoculated samples), the counts areunlikely to exceed 106 CFU/g directly after production when irradiation would
typically be employed, and a target dose of 4 kGy would thus probably also be
effective for elimination in such a case. In contrast, the edible coating had noeffect on the level of S. aureus when compared with uncoated samples(p > 0.05).
Similar results were found for the total bacteria plate counts, irrespectiveof inoculation with S. aureus ATCC 9441 or not. This reduction is highly
significant in terms of potential spoilage bacteria such as lactic acid bacteria,
which at high counts may cause spoilage of vacuum packaged moist biltong. In
addition, the edible coating did not affect (p > 0.05) the total bacteria counts
significantly.
As was the case for bacteria, the edible coating did not affect (p > 0.05)
yeast and mould counts significantly. No inhibitory effect on microbial growth
was therefore observed for the casein-whey protein coating, and it can thus beconcluded that it did not have any significant oxygen barrier properties. A
possible reason for this is that the biltong used during the experiments had
higher than expected moisture levels (~54% moisture and water activity of0.98) under which conditions the barrier properties of protein coatings arediminished [30]. Since the effect of the edible coating was determined after 24 h
(48 h in conjunction with irradiation), it may be that the time period was notlong enough for a significant effect to be observed. For this reason, it wasplanned to test samples after 7 d of storage. Owing to gross fungal spoilage inless than 48 h under the specific storage conditions used, these samples weredeemed unfit for human consumption and consequently not tested. No visualdifference between coated and non-coated samples could be seen, but it is not

226MINNAAR et al.

known whether it would have had any effect if lower numbers of microbes
survived irradiation and/or if less favourable conditions were employed.
As anticipated, irradiation caused a significant reduction (p < 0.05) inyeast and mould counts. However, because fungi are more resistant toirradiation than bacteria [31], a relatively smaller reduction in counts (1–2 log
cycles) compared with that of bacteria (i.e. 6 log cycles) was observed. When
good manufacturing practices are used during manufacture of biltong, levels ofyeasts and moulds are not expected to exceed 100–1000 CFU/g (as found forthe biltong samples during the third replicate of the experiment) [7]. Therefore,
reductions in fungal counts by 1–2 log cycles due to irradiation at doses
between 4 and 5 kGy could extend the shelf life of moist beef biltong significantly under these circumstances. However, in the biltong samples tested
during the first two repetitions, yeast and mould counts of up to 104–105 CFU/g
were found [7]. Irradiation at between 4 and 5 kGy would clearly not beadequate in this case to prevent microbial spoilage due to surviving yeasts andmoulds (i.e. 103–104 CFU/g).

4.

CONCLUSIONS AND RECOMMENDATIONS

Gamma irradiation at doses of between 4 and 5 kGy will be adequate toensure the safety of moist beef biltong in terms of S. aureus. This dose will not,however, be effective in controlling fungal growth in moist beef biltong if initial
contamination levels are high (≥104 CFU/g) and conditions are favourable forfungal growth. It is therefore clear that strict hygienic practices and microbiological standards must be adhered to during and after the manufacture of moist
biltong, since irradiation up to 5 kGy will not be effective in eliminating highfungal loads.
Since it was found that irradiation at doses up to 10 kGy did not detrimentally affect the sensory quality of moist beef biltong, irradiation at higher
doses may potentially be used to control yeast and mould growth on moist
biltong. Otherwise, the use of a combination of ‘hurdles’ (e.g. vacuum
packaging and protein coatings with incorporated preservatives), together withlow dose irradiation (≤5 kGy), may be employed to attain extended microbiological stability.

ACKNOWLEDGEMENTS
This research was funded by the IAEA (research agreement no. 11909) andthe National Research Foundation, South Africa (project no. GUN 2053908).

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[28]

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HAMPSON, J.W., FOX, J.B., LAKRITZ, L., THAYER, D.W., Effect of low dose
gamma radiation on lipids in five different meats, Meat Science 42 (1996) 271–276.
ZHU, M.J., LEE, E.J., MENDONCA, A., AHN, D.U., Effect of irradiation on thequality of turkey ham during storage, Meat Science 66 (2003) 63–68.
GREENE, B.E., CUMUZE, T.H., Relationship between TBA numbers and inexperienced panelists’ assessments of oxidized flavor in cooked beef, Journal of
Food Science 47 (1981) 52–58.
CABALLERO, B., TRUGO, L.C., FINGLAS, P.M., Encyclopedia of Food
Science and Nutrition (Vol. 4) (2nd edition), Academic Press, Oxford, UK (2003).
LUCHSINGER, S.E., et al., Sensory analysis of irradiated ground beef patties
and whole muscle beef, Journal of Sensory Studies 12 (1997) 105–126.
ROODT, M., Gull Foods, personal communication, 2004.
PATTERSON, M., Sensitivity of bacteria to irradiation on poultry meat undervarious atmospheres, Letters in Applied Microbiology 7 (1988) 55–58.
MONK, J.D., CLAVERO, R.S., BEUCHAT, L.R., DOYLE, M.P., BRACKETT,
R.E., Irradiation inactivation of Listeria monocytogenes and Staphylococcus
aureus in low- and high-fat, frozen and refrigerated ground beef, Journal of Food
Protection 57 (1994) 969–974.
THAYER, D.W., BOYD, G., FOX, J.B., LAKRITZ, L., HAMPSON, J.W., Variations in radiation sensitivity of foodborne pathogens associated with thesuspending meat, Journal of Food Science 60, (1995) 63–67.
THAYER, D.W., BOYD, G., Gamma ray processing to destroy Staphylococcus
aureus in mechanically deboned chicken meat, Journal of Food Science 57 (1992)
848–851.
LAMB, J.L., GOGLEY, J.M., THOMPSON, M.J., SOLIS, D.R., SEN, S., Effect of
low-dose gamma irradiation on Staphylococcus aureus and product packaging inready-to-eat ham and cheese sandwiches, Journal of Food Protection 65 (2002)
1800–1805.
GRANT, I.R., PATTERSON, M.F., Sensitivity of foodborne pathogens toirradiation in the components of a chilled ready meal, Food Microbiology 9 (1992)
95–103.
GRANT, I.R., NIXON, C.R., PATTERSON, M.F., Effect of low-dose irradiation
on growth of and toxin production by Staphylococcus aureus and Bacillus cereus
in roast beef and gravy, International Journal of Food Microbiology 18 (2003)
25–36.
GUILBERT, S., Technology and application of edible protective films, In: Mathlouthi, M. (Ed.), Food Packaging and Preservation: Theory and Practice, Elsevier
Applied Science Publishers, London (1986) 371-394.
MONK, J.D., BEUCHAT, L.R., DOYLE, M.O., IRRADIATION INACTIVATION OF FOOD-BORNE MICROORGANISMS, JOURNAL OF FOOD
PROTECTION 58 (1995) 197-208.

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USE OF IRRADIATION TO IMPROVE
THE SAFETY AND QUALITY OF
ETHNIC SOUTH AFRICAN FOODSPart II: Effect of gamma irradiation on the sensory and microbiologicalquality of ready-to-eat bovine tripe
A. MINNAAR, K. NORTJÉ, A.M.A. PARRY-HANSON, E.M. BUYS
Department of Food Science, Faculty of Natural and Agricultural
Sciences,
University of Pretoria,
Pretoria,
South Africa10

Abstract
South Africa is a multicultural country with different eating habits and food preferences. Traditional African foods such as bovine tripe form a part of the diet of black South
Africans. These foods are laborious to prepare, not generally available commercially, andhave a limited shelf life. Other popular ethnic foods in South Africa include meat products
such as biltong, an intermediate moisture dried raw meat product. Moist beef biltong has
the potential to cause food poisoning. The application of irradiation alone or in combination with other technologies can help solve these problems. Lean moist beef biltong(47% moisture, 3.7% NaCl, 1.5% crude fat, water activity 0.92) can be irradiated withdoses up to 10 kGy without adversely affecting sensory acceptability, provided that theirradiation is performed under vacuum conditions and that the biltong is exposed toaerobic conditions after irradiation to dissipate off odour volatiles. However, low dose
irradiation (£4 kGy) was perceived to be more acceptable and preferable by consumers.
Gamma irradiation of moist beef biltong (53.6% moisture, 1.91% NaCl, water activity
0.979) at doses between 4 and 5 kGy was adequate to ensure safety from Staphylococcus
aureus even if contamination levels as high as 107 CFU/g were initially present.
However, doses up to 5 kGy were insufficient to prevent yeast and mould spoilage if
initial fungal contamination levels were high (>103 CFU/g). Casein-whey protein edible
coatings did not inhibit microbial growth on moist beef biltong, probably owing todiminished oxygen barrier properties resulting from the very high moisture content of
the biltong. Ready-to-eat bovine tripe can be irradiated up to 9.3 kGy without affecting
the consumer acceptance adversely. Gamma irradiation at a target dose of 9 kGy significantly reduced total bacteria counts and aerobic spore counts and extended the shelf
life of ready-to-eat bovine tripe to at least 14 d at both 5 and 15°C when aerobic conditions prevailed. However, this dose may not be sufficient to assure safety of the productif surviving aerobic spores are pathogenic Bacillus cereus spores. When anaerobic
conditions prevail during processing of ready-to-eat bovine tripe, the use of boiling in

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combination with gamma irradiation at a dose of 9 kGy and chilling at 5°C can be used
to produce ready-to-eat bovine tripe that is safe from a Clostridium sporogenes perspective with an extended shelf life.

1.

INTRODUCTION

Bovine tripe is not optimally used in South Africa because it is highly
perishable [1], not readily available in a convenient form and it requires longcooking time [2]. For these reasons, ready-to-eat technology was used toprocess tripe. One organism of particular concern in cook–chill foods is
Clostridium perfringens. Furthermore, this organism has been found on
intestinal tract offal [3, 4]. The current research was undertaken to determine
the effect of vacuum packaging and boiling of tripe in combination with gamma
irradiation on the microbiological safety, with respect to inoculate
C. perfringens ATCC 13124 spores, and microbiological quality of ready-to-eat
bovine tripe.

2.

MATERIALS AND METHODS

The initial intention was to inoculate ready-to-eat bovine tripe andprocess it as a sous vide product in an anaerobic environment (vacuum
packaged). This is shown in the experimental design provided (Experiment 1,
Fig. 1). However, no C. perfringens was detected in inoculated samples after
boiling or during storage as a result of the presence of oxygen in the system.
Consequently, a second experiment was performed where raw tripe was first
boiled, then chilled and inoculated prior to vacuum packaging and gamma
irradiation. Since a shelf-life study (14 d) was conducted in Experiment 1, theshelf life study in Experiment 2 was shortened to 7 d. Figure 2 illustrates theexperimental design for Experiment 2.
However, before any microbiological studies were conducted it was
important to determine the effect that gamma irradiation would have on
consumer sensory acceptance of ready-to-eat bovine tripe.
2.1. Effect of gamma irradiation on consumer sensory acceptanceof ready-to-eat bovine tripe
Fresh, roughly washed bovine tripe (i.e. rumen, reticulum and omasum)
was cleaned further by washing thoroughly with 21ºC tap water. It was then232

MINNAAR et al.

ROUGH WASHED TRIPE
LEGEND
TBC: total bacteria count

WASH (21ºC)

ASC: aerobic spore count

TBC
ASC
CC

CC: C. perfringens count

ENZYME (0.5% papain)

INOCULATED (107 C. perfringens spores/g)

CONTROL

VACUUM PACKAGING

BOILING
CHILL
TBC
ASC
CC

CONTROL

9 kGy

STORAGE

5ºC

15ºC

CONTROL

9 kGy (10 r 1ºC)

STORAGE

5ºC

15ºC
TBC
ASC
CC

0d 3d 7d 10d 14d

0d 3d 7d 10d 14d 0d 3d 7d 10d 14d 0d 3d 7d 10d 14dFIG. 1. Experimental design for determination of the effect of boiling and gamma irradiation at a dose of 9 kGy on the bacterial quality of ready-to-eat bovine tripe stored for
14 d at 5 and 15°C [4].

233MINNAAR et al.

ROUGH WASHED TRIPE

CC, TBC
Washed and papain
tenderized (2 h)

LEGEND

BOILED (1 h)

TBC: total bacteria count
CC: C. perfringens countCC, TBCINOCULATED(1 mL of 107 C. perfringens ATCC 13124 in
vacuum bag)CC, TBC

Seal vacuum bag

10ºC

CONTROL

9 kGy IRRADIATIONSTORAGE

5ºC

0d 3d

7d

CC, TBC

15ºC

0d

3d

CC, TBC

5ºC

7d

0d

3d

15ºC
7d

CC, TBC0d

3d 7d

CC, TBC

FIG. 2. Experimental design to determine the effect of gamma irradiation at a target doseof 9 kGy on survival of C. perfringens ATCC 13124 spores on ready-to-eat bovine tripe
stored at 5 and 15°C for 7 d [4].

partially defatted before cutting into 4 cm × 4 cm pieces. Tripe was tenderized
by soaking the pieces in a 0.5% (w/v) solution of papain (pH4.5) at room
temperature for 2 h. After enzyme treatment, one hour of cooking was
required to produce a ready-to-eat product. After cooking, the samples werevacuum packaged and irradiated to target doses of 2, 4, 6 and 8 kGy using 60Co
gamma rays at Isotron SA (Isando, South Africa). The actual doses received
were 2.6, 5.0, 6.4 and 9.3 kGy, respectively.
2.1.1. Microbiological analyses
To ensure that only samples fit for human consumption would be
provided to the consumer panel, total plate counts and aerobic spore counts(ASC) were conducted on samples irradiated to target doses of 2, 4, 6 and8 kGy.

234

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2.1.2. Consumer sensory evaluation
The 9 point hedonic scale (1 = dislike extremely, 9 = like extremely) wasused to evaluate the appearance, texture, flavour and overall acceptability ofthe tripe samples. A total of 51 consumers participated in the evaluations. The
majority of the consumers were older than 30 years of age and 69% of the panel
were black South Africans. More males (69%) than females (31%) participatedin the evaluation.
2.2. Effect of boiling and gamma irradiation on bacterial quality
and C. perfringens ATCC 13124 spores inoculated
on ready-to-eat bovine tripe, and the shelf life ofready-to-eat bovine tripe stored at 5 and 15ºC for 14 d [3]
In Experiment 1, fresh tripe was processed as a sous vide product.
Washed tripe was inoculated with 7 ln CFU/g C. perfringens ATCC 13124
spores in bags, vacuum sealed, boiled in bags for 1 h and irradiated with a doseof 9 kGy (actual doses: 9.2, 9.0 and 7.9 kGy). Aerobic conditions prevailed
owing to the presence of residual oxygen in the packs resulting in the inhibitionof C. perfringens after boiling. Preparation of ready-to-eat bovine tripe took 1 dand the irradiation treatment took 2 d. Therefore, storage days 0, 3, 7, 10 and 14
at 5 and 15°C were actually days 3, 6, 10, 13 and 17. In Experiment 2, bovine
tripe was boiled for 1 h prior to inoculation with spores, vacuum packaged andirradiated with a target dose of 9 kGy (actual doses: 8.4 and 8.9 kGy).
Preparation of ready-to-eat bovine tripe also took 1 d, but the irradiation
treatment took 3 d. Therefore storage days 0, 3 and 7 were actually days 4, 7
and 11 at 5 and 15°C after preparation, respectively.
For both experiments, total bacteria counts (TBC), ASC andC. perfringens counts were done on the following samples: roughly washedbovine tripe, papain tenderized samples, after boiling, immediately after
gamma irradiation and at different time intervals during storage at 5 and 15°C.
The C. perfringens spore count was made after heat shocking the samples at
70ºC for 20 min. Optical microscopy was also used to confirm that spores werecounted and not vegetative cells.
To study the potential synergistic effect of boiling in combination withgamma irradiation, transmission electron microscopy was conducted on pure
C. perfringens ATCC 13124 spores as follows: untreated, boiled alone for 1 h at
100°C, irradiated alone at 9 kGy, boiled in combination with irradiation
treatment.

235

MINNAAR et al.

3.

RESULTS AND DISCUSSION

3.1. Effect of gamma irradiation on consumer sensory acceptanceof cooked ready-to-eat bovine tripe
3.1.1. Microbiological assays
The TBC (Fig. 3) of the uncooked tripe was high (i.e. 6.27 ln CFU/g), but
as expected for fresh tripe [1–5]. There was only a slight reduction in TBC after
cooking (0 kGy) to 6.02 ln CFU/g. This may be due to the fact that a large partof the TBC consisted of aerobic spore formers. As the irradiation dose
increased, both the TBC (Fig. 3) and aerobic spore former counts (Fig. 4)
decreased. A 3 ln CFU/g reduction was evident with the samples irradiated to atarget dose of 8 kGy in both counts. No C. perfringens was detected in thesamples, either before or after irradiation. Therefore, regarding C. perfringens,the ready-to-eat tripe was considered to be safe. However, the results indicatedthat if aerobic spore formers comprise a large component of the TBC, theirradiation dose necessary to reduce the count to an acceptable level may haveto be equal to or exceed 6 kGy. Subsequently, a target dose of 9 kGy was used
for irradiation of ready-to-eat bovine tripe.

109

Log cfu/g

8
7
6
5
4
3
2
1
UNCOOKED

0 kGy

2 kGy

4 kGy

6 kGy

8 kGy

FIG. 3. TBC of uncooked (unirradiated) versus cooked ready-to-eat bovine tripe after
irradiation at doses of 2, 4, 6 and 8 kGy.

236

Log cfu/g

MINNAAR et al.

10
9
8
7
6
5
4
3
2
1
UNCOOKED

0 kGy

2 kGy

4 kGy

6 kGy

8 kGy

FIG. 4. Effect of gamma irradiation on ASC of ready-to-eat bovine tripe.

3.1.2. Consumer sensory evaluation
There were no significant differences in the mean hedonic ratings for theappearance, aroma, texture, flavour and overall acceptability (p > 0.05)
between irradiated and control tripe samples (Table 1).
The mean rating scores were quite low, i.e. dislike slightly to neither liked
nor disliked. The standard deviations were also quite large. The reason for thisbecame evident after cluster analyses were conducted. It was clear that the
majority of panellists (black consumers) gave relatively high ratings for all
samples, whereas the minority of panellists (white, coloured and Asian
consumers) gave relatively low scores.
The majority of the consumers (59–74%) gave positive response ratings(above 6 on the 9 point scale) for all of the attributes evaluated, while the restof the consumers were more negative. The negative results could be the resultof the toughness of the tripe as well as a bland flavour. Not every consumer wasused to consuming tripe on its own, without a sauce or other food items added.
This might also have had an influence on the negative responses of some of theconsumers. This was probably due to the fact that the samples were prepared ina way familiar to African consumers but not necessarily familiar to the otherethnic groupings. In fact, some white consumers declined to evaluate thesamples when they saw that they were not prepared in the way that they wereused to.

237

MINNAAR et al.

TABLE 1. EFFECT OF IRRADIATION ON THE AVERAGE HEDONIC
RATINGS (± STANDARD DEVIATION) OF COOKED, READY-TO-EATBOVINE TRIPE
Sensory
characteristics

Dose (kGy)ap value
0

2

4

6

8

Look/appearance

5.43 ± 2.73b 5.65 ± 2.64 5.54 ± 2.64 5.85 ± 2.44 5.77 ± 2.74

0.94

Smell/aroma

5.56 ± 2.37

5.59 ± 2.33 5.73 ± 2.24 5.63 ± 2.24 5.90 ± 2.43

0.96

Texture4.80 ± 2.64

5.20 ± 2.51 5.02 ± 2.45 5.23 ± 2.41 5.69 ± 2.64

0.54

Flavour/taste

4.67 ± 2.37

5.04 ± 2.47 4.94 ± 2.35 4.81 ± 2.58 5.25 ± 2.69

0.83

Overall
acceptability

4.79 ± 2.46

5.06 ± 2.55 4.85 ± 2.58 5.06 ± 2.56 5.37 ± 2.50

0.82

a
b

Actual irradiation doses: 2.6, 5.0, 6.4 and 9.3 kGy.
Mean hedonic ratings where: 1 = dislike extremely, 5 = neither like nor dislike, 9 = likeextremely.

3.2. Effect of boiling and gamma irradiation on bacterial quality andC. perfringens ATCC 13124 spores inoculated on ready-to-eat bovine tripe,and on the shelf life of ready-to-eat bovine tripe stored at 5 and 15ºC for 14 d3.2.1. Experiment 1: Aerobic conditions prevailingAs expected, the raw bovine tripe had high microbiological loads for TBC
and ASC as well as relatively high levels of C. perfringens (Table 2). This is dueto the high levels of microorganisms naturally present in the ruminant stomach.
Although boiling for 1 h reduced both TBC and ASC, this was not statisticallysignificant. Furthermore, these levels remained high after boiling, probably due
to the presence of heat resistant aerobic spore formers [6]. This is in agreementwith studies by researchers [1, 6] who reported the presence of heat resistantDeinococcus and lactobacillus on cooked bovine tripe and heat resistantAeromonas spp., Clostridium sporogenes and Bacillus spp. on minced tripe.
Overall, gamma irradiation had a statistically significant (p = 0.017) effecton the TBC of ready-to-eat bovine tripe. There were, however, no significant
effects between storage temperature and storage time on the TBC of ready-toeat bovine tripe samples (Fig. 5). Similarly, gamma irradiation overall significantly (p = 0.014) reduced the TBC on ready-to-eat bovine tripe. Again, there
were no significant storage temperature or time effects or any significant
interactions between the variables (Fig. 6).

238

MINNAAR et al.

TABLE 2. EFFECT OF ROUGH WASHING, PAPAIN TREATMENT
AND BOILING ON THE BACTERIAL QUALITY (± STANDARD
DEVIATION) OF FRESH BOVINE TRIPE (n = 18) (adapted from Ref. [3])Treatment

TBC

ASC

C. perfringens countRough washed8.6 ± 1.6a*

8.6 ± 1.6a

4.5 ± 1.2a

Papain tenderized

8.8 ± 0.7a

8.6 ± 1.0a

2.2 ± 2.0a

Boiled6.3 ± 0.4a

6.1 ± 0.7a

2.0 ± 2.2a*

Mean values followed by a different letter within the same column are significantly
different from each other (p < 0.05).

14

12

APC (log10 cfu'g)

10

8

6

4

2

0

-2
Time (day s):
0

3

10
7

5°C

14

Time (day s):
0

3

10
7

14

Irradiation
0
Irradiation
915°C

FIG. 5. Effect of irradiation at a target dose of 9 kGy on TBC of ready-to-eat bovine tripe
stored for 14 d at 5 and 15°C (adapted from Ref. [3]).

Gamma irradiation caused a significant reduction in TBC (Fig. 5) andASC (Fig. 6) on ready-to-eat bovine tripe. The levels of TBC and ASC overall,
after irradiation, were 4 ln CFU/g and 3.9 ln CFU/g, respectively. These levels
suggest that the aerobic bacteria and aerobic spores on tripe show highresistance to boiling and irradiation. Although most of the enteric bacteria
found on fresh tripe are sensitive to low doses of ionizing irradiation (~1 kGy),
irradiation resistant Deinococcus, Aeromonas, Staphylococcus and Streptococcus

239

MINNAAR et al.

FIG. 6. Effect of irradiation at a target dose of 9 kGy on ASC of ready-to-eat bovine
tripe stored for 14 d at 5 and 15˚C (adapted from Ref. [3]).

have been reported on tripe [1, 7–9]. It is also postulated that most of the
aerobic spores on ready-to-eat bovine tripe belong to the genus Bacillus [2].
An identical pattern of growth was observed for both TBC and ASC and 0 and
9 kGy on ready-to-eat bovine tripe stored for 14 d at 5 and 15°C. For thisreason, as well as the high resistance of APC to boiling (95°C) and gamma
irradiation, it is postulated that the TBC reported in this study were predominantly aerobic spores.
Interestingly, the TBC and ASC on 9 kGy ready-to-eat bovine tripe
stored at 15°C also followed the same trend as the 0 and 9 kGy samples stored
at 5°C. The TBC and ASC of the 0 kGy ready-to-eat bovine tripe samples
stored at 15°C increased progressively until they reached unacceptable levels of
8.6 ln CFU/g and 8.8 ln CFU/g, respectively, by day 14.
It has been reported that processed and vacuum packaged tripe showedsigns of spoilage when its bacterial numbers reached 7 ln CFU/g [8]. Growth of
TBC and ASC on 0 and 9 kGy ready-to-eat bovine tripe was restricted at 5°C
with TBC and ASC remaining below 6 ln CFU/g throughout storage, thus
extending the shelf life to at least 14 d. Therefore, storage of ready-to-eat
bovine tripe, packed under aerobic conditions, at 5°C is sufficient to prevent

240

MINNAAR et al.

germination and rapid proliferation of aerobic bacteria and aerobic spores.
Even when the initial ASC is high, they can be contained at this refrigerated
temperature.
Similarly, TBC and ASC on irradiated ready-to-eat bovine tripe samples
stored at 15°C were contained around 4 ln CFU/g throughout 14 d of storage.
Although this temperature could be conducive for repair and proliferation, theincrease in APC and ASC was controlled. This is probably because gamma
irradiation induced injuries to aerobic bacteria and aerobic spores in such a
way that they were unable to germinate and grow at 15°C. This suggests that
gamma irradiation at a target dose of 9 kGy is sufficient to prolong the shelf lifeof ready-to-eat bovine tripe to at least 14 d, even at an abusive temperature of
15°C. Similarly, it has been reported [7] that irradiation of beef sauce at 5 and
10 kGy reduced the microbiological counts of thermophilic bacteria, whose
numbers remained low throughout the 4 weeks of storage at 20°C. However,unlike irradiated samples stored at 15°C, non-irradiated samples stored at 15°C
showed a steady increase in spore numbers. By day 7, ASC had exceeded 7 ln
CFU/g and thus by day 7, the non-irradiated samples stored at 15°C wereconsidered to be spoiled.
3.2.2. Experiment 2: Anaerobic conditions prevailing
As with Experiment 1, the raw bovine tripe recorded a very high TBC(8.4 ln CFU/g), which was significantly reduced by gamma irradiation. This was
expected since most of the enteric bacteria on tripe are sensitive to low doses ofgamma irradiation [1].
Overall, gamma irradiation had a statistically significant (p = 0.000) effecton the TBC of inoculated ready-to-eat bovine tripe as well as on C. perfringens
ATCC 13124 spores. There were, however, no significant effects between
storage temperature and storage time on the TBC of ready-to-eat bovine tripe
samples (Table 3). There were no significant storage temperature or storage
time effects or interactions in terms of survival of C. perfringens ATCC 13124.
Initially, no growth of aerobic bacteria was detected on irradiated samples
stored at 5 and 15°C. However, during storage at both 5 and 15°C, aerobic
bacteria re-emerged on irradiated samples probably due to repair of irradiation
injury. A lag phase was observed before regrowth occurred.
Transmission electron microscopy of isolated C. perfringens ATCC 13124
spores showed that boiling alone caused reduction of spore material possibly
due to initiation of germination. Gamma irradiation alone caused elongation of
C. perfringens spores indicating that outgrowth was inhibited even though
germination occurred [4]. The heat–irradiation combination had a synergistic241

MINNAAR et al.

TABLE 3. EFFECT OF IRRADIATION ON TBC OF INOCULATEDREADY-TO-EAT BOVINE TRIPE AND ON SURVIVAL OF C. perfringens
ATCC 13124 SPORES ON INOCULATED READY-TO-EAT BOVINETRIPE STORED FOR 7 d AT 5°C AND 15°C (adapted from Ref. [3])C. perfringens ATCC
13124 (ln CFU/g)

TBC (ln CFU/g)
Storage time (d)Irradiation dose (kGy)*
0

9

0

9

0

10.13 ± 0.57

<1**

3

6.09 ± 0.16

<1

9.02 ± 0.29

<1

6.65 ± 0.73

<17

10.07 ± 0.07

1.41 ± 1.99

5.54 ± 1.02

<1

5°C

15°C

<1

0

10.13 ± 1.20

<1

6.09 ± 0.16

<13

9.88 ± 0.29

1.88 ± 2.70

6.70 ± 1.02

<17

10.43 ± 0.37

1.91 ± 2.70

6.81 ± 0.96

<1a

10.0b

1.0a

6.4b

<1a

Overall irradiation
effect****Actual irradiation doses: 8.4 kGy and 8.9 kGy for replicates 1 and 2.
Minimum growth detection limit: 1 ln CFU/g.
***
Mean values followed by a different letter within the same cell are significantly
different from each other (p < 0.05).
**

effect on C. perfringens spores as indicated by the complete loss of spore
material [4].
Under the anaerobic conditions prevailing in Experiment 2,
inoculated C. perfringens ATCC 13124 spores were eliminated by gamma
irradiation. This is in agreement with Van den Heever [1], who reported
that irradiation at 4–6 kGy is sufficient to reduce 6 ln CFU/g C. perfringens
below levels that are easily recoverable by conventional bacteriologicalmethods. Gamma D10 values for C. perfringens have been reported to range
between 1.2 and 3.4 kGy [8]. Furthermore, no C. perfringens was detected onirradiated ready-to-eat bovine tripe samples stored at both 5 and 15°C
throughout the 7 d of storage. Parry-Hanson [4] proposed that the injury to thepost-germination system of C. perfringens ATCC 13124 was permanent, thus
not allowing for spore injury repair during the storage period.

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MINNAAR et al.

4.

CONCLUSIONS

Consumer sensory evaluation indicated that gamma irradiation up to
9.3 kGy did not have an adverse effect on acceptability of ready-to-eat bovine
tripe. However, the results indicated that fresh tripe has high TBC and ASC,making it an ideal product for irradiation. Therefore, an irradiation dose equal
to or exceeding 6 kGy would be necessary to reduce the microbial contaminationto acceptable levels in order to attain an acceptable shelf life.
Gamma irradiation at a target dose of 9 kGy is sufficient to prolong theshelf life of ready-to-eat bovine tripe to at least 14 d storage under aerobic
conditions, even at the abusive temperature of 15°C. However, owing to thehigh levels of aerobic spores and aerobic bacteria that persisted after
irradiation processing, sous vide processing of bovine tripe is not recommended
because it might be unsafe for consumption if pathogenic B. cereus spores arepresent. Irradiated ready-to-eat bovine tripe prepared in an anaerobic
environment proved to be safe for human consumption from a C. perfringens
point of view for at least 7 d of storage, even under abusive storage temperatures (i.e. 15°C).

ACKNOWLEDGEMENTS
This research was funded by the IAEA (research agreement no. 11909)
and the National Research Foundation, South Africa (project no. GUN
2053908).

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ICMSF, Microbiology in Foods 5, In: Microbiological Specifications of Food
Pathogens, Blacking Academic and Professional, Glasgow (1996) 112–124.

EFFECT OF GAMMA IRRADIATIONON THE MICROBIAL LOAD AND
CHEMICAL AND SENSORY PROPERTIESOF LOCALLY PREPARED FAST MEALS
M. AL-BACHIR
Radiation Technology Department,
Syrian Atomic Energy Commission,
Damascus,
Syrian Arab Republic

Abstract
Locally prepared meals (kubba, borak, cheese borak and sheesh tawoq) weretreated with 2, 4 or 6 kGy doses of gamma irradiation. Treated and untreated samples
were kept in a refrigerator (1–4oC). Microbiological and chemical analyses were
performed on each treated sample immediately after processing, and weekly throughout
the storage period, which lasted for 3 weeks for kubba, 6 weeks for borak and cheeseborak and 20 weeks for sheesh tawoq. Sensory evaluation and proximate analysis weredone within one week after irradiation. Results of the proximate analysis of borak,cheese borak and sheesh tawoq showed that the irradiation doses did not have a significant effect on the moisture, protein and fat contents of meals, whereas for kubba, irradiation decreased the moisture, protein and fat contents. The doses of gamma irradiation
selected decreased the microorganism load and increased the shelf life of all meals
studied. The radiation doses required to reduce Salmonella and Escherichia coli by one
log cycle (D10) in borak were 0.46 and 0.51 kGy, in cheese borak 0.30 and 0.50 kGy andfor sheesh tawoq 0.44 and 0.39 kGy, respectively. The three chemical parameters, total
acidity, lipid peroxide and volatile basic nitrogen, which were chosen as the indices offreshness, were all well within the acceptable limit for up to 3 weeks for kubba, 6 weeks
for borak and cheese borak and 20 weeks for sheesh tawoq treated with 6 kGy. Sensory
evaluation showed no significant differences between irradiated and non-irradiatedsamples.

1.

INTRODUCTION

Ready meals are meals that are cooked and stored in a frozen state (–18°C)
until required for consumption. In recent years, the market for chilled readymeals that are cooked, stored under chilled conditions (0–3°C) and reheatedprior to consumption has also shown substantial growth, largely as a result of245

AL-BACHIR

consumer perception that chilled foods are ‘closer’ to fresh than frozen foods[1–4].
Ready meals have a very limited shelf life at refrigeration temperatures
and therefore there are concerns about the microbiological safety [5], sensory
quality [6] and nutritive value [7]. Various methods, such as the modified
atmosphere packaging, have been used to help preserve the sensory quality andto extend the shelf life of cook–chill foods [8]. However, many of thesemethods have not been developed to inactivate potential pathogens [9].
An alternative approach could be the use of medium dose irradiation to
improve the microbiological safety and shelf life of chilled ready meals [1].
Irradiation treatment of ready-to-eat food can improve the shelf life andmicrobiological safety by destroying spoilage and pathogenic microorganisms[10–12].
Syrian consumers have recently started using ready meals which areprepared and marketed by local supermarkets. The Syrian food industry is
traditionally dominated by kubba, borak and sheesh tawoq. Indeed, these meals
are consumed not only in the Syrian Arab Republic, but also in neighbouring
countries.
The objectives of this research were to investigate the use of gamma
irradiation in order to improve the microbiological quality of certain kinds ofSyrian precooked prepared meals (kubba, borak, cheese borak and sheesh
tawoq) stored at low temperature (1–4oC), and to evaluate the changes in
product quality and performance of irradiated products during storage.

2.

MATERIALS AND METHODSThe experiments were conducted over four years on kubba, borak, cheeseborak and sheesh tawoq. Each year one of these products was evaluated.
2.1. Preparation and formulation of kubba, borak,cheese borak and sheesh tawoq
The kubba, borak, cheese borak and sheesh tawoq were prepared by alocal caterer. No changes were made to the way in which these meals wereusually prepared in this industry.
Kubba has two parts, the outer layer of which consists of ground
preboiled wheat (bulgar) mixed with minced beef (70% bulgar and 30% beef)
and spices (allspice, black pepper, white pepper, onion and salt). The outerlayer is stuffed with precooked lamb, onion, fat, pistachio and spices (allspice,246

AL-BACHIR

black pepper, white pepper, nutmeg, cumin and salt). After preparing, kubba isfried in sunflower oil for 2–3 min.
Borak has two parts; the outer part is a form of dough made of wheat
flour (1 kg) mixed with 3 eggs, oil (200 mL), salt and water (300 mL). The
dough is stuffed with a mixture of precooked lamb (1 kg), onion (200 g), fat(100 g), pistachio (200 g) and spices (black pepper, white pepper and salt).
Cheese borak has two parts; the outer part is a kind of dough and made ofwheat flour (1 kg) mixed with 3 eggs, oil (200 mL), salt and water (300 mL). The
slices of dough are stuffed with a mixture of uncooked baladi cheese.
After preparation, eight pieces of kubba, borak or cheese borak wereplaced on polystyrene trays and covered with lids made of polyethylene film.
Each tray of borak was considered as a replicate.
Sheesh tawoq was prepared from boneless chicken breast, which was
chopped into pieces of between 5 and 7 g each. To each kilogram of bonelesschicken were added the following ingredients: 5 g ground garlic, 5 g coriander,
5 g white pepper, 5 g salt, 5 g cardamom, 5 g paprika, 10 g mustard, 5 g tomato
paste, 10 g vinegar, 10 g olive oil, 30 g sunflower oil and 5 g lemon.
After preparation, 300 g of sheesh tawoq were placed on polystyrene
trays and covered with lids made of polyethylene film. Each tray of sheesh
tawoq was considered a replicate.
2.2. Treatments and analysis performed during storage
Samples from packed meals were exposed to gamma radiation at doses of
2, 4 and 6 kGy in a 60Co package irradiator (dose rate 730 Gy/h). The
irradiation was performed at room temperature (10–20°C). The absorbed dose
was determined using an alcohol chlorobenzene dosimeter [13]. For eachtreatment, 20 trays of kubba, borak, cheese borak and sheesh tawoq wereallocated and all were stored at refrigerated temperatures (1–4°C). Microbiological and chemical analyses were performed on controls and treated samples
immediately after processing, and weekly throughout the storage period, whichlasted 3 weeks for kubba, 6 weeks for borak and cheese borak and 20 weeks forsheesh tawoq. Sensory evaluation and proximate analysis were done within twodays of irradiation.
2.3. Microbiological evaluation
Three replicates from each treatment were aseptically opened, and 10 g of
the whole tested product was serially diluted according to standard methods[14]. The media used for the microbiological study were nutrient agar, for the
total bacteria counts (TBC) (Oxoid, CM 325, United Kingdom) (48 h247

AL-BACHIR

incubation at 30°C). A cut-off value of 107 CFU/g for TBC [15] was used for theunacceptable samples and no further analyses were carried out when thoseindicator values were exceeded. Total coliforms were determined on violet red
bile agar (Oxoid) at 37°C for 48 h. Yeasts were enumerated on dichloran rose–
Bengal chloramphenicol agar (Merck) after incubation at 25°C for 5 d. In orderto determine the survival curves before irradiation, the borak, cheese borak
and sheesh tawoq were artificially inoculated by thoroughly mixing it with apure culture of Salmonella spp. and Escherichia coli. The used Salmonella spp.
and E. coli had been isolated in the laboratory from contaminated local food.
The above mentioned strains were identified by biochemical tests. The initial
numbers of artificial contamination were 1.2 × 107 and 2.0 × 106 CFU/g for
Salmonella spp. and E. coli, respectively. The survival curve was estimated from
irradiation doses of 0.20, 0.40, 0.60, 0.80 and 1.00 kGy. The survival level of
Salmonella spp. was determined by plate counting on xylose lysine desoxycholate agar and the survival level of E. coli was determined by plate counting
on eosin methylene blue agar after 2 d of incubation at 37°C.
2.4. Chemical evaluation
Approximately 150 g samples of the prepared products were blended for
15 s in a laboratory blender and subjected to chemical analysis. Each sample
was homogenized and analysed in triplicate to determine moisture and ash(drying for 6 h at 105°C and ashing for 4 h at 550°C), fat (as extractablecomponent in Soxhlet apparatus) and protein (as Kjeldahl nitrogen) contents
using standard methods [16]. The pH values of the solutions of kubba, borak
and cheese borak were determined using an HI 8521 pH meter (Hanna
Instruments, United States of America).
2.5. Total acidity
The total acidity was obtained by a direct titration with 0.1N NaOH andphenolphthalein as an indicator [17]. Samples (10 g) of the meals were magnetically stirred in a total volume of 100 mL distilled water for 30 min and filtered.
A 10 mL aliquot of the filtrate was titrated with 0.1N NaOH using 3 drops of aphenolphthalein indicator. The total acidity was calculated on the basis of 1 mL
0.1N NaOH = 0.0090 g lactic acid.
2.6. Total volatile basic nitrogen (VBN)
Samples (10 g) of the meals studied were mixed with 100 mL distilledwater and washed into a distillation flask with 100 mL distilled water, followed248

AL-BACHIR

by 2 g of magnesium oxide and an antifoaming agent. The mixture was distilledusing the micro-Kjeldahl distillation apparatus. Distillate was collected for
25 min into 25 mL of 4% boric acid and 5 drops of Tashero indicator added.
The solution was titrated by 0.1N HCl to calculate the total VBN in the sample
in terms of milligrams of VBN per kilogram of kubba, borak, cheese borak andsheesh tawoq (ppm) [18].
2.7. Lipid oxidation
Lipid peroxidation in terms of grams of iodine per 100 grams of fat of
kubba, borak and cheese borak was determined by the modified method of
Buege and Aust [19]. A fat sample of 1 g was placed in a 250 mL test flask andhomogenized with a 20 mL solution of acetic acid (50% acetic acid, 50%
chloroform). The mixture was vortexed, incubated in a hot water bath at 50°C
for 30 min and the samples filtered. The filtrate was collected into 0.5 mL ofpotassium iodide (50%) and kept in a dark place for 2 min. Distilled water(100 mL) and 3 drops of starch 1% as an indicator were added, then the
mixture was titrated by sodium thiosulphate pentahydrate (0.01N), added
drop-wise until the end point.
2.8. Sensory evaluation
The sensorial criteria, especially the taste, odour, colour and texture of
the irradiated and non-irradiated kubba, borak, cheese borak and sheesh
tawoq were evaluated within two days of irradiation. In an equipped room,each panellist received four coded sample pieces (one non-irradiated and threeirradiated samples, one at each dose). All the meals were tasted by 25 persons.
Before testing, all samples of the meals were cooked. Kubba, borak and cheeseborak were fried in sunflower oil for 5 min. Each member independently
evaluated the kubba, borak, cheese borak and sheesh tawoq for taste, odour,colour and texture on a 5 point hedonic scale (1 = extremely poor, 2 = poor,
3 = acceptable, 4 = good, 5 = excellent), according to Ref. [20].
2.9. Statistical analysis
The four treatments were distributed in a completely randomized design
with three replicates. The data were subjected to the analysis of variance test
(ANOVA) using the SUPERANOVA computer package (Abacus Concepts
Inc., USA (1998)). A separation test on treatment means was conducted using
Fisher’s least significant differences (LSD) methods at the p < 0.05 significancelevel. The D10 values were calculated using the Cricket graph computer package.

249

AL-BACHIR

3.

RESULTS3.1. Results of the effect of gamma irradiation on kubba
3.1.1. Kubba characteristics
The mean of kubba characteristics in this study were: fat (12.16 ± 0.10%),protein (9.88 ± 0.75%), ash (1.93 ± 0.06%) and moisture (52.73 ± 0.43%).
Results of the proximate analysis of kubba showed that the moisture,protein and fat contents decreased in the samples irradiated with higher doses(4 and 6 kGy) (Table l).
3.1.2. Microbiological quality of irradiated kubba
Data in Table 2 indicate that 2, 4 and 6 kGy doses significantly (p > 0.05)
decreased the TBC of kubba compared with the controls. The reduction was
more than 1 or 2 log cycles for 4 and 6 kGy, respectively. Control and samples
treated with 2 kGy presented a microbial load of 107/g [15] after one week ofstorage, whereas the samples treated with 4 or 6 kGy had not reached the same
number after 3 weeks, representing satisfactory microbiological quality.
Therefore, the microbiological shelf life of kubba samples treated with 4
or 6 kGy was significantly extended from one week (control) to more than
three weeks.

TABLE 1. EFFECT OF IRRADIATION ON MOISTURE, PROTEIN, FAT
AND ASH CONTENTS OF KUBBA (%)
Treatment

Moisture

Protein

Fat

Ash

0 kGy

52.73 ± 0.43b*

9.88 ± 0.75b

12.16 ± 0.10b

1.93 ± 0.06b

2 kGy

51.09 ± 1.52ab

9.60 ± 0.47ab

12.09 ± 0.67b

1.86 ± 0.02a

4 kGy

50.53 ± 0.26a

9.67 ± 0.59ab

10.18 ± 0.40a

1.9 ± 0.04b

6 kGy

50.44 ± 1.24a

8.75 ± 0.38a

9.32 ± 0.53a

1.96 ± 0.01b

LSD

1.91

1.06

0.89

0.07

*

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.

250

AL-BACHIRTABLE 2. EFFECT OF IRRADIATION ON MICROBIAL LOAD
(ln CFU/g) OF KUBBA STORED AT 1–4°C
Storage period (weeks)
Dose (kGy)
0

1

2

3

0

2.96 ± 0.04a*

R**

R

R

2

2.20 ± 0.18ab

9.60 ± 0.47ab

R

R

4

1.71 ± 0.30b1.52 ± 0.45a

0.97 ± 0.851a

3.89 ± 0.01a6

0.93 ± 0.81b

0.87 ± 0.81a

1.00 ± 0.00a

2.15 ± 0.21b*

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.
**
R: rejected.

3.1.3. Chemical quality of irradiated kubba
Total acidity: Table 3 shows that immediately after treatment, all doses (2,4 and 6 kGy) had no effect on total acidity. After one week of storage, the total
acidity of the samples treated with 4 and 6 kGy was significantly (p < 0.05)
lower. Throughout storage periods, the total acidity of both irradiated and nonirradiated samples increased. The increase was higher in the control than in theirradiated samples.

TABLE 3.
EFFECT OF IRRADIATION ON TOTAL ACIDITY(% LACTIC ACID) OF KUBBA
Storage period (weeks)
Dose (kGy)
0

1

2

3

0

0.18 ± 0.01a*

0.317 ± 0.030a

R**

R

2

0.16 ± 0.01a

0.244 ± 0.024a

R

R

4

0.18 ± 0.00a

0.202 ± 0.031b

0.222 ± 0.054a

236 ± 0.052a

6

0.17 ± 0.02a

0.224 ± 0.009b

0.244 ± 0.036a

0.211 ± 0.005a

0.03

0.047

0.104

0.084

LSD
*

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.
**
R: rejected.

251

AL-BACHIR

VBN: There is an effect that irradiation treatments and storage time haveon the VBN values (Table 4). Immediately after treatment, the VBN values ofkubba samples treated with 2 and 4 kGy were significantly (p < 0.05) higher
than the controls, whereas after one week of storage, these values in samples
irradiated with 2, 4 and 6 kGy were significantly lower.
Lipid oxidation: The effects of gamma irradiation on lipid oxidation of
kubba were compared (Table 5). Immediately after treatment, the lipidoxidation values of samples were no different from the non-irradiated ones.
After one week of storage, the 4 and 6 kGy samples presented a significant(p < 0.05) increase in lipid oxidation. During storage, the lipid oxidation valuesof irradiated samples also increased.

TABLE 4. EFFECT OF IRRADIATION ON VBN OF KUBBA (ppm)
Dose (kGy)

Storage period (weeks)
0

1

2

3

0

*

76.0 ± 7.0a

119.0 ± 1.0aR

2

106.0 ± 5.0b62.3 ± 1.5b

R

R

4

138.0 ± 7.0c

77.0 ± 8.0cb

111.3 ± 1.5a

123.0 ± 11.0a675.7 ± 2.5a

72.3 ± 10.5bc

101.3 ± 7.5a

105.0 ± 5.0a

10.7

12.6

12.3

19.4

LSD

**

R

*

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.
**
R: rejected.

TABLE 5. EFFECT OF IRRADIATION ON LIPID PEROXIDE IN
KUBBA (g iodine/100 g fat)
Dose (kGy)

Storage period (weeks)
0

1

2

3

0

0.035 ± 0.001a*

0.042 ± 0.006a

R

2

0.038 ± 0.008a

0.043 ± 0.007a

R

R

4

0.045 ± 0.02a

0.055 ± 0.005b

0.064 ± 0.05a

0.065 ± 0.011a

6

0.038 ± 0.005a

0.060 ± 0.0002b

0.068 ± 0.02a

0.078 ± 0.023a

0.023

0.010

0.008

0.041

LSD
*

**

R

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.
**
R: rejected.

252

AL-BACHIRTABLE 6.
EFFECT OF IRRADIATION ON TASTE, TEXTURE,
COLOUR AND FLAVOUR OF KUBBA*
Dose (kGy)

Taste
**

Flavour

ColourTexture0

4.00 ± 0.95a

4.26 ± 0.97aa

4.27 ± 1.19a

3.83 ± 1.27a

2

4.00 ± 0.85a

4.26 ± 0.75a

4.46 ± 0.82a

3.83 ± 1.03a

4

4.08 ± 0.90a

4.08 ± 0.79a

4.64 ± 0.51a

4.33 ± 0.99a

6

4.08 ± 0.79a

3.83 ± 1.19a

4.27 ± 0.91a

4.25 ± 0.75a

0.72

0.78

0.77

0.84

LSD
*
**

Data represent a 5 point scale ranging from 1 (very bad) to 5 (very good).
Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.

3.1.4. Sensory quality of irradiated kubba
Table 6 indicates that taste, odour, colour and textural characteristics ofkubba samples were not affected by gamma irradiation treatment.
3.2. Results of the effect of gamma irradiation on borak
3.2.1. Borak characteristics
The mean characteristics of borak in this study were: fat (5.25 ± 0.60%),protein (8.06 ± 0.53%), ash (2.88 ± 0.27%) and moisture (39.03 ± 2.70%). The
water activity value for borak was 0.95 at 24°C and the pH was 6.03 ± 0.04.
Results of the proximate analysis of borak showed that although
irradiation affects the moisture, protein and fat contents and pH, the increase
was not significant.
3.2.2. Microbiological quality of irradiated borak
Results of the microbial assessment of borak before and after irradiation
are presented in Table 8. It was found that before irradiation, the samples
presented TBC, total coliform and yeast values in the order of 106, 104 and
103 CFU/g, respectively. Irradiation with 2, 4 and 6 kGy of gamma irradiation
significantly (p > 0.05) reduced TBC, total coliform and yeast content. The
reduction was about 2, 4 and 6 log cycles for 2, 4 and 6 kGy, respectively. A doseof 6 kGy reduced the microbial load (TBC, total coliform and yeast) below the253AL-BACHIRTABLE 7. EFFECT OF GAMMA IRRADIATION ON MOISTURE,
PROTEIN, FAT AND ASH CONTENTS OF BORAK (%)
Dose (kGy)

Moisture

Protein

Fat

Ash

pH

0

39.03 ± 2.70

8.06 ± 0.53

5.25 ± 0.60

2.88 ± 0.27

6.03 ± 0.04

245.87 ± 7.72

11.48 ± 0.13

6.36 ± 0.65

2.89 ± 0.80

5.93 ± 0.01

441.11 ± 0.82

12.15 ± 0.12

6.38 ± 0.98

2.96 ± 0.08

5.97 ± 0.05

2.90 ± 0.12

5.87 ± 0.8

0.30

0.061

6

43.93 ± 2.94

11.46 ± 0.16

5.85 ± 0.51a

8.23

4.96

1.33

LSD
*

*

Values within a column followed by the same letters are not significantly different at
p < 0.05 significance level.

TABLE 8. EFFECT OF IRRADIATION ON MICROBIOLOGICALQUALITY OF BORAK STORED AT 1–4°C
Dose
(kGy)

Storage period (weeks)
0

1

2

3

5

6

Ra

R

R

R

R

TBC (ln CFU/g)
0

6.17 ± 0.10

24.08 ± 0.08

6.72 ± 0.29

5.35 ± 0.17

R

R

R

4

2.05 ± 1.38

6.18 ± 0.42

5.35 ± 0.17

5.88 ± 0.27

R

R

6

<1

3.1 ± 0.66

1.93 ± 1.42

3.45 ± 0.45

6.61 ± 0.40

TBC (ln CFU/g)
04.14 ± 0.05

6.50 ± 0.10

R

R

R

R

2

2.57 ± 0.58

6.18 ± 0 .42

R

R

R

R

4

<1

4.78 ± 0.006

5.62 ± 0.07

4.54 ± 0.22

R

R

6

<1

<1

3.34 ± 0.11

<12.74 ± 0.30

5.25 ± 0.7

8.90 ± 0.25

R

R

R

R

R

R

R

R

TBC (ln CFU/g)0

3.32 ± 0.13

2

<1

4

<1

4.25 ± 1.03

4.67 ± 0.08

4.70 ± 0.14

R

R

6

<1

3.15 ± 1.24

4.10 ± 0.36

3.89 ± 0.15

4.83 ± 0.40

5.97 ± 0.07a

R: rejected.

254

AL-BACHIR

accepted limit. Therefore, it was concluded that 6 kGy should be used for
future studies.
The radiation doses required to reduce the microbial loads by one log
cycle (D10 value) in Borak were 0.46 and 0.51 kGy for Salmonella and E. coli,
respectively.
3.2.3. Chemical quality of irradiated borak
Total acidity: Table 9 shows that, immediately after irradiation treatment,
the samples did not present changes in the total acidity, indicating that very few
hydrolysis reactions occurred owing to irradiation treatment. After one weekof storage, samples treated with 4 and 6 kGy presented a significant (p < 0.05)
low total acidity. However, these values, both irradiated and non-irradiatedsamples, increased during the storage period.
VBN: Irradiation treatment and storage affected the VBN values(Table 4). Immediately after treatment (4 and 6 kGy), the VBN was significantly (p < 0.05) lower than in the controls. However, after one week ofstorage, there were no significant (p < 0.05) differences between treatments.
Throughout the storage periods, the VBN concentration in the controls andsamples irradiated with 2 kGy decreased, whereas the VBN of borak irradiatedwith 6 kGy increased.
Lipid oxidation: Immediately after treatment and one week of storage,
the lipid oxidation values of irradiated samples were no different than those of
non-irradiated controls. However, these values decreased during storage. Thisparameter, being a measure of rancidity, which is important for both thesensory and the nutritional points of view, would have been expected toincrease in fat-containing products after irradiation treatment, especially at thehigher doses employed. The data for this are not shown.
3.2.4. Sensory quality of irradiated borak
Sensory data presented in Table 10 indicate that taste, odour, colour andtextural characteristics of borak were initially unaffected by gamma irradiation
treatment. Sensory evaluation scores were essentially the same for both
irradiated and non-irradiated samples.

255

256

0

0.25 ± 0.006

0.26 ± 0.05

46

0.13 ± 0.03

0.16 ± 0.02

4

6

a

R: rejected.

0.05

0.16 ± 0.03

2LSD

0.15 ± 0.02

0Liquid peroxide (g iodine/100g fat)

67.79

106.77 ± 9.16

6

LSD

209.14 ± 43.14

137.52 ± 3.4

24

251.47 ± 56.82

0

VBN (ppm)

0.091

0.34 ± 0.06

2LSD

0.28 ± 0.056

0Total acidity (% lactic acid)

Dose
(kGy)

0.1

0.11 ± 0.04

0.13 ± 0.08

0.08 ± 0.06

0.07 ± 0.01

46.76

146.63 ± 16.43

173.15 ± 7.06

142.23 ± 16.06

126.84 ± 43.47

18.83

26.53 ± 0.81

25.64 ± 2.60

46.22 ± 10.03

57.88 ± 17.09

1

0.026

0.083 ± 0.006

0.052 ± 0.02

R

R

45.72

239.30 ± 28.35

151.39 ± 0.39

R

R

34.89

44.47 ± 17.69

39.55 ± 12.69

R

Ra

2

0.075

0.18 ± 0.05

0.17 ± 0.07

R

R

28.03

238.52 ± 11.21

234.46 ± 13.47

R

R

16.7

41.86 ± 9.52

45.04 ± 4.24

R

R

3

Storage period (weeks)

0.41 ± 0.07

R

R

R

156.19 ± 7.92

R

R

R

26.3 ± 2.84

R

R

R

5

0.0076 ± 0.00365

R

R

R

150.66 ± 8.09

R

R

R

27.09 ± 8.87

R

R

R

6

TABLE 9. EFFECT OF IRRADIATION ON TOTAL ACIDITY, pH VALUE AND VBN OF BORAK STORED AT 1–4°C

AL-BACHIRAL-BACHIRTABLE 10. EFFECT OF IRRADIATION ON TASTE, TEXTURE,
COLOUR AND FLAVOUR OF BORAKa
Dose (kGy)

TextureFlavour

ColourTaste

03.82 ± 1.02

3.58 ± 1.36

3.77 ± 1.11

3.50 ± 1.27

2

3.35 ± 1.16

3.50 ± 1.48

3.27 ± 1.15

3.23 ± 1.24

4

3.58 ± 1.07

3.77 ± 1.28

3.27 ± 1.43

3.35 ± 1.20

6

3.85 ± 0.9

3.58 ± 1.39

3.27 ± 1.43

3.46 ± 1.42

0.57

0.76

0.65

0.73

LSD
a

Data represent a 5 point scale ranging from 1 (very bad) to 5 (very good).

TABLE 11. EFFECT OF IRRADIATION ON MOISTURE, PROTEIN,FAT AND ASH CONTENTS OF CHEESE BORAK (%)
Dose (kGy)

Moisture

Protein

Fat

Ash

0

44.50 ± 1.34

11.15 ± 0.78

8.62 ± 2.06

1.60 ± 0.26

243.50 ± 0.72

11.56 ± 0.12

8.77 ± 1.77

1.10 ± 0.21

445.10 ± 1.64

10.35 ± 0.34

9.18 ± 1.12

1.58 ± 0.23

645.19 ± 1.32

10.17 ± 0.70

9.35 ± 1.35

1.45 ± 0.10

LSD

2.36

1.81

3.05

0.39

3.3. Results of the effect of gamma irradiation on cheese borak
3.3.1. Cheese borak characteristics
The mean characteristics of cheese borak in this study were: fat(8.62 ± 2.06%), protein (11.15 ± 0.78%), ash (1.60 ± 0.26%) and moisture(44.50 ± 1.34%). The water activity value for cheese borak was 0.92 at 24°C andthe pH was 6.37 ± 0.04. Results of the proximate analysis of cheese borak
showed that irradiation doses had no effect on moisture, protein or fat contents(Table 11).
3.3.2. Microbiological quality of irradiated cheese borak
The results of the microbiological analysis of cheese borak before andafter irradiation are given in Table 12. It shows that the non-irradiated, tested
cheese borak recorded TBC, total coliform and yeast in the order of 107, 105

257

258
0

4.38 ± 0.09

3.46 ± 0.33
<1

2

4

6

2.57 ± 0.58
<1
<1

2

4

6

2.75 ± 0.30
<1

4

6

R: rejected.

3.08 ± 0.04

2a4.62 ± 0.16

0Total yeast load (ln CFU/g)

5.06 ± 0.21

0Total coliform load (ln CFU/g)

7.16 ± 0.24

0Total microbial load (ln CFU/g)

Dose (kGy)<1

4.74 ± 0.57

5.96 ± 0.59

R

<1

3.82 ± 0.14

4.19 ± 0.13

R

<1

4.94 ± 0.82

6.45 ± 0.39

Ra

1

4.84 ± 0.36

R

R

R

<1

R

R

R

<1

R

R

R

2

5.55 ± 0.65

R

R

R

<1

R

R

R

<1

R

R

R

3

Storage period (weeks)

5.24 ± 1.17

R

R

R

<1

R

R

R

<1

R

R

R

4

6.55 ± 0.6

R

R

R

<1

R

R

R

<1

R

R

R

5

6.84 ± 0.07

<1

R

R

R

<1

R

R

R

6

TABLE 12. EFFECT OF IRRADIATION ON MICROBIOLOGICAL QUALITY OF CHEESE BORAK STORED
AT 1–4°C

AL-BACHIRAL-BACHIR

and 104 CFU/g, respectively. Irradiation with 2, 4 and 6 kGy of gamma
irradiation significantly (p < 0.05) reduced TBC, total coliform and yeast in thecheese borak compared with the non-irradiated control. Irradiation with 2, 4
and 6 kGy reduced the TBC by about 2, 4 and 6 log cycles, respectively.
The radiation doses required to reduce the microbial loads by one log
cycle (D10 value) were 0.30 and 0.50 kGy for Salmonella spp. and E. coli,
respectively.
3.3.3. Chemical quality of irradiated cheese borak
Total acidity and pH: The total acidity of cheese borak samples arepresented in Table 13. Immediately after treatment (2 and 4 kGy), the total
acidity was similar for control and irradiated samples. After one week ofstorage the irradiated samples presented a significantly (p < 0.05) lower
activity. These changes are reflected by the pH values.
VBN: The measurements of VBN were performed at the beginning and atweekly intervals for up to 6 weeks of storage. Data are presented in Table 13. It
can be seen that immediately after treatment, the values of VBN in samples
irradiated with 4 and 6 kGy were significantly (p < 0.05) lower than the control
samples. Throughout the storage, the VBN values increased. Indeed, after one
week of storage, the value of VBN in cheese borak irradiated with 2, 4 and6 kGy was significantly (p < 0.05) higher than the control samples.
3.3.4. Sensory quality of irradiated cheese borak
Sensory testing (Table 14) showed that the taste, odour, colour andtextural characteristics of cheese borak were initially unaffected by gamma
irradiation. Sensory evaluation scores given by panellists were basically thesame for both irradiated and non-irradiated samples. A correlation between
sensory evaluation and chemical parameters was observed in relation toirradiated cheese borak.
3.4. Results of the effect of gamma irradiation on sheesh tawoq
3.4.1. Sheesh tawoq characteristics
The mean characteristics of sheesh tawoq in this study were: fat(9.84 ± 0.65%), protein (23.82 ± 1.13%), ash (1.78 ± 0.20%) and moisture(74.11 ± 0.49%), and the pH was 4.98 ± 0.25. Results of the proximate analysisof sheesh tawoq showed that irradiation doses had no effect on the moisture,protein and fat contents (Table 15).

259

260
0

0.10 ± 0.02

0.09 ± 0.01

46

6.37 ± 0.04

6.39 ± 0.06

46

28.40 ± 3.67

23.29 ± 1.63

4

6

R: rejected.

33.57 ± 0.39

2a32.28 ± 2.50

0

VBN (ppm)

0.08

6.43 ± 0.01

2

LSD

6.37 ± 0.4

0

pH

0.03

0.12 ± 0.02

2LSD

0.12 ± 0.01

0Total acidity (% lactic acid)

Dose (kGy)

88.44 ± 20.94

67.45 ± 4.64

58.95 ± 16.41

33.05 ± 9 9.84

0.33

6.37 ± 0.04

6.02 ± 0.14

5.86 ± 0.23

4.72 ± 0.22

0.19

0.19 ± 0.04

0.25 ± 0.03

0.24 ± 0.03

0.57 ± 0.19

172.57 ± 5.25

41.84 ± 9.33

R

R

0.12

6.34 ± 0.08

5.75 ± 0.09

R

R

0.03

0.15 ± 0.01

0.19 ± 0.03

R

Ra

2

104.75 ± 0.03

R

R

R

6.30 ± 0.02

R

R

R

16.7

0.20 ± 0.03

R

R

R

3

R

R

R

6.30 ± 0.02

R

R

R

0.24 ± 0.09

R

R

R

4

107.48 ± 1.01

Storage period (weeks)

100.67 ± 7.82

R

R

R

5.97 ± 0.07

R

R

R

0.25 ± 0.02

R

R

R

5

151.91 ± 0.04

5.58 ± 0.27

R

R

R

0.29 ± 0.02

R

R

R

6

TABLE 13. EFFECT OF IRRADIATION ON TOTAL ACIDITY, pH VALUE AND VBN OF CHEESE BORAKSTORED AT 1–4°C

AL-BACHIRAL-BACHIRTABLE 14. EFFECT OF IRRADIATION ON TASTE, TEXTURE,
COLOUR AND FLAVOUR OF CHEESE BORAKa
Dose (kGy)

Taste

Texture

Color

Taste

0

3.67 ± 1.13

3.79 ± 1.11

4.44 ± 0.92

3.72 ± 1.13

2

3.78 ± 1.00

3.83 ± 0.86

4.33 ± 0.84

3.78 ± 0.73

43.50 ± 1.15

3.56 ± 1.20

4.17 ± 1.04

3.28 ± 1.27

6

3.67 ± 0.91

3.33 ± 1.09

4.44 ± 0.71

3.28 ± 1.30

0.74

0.71

0.59

0.76

LSD
a

Data represent a 5 point scale ranging from 1 (very bad) to 5 (very good).

TABLE 15. EFFECT OF IRRADIATION ON MOISTURE, PROTEIN,FAT AND ASH CONTENTS OF SHEESH TAWOQ (%)
Dose
(kGy)

Moisture

Protein

Fat

Ash

pH

0

74.11 ± 0.49

23.82 ± 1.13

9.84 ± 0.65

1.78 ± 0.2

4.98 ± 0.25

273.44 ± 1.11

23.16 ± 0.45

8.55 ± 1.69

2.02 ± 0.13

5.22 ± 0.05

471.12 ± 1.47

25.10 ± 0.06

8.80 ± 0.17

1.47 ± 0.44

5.11 ± 0.37

673.93 ± 0.48

26.51 ± 0.13

11.15 ± 0.97

1.82 ± 0.21

4.81 ± 0.10

1.85

1.15

1.88

0.51

0.43

LSD

3.4.2. Microbiological quality of irradiated sheesh tawoq
The results of the microbiological analysis of sheesh tawoq before andafter irradiation are given in Table 16. It shows that the non-irradiated sample
recorded TBC, total coliform and yeast values of 104, 102 and 102 CFU/g,
respectively. Irradiation with 2, 4 and 6 kGy of gamma irradiation significantly(p < 0.05) reduced the microbial load in the sheesh tawoq compared with thecontrol samples.
The radiation doses required to reduce the microbial loads by one log
cycle (D10) in sheesh tawoq were 0.44 and 0.39 kGy for Salmonella spp. andE. coli, respectively.

261

262

3.88 ± 0.03

2.21 ± 0.18
<1

2

4

6

<1

6

<1
<1

4

6

R: rejected.

2.00 ± 0.00

2a2.71 ± 0.05

0Total yeast load (ln CFU/g)

<1
<1

2

4

2.33 ± 0.02

0Total coliform load (ln CFU/g)

4.76 ± 0.03

0

0

Dose
(kGy)

<1

2.58 ± 0.03

3.69 ± 0.08

5.74 ± 0.03

<1

<1

<1

2.66 ± 0.04

<1

2.91 ± 0.07

3.49 ± 0.08

4.76 ± 0.03

4<1

3.91 ± 0.02

5.52 ± 0.06

6.60 ± 0.03

<1

<1

<1

3.49 ± 0.17

<12.73 ± 0.03

3.45 ± 0.49

4.76 ± 0.03

8
R

<1

4.28 ± 0.16

R

R

<1

<1

R

R

<1

2.62 ± 0.25

<1

4.42 ± 0.23

R

R

<1

<1

R

R

<1

3.80 ± 0.02

R

Ra
R

16

12

Storage period (weeks)<1

4.57 ± 0.12

R

R

<1

<1

R

R

<1

2.68 ± 0.10

R

R

20

TABLE 16. EFFECT OF IRRADIATION ON MICROBIOLOGICAL QUALITY OF SHEESH TAWOQ STORED
AT 1–4°C

AL-BACHIRAL-BACHIR

3.4.3. Chemical quality of irradiated sheesh tawoq
Total acidity and pH: The total acidity values are presented in Table 17.
Immediately after treatment (2 and 4 kGy) there was no effect on thisparameter, but during storage, the total acidity of non-irradiated samples
increased. After 12 and 16 weeks of storage, 2, 4 and 6 kGy doses of gamma
irradiation significantly (p < 0.05) decreased the total acidity.
The pH of sheesh tawoq was 4.98. Table 17 shows that the irradiation
treatment had no effect on pH.
VBN: The measurements of VBN were performed at the beginning and at
monthly intervals for up to 5 months of storage. Data presented in Table 17
indicate that immediately after treatment, the values of VBN of sheesh tawoq
irradiated with 6 kGy doses of gamma irradiation were significantly (p < 0.05)
higher than those of the control. After 4, 8, 12, 16 and 20 weeks of storage, thevalues of VBN of sheesh tawoq irradiated with 2, 4 and 6 kGy doses weresignificantly (p < 0.05) lower than those of the control.
3.4.4. Sensory quality of irradiated sheesh tawoq
Sensory evaluation (Table 18) showed that the taste, odour, colour andtextural characteristics of sheesh tawoq were initially unaffected by gamma
irradiation. Sensory evaluation scores were basically the same for both
irradiated and non-irradiated samples.

4.

DISCUSSION

Bognar [21] carried out a detailed study of the nutritive content of avariety of commercially prepared chilled, frozen, sterilized and fresh readymeals packaged into multiportion trays and it was found that on the day after
preparation, there were no significant differences in the protein, fat and carbohydrate contents of the meals. Results of the proximate analysis showed that in
the current studies, the irradiation doses applied had no effect on moisture,protein and fat of borak, cheese borak and sheesh tawoq.
A dose of 2 kGy was not effective in extending the shelf life of kubba.
A dose of 2 kGy was, however, beneficial in improving the microbial qualityof chilled meat products, including roast beef and ground beef patties[1, 23–26].
However, other authors have found that doses of 4 and 6 kGy reduced
the microbial load and improved the shelf life of kubba, borak, cheese borak
and sheesh tawoq, which agrees with the findings reported by Desmonts et al.

263

264

0

2.68 ± 0.25

3.69 ± 0.16

6

5.11 ± 0.37

4.81 ± 0.10

46

520.15 ± 29.75

622.79 ± 11.93

4

6

a

R: rejected.

38.96

550.1 ± 17.1

2

LSD

543.52 ± 19.84

0

VBN (ppm)

0.43

5.22 ± 0.05

2LSD

4.98 ± 0.25

0

pH

0.03

2.88 ± 0.24

2

4

LSD

2.9 ± 0.21

0Total acidity (% lactic acid)

Dose
(kGy)

122.1

724.22 ± 14.86

671.92 ± 3.37

780.62 ± 106.31

1049.72 ± 72.62

0.33

4.89 ± 0.22

4.69 ± 0.03

4.86 ± 0.11

4.60 ± 0.25

0.19

3.3 ± 0.31

3.97 ± 0.18

4.36 ± 2.7

4.18 ± 10.56

4

499.28691.89 ± 33.34

821.22 ± 80.22

1450.48 ± 353.1

2029.1 ± 386.1

0.34

4.79 ± 0.03

4.86 ± 0.07

4.97 ± 0.21

4.95 ± 0.28

0.03

3.15 ± 0.04

3.39 ± 0.33

3.17 ± 0.33

3.93 ± 0.17

8

359.6

746.01 ± 104.38

804.6 ± 33.99

R

R

0.38

4.73 ± 0.39

4.85 ± 0.07

R

R

16.7

3.53 ± 0.34

3.65 ± 0.24

R

Ra

12

Storage period (weeks)

751.6

789.1 ± 43.49

929.97 ± 95.04

R

R

0.38

4.80 ± 0.04

4.93 ± 0.35

RR

3.27 ± 0.1

3.52 ± 0.5

R

R

16

150.94761.82 ± 95.08

694.86 ± 70.20

R

R

0.75

4.74 ± 0.1

4.76 ± 0.13

RR

3.02 ± 0.09

2.97 ± 0.05

R

R

20

TABLE 17. EFFECT OF IRRADIATION ON TOTAL ACIDITY, pH VALUE AND VBN OF CHEESE SHEESHTAWOQ AT 1–4°C

AL-BACHIRAL-BACHIRTABLE 18. EFFECT OF IRRADIATION ON TASTE, TEXTURE,
COLOUR AND FLAVOUR OF SHEESH TAWOQa
Dose (kGy)

TextureFlavour

ColourTaste

0

3.8 ± 0.89

3.83 ± 0.83

3.67 ± 1.1

3.50 ± 1.27

2

4.03 ± 0.96

4.03 ± 0.81

3.80 ± 1

3.23 ± 1.24

4

3.33 ± 0.92

3.47 ± 1.01

3.33 ± 0.71

3.35 ± 1.20

6

4.10 ± 1.9

3.60 ± 0.81

3.67 ± 0.71

3.46 ± 1.42

0.64

0.45

0.45

0.48

LSD
a

Data represent a 5 point scale ranging from 1 (very bad) to 5 (very good).

[27]. In contrast, salmon patties irradiated at 6 kGy had a shelf life of 23 d at
4°C. Also, irradiation with 4 or 6 kGy and storage under refrigeration (5°C)
increased the shelf life of corned beef [28] and chicken [29] from 10 d to 28 d.
Control samples of borak and cheese borak exceeded the limit of 107/g
TBC [15] after one week of storage at 1–4°C. Samples irradiated at 6 kGy,
however, remained acceptable after 6 weeks of storage at 1–4°C. These results
are in agreement with the results of previous studies which indicated that 6 kGy
was effective in extending the shelf life of precooked dishes [27], kebabs [30]and salmon patties [28].
Control samples of sheesh tawoq exceeded the limit of 107/g TBC [15]after 16 weeks of storage at 1–4°C. Samples irradiated at 2, 4 or 6 kGy,
however, remained acceptable after 20 weeks of storage at 1–4°C.
Borak and cheese borak had high initial microbial numbers (106–710 CFU/g). A dose of 2 kGy had an effect in reducing the microbial counts ofthese meals and a slight effect in extending shelf life. Farkas et al. [23] and Paulet al. [24] found that irradiation of chilled meat products with a 2 kGy dose
reduced the total viable cell counts and extended the microbiological shelf lifeof chilled meat. A dose of 2 kGy was beneficial in improving the microbial
quality of the roast beef [1], meat as prepared food [25] and ground beef patties[26].
The radiation doses required to reduce the microbial loads by one log
cycle (D10) in borak, cheese borak and sheesh tawoq were estimated. Thayer[31] reported that the D10 values of E. coli and Salmonella spp. in ground beef
at 0–4°C were 0.39 and 0.62 kGy, respectively. Mallett et al. [32] found that theD10 values of E. coli and Salmonella spp. in ground beef were 370 and 510 Gy,
respectively, in oyster mantle fluid. The D10 values of Salmonella were 0.57,
0.42, 0.59, 0.46 and 0.49 Gy in ready prepared meals of roast beef, gravy, cauliflower, roast potatoes and mashed potatoes respectively [1]. Irradiation of265

AL-BACHIR

fresh chicken [33] and meat products [24] with a dose of 2.5 kGy seems to beeffective in controlling Salmonella spp. contamination. However, there areindications that doses higher than 2.5 kGy may be required for complete
elimination of Salmonella spp. in chicken [34].
The results of the effect of gamma irradiation on the total acidity of
Syrian prepared meals (kubba, borak and sheesh tawoq) are in agreement withKing et al. [22] who reported that no differences were found for the free fatty
acids on day 0 and after 14 d of storage between the non-irradiated andirradiated beef, trout and pork at doses up to 3.5 kGy. Other authors [24, 35],
however, indicated that the free fatty acid content in meat decreased after
irradiation. The amount of lactic acid in irradiated nham was found to be lower
than that in the non-irradiated samples after the same period of storage [36].
The values of lipid oxidation in kubba and borak indicate that these were
within the acceptable limit.
The oxidative stability of fats in vacuum packaged products was reported
by Taub et al. [37] who indicated that irradiation removed oxygen thatremained in the head space or meat tissue of the vacuum packaged product,thus retarding autoxidation. On the other hand, Peter et al. [26] reported thatno difference in lipid oxidation in ground beef patties was found within the firstweek of storage, regardless of packaging atmosphere. Paul et al. [24] also
reported that meat treated with antioxidants prior to irradiation had lower
values than untreated irradiated counterparts.
Luchsinger et al. [38] found that optimum packaging conditions cancontrol rancidity changes in boneless chops, thereby enabling irradiation to bea useful intervention technology.
The VBN value, which is regarded as one of the standard chemical indicesof freshness of meat, was assessed because the Syrian prepared meals (kubba,
borak and sheesh tawoq) contained meat as the major component. After one
week, irradiation resulted in a definite improvement in the keeping quality of
the kubba and borak, as evidenced by their low VBN values compared withthose of the control samples. The free radicals generated by irradiation can
destroy antioxidants in muscle, reduce storability and increase total volatilecompounds and off flavour production in meat [39, 40]. Dietary dl-α-tocopheryl
acetate at >200 IU/kg decreased lipid oxidation and reduced the total volatilityof raw turkey patties after 7 d of storage [41].
Many investigators have studied the effects of gamma irradiation on thesensory qualities of chilled ready meals. Most of them found that irradiation
had no detrimental effects on the sensory quality of meals [1, 36, 38, 42].
Stevenson et al. [43] reported on a consumer trial carried out to assess theacceptability of a chilled irradiated (2 kGy) and non-irradiated ready meal.
One hundred and seven consumers participated in this trial and found the266

AL-BACHIR

irradiated meal to be “moderately to very acceptable” and not significantly
different from the non-irradiated meal. It therefore appears that untrained
consumers may not be able to detect differences noted by trained panellists.
Some studies reported sensory improvement of irradiated ready meals [27, 44,45], whereas other studies revealed that the sensory qualities of ready meals are
impaired when subjected to gamma irradiation. Sensory profiling techniques,using a trained panel of assessors, showed significant differences between the
non-irradiated and irradiated chilled ready meals [1, 11]. Kilcast [46] reported
that the production of off flavours was a limiting factor in the acceptability of arange of hot and cold irradiated (1–4 kGy) ready meals. Lipid oxidation, which
often occurs in uncured cooked irradiated products, also contributes to theflavour changes in irradiated meat products [26, 41].

5.

CONCLUSION

From the results of this research it can be concluded that an irradiationdose of 6 kGy can inactivate all spoilage and pathogenic microorganisms inborak and cheese borak. The shelf life of locally prepared meals (kubba, borak
and cheese borak) stored at 1–4°C was increased to more than 3 weeks, and to
6 weeks using doses of 6 kGy, as opposed to less than one week for controls forkubba and borak. Use of gamma irradiation has resulted in the production of
locally prepared meals that are microbiologically safe without incurring any
changes in their nutritional values. All samples of locally prepared meals wereof acceptable sensory quality, even after the highest dose of 6 kGy was applied.

ACKNOWLEDGEMENTS
The author wishes to express deep appreciation to the Director Generalof AECS. Partial support of this work by the IAEA under research contract
no. 11910 is gratefully acknowledged. Additional financial support was
obtained from the Syrian Atomic Energy Commission.

267

AL-BACHIR

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[27] DESMONTS, M.-H., PIERRAT, N., INGERSHEIM, A., STRASSER, A., “Useof irradiation in combination with other treatments to improve the quality of
precooked meals”, Combination Processes for Food Irradiation (Proc. FAO/
IAEA Mtg Pretoria, 1995), IAEA, Vienna (1998) 201–221.
[28] SALLAM, Y.I., EL-MAGOLI, S.B.M., MOHAMED, H.H., Irradiation of refrigerated corned beef for shelf-life extention, Egypyian Journal of Radiation
Sciences and Applications. 14 (1) (2000) 79–94.
[29] SPOTO, M.H.F., et al., Gamma irradiation in the control of pathogenic bacteria inrefrigerated ground chicken meat. Scientia Agricola. 57 (3) (2000) 389–394.
[30] CHOUDHURY, N., et al., “Preservation of semi-perishable food and development of convenience food using a combination of irradiation and other physicochemical treatments”, Combination Processes for Food Irradiation (Proc. FAO/
IAEA Mtg Pretoria, 1995), IAEA, Vienna (1998) 77–95.
[31] THAYER, D.W., “Development of predictive models for the effects of gamma
radiation, irradiation temperature, pH, and modified atmosphere packaging on
Bacillus cereus, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella
typhimurium and Staphylococus aureus”, Radiation Processing for Safe, Shelfstable and Ready-to-eat Food, IAEA-TECDOC-1337, IAEA, Vienna (2003)
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Martin, R.E., Eds). CRC PRESS, Boca Raton, FL. (1991) 247–258.
LACROIX, M., et al., “Effect of the rate and dose rate of irradiation on thequality of mushrooms, shrimps and marinated poultry”, Combination Processes
for Food Irradiation (Proc. FAO/IAEA Mtg Pretoria, 1995), IAEA, Vienna(1998) 41–51.
KATTA, S.R., RAO, D.R., SUNKI, G.R., CHAWAN, C.B., Effect of irradiation onwhole chicken carcass bacterial load and fatty acids, J. Food Sci. 56, (1991) 371–372.
KANATT, S.R., PAUL, P., DSOUZA, S.F., THOMAS, P., Effect of gamma irradiation on the lipid peroxidation in chicken, lamb and buffalo meat during chilledstorage. Journal of Food Safety, 17 (4) (1997) 283–294.
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of Nham (fermented pork sausage) by gamma irradiation. Final report, Available
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Effect of irradiation on meat proteins. Food Technol., 33, (5), (1979) 184–193.
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chops, Abstract 38-7, Annual Meeting of the Inst. of Food Technologists, New
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THAYER, D.W., FOX, Jr., J.B., LAKRITZ, L., Effects of ionizing radiation treatments on the microbiological, nutritional, and structural quality of meats,
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AHN, D.U., et al., Dietary vitamin E affects lipid oxidation and total volatiles ofirradiated raw turkey meat, Journal of Food Science. 62 (5) (1997) 954–958.
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shelf-life extension and for improving its bacterial quality, Office of atomic energy
for peace, Bangkok (Thailand), Proceedings of the 6th nuclear science and technology conference Dec. (1996) 761 pp.
STEVENSON, M.H., STEWART, E.M., McATEER, N.J., A consumer trial toassess the acceptability of an irradiated chilled ready meal. Radiat. Phys. Chem.
46 (4–6) (1996) 785–788.
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sensory analysis of irradiated frozen or refrigerated chicken. Journal of Food
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KILCAST, D. Irradiation and combination treatments, Food control. 2 (1991) 6–8.

USE OF IRRADIATION TO IMPROVE THE SAFETY
AND QUALITY OF THAI PREPARED MEALS
A. NOOMHORM, T. KOOMSANIT, K. PUNGSAWAT,
T. THEAMHONG, W. SRISAWAS
School of Environment, Resource and Development,
Asian Institute of Technology,
Pathumthani
P. SIRISOONTARALAK
Department of Home Economics,
Srinakharinwirot University,
Bangkok
P. VONGSAWASDI
Department of Microbiology,
King Mongkut’s University of Technology Thonburi,
BangkokA. VITITTHEERANON
Office of Atoms for Peace,
BangkokThailand

Abstract
Gamma irradiation was applied to extend the shelf life of selected Thai prepared
meals, which comprised rice, meats and vegetables and which were kept under chilledconditions. For Thai spicy chicken basil rice (kao ka pao kai), cooked rice was preparedso as to obtain a harder texture and irradiated at 2 kGy. Three components (cookedchicken, sauce and blanched basil leaf) were separately packed and irradiated at 2 kGy
for chicken and sauce and 0.1 kGy for basil leaves. The shelf life of irradiated spicy
chicken (2 kGy) separately packed (>4 weeks) was much longer than the control sample(2 weeks), considering sensory quality. However, this dose was not enough to killentirely the inoculated Listeria monocytogenes in spicy cooked chicken. Likewise, there
is a need to preserve basil leaf, since it was microbiologically spoiled by the second weekof storage. For stir-fried rice noodle with dried shrimp (pad Thai), a dose of 4 kGy wasrecommended because the product was free from L. monocytogenes and Escherichia
coli, safe from microbial spoilage and had acceptable sensory quality. Irradiation at
4 kGy could extend the shelf life of chilled pad Thai to more than 4 weeks compared

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with a normal chilled ready meal, which has a shelf life of 5–7 d. For steamed sticky rice,
roasted chicken and papaya salad (kao neaw som tom), a dose of 3 kGy was enough tocontrol L. monocytogenes and E. coli during chilled storage. The product irradiated at
3 kGy and upwards remained microbiologically safe after 8 weeks of chilled storage
whereas the non-irradiated sample was spoiled after the second week. Panellists
accepted irradiated steamed sticky rice and roasted chicken, which kept under chilledconditions for 8 weeks, but they rejected irradiated papaya salad owing to the soft
texture and tainted taste.

1.

INTRODUCTION

Many traditional Thai dishes are popular in Thai restaurants all over theworld. Usually, they comprise herbs and spices with different types of meat andthese are supplemented with rice. Thais prefer to eat aromatic rice or highamylose rice, but for those who come from the northern and northeastern partsof Thailand, ‘sticky’ rice is popular. The rice noodle is also a popular
component in Thai cuisine. Rice noodle is cooked, added to soup containing
various meats or stir-fried with different kinds of sauces. In this study, three ofthe famous Thai cuisines with various components were selected owing to theirpotential in commercial production.
However, apart from the traditional style of cooking at home or serving
fresh in restaurants, there is increased consumption of prepared meals owing to
the change in the lifestyle of people in both developed and developing
countries. Such meals offer convenience and less preparation time. The meals
are marketed in developed countries either chilled or frozen. Storage in thefrozen state can extend the shelf life of prepared meals for several months, but
this method is costly and needs to maintain the temperature at freezing tomaintain the product’s shelf life. Under chilled conditions, it is relatively moreconvenient, with only the need for a refrigerator for distribution and therefore
easy for consumers to keep at home.
There is dynamic growth in the domestic market for chilled prepared
meals because of the growth of food services in supermarkets and convenience
stores. However, the shelf life for ready-to-eat chilled food, including chilled
prepared meals, is quite short and sometimes insufficient to meet market
requirements [1]. Furthermore, chilled foods, especially prepared and ready-toeat meals, have been implicated in a number of serious foodborne disease
outbreaks [2]. These were considered to be due to a new generation of refrigerated food [3], one which has partial processing to prevent normal spoilage
bacteria but which also enhances the growth of pathogens.

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Irradiation can provide the potential to improve the microbiologicalsafety and extend the shelf life of chilled prepared meals. It can be used alone
or combined with chilling. Using a combination of irradiation and chilling,frozen conditions can be replaced, resulting in energy savings and a lowering ofoperation costs. However, there is limited information about the application ofirradiation on chilled prepared meals with respect to their shelf life quality andsafety from foodborne pathogenic bacteria. Therefore, the study aims toinvestigate the possibility of using irradiation to extend shelf life and ensure themicrobiological safety of three selected Thai chilled prepared meals: Thai spicy
chicken and basil rice (kao ka pao ka), stir fried rice noodle with dried shrimp(pad Thai) and steamed sticky rice with roasted chicken and papaya salad (kaoneaw som tom).
To ensure their safety from pathogens, these prepared meals were artificially contaminated with pathogenic bacteria including Listeria monocytogenes,
Escherichia coli and Salmonella typhimurium. The radiation sensitivities ofthese bacteria were then determined, together with their survival after
irradiation and during chilled storage, to suggest optimum irradiation doses.
Apart from the microbial safety, the effects of irradiation on the products’
physicochemical quality were evaluated and this is interesting because theselected meals comprise starch (steamed aromatic rice, sticky rice or rice
noodle), protein (chicken or shrimp) and vegetables (basil leaf or papaya). The
qualities were determined after irradiation and during storage under chilledconditions to assess their shelf lives.

2.

REVIEWS

2.1. Microbiological contamination in chilled prepared meals
The US Food Safety and Food Inspection Service [1] provided
information on refrigeration and food safety, including data on storage times ofhome refrigerated foods. The examples include cooked egg dishes, prepared
salads, steaks or chops or roasts, soups and stews, and gravy and broth, whose
shelf lives are around 3–4, 3–5, 3–5, 3–4 and 1–2 d, respectively. Besides theshort shelf life, chilled foods are susceptible to foodborne disease outbreaks.
Bryan [2] reported that numerous microbiological hazards and risks areassociated with the preparation and storage of chilled foods in retail markets
and food service establishments. Psychrotropic pathogenic bacteria such as
Clostridium botulinum type E, L. monocytogenes, Yersinia enterocolitica andAeromonas hydrophila continue to multiply during cold, but not frozen,
storage. Microbiological spoilage occurs when the cold storage time exceeds

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the shelf life of a product. Certain prepared foods are implicated repeatedly as
vehicles in outbreaks of foodborne diseases. These include, in decreasing orderof risk, roast beef, turkey, chicken, ham, other pork products, Mexican stylefoods, Chinese foods (usually rice), potato salad, rice, chicken salad, pizza andbarbecue meat.
Chilled prepared meals were categorized by Corlett [3] as a newgeneration of refrigerated foods. Unlike traditional refrigerated foods, newgeneration products do not have a readily apparent preservation system.
Furthermore, many of these products may have an extended shelf life and be
packaged so as to inhibit ‘normal’ spoilage but which also enhances growth ofpathogens. Other risk characteristics associated with new generation refrigerated products are inadequate temperature control, an inadequate distribution system and partial processing which prevents the normal warning of
hazards by destruction of spoilage flora.
2.2. Radiation sensitivity of foodborne bacteria
Irradiation can damage and destroy most foodborne bacteria. Salmonella
and Listeria proved to be more resistant to irradiation than E. coli, Arcobacter,
Campylobacter, Yersinia and Staphylococcus [4–8].
2.2.1. L. monocytogenes
Among pathogenic bacteria, L. monocytogenes has the ability to growover a wide range of environmental conditions such as heat and cold (from 1.1
to 50°C), low water activity and acid conditions [9] and, more importantly, it isresistant to irradiation. L. monocytogenes is significantly more resistant toirradiation in meats than in culture media [10–16]. Neither the fat content ofmeat [6] nor the source of raw meat (beef, chicken, lamb, pork, turkey (breastor leg)) had a significant effect on D values for irradiation [8, 15]. However, theeffectiveness of a radiation dose in meat depended on cooking, the concentration of bacteria in the meat and the temperature during irradiation. When
added to raw turkey nuggets, L. monocytogenes was more susceptible toradiation than when added to cooked turkey nuggets [17]. Radiation resistancewas observed more at low temperatures [8, 13, 15]. With larger concentrationsof L. monocytogenes in meat, higher doses were required to destroy the cells[13, 18].
Several researchers demonstrated that L. monocytogenes can grow in thecold and surviving and damaged cells may begin to multiply if the irradiatedmeat is stored under refrigeration [16, 19]. Food additives such as salt, nitrites
and other compounds added to preserve meat have been found to enhance the274

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safety of irradiated foods as well as L. monocytogenes is more radiation
resistant in uncured pork than in ham [20]. These techniques may act byincreasing the effect of irradiation or by preventing the repair and growth ofdamaged and surviving cells. Among ready-to-eat meats, radiation resistance interms of D10 values were 2.5 kGy for bologna, roast beef and smoked turkey
and 3.0 kGy for frankfurters and ham. There was no difference between
smoked turkey added with or without lactate [9]. However, when sodium
diacetate and potassium lactate were added in beef bologna, radiation
resistance was observed less [21] although this was not affected by dextrose
concentration [22]. There was also a synergistic effect between pediocin andirradiation for inhibition of L. monocytogenes in frankfurters [23].
Some recommended doses to combat L. monocytogenes include:• 3 kGy for elimination of 103 cells/g in air packed frozen chicken [14];• 2.5 kGy to kill 104.1 cells/g in ground beef [6];• 2 kGy to destroy 104 cells/g in mechanically deboned chicken meat stored
at 2–4°C [11].
Similar observations were made for vegetables. Niemira et al. [24]reported that the radiation sensitivities of the two strains, L. monocytogenes(ATCC 49594) and Listeria innocua (ATCC 51742), were similar when they
were inoculated on endive. Type of vegetable (broccoli, corn, lima beans, peas,
cabbage, tomato, mung bean sprouts) had a significant effect on the irradiation
sensitivity of inoculated L. monocytogenes [25, 26]. Resistances increased withdecreasing temperatures [25], reflected in the D10 values ranging from 0.51–
0.61 kGy at –5°C to 0.77–0.92 kGy at –20°C.
It should be noted that various food additives and changes in processing
parameters may affect the effectiveness of a radiation dose and that any
surviving L. monocytogenes may grow to dangerous levels during storage at
refrigeration temperatures. However, there has been very little publishedresearch on the effects of irradiation on prepared meals related to L. monocytogenes contamination.
Clardy et al. [27] found D10 values ranged from 0.71 to 0.81 kGy for L.
monocytogenes in ready-to-eat ham and cheese sandwiches. Between theindividual components of ready to eat sandwiches, Sommers and Boyd [28]reported D values of 0.27–0.37 kGy in tortilla and cheese interfaces, 0.33–
0.41 kGy in cheese and turkey interfaces and 0.25–0.33 kGy in turkey andtortilla interfaces. Grant and Patterson [29] reported that radiation induced
heat sensitization of L. monocytogenes and reheating kills contaminating
pathogens in cooked, chilled roast beef and gravy.

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2.2.2. E. coli
E. coli contaminates food through poor sanitation. Prepared meals are
susceptible to this bacterium from many preparation methods. Radiation
resistance of E. coli was different among strains when tested in media broth.
Decreasing pH of the broth had relatively little effect on radiation resistance
whereas induction of acid resistance to this type of bacteria consistently
increased radiation resistance [30].
Many researchers studied radiation sensitivity of E. coli, especially an
outbreak strain of E. coli 0157:H7, in many kinds of food. It was confirmed that
not only in media but also in food did radiation sensitivity vary among strains.
Rajkowski et al. [31] reported that D10 values of non-vegetable and vegetable
isolated strains of E. coli 0157:H7 were 1.43 and 1.11 kGy, respectively. Niemira
et al. [32] found that relatively subtle differences in lettuce types could significantly influence the radiation sensitivity of E. coli 0157:H7.
The nature of food contaminated with the pathogen also contributed toradiation sensitivity of the bacteria. Jo et al. [33] studied inactivation of S.
typhimurium, E. coli, Staphylococcus aureus and Listeria ivanovii inoculated
into prepared seafood products for manufacturing kimbab, steamed rice rolledin dried seaweed, by gamma irradiation. The D10 values of these organisms
ranged from 0.23 to 0.62 kGy in imitation crab leg, 0.31–0.44 kGy in surimi gel
and 0.27–0.44 kGy in dried seaweed. Chawla et al. [34] reported D10 values ofE. coli in kwamegi, a traditional Korean semi-dried seafood, at 0.55 kGy.
Apart from strains and types of food, irradiation temperature also
affected the inactivation of E. coli 0157:H7. The resistance in ground beef wassignificantly higher at sub-zero temperatures than above freezing, showing in
D10 values for E. coli 0157:H7 in ground beef at 4 and –20°C of 0.39 and0.98 kGy, respectively [35].
2.2.3. S. typhimurium
Salmonella spp. was among the important pathogens contaminatingmeats. This bacterium was also proved to be resistant to irradiation. Irradiation
at a dose of 1 kGy eliminated Salmonella in raw meat samples sourced frombutchers [36]. When raw beef mixed with and without sauce was artificiallycontaminated with the pathogens and irradiated up to 1.5 kGy, D values werehigher at 0.37 and 0.55 kGy for S. typhimurium in raw meat with and withoutsauce than for Y. enterocolitica (0.043–0.080 and 0.10–0.21 kGy) and Campylobacter jejuni (0.08–0.11 and 0.14–0.16 kGy). A dose of 1 kGy is effective in
reducing Salmonella by approximately 1.3–2.7 log cycles [37]. Irradiation at
1.25 and 2.50 kGy could reduce bacterial levels by 2.23 and 3.44 log cycles,

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respectively, in mechanically deboned chicken meat. An insignificant change in
the amount of S. typhimurium was found during storage for 9 d at 5oC [38]. The
combined effect of gamma irradiation and heating on the destruction of
L. monocytogenes and S. typhimurium was also studied in cooked, chilled roast
beef and gravy [29].
2.2.4. Factors affecting radiation sensitivity
Niemira [39] studied the irradiation inactivation of four Salmonella
serotypes in orange juices with various turbidities. It was found that theserotype was the more significant factor determining radiation resistance thanturbidity or antioxidant power. Moreover, Niemira [39] reported that
Salmonella enteritidis sensitivity to gamma irradiation was also not strongly
influenced by the composition of formulated commercial orange juices in termsof the difference in pH, calcium concentration, juice composition andantioxidant power.
2.3. Application of irradiation for rice
Irradiation was introduced to paddy, brown and milled rice for the
purpose of killing insects. Despite the fact that irradiation effectively controls
insects, many studies reported the changes in rice quality either before or after
cooking, such as colour, flavour, odour, cooking time, water absorption,
viscosity, amylose content, oxidative rancidity, etc. Some studies recommended
that the dose not exceed 1 kGy [40–42] while others argued that with doses
above 1 kGy (1–5 kGy) milled rice was still accepted by consumers and thequality was not significantly changed [43–45]. However, there is limited
information on cooked rice irradiation.
2.4. Application of irradiation for processed meat and fishery products
Numerous studies have been made on the effectiveness of irradiation ineliminating spoilage bacteria and pathogens in fresh and processed meat.
Lacroix [46] determined if irradiation at a particular dose would be required toeliminate Salmonella completely on fresh poultry, combined withpretreatment. The results of sensory evaluation have shown significantly better
odour and flavour for the irradiated chicken at 5 kGy than for the control. For
cured meats, Shahidi et al. [47] reported that irradiation had no detrimental
effects on the colour or flavour of either nitrite or nitrite-free cured samples. Fu
et al. [7] showed there were no colour differences with respect to HunterLabvalues and visual evaluation scores between control and beefsteaks irradiated277

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at 1.5 kGy. However, an increase in redness due to irradiation has been statedfor various raw and cooked pork products [4, 48, 49]. The improvement in ham
colour by irradiation was also cited by Byun [50]. A dose of 5 kGy wasobserved to be as effective as the use of 200 ppm of sodium nitrite in providing
and maintaining the desired colour of the product for 30 d, although it
increased peroxidation of the product. However, the organoleptic quality of
the irradiated ham without added sodium nitrite was acceptable. Sommers etal. [21] reported little effect on lipid oxidation or colour of the control bologna
or bologna containing sodium diacetate and potassium lactate mixtures ateither 1.5 or 3.0 kGy. A radiation dose of 3 kGy prevented the proliferation of
L. monocytogenes and background microflora in bologna containing SDA-PL
over 8 weeks of storage at 9°C. However, Sommers and Fan [22] found that ahigh dextrose concentration in combination with gamma irradiation increased
lipid oxidation significantly. No growth of L. monocytogenes (inoculated at
105 CFU/g) was reported in ready-to-eat meats (frankfurters, ham, roast beef,bologna, smoked turkey) irradiated at 4.0 kGy stored at 4 and 10oC for
12 weeks. Survivors were observed for irradiated meats at 2.0 kGy stored at
10°C after the second week but it was not observed when stored at 4°C until thefifth week [9]. A combination treatment of vacuum–steam–vacuum andirradiation at 2.0 kGy did not cause significant changes in product structure,colour (redness) or lipid oxidation and resulted in an additive reduction of L.
innocua on ham [51]. There was also a synergistic effect between pediocin andirradiation (1.2 or 2.3 kGy) for inhibition of L .monocytogenes in frankfurters.
The treatments did not affect the sensory quality of the products [23].
For fresh seafood, Lacroix et al. [52] suggested a radiation dose of
2.5 kGy to eliminate pathogenic bacteria and increase the storage life ofthawed shrimp for 1 month at cold temperatures (4°C) without any effects toquality. For processed fishery products, Adulpichit [53] reported that an
irradiation dose of 4 kGy was more efficient in reducing the microbial load ofsemi-dried shrimps and shelf life could be extended to 7 weeks with respect toconsumer acceptability and microbial safety compared with 10 d for the nonirradiated product. Four pathogens (S. aureus, Bacillus cereus, S. typhimurium
and E. coli) inoculated in kwamegi, a traditional Korean semi-dried seafood,were eliminated by irradiation at 4 kGy. The product was safe during storage at–5 to 5°C for 4 weeks [34].
2.5. Application of irradiation for vegetables
Prakash et al. [54] studied the effects of 0.5 and 1.0 kGy gamma
irradiation on the microbial and sensory characteristics of diced celery
compared with conventional treatments such as acidification, blanching and

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chlorination. Irradiation at 1.0 kGy could eliminate inoculated L. monocytogenes and E. coli and could extend the microbiological and sensory shelf lifeof diced celery compared with controls or other conventional treatments.
Niemira et al. [25] studied the effect of irradiation on the quality of frozen
vegetables. At –20°C radiation doses sufficient to achieve a 5 log cycle killing(3.9–4.6 kGy) of L. monocytogenes caused significant softening of peas andbroccoli stems but not of corn or lima beans. Lower doses delivered at –5°C
(2.5–3.1 kGy) did not cause significant changes in texture in any vegetable.
Colour varied significantly among the dose–temperature combinations.
Niemira et al. [24] found that a dose of 0.84 kGy, equivalent to a 99.99%
reduction, suppressed L. monocytogenes throughout refrigerated storage.
Doses up to 1.0 kGy had no significant effect on the colour and texture ofendive leaf.
This was confirmed by Bari et al. [26], who reported the effective use of
low dose irradiation to eliminate L. monocytogenes in fresh and freshly cut
vegetables (broccoli, cabbage, tomatoes and mung bean sprouts). A dose of
1 kGy could reduce this pathogen by around 4.14–5.25 log CFU/g and theappearance, colour, texture, taste and overall acceptability did not undergo
significant changes after 7 d of irradiation during storage at 4°C. Niemira et al.
[32] also reported that doses of up to 0.5 kGy did not soften lettuce leaves.
Doses ranged from 0.12 to 0.14 kGy and from 0.10 to 0.34 kGy and these could
reduce the E. coli population by 90% when inoculated in lettuce leaf andhomogenized leaf suspension, respectively. Rajkowski et al. [31] suggested thata dose of up to 2 kGy could extend the shelf life of broccoli sprouts, but doses>2 kGy would have an adverse effect on the broccoli seed and decrease theyield of broccoli sprouts. Similar results were presented by Bari et al. [55].
Treated at 1.5 and 2.0 kGy, E. coli was significantly reduced in mung bean andradish sprouts. Total vitamin C content was gradually reduced but the colour,
firmness and overall visual quality of the tested sprouts was acceptable.
2.6. Application of irradiation for chilled prepared meals
Irradiation is known as an alternative means of extending the shelf life ofchilled food in either raw or cooked form. Combined with another preservation
method such as refrigeration, low dose irradiation can be applied to destroy
contaminating organisms. Because of the low dose, changes in the sensory
characteristics are small. Prepared meals ordinarily comprise two or more foodcomponents in one package and the use of irradiation for this type of productmay be different and more complicated.
For salads, which comprise various kinds of fruits and vegetables,
irradiation with doses to accomplish the intended purpose has resulted in

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softening associated with changes in pectic substances. For pico de gallo, which
is a cold Mexican style salad prepared by chopping and mixing fresh tomatoes,
onions and jalapeno peppers, Howard et al. [56] reported that the colour,
flavour, texture, odour and sensory attributes were not affected by radiation
treatment (1 kGy). The treatment decreased populations of aerobic mesophilic,heterofermentative and total lactic microflora during storage. The L-ascorbic
acid content declined 50% in response to gamma processing. Pectin solubility
was also affected by radiation treatment.
For composite prepared meals, the IAEA [57] studied irradiation ofmeals which consisted of roast pork, gravy, mixed vegetables and boiled
potatoes at doses of 1, 2 and 3 kGy. A dose of 2 kGy was found to be sufficient
to extend the microbiological shelf life of the meals by at least 7 d. The microbiological results (total bacteria counts) showed that irradiation at a dose of 2
or 3 kGy followed by storage at 3°C was most appropriate for achieving shelf
life extension. Reher et al. [58] studied the effectiveness of gamma irradiation(0.4, 0.8 and 3 kGy) on the microbial population, physical and chemical
attributes and sensory stability of a refrigerated Salisbury steak, mashedpotatoes and gravy meal packaged under a modified atmosphere. Irradiation
appears to be an effective means of reducing pathogen counts in ready-to-eat
meals without adverse effects on quality. The effectiveness of higher dose levels
in eliminating L. monocytogenes and reducing yeast and mould counts in all
meal components merits investigation. Clardy et al. [27] found that irradiation
at 3.9 kGy could reduce L. monocytogenes contaminated in frozen ham andcheese sandwiches by 5 log units and it decreased further during storage at 4°C.
Panellists could distinguish irradiated and non-irradiated products but thecomments on whether irradiation adversely affected sandwich quality weredivided. Lamb et al. [59] added that during refrigerated storage there was no
growth of S. aureus in contaminated sandwiches when irradiated at 5.9 kGy.
However, Sommers and Boyd [28] commented that the capability of irradiation
to reduce pathogen levels on the complex tortilla, cheese and luncheon
sandwiches was limited by the higher radiation resistance of L. monocytogenes
when inoculated onto the ready-to-eat turkey meat components. The growth of
S. typhimurium, E. coli, S. aureus and L. ivanovii inoculated into preparedseafood products for manufacturing kimbab, steamed rice rolled in dried
seaweed, was inhibited by irradiation. L. ivanovii was not detected after a
3 kGy treatment, but the other pathogens were undetected at 2 kGy [33].

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3.

MATERIALS AND METHODS

3.1. Preparation of irradiated Thai prepared meals
3.1.1. Spicy chicken basil rice (kao ka pao kai)
Thai aromatic milled rice (KDML 105) and skinless boneless chicken
breast and other ingredients such as vegetable oil, fish sauce, chilli and basil
were purchased from a local market. Milled rice was soaked at 55°C for 1 h,boiled for 15 min and then steamed for 10 min. Then, each 200 g of cooked rice
was packed in a plastic bag (nylon laminated with LDPE). To prepare spicy
chicken basil, the fat of skinless boneless chicken breast was trimmed andremoved and the meat chopped. The ingredients (vegetable oil, sliced chilli,
basil, water and fish sauce) were added to the chopped chicken. They were
cooked with a core temperature of chicken remaining above 70°C for 15 min.
Then the 120 g of chicken basil was filled in each plastic bag (nylon/LDPE).
In this study, the cooked rice was prepared by three different methods:
(1)
(2)
(3)

Soaking (25°C) 3 h, boiling 15 min, steaming 15 min (T1);
Soaking (25°C) 3 h, boiling 13 min, steaming 15 min (T2);
Boiling 15 min, steaming 15 min (T3).
Spicy chicken basil samples were packed differently by:

(1)
(2)
(3)

Packing spicy chicken basil (T1);
Packing cooked chicken meat with spicy sauce separately with blanchedbasil leaf (T2);
Packing cooked chicken separately with spicy sauce and blanched basil
leaf (T3).

The basil leaves were blanched in hot water at 98°C for 20 s [54]. Afterblanching, the basil leaves were rinsed with cold water and then packed in anylon 15/DL/CPP 100 µm bag. The samples were irradiated at the Office ofAtomic Energy for Peace, Bangkok, using a 60Co Gammacell 220 facility(Nordion International Inc., Canada) at a dose rate of 0.086 kGy/min. The
doses were varied to 1, 2, 3 and 4 kGy for preliminary study to find out the
optimum dose for cooked rice and spicy chicken basil samples. The blanchedbasil leaves were irradiated at 0.1 and 0.2 kGy while the cooked rice andchicken and spicy sauce were irradiated at selected doses. Then, irradiated andnon-irradiated samples were stored in a refrigerator (5 ± 1°C) for 4 weeks.
Secondly, the cooked rice and spicy chicken basil were irradiated at 2 kGy. The

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cooked rice was prepared by using T3 treatment. All irradiated samples were
kept in a refrigerator (5 ± 1°C) for 4 weeks.
3.1.2. Stir-fried rice noodle with dried shrimp (pad Thai)
Dried rice noodles and dried shrimps were purchased from a local
market. Spicy sauce (pad Thai sauce) was sourced from Pan Tai Norasingh
Industry Co. To prepare pad Thai, 400 g of dried rice noodles were soaked inwater for 10 min, then cooked in boiling water for 5 min. It was immediately
cooled with cold water for a few seconds and then drained for 2 min. A 30 g
sample of dried shrimps was blanched for 30 s in boiling water and 85 g of spicy
sauce was heated to 85oC using a hot plate. Hot sauce was added, mixed withthe dried shrimp and then added with 5 g of vegetable oil. The cooked rice
noodles and spicy sauce containing dried shrimp were separately packed inplastic bags (nylon/LDPE) and sealed. They were then irradiated at 0, 3 and4 kGy and stored in a refrigerator under chilled conditions (5 ± 1°C) for 4 weeks.
3.1.3. Steamed sticky rice, roasted chicken and papaya salad (kao neaw som
tom)
Sticky rice was soaked for 6 h, drained and placed over a thin white cloth.
It was then steamed for 25 min. The chicken was mixed with the ingredients for
6 h and roasted in an oven at 100°C for 15 min. Papaya was washed, peeled andsliced. It was served with a dressing composed of fish sauce, lemon juice, garlicand sugar. Finally, 200 g of steamed sticky rice, roasted chicken and papaya
salad were packed in nylon/LDPE bags.
3.2. Evaluation of radiation sensitivity of pathogens
3.2.1. Preparation of pure stock cultures and inoculums
A loopful of L. monocytogenes (4335) from the previous stock culture
was transferred into 100 mL trypicase soy broth (TSB). For E. coli and S.
typhimurium, 0.5 mL of lyophilized culture was added to each tube underaseptic conditions before being transferred into 100 mL of TSB. Both were put
in an incubator at 37 + 2°C for 24 h. The broth was then streaked into a petri
dish with trypicase soy agar (TSA) and incubated for another 24 h at 37 + 2°C.
The single colonies were transformed into TSA slants and returned to the
incubator for 24 h at 37 + 2°C. The pure culture at this stage was kept in arefrigerator at 5°C and used as a stock culture of L. monocytogenes, E. coli andS. typhimurium. To prepare the inoculum, a loopful of a single colony from282

NOOMHORM et al.

each stock culture of L. monocytogenes, E. coli and S. typhimurium wastransferred to 100 mL of TSB, shaken well to disperse the bacteria andincubated for 24 h at 37 + 2°C. Standardization of each bacteria was done in
TSB until the turbidity equalled MacFarland No. 0.5, which is equivalent to thebacteria concentration of 107 CFU/mL. The amount of bacteria in the inoculum
was confirmed by the surface plate method.
3.2.2. Artificial contamination
For kao ka pao kai, cooked rice and spicy chicken without basil leaf were
packed separately in OPP20/PE20/L-LDPE40 bags, sterilized at 121°C for
15 min and cooled to ambient temperatures. Sterilized cooked rice was
inoculated with L. monocytogenes and E. coli, whereas spicy chicken basil was
inoculated with L. monocytogenes and S. typhimurium at a concentration of
106 cells/g of sample. For pad Thai, L. monocytogenes and E. coli wereseparately inoculated into sterilized cooked rice noodles and dried shrimp in
spicy sauce samples. The two pathogens were also inoculated into the sterilized
steamed sticky rice, roasted chicken and papaya salad (kao neaw som tom).
3.2.3. Determination of D10 values
The cooked rice noodles and spicy sauce with dried shrimp (pad Thai)and steamed sticky rice, roasted chicken and papaya salad (kao neaw som tom),which were separately packed and inoculated with two selected pathogens,were irradiated at 1, 2, 3 and 4 kGy. After irradiation, survival of the twopathogens at each dose was determined. Total numbers of the two pathogens incontaminated samples were also determined in non-irradiated samples (thecontrol sample). To calculate D10 radiation values, two methods were proposed.
For the linear regression analysis method, the inactivation curves were plotted
between log N/N0 and D, where N is the quantity of surviving microorganism,
N0 is the initial number of organisms present and D is the dose absorbed by the
product. The curves were fitted using least square regression through the data
points in such a way that the non-linear parts were excluded. The D10 value wascalculated from the negative inverse of the slope. For the total dose method,the D10 value is equal to the output from the amount of irradiation required toeliminate any survivors divided by the initial cell population (log CFU/g).
3.2.4. Evaluation of pathogen survival under chilled storage
The artificially contaminated cooked rice noodles and dried shrimp in
spicy sauce (pad Thai), steamed sticky rice, roasted chicken and papaya salad

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(kao neaw som tom) were irradiated at 3 and 4 kGy and kept in a refrigerator(5 ± 1oC), while the contaminated cooked rice and spicy chicken basil (kao ka
pao kai) sample was irradiated at 3 kGy. After irradiation, samples were takenout weekly to evaluate the quantity of surviving pathogenic bacteria.
3.3. Shelf life evaluation
Optimum irradiation doses and shelf lives of three selected Thai meals
were evaluated for changes of their physicochemical and microbiologicalproperties after irradiation and during storage under chilled conditions (5 ± 1°C).
For kao ka pao kai, the cooked rice was determined for microbial count,cooked rice hardness (back extrusion test), whiteness, pH and moisture
content, whereas the spicy chicken basil was analysed for colour and pH. Bothwere tasted by panellists for sensory attributes using a scoring test (hedonictest). For pad Thai, cooked rice noodle was determined for moisture content,
colour and noodle hardness (texture profile analysis by texture analyser) as
well as pH and colour of spicy sauce and dried shrimp. Microbial quality wasevaluated in terms of total plate counts and panellists were asked to evaluate
the sensory quality (hedonic test). For kao neaw som tom, steamed sticky rice,
roasted chicken and papaya salad were determined in terms of moisture
content, colour and textural properties (texture profile analysis by texture
analyser). Oxidative rancidity of the roasted chicken was determined bymeasurement of the thiobarbituric acid number (TBA).

4.

RESULTS4.1. Radiation sensitivity of pathogenic bacteria in chilled Thai preparedmeals
4.1.1. Radiation sensitivity
Irradiation (D10) values for L. monocytogenes and E. coli in cooked rice
noodles and in spicy sauce with dried shrimp (pad Thai) under chilledconditions (5 ± 1°C) are shown in Table 1. The D10 value for L. monocytogenes
was lower in cooked rice noodles. This may be because the spicy sauce had
nutrients such as sugar, salt, tamarind juice and water to facilitate the growth of
the bacteria whereas cooked rice noodles had only starch and water. The D10
value for L. monocytogenes in spicy sauce with dried shrimp was relatively
higher compared to ready-to-eat meat such as frankfurters, ham, roast beef,bologna, smoked turkey (0.42–0.44 kGy at 4 and 10°C) [9] and chicken (0.77 at

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TABLE 1. COMPARISON OF RADIATION D10 VALUES FOR
L. monocytogenes AND E. coli IN COOKED RICE NOODLE AND
SPICY SAUCE WITH DRIED SHRIMP (PAD THAI)
D10 value

Type of pathogen

L. monocytogenes
E. coli

Linearregression
analysis
method(kGy)

Total dose
method(kGy)

Cooked rice noodle

0.27

0.27

Spicy sauce with dried shrimp

0.69

0.67

Cooked rice noodle

0.49

0.47

Spicy sauce with dried shrimp

0.68

0.64

Type of substrate

2–4°C) [11]. The D10 value for E. coli was also lower in cooked rice noodles. The
nature of the substrate influenced the radiation sensitivity of pathogens [8, 11,13]. The D10 value for L. monocytogenes in spicy sauce with dried shrimp was
also relatively higher compared with meat such as minced chicken (0.35–
0.39 kGy at 4°C), mechanically deboned chicken meat (0.28 and 0.44 kGy at 5and –5°C) [12] and ground beef (0.24 and 0.31 kGy at 2–5°C and –17°C) [60].
Radiation can cause damage to microbial cells by destroying genetic materials
and producing free radicals and other radiolytic products whose interaction
with water can cause much more damage to cells [8]. It was determined that E.
coli can adapt itself to grow and multiply in the two media of this study so wellthat it became more resistant than E. coli 0157:H7 in ground beef at 2–5°C.
Compared with the D10 values obtained by the two methods, those from thelinear regression analysis method were higher than those from the total dose
method. It was suggested that the total dose method is appropriate to use when
the low cell concentration of the microorganism has been applied because theskew in survival plots can introduce error. However, in this study, the initial cellconcentration of 106 CFU/g was inoculated and therefore the linear regression
analysis method, which resulted in a higher D10 value, might be capable ofbeing applied in this case. The higher value obtained from the linear regression
analysis method was confirmed by Andrews and Grodner [13].
Irradiation (D10) values for L. monocytogenes and E. coli in steamed
sticky rice, roasted chicken and papaya salad (kao neaw som tom) under chilledconditions (5 ± 1°C) are shown in Table 2. The D10 values of L. monocytogenes
in steamed sticky rice were slightly higher than in cooked rice (0.27 kGy) as
reported by Pungsawat [61]. There was a difference in the D10 values of this285

NOOMHORM et al.

TABLE 2. COMPARISON OF RADIATION D10 VALUES FOR
L. monocytogenes AND E. coli IN STEAMED STICKY RICE,ROASTED CHICKEN AND PAPAYA SALAD (KAO NEAW SOM TOM)
D10 value
Linearregression
analysis method(kGy)Total dose
method(kGy)Type of pathogen

Type of substrate

L. monocytogenes

Sticky rice

0.33

0.37

Roasted chicken

0.51

0.47

Papaya salad

0.23

0.24

Sticky rice

0.15

0.15

Roasted chicken

0.52

0.48

Papaya salad

0.44

0.42

E. colipathogen determined by the two methods when inoculated in roasted chicken;
they were slightly lower compared with those in ground beef and bologna [21].
The D10 values of L. monocytogenes in papaya slices were comparable to thoseof broccoli, mung bean sprouts, cabbage and tomato [55]. E. coli inoculated insteamed sticky rice seemed to be more susceptible to gamma irradiation than incooked rice noodles [61], showing low D10 values. In roasted chicken, the D10
value of E. coli was comparable to that in minced turkey [62] but it was higher
than that in minced chicken and pork [63]. The D10 values of E. coli in papaya
salad were higher than those of E. coli 0157:H7 on the surface and inhomogenized leaf suspension of lettuce [32].
4.1.2. Pathogen survival during storage of Thai prepared meals under chilledconditions
When contaminated kao ka pao kai was irradiated at 2 kGy, E. coli incooked rice and S. typhimurium in spicy chicken basil were effectively reduced
from a heavy contamination rate (108 and 104, respectively) to a safe level, andsamples were free from these two pathogens until the end of storage (4 weeks)
under chilled conditions (Table 3). Doses of 2 kGy also effectively killed all
L. monocytogenes in the cooked rice, although it was not enough to decontaminate L. monocytogenes (CFU/g) in the spicy chicken basil. During chilledstorage, the concentration decreased but then increased after 2 weeks. The
inoculation rate of L. monocytogenes was high (2 × 107 CFU/g) compared with

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TABLE 3. SURVIVAL OF PATHOGENS IN KAO KA PAO KAI AFTERIRRADIATION AT 2 kGy AND STORAGE UNDER CHILLED
CONDITIONS

Samples

Concentration during chilled storage (CFU/g)
Storage time

Initialconcentration(CFU/g)0d

1 week2 week3 week

4 week

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

Control
Cooked rice
Spicy chicken

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

L. monocytogenes
Cooked rice

2.12 × 107

n.d.a

n.d.

n.d.

n.d.

n.d.

7

n.d.

n.d.

n.d.

n.d.

n.d.

2.25 × 10
Spicy chicken

2.23 × 107

4.40 × 103 1.35 × 102

160

1.25 × 102 2.76 × 103

2.05 × 107

4.85 × 103 1.40 × 102

1301.30 × 102 2.58 × 103

S. typhimurium
Spicy chicken

1.35 × 104

n.d.

n.d.

n.d.

n.d.

n.d.

4

1.48 × 10

n.d.

n.d.

n.d.

n.d.

n.d.

2.64 × 108

n.d.

n.d.

n.d.

n.d.

n.d.

8

n.d.

n.d.

n.d.

n.d.

n.d.

E. coli
Cooked rice

2.42 × 10
an.d.: not detected.

the microbiological quality of ready-to-eat foods at the point of sale whosethreshold of 103 was unacceptable and potentially hazardous.
For pad Thai, no colony of contaminated E. coli was found in cooked rice
noodles or spicy sauce with dried shrimp after irradiation at 3 or 4 kGy andstorage for 4 weeks under chilled conditions (Table 4). It also happened for L.
monocytogenes in spicy sauce with dried shrimp but injured L. monocytogenes
in 3 kGy cooked rice noodles recovered in the second week of storage. E. coli,
the Gram negative bacteria, was generally more susceptible to gamma
irradiation than Gram positive bacteria because of the composition of the cellwall. Furthermore, irradiation has been reported to be an effective method for

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TABLE 4. SURVIVAL OF PATHOGENS IN PAD THAI IRRADIATED
AT 3 AND 4 kGy AND STORED UNDER CHILLED CONDITIONS

Samples

Initialconcentration(CFU/mg)

Concentration during chilled storage (CFU/g)
Storage time (weeks)
0

1

2

3

4

L. monocytogenes
3 kGy
Cooked rice noodle

1.59 × 107

<10

<10

80

285

190

Sauce and dried shrimp

1.03 × 106

<10

<10

<10

<10

<10

1.59 × 107

<10

<10

<10

<10

<10

6

<10

<10

<10

<10

<10

Cooked rice noodle

2.25 × 106

<10

<10

<10

<10

<10

Sauce and dried shrimp

1.79 × 106

<10

<10

<10

<10

<10

Cooked rice noodle

2.25 × 106

<10

<10

<10

<10

<10

Sauce and dried shrimp

1.79 × 106

<10

<10

<10

<10

<10

4 kGy
Cooked rice noodle
Sauce and dried shrimp

1.03 × 10

E. coli
3 kGy

4 kGy

the control of E. coli 0157:H7 [64]. It was proved in this study that an
irradiation dose of 3 kGy was sufficient to eliminate contaminated E. coli in thetwo components of pad Thai stored under chilled conditions. For L. monocytogenes, this was confirmed by Foong et al. [9], who reported no survivors when
4 kGy was applied in ready-to-eat meat stored at 4 and 10°C for 12 weeks.
When survival of both pathogens was considered, a dose of 4 kGy wasrecommended to ensure the safety of pad Thai during storage under chilledconditions.
After kao neaw som tom was irradiated at 3 and 4 kGy, there was nosurvival of L. monocytogenes during 4 weeks of storage (Table 5). Varabioff etal. [19] confirmed no recovery of L. monocytogenes in air packaged chicken
irradiated at 2.5 kGy and stored at 4°C. There was also no survival of E. coli inthis prepared meal when irradiated at 3 and 4 kGy and stored under chilledconditions.

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TABLE 5. SURVIVAL OF PATHOGENS IN KAO NEAW SOM TOM
IRRADIATED AT 3 AND 4 kGy AND STORED UNDER CHILLED
CONDITIONS

Samples

Initialconcentration(CFU/g)Concentration during chilled storage (CFU/g)
Storage time (weeks)
0

1

2

3

4

1.04 × 109

<10

<10

<10

<10

<10

Roasted chicken

8

3.82 × 10

<10

<10

<10

<10

<10

Papaya salad

1.63 × 108

<10

<10

<10

<10

<10

1.04 × 109

<10

<10

<10

<10

<10

Roasted chicken

8

3.82 × 10

<10

<10

<10

<10

<10

Papaya salad

1.63 × 108

<10

<10

<10

<10

<10

2.91 × 108

<10

<10

<10

<10

<10

8

1.85 × 10

<10

<10

<10

<10

<10

8

3.93 × 10

<10

<10

<10

<10

<10

2.91 × 108

<10

<10

<10

<10

<10

8

1.85 × 10

<10

<10

<10

<10

<10

8

<10

<10

<10

<10

<10

L. monocytogenes
3 kGy
Sticky rice

4 kGy
Sticky rice

E.coli3 kGySticky rice
Roasted chicken
Papaya salad
4 kGy
Sticky rice
Roasted chicken
Papaya salad

3.93 × 10

4.2. Shelf life extension of chicken basil rice (kao ka pao kai) by irradiation
4.2.1. Effect of irradiation on cooked rice and spicy chicken basil
For cooked rice (Table 6), the moisture content increased after irradiation, with significance observed at 4 kGy (p < 0.05). The cell structure of thecomponents in rice may be ruptured by irradiation. Ionization can breakchemical bonds resulting in loss of water holding capacity [65]. Cooked rice
hardness decreased significantly (p <0.05) at the lowest dose of 1 kGy.
Reduction in cooked rice hardness after irradiation was confirmed [66, 67]. The

289

290

73.02 ± 0.54ab

73.77 ± 1.79b

34

12.00 ± 0.23a

14.09 ± 1.18b

14.93 ± 0.18bc

16.15 ± 0.29cd

16.30 ± 0.82d

Hardness

59.13 ± 0.06a

61.07 ± 0.06b

61.83 ± 0.06c

62.70 ± 0.17d

63.43 ± 0.12e

Whiteness(%)

Cooked rice

5.35 ± 0.11c

4.57 ± 0.13b4.48 ± 0.14b4.42 ± 0.21b3.68 ± 0.15a

Yellowness

6.20 ± 0.01

6.20 ± 0.01

6.20 ± 0.02

6.18 ± 0.01

6.17 ± 0.02

pH

5.28 ± 0.11a6.30 ± 0.45b

7.65 ± 0.15c

10.26 ± 0.16d

11.55 ± 0.73e

Redness

5.41 ± 0.03

5.41 ± 0.01

5.40 ± 0.01

5.39 ± 0.02

5.36 ± 0.03

pH

Spicy chicken basil

Note: Means for each characteristic followed by the same letter are not significantly different at p < 0.05 by LSD test.

71.81 ± 1.61ab

72.02 ± 0.68ab

1

2

71.23 ± 0.74a

Moisture content(%)

0

Irradiation
dose
(kGy)

TABLE 6. EFFECT OF IRRADIATION ON QUALITY OF COOKED RICE AND SPICY CHICKEN BASIL

NOOMHORM et al.

NOOMHORM et al.

colour of cooked rice changed from white to yellow after irradiation, with asignificant difference noted at 1 kGy. This was also confirmed by the study ofWang et al. [43]. Gamma irradiation induces more reducing sugars and more
maillard product formation. The pH did not change appreciably and there wasno significant difference among the irradiation doses. The redness of chicken
meat reduced (Table 6) significantly (p < 0.05) at 1 kGy due to the degradationof pigment in meat by the gamma irradiation process. The pH of chicken meat
did not change much after irradiation. Panellists gave a lower score for cookedrice irradiated at higher dose (Fig. 1) owing to an unduly soft texture and to theslimy appearance of samples. As shown in Fig. 2, there was no significant

9

0 k Gy1 k Gy2 k Gy3 k Gy4 k Gy8sensory score

7
6
5
4
3
2
1

ll
ra
ve
O

Fl

av

or

te
as

ol
C

T

or

s
So
f

iv
oh

es

tn

es
en

nc
ra
ea
pp

sens ory p aramet er

C

A

es

s

e

0

FIG. 1. Effect of irradiation on sensory quality of cooked rice.

0 kGy

8

1 kGy

2 k Gy3 kGy

4 k GySensory sc ore

7
6
5
4
3
2
1
0
Ap pearance

T ext ure

Flavo rCo lorT ast eOverallSensory parameter
FIG. 2. Effect of irradiation on sensory quality of spicy chicken basil.

291

NOOMHORM et al.

difference among overall acceptability scored for spicy chicken basil irradiatedat 1–3 kGy, but it significantly reduced at 4 kGy (p < 0.05).
4.2.2. Shelf life of irradiated Thai spicy chicken basil rice during chilled storage
Doses of 1 and 2 kGy were selected based on the effects of irradiation on
the quality of cooked rice and spicy chicken basil. To improve the cooked ricetexture, the preparation method was changed (T1, T2 and T3). From Table 7,
microbial populations reduced from 43.38 to 45.22% for irradiated cooked rice
(T1–T3) and 45.84% for irradiated spicy chicken basil (T1). Irradiated cookedrice can be kept under chilled conditions for more than 1 month. For spicy
chicken basil, the microbial population of T2 treatment, which was packed
separately, was less probably due to the preservation effects of the spices in the

TABLE 7. MICROBIAL QUALITY OF NON-IRRADIATED AND IRRADIATED SPICY CHICKEN BASIL RICE DURING CHILLED STORAGE
Microbial population (CFU/g)
Storage time (weeks)

Treatments
(kGy)
0

1

2

3

4

0

1.8256a2.3482b2.6713c

3.0324d3.1849e11.0000a1.1276b1.1901b1.5167c

1.8435dT201.9002a2.2876b2.3567b2.5862c2.7734d11.0000a1.0000a1.2414b1.5191c1.6989dT301.7919a2.2563b2.8065c

3.1374d

3.3006e11.0000a1.1220ab1.3383bc

1.4375c1.6350d

02.9581a4.4813b5.5801c6.8028d21.6021a2.1461b2.5514c

2.9370d3.3336e02.0792a2.2553b2.4771c2.6590d2.9943e2<2.0000<2.0000<2.0000<2.0000

2.000002.1760a3.3193b3.7353c7.0000d2<2.0000<2.0000<2.0000<2.0000

Cooked rice
T1

Spicy chicken basil
T1
T2
T3

2.0000Note: Means for each characteristic followed by the same letter are not significantly
different at p < 0.05 by LSD test.

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NOOMHORM et al.

sauce and reduced microbial contamination from basil leaves. There was aslight change of microbial growth in irradiated spicy chicken basil, especiallywhen components were packed separately (T2 and T3). These could be kept
for more than 4 weeks compared with 3 weeks for the control sample. In termsof sensory quality, T2 obtained the lowest score among three different cooking
methods whereas T3 received more preference. This may be due to the unduly
soft texture of the T2 sample. Therefore, T3 was the suitable cooking methodwith which to prepare irradiated cooked rice.
For a more practical process, cooked rice and spicy chicken basil shouldbe irradiated at the same dose (2 kGy). With this condition, panellists accepted
irradiated cooked rice after 4 weeks of storage compared with the control
sample, which was rejected at 3 weeks (Table 8). For irradiated spicy chicken
basil (T1), the sensory acceptability decreased during storage mainly due to thedevelopment of an off flavour, which was associated with the rapid incrementin acetaldehyde and ethanol during storage [54] and the colour change ofirradiated basil leaf. As recommended by Prakash et al. [54], the irradiationdose for vegetables should be 0.1–0.35 kGy. Hence, it was necessary to treat theTABLE 8. SENSORY QUALITY OF COOKED RICE PREPARED WITH
T3 METHOD AND TREATED WITH 2 kGy AND WITHOUTIRRADIATION DURING CHILLED STORAGE
Treatment
(kGy)
0

2

Sensory attributes

Storagetime(weeks)Cohesiveness

Softness

Flavour/aroma

ColourOverall
acceptability

0

7.0b

6.8c

6.0c

7.6b

6.8c

1

7.0b

6.6c

5.8c

7.4ab

6.6bc

2

6.6b

6.2bc

5.4ab

7.2ab

6.2bc

3

5.0a

5.6b

5.2ab

7.0a

5.8b

4

4.2a

4.2a

4.8a

7.0a

4.6a

0

6.6c

6.8c

5.4

7.4

6.6b

1

6.2bc

6.6c

5.4

7.2

6.4b

2

6.0abc

6.4bc

5.4

7.0

6.4b

3

5.4ab

5.8ab

5.2

7.0

5.2a

4

5.2a

5.4a

4.8

7.0

5.0a

Note: Means for each characteristic followed by the same letter are not significantly
different at p < 0.05 by LSD test.

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NOOMHORM et al.

basil leaf with a lower irradiation dose and keep it separate from the chicken(T2 and T3). The basil leaf was irradiated at 0.1 kGy.
From Table 9, it can be seen that T2 (mixed sauce with chicken) treated withor without irradiation could be kept for more than 3 weeks. However, the effect ofirradiation could be seen clearly in T3 (separate chicken and sauce) where shelf lifeof the irradiated sample (>4 weeks) was longer than the control sample (2 weeks).

TABLE 9. SENSORY QUALITY OF SPICY CHICKEN BASIL PACKEDDIFFERENTLY AND TREATED WITH 2 kGy AND WITHOUT IRRADIATION DURING CHILLED STORAGE
Treatment
(kGy)

T2

0

2

T3

0

2

Sensory attributes

Storagetime(weeks)TextureJuiciness

Flavour/aroma

ColourOverall
acceptability

0

5.6

6.2c

6.0c

7.0c

6.4c

1

5.4

5.8bc

5.8bc

6.6c

6.2bc

2

5.2

5.2ab

5.2bc

6.4bc

5.8bc

3

5.0

5.0ab

4.8ab

5.8b

5.4b

4

4.8

4.8a

3.8a

5.4a

4.4a

0

5.8b

6.2

6.0b

7.0b

6.4b

1

5.6ab

6.0

5.8ab

6.8ab

6.0b

2

5.4ab

5.8

5.6ab

6.6ab

5.8b

3

5.0ab

5.4

5.4ab

6.4ab

5.8b

4

4.8a

5.0

5.2a

6.2a

4.8a

0

5.6b

6.4c

7.0c

6.6

6.6c

1

5.4b

6.2bc

6.8c

6.4

6.4bc

2

5.2b

5.6b

5.6b

6.4

5.8b

3

4.0a

4.4a

3.8a

6.4

4.4a

0

5.4b

6.4b

6.8b

6.6b

6.4b

1

5.4b

6.2b

6.2ab

6.4b

6.2b

2

5.0ab

5.8ab

5.8ab

6.2ab

6.0ab

3

4.6ab

5.4ab

5.4a

5.6ab

5.8ab

4

4.2a

5.0a

5.4a

5.2a

5.2a

Note: Means for each characteristic followed by the same letter are not significantly
different at p < 0.05 by LSD test.

294

NOOMHORM et al.

However, this result was from a sensory test that did not include basil leaves
because it was microbiologically spoiled by the second week of storage.
4.3. Shelf life extension of stir-fried rice noodle with dried shrimp (pad Thai)by irradiation
4.3.1. Quality of cooked rice noodle
After irradiation at 3 and 4 kGy, the moisture content of irradiatedcooked rice noodle increased. This was confirmed by Lu et al. [68], who foundan increase in the moisture content of irradiated sweet potato, and Sabularse etal. [69], who reported that modification of the starch structure caused anincrease in the water uptake during the cooking of rice. During storage underchilled conditions, the moisture content of all samples decreased significantly
by around 2% (Table 10) owing to the diffusion of water vapour from food tostorage environments. The lightness value of cooked rice noodles decreased
after irradiation at 3 and 4 kGy. Likewise, an increase in yellowness wasobserved. This was confirmed by Koomsanit [70], who found the colour of
cooked rice changed from white to yellow after exposure to radiation, even at
1 kGy. Maillard’s reaction was cited to be a reason for the increase inyellowness of the rice products after irradiation [43]. However, during storage
under chilled conditions, the lightness value of all samples tended to increase
with time (Table 10) owing to more opacity of the rice noodles resulting fromreassociation and crystal formation of the amylopectin fraction in gelatinizedstarch [71]. Whereas the yellowness decreased slightly with storage time for the
non-irradiated cooked rice noodles, it did not change significantly (p < 0.05) in
irradiated noodles. The retrogradation of starch in the cooked rice noodles
during chilled storage made for opacity of the products and resulted in adecrease in yellowness. However, irradiation initially caused increased
yellowness in noodle colour, so that the observed decrease was less evident.
Reduced hardness of the cooked rice noodles was noticed after irradiation at 3
and 4 kGy; it was dose dependent. This might be due to a breakdown of starch
molecules induced by gamma irradiation. Furthermore, this was observed
together with an increase in the moisture content of cooked rice noodles after
irradiation. The texture of irradiated cooked rice noodles was softer and theirappearance slimy. When noodle samples were kept under chilled conditions,
their hardness increased significantly (p < 0.05) with storage time (Table 10).
However, owing to the breakdown of starch molecules after irradiation, lower
hardness of the cooked rice noodles irradiated at 3 and 4 kGy was observed at
the end of storage, compared with the non-irradiated sample. The harder295

NOOMHORM et al.

TABLE 10. QUALITIES OF NON-IRRADIATED AND IRRADIATEDPAD THAI DURING CHILLED STORAGE

Components

Quality
attributes

Cooked rice
Moisture
noodlecontent (%)

Lightness

Yellowness

Hardness

Spicy sauce

RednesspH

Driedshrimp296

Lightness

Storagetime(weeks)

Irradiation dose (kGy)

0

3

4

1

68.47 + 0.28aa

69.10 + 0.17a

69.59 + 0.39a268.28 + 0.40a

68.67 + 0.29ab

68.84 + 0.04b

367.24 + 0.08b

68.41 + 0.04b68.31 +0.50b

466.51 + 0.34c

67.39 + 0.51c

67.37 + 0.12c

172.53 + 0.08b

70.20 + 0.09a

69.43 + 0.08b

272.59 + 0.06b

70.52 + 0.04b

69.38 + 0.07b

372.64 + 0.05b

70.62 + 0.03b

69.22 + 0.09a

472.80 + 0.12a

70.82 + 0.07c

69.78 + 0.07c

17.82 + 0.07a

9.07 + 0.17a

9.67 + 0.20a2

7.72 + 0.17ab

9.15 + 0.19a

9.69 + 0.05a3

7.57 + 0.07b9.21 + 0.05a

9.82 + 0.28a4

7.34 + 0.10c

9.24 + 0.33a

9.83 + 0.29a

140.44 + 0.14a

36.64 + 2.01a

33.30 + 0.58a

244.36 + 3.09b

39.88 + 1.36b

37.72 + 2.64b

345.71 + 0.58bc

41.94 + 2.43bc

39.66 + 1.13b

448.31 + 0.79c

44.78 + 1.35c

40.63 + 2.16b

1

4.10 + 0.10a

3.36 + 0.02a

3.19 + 0.07a2

3.23 + 0.06b

2.82 + 0.02b

2.44 + 0.07b32.86 + 0.03c

2.29 + 0.09c

2.37 + 0.12b4

2.59 + 0.01d

2.02 + 0.09d

1.83 + 0.01c

14.55 + 0.01a

4.82 + 0.01a

4.86 + 0.01a2

5.26 + 0.00b5.33 + 0.01b5.41 + 0.01b3

5.21 + 0.01c

5.54 + 0.01c

5.72 + 0.01c

45.44 + 0.02d

5.69 + 0.00d

5.76 + 0.01d

143.57 + 0.05a

43.48 + 0.06a

45.74 + 0.09a

2

40.26 + 0.07b

41.44 + 0.02b

44.05 + 0.04b

341.02 + 0.05c

41.05 + 0.05c

39.17 + 0.02c

441.25 + 0.03d

41.55 + 0.03d

41.41 + 0.05d

NOOMHORM et al.

TABLE 10. QUALITIES OF NON-IRRADIATED AND IRRADIATEDPAD THAI DURING CHILLED STORAGE (cont.)

Components

Quality
attributes

Storagetime(weeks)Redness

Irradiation dose (kGy)

0

3

4

1

21.96 + 0.07a

18.76 + 0.09a

17.01 + 0.05a2

18.27 + 0.06b

17.63 + 0.04b

16.92 + 0.04b

319.06 + 0.06c

17.06 + 0.05c

16.63 + 0.04c

418.45 + 0.03d

15.26 + 0.02d

15.95 + 0.04d

Note: Means for each characteristic followed by the same letter in each sample during
4 weeks of storage are not significantly different at p < 0.05 by LSD test.

texture of starch based products which occurred during cold storage was
explained by retrogradation [72].
4.3.2. Quality of spicy sauce
After irradiation, the lightness of spicy sauce decreased because of thereflection from vegetable oil floating on the sauce surface. The redness
decreased with gamma dose. Gamma irradiation may cause the degradation of
the colour pigments in spicy sauce, but there was no significant change inyellowness after irradiation. During chilled storage, the redness value gradually
decreased in the non-irradiated sauce but decreased more in the irradiatedsauce (Table 10). There was an increase in pH due to the radiolysis of water inthe product after irradiation. The pH of the spicy sauce significantly increased(p < 0.05) during storage in both the non-irradiated and irradiated samples(Table 10). The increase in pH was evident, especially at high doses. The sauce
comprised water, tamarind juice, sugar, salt, acetic acid and paprika oleoresin
colour. The majority of the components, such as water, may change byradiolysis, induced by gamma irradiation [73]. The consequences of theradiolysis reaction are free radicals, which then react to other food molecules
and become radiolytic products. The highly reactive entities formed canevaporate rapidly during irradiation treatment. Consequently, the concentration of solutes in spicy sauce was increased and resulted in a slightly salty
taste. Thus, increase in pH during storage might be due to the sauce becoming
more concentrated after irradiation and during storage.

297

NOOMHORM et al.

4.3.3. Quality of dried shrimp
After irradiation, the lightness of the dried shrimp increased but theredness value decreased. This was confirmed by Adulpichit [53]. Irradiation
may cause the degradation of the main pigment (astaxanthin) in dried shrimp.
Astaxanthin comprises terpenoid, which provides the yellow, orange and red
colour of the products and therefore oxidation of astaxanthin by gamma
irradiation induced a paler colour of dried shrimp. The redness continually
decreased during chilled storage (Table 10). The sauce and dried shrimp were
packed in an abundance of oxygen and this may have been responsible for theoxidation of astaxanthin, resulting in discoloration of the dried shrimp.
4.3.4. Microbial quality of irradiated pad Thai
It was expected that irradiation would extend the shelf life from 5 to 7 dfor normal chilled prepared meals to 4 weeks. Samples were not at risk of
spoilage because the cooked rice noodles and spicy sauce with dried shrimp
were packed separately. Likewise, the lower microbial load was in cooked rice
noodles, which were boiled for 5 min, and in dried shrimp, which was blanchedin hot water before packing, and also in spicy sauce, which had a low pH.
However, under chilled storage, the microbial load grew in cooked rice noodles
as observed by higher microbial counts in the irradiated and non-irradiatedsamples (1.3–6.2 ln CFU/g) at the end of storage compared to spicy sauce (<1–2.3 ln CFU/g) (Table 11). This may be because the spicy sauce had a low pH,

TABLE 11. TOTAL PLATE COUNTS OF NON-IRRADIATED AND
IRRADIATED PAD THAI DURING CHILLED STORAGE

Components

Cooked rice
noodleSpicy sauce withdried shrimp

298

Irradiation
dose
(kGy)

Population density (ln CFU/g)
Storage time (weeks)
0

1

2

3

4

0

1.81

2.26

3.95

5.10

6.15

3

1.00

1.18

1.88

3.84

4.30

4

<1.00

1.00

1.00

1.18

1.30

0

1.00

1.40

1.74

2.10

2.29

3

1.00

1.00

1.18

1.30

1.48

4

<1.00

<1.00

<1.00

<1.00

<1.00

NOOMHORM et al.

which can inhibit the growth of bacteria. With irradiation, fewer microbial
counts were noticed in both components, especially at a high gamma dose. With
respect to criteria for food spoilage at 7 ln CFU/g, pad Thai irradiated at 4 kGy
had a shelf life much longer than 4 weeks.
4.3.5. Sensory quality of irradiated pad Thai
To serve in a sensory test, cooked rice noodle was mixed with the spicy
sauce and dried shrimp. From Table 12, after irradiation, panellists preferred
non-irradiated to irradiated pad Thai. Among the samples, pad Thai irradiatedat 4 kGy had a lower overall acceptability score during the early period ofstorage (1–2 weeks). Panellists commented that irradiated pad Thai appearedslimy and the texture was too soft. Moreover, the flavour of a 4 kGy sample
seemed to be more salty than non-irradiated and lower dose irradiated noodles.
However, after 3 weeks of storage, overall acceptability of pad Thai irradiatedat 4 kGy was better and comparable to other samples. This was consistent withan increase in hardness of the cooked rice noodle during storage as determinedby objective methods.
TABLE 12. SENSORY QUALITY OF NON-IRRADIATED AND
IRRADIATED PAD THAI DURING CHILLED STORAGE
Irradiation Storage
time
dose
(weeks) Appearance Texture
(kGy)
0

3

4

Sensory scores
ColourTaste

FlavourOverallpreference

1

7.2a

6.2a

6.7ab

6.4b

6.4a

6.8a

2

7.0a

6.6a

6.3a

5.6a

5.9a

6.2ab

3

7.5a

6.0a

7.2b

6.1ab

6.5a

6.2ab

4

6.7a

6.0a

6.1a

5.4a

5.6a

5.7b

1

7.0b

6.4a

6.6b

6.6a

6.4b

6.5a

2

6.1a

6.6a

5.4a

5.3a

5.3a

6.2a

3

7.1b

7.2a

6.4b

6.0a

5.6ab

6.2a

4

6.6ab

7.3a

6.0ab

5.6a

5.2a

6.7a

1

6.6ab

5.7a

6.6a

5.6a

5.4a

5.7ab

2

5.7a

5.6a

5.8a

5.4a

5.7a

5.4a

3

7.0b

6.9b

6.1a

6.1a

6.0a

6.4b

4

6.5ab

7.2b

6.0a

6.0a

6.1a

6.4a

Note: Means for each characteristic followed by the same letter in each sample during
4 weeks of storage are not significantly different at p < 0.05 by LSD test.

299

NOOMHORM et al.

4.4. Shelf life extension of steamed sticky rice, roasted chicken and papaya
salad (kao neaw som tom) by irradiation
4.4.1. Quality of steamed sticky rice
From Table 13, the moisture content of non-irradiated steamed sticky rice
did not change during chilled storage but increased slightly for irradiated sticky
rice. This was in contrast to the studies of Pungsawat [61] and Koomsanit [70]TABLE 13. QUALITIES OF NON-IRRADIATED AND IRRADIATED
KAO NEAW SOM TOM DURING CHILLED STORAGE

Components

Steamedsticky rice

Quality
attributes
Moisturecontent (%)

pH

Lightness

Hardness

300

Storagetime(weeks)

0

3

4

0

42.63 ± 0.36a

42.63 ± 0.36a

43.75 ± 0.42a244.18 ± 0.38a

42.68 ± 0.09a

48.61 ± 0.36a

442.97 ± 0.77b

42.25 ± 0.15b45.69 ± 0.52b

Irradiation dose (kGy)642.76 ± 0.37a

44.20 ± 0.81a

44.65 ± 0.53a

843.57 ± 0.67b

46.18 ± 0.41b

43.01 ± 0.23b

05.94 ± 0.03a

5.85 ± 0.02a

5.85 ± 0.02a2

5.45 ± 0.01b5.91 ± 0.01b6.02 ± 0.01b45.65 ± 0.01ab

6.01 ± 0.02ab

6.02 ± 0.01ab

6

6.04 ± 0.05b6.01 ± 0.05b

5.98 ± 0.03b8

5.96 ± 0.08a

6.01 ± 0.02a

5.97 ± 0.03a

067.58 ± 0.13a

69.80 ± 0.13a

73.73 ± 0.13a

273.49 ± 0.03ab

71.63 ± 0.05ab

74.50 ± 0.03ab

4

74.19 ± 0.05c

74.57 ± 0.07c

72.74 ± 0.12c

675.01 ± 0.20ab

73.73 ± 0.14ab

72.84 ± 0.23ab

8

74.06 ± 0.12bc

71.39 ± 0.06bc

73.99 ± 0.13bc

05249 ± 87a

6658 ± 111a

7477 ± 136a27447 ± 183b

8308 ± 217b

8635 ± 68b

49276 ± 112c

8801 ± 293c

9626 ± 105c

69219 ± 170c

8982 ± 188c

9661 ± 188c

89358 ± 278c

10121 ± 297c

9120 ± 103c

NOOMHORM et al.

TABLE 13. QUALITIES OF NON-IRRADIATED AND IRRADIATED
KAO NEAW SOM TOM DURING CHILLED STORAGE (cont.)

Components

Roastedchicken

Quality
attributes

Storagetime(weeks)0

3

4

Stickiness

03106 ± 59a

2312 ± 22a

2237 ± 58a

22641 ± 68b

2148 ± 45b

2138 ± 26b

Lightness

Hardness

TBA value

Papayasalad

pH

Irradiation dose (kGy)42372 ± 75c

1704 ± 29c

2109 ± 22c

62270 ± 72d

1818 ± 38d

1549 ± 32d81460 ± 23e

785 ± 59e981 ± 6e037.14 ± 4.09a

41.58 ± 0.12a

44.18 ± 0.07a240.42 ± 0.01a

41.23 ± 0.08ab

51.21 ± 0.08ab

4

46.10 ± 0.03ab

42.55 ± 0.20ab

42.95 ± 0.02ab

6

49.45 ± 0.31ab

40.14 ± 0.14ab

42.63 ± 0.11ab

8

44.02 ± 1.16b

50.74 ± 0.10b

45.88 ± 3.59b04712 ± 50a

5482 ± 203a

6012 ± 208a

25551 ± 112ab

5242 ± 255ab

4533 ± 72ab

44198 ± 126a

5743 ± 208a

5917 ± 141a

64633 ± 41b

4456 ± 74b

5240 ± 86b

84892 ± 77ab

5566 ± 145ab

4814 ± 125ab

00.039 ± 0.002a

0.049 ± 0.011a

0.060 ± 0.002a

2

0.055 ± 0.004b

0.059 ± 0.014b

0.061 ± 0.003b

4

0.081 ± 0.002c

0.106 ± 0.012c

0.110 ± 0.007c6

0.115 ± 0.003d

0.123 ± 0.003d

0.136 ± 0.007d8

0.121 ± 0.009e

0.131 ± 0.001e

0.152 ± 0.010e

06.46 ± 0.01a

6.01 ± 0.01a

6.01 ± 0.01a2

6.36 ± 0.01b5.55 ± 0.01b5.37 ± 0.01b4

5.14 ± 0.01c

5.34 ± 0.01c

5.25 ± 0.00c

6

4.86 ± 0.04cd

5.12 ± 0.01cd

5.03 ± 0.02cd

8

4.20 ± 0.02d

4.99 ± 0.02d

5.16 ± 0.01d

301

NOOMHORM et al.

TABLE 13. QUALITIES OF NON-IRRADIATED AND IRRADIATED
KAO NEAW SOM TOM DURING CHILLED STORAGE (cont.)

Components

Quality
attributes

Storagetime(weeks)0

34Lightness

064.65 ± 3.21c

64.23 ± 0.04c

61.73 ± 0.05c

2

63.08 ± 0.06bc

63.60 ± 0.00bc

60.45 ± 0.06bc

4

64.84 ± 0.03bc

60.94 ± 0.03bc

63.61 ± 0.11bc

6

65.07 ± 0.08b

58.13 ± 0.08b

60.90 ± 0.09b864.79 ± 0.13a

57.53 ± 0.03a

55.90 ± 0.01a

Irradiation dose (kGy)

Note: Means for each characteristic followed by the same letter in each sample during 8 weeks
of storage are not significantly different at p < 0.05 by LSD test.

who reported a decrease in the moisture content of cooked rice and rice
noodles during chilled storage. The pH of non- and irradiated steamed sticky
rice had a fluctuating trend. For colour, there was no clear trend in changes ofredness or yellowness of steamed cooked rice. However, irradiation increased
lightness and a slight increase in this value was observed in the non-irradiatedsample. Irradiation increased the hardness of sticky rice. This was different
from the report of Sirisoontaralak and Noomhorm [74] who reported adecrease in the cooked rice hardness after irradiation. This might be due to adifference in the amylose and amylopectin ratio and also their structures. All
samples showed an increase in the hardness value during storage under chilledconditions from retrogradation, although less increase was observed in a highdose irradiated sample. Stickiness decreased, depending on the irradiation
dose. During chilled storage, it decreased in all samples.
4.4.2. Quality of roasted chicken
The changes in the redness and yellowness values of roasted chicken after
irradiation and during storage were hardly perceptible. Lightness increased after
irradiation and it increased during chilled storage (Table 13). Irradiation also
increased the hardness of roasted chicken and it varied with doses, although it
remained almost constant during storage. From the TBA values, irradiationinduced more lipid oxidation and this increased significantly (p < 0.05) during
chilled storage. This proved that irradiation induced more lipid oxidation in meatproducts [50].

302NOOMHORM et al.

4.4.3. Quality of papaya salad
As is apparent from Table 13, irradiation did not affect the pH of thepapaya salad, although it decreased significantly (p < 0.05) with storage time.
This might be due to microbial spoilage. Lightness decreased after irradiation,
especially at a high dose (4 kGy), and it decreased significantly (p < 0.05) in theirradiated sample during chilled storage whereas that of the non-irradiatedsample was unchanged.
4.4.4. Microbial quality of irradiated kao neaw som tom
From Table 14, steamed sticky rice was microbiologically safe during
chilled storage for 8 weeks when irradiated at 3 and 4 kGy, while the nonirradiated sample was spoiled before 8 weeks. Roasted chicken had a shorter
shelf life than sticky rice because it was protein rich. It was spoiled before
6 weeks under chilled condition but irradiation at 3 and 4 kGy could extend its
shelf life to longer than 8 weeks. Among the three components, papaya salad
was the most susceptible to microbial spoilage. A non-irradiated sample was
spoiled before 2 weeks, but irradiation was effective in extending its shelf life tomore than 8 weeks. When considering all the components of kao neaw som

TABLE 14. TOTAL PLATE COUNTS OF NON-IRRADIATED AND
IRRADIATED KAO NEAW SOM TOM DURING CHILLED STORAGE

Components

Steamedsticky rice

Roastedchicken

Papayasalad

Irradiation
dose
(kGy)

Population density (ln CFU/g)
Storage time (weeks)
0

2

4

6

8

0

3.04

5.00

6.31

6.88

7.58

3

<1.00

<1.00

<1.00

<1.00

1.04

4

<1.00

<1.00

<1.00

<1.00

<1.00

0

5.42

6.09

6.09

7.67

7.63

3

<1.00

<1.00

<1.00

<1.00

1.00

4

<1.00

<1.00

<1.00

<1.00

<1.00

0

5.41

7.62

>7.00

>7.00

>7.00

3

<1.00

<1.00

<1.00

<1.00

2.58

4

<1.00

<1.00

<1.00

<1.00

<1.00

303

NOOMHORM et al.

tom, the shelf life under chilled conditions could be extended from 2 weeks for
untreated samples to more than 8 weeks using irradiation at 3 or 4 kGy.
4.4.5. Sensory quality of irradiated kao neaw som tom
There were no differences in the appearance, cohesiveness, softness andcolour scores of non- and irradiated steamed sticky rice during chilled storage(Table 15). Panellists gave slightly lower scores for flavour and taste ofirradiated sticky rice and this resulted in lower overall acceptability. Thesescores were almost unchanged during storage.
For roasted chicken, scores for all sensory attributes (appearance, colour,
texture, flavour and taste) were not different among non- and irradiatedsamples at 3 and 4 kGy (Table 16). The scores did not change much during

TABLE 15. SENSORY QUALITY OF NON-IRRADIATED AND
IRRADIATED STEAMED STICKY RICE DURING CHILLED STORAGE
Dose
(kGy)
0

Storage
Overalltime Appearance Cohesiveness Softness Colour Flavour Taste
acceptability(weeks)
0

7.10a

6.08a

6.40a

7.30a

6.70bc

7.10b

7.20a

2

6.90a

7.00a

7.00a

7.60a

7.20ab 7.30ab

7.20a

0

6.40a

6.30a

5.50a

6.30a

6.00bc

5.50b

5.90a

2

6.70a

6.10a

6.60a

7.40a

6.80ab 6.90ab

6.70a

4

7.00a

5.90a

6.40a

7.40a

6.30c

6.50b

6.50a

6

6.90a

6.80a

6.40a

7.30a

6.90ab

6.50b

6.90a

8

7.20a

6.40a

6.90a

7.50a

7.30a

7.30a

6.70a

4
6
8
3

4

0

7.50a

6.10a

6.30a

7.30a

6.80bc

6.70b

6.80a

2

7.30a

7.00a

6.70a

7.80a

6.70ab 6.30ab

6.40a

4

6.90a

6.20a

5.80a

7.20a

6.00c

6.10b

6.50a

6

7.50a

6.10a

6.30a

7.30a

6.80ab

6.70b

6.80a

8

6.90a

6.90a

6.80a

7.50a

7.20a

7.40a

7.10a

Note: Means for each characteristic followed by the same letter in each sample during 8 weeks
of storage are not significantly different at p < 0.05 by LSD test.

304

NOOMHORM et al.

TABLE 16. SENSORY QUALITY OF NON-IRRADIATED AND
IRRADIATED ROASTED CHICKEN DURING CHILLED STORAGE
Dose
(kGy)
0

Storagetime(weeks)Appearance

TextureColour

Flavour

Taste

Overall
acceptability

0

6.80b

7.50a

6.80a

6.80b

7.00a

7.30a

2

7.80a

7.70a

7.20a

7.30a

7.20a

7.70a

4

7.30ab

7.20a

7.10a

7.70ab

7.30a

7.50a

6
8
3

4

0

7.00b

8.00a

7.00a

6.60b

7.50a

7.60a

2

7.40a

7.10a

6.80a

7.50a

7.50a

7.30a

4

6.80ab

6.70a

6.60a

7.20ab

6.70a

6.80a

6

7.50ab

7.10a

7.20a

7.40ab

7.20a

7.40a

8

7.40ab

6.70a

7.20a

7.40a

7.30a

7.10a

0

7.10b

6.80a

6.90a

6.70b

6.80a

6.90a

2

7.50a

6.50a

7.00a

7.50a

6.70a

7.10a

4

7.20ab

6.60a

7.00a

7.00ab

6.60a

6.90a

6

7.30ab

6.60a

6.90a

6.90ab

7.00a

6.90a

8

7.00ab

7.60a

7.20a

7.70a

7.60a

7.40a

Note: Means for each characteristic followed by the same letter in each sample during 8 weeks
of storage are not significantly different at p < 0.05 by LSD test.

storage. Panellists still accepted irradiated steamed sticky rice and roasted
chicken after 8 weeks of storage. The sensory quality of papaya, however, wasseverely affected by irradiation. Although panellists could not detect thedifference in appearance of the non- and irradiated samples, they rejected theirradiated papaya salad because of the soft texture and impaired taste, even at
the very low dose of 1 kGy (Table 17).

5.

CONCLUSIONS

To obtain the longer shelf life of Thai spicy chicken basil rice (kao ka
pao kai), cooked rice was prepared to obtain a harder texture and irradiatedat 2 kGy. Three components: cooked chicken, sauce and blanched basil leaf

305

NOOMHORM et al.

TABLE 17. SENSORY QUALITY OF NON-IRRADIATED AND
IRRADIATED PAPAYA SALAD DURING CHILLED STORAGE
Dose
(kGy)
0
1

Storagetime Appearance(weeks)TextureColourTaste

FlavourOverall
Acceptability

0

6.90a

7.70a

6.90a

7.40a

7.40a

7.70a

1

7.00a

7.50a

7.30a

7.00a

6.90b

7.50b

0

7.00a

4.00a

6.90a

6.30a

6.90a

5.60a

1

5.90a

3.40a

5.70a

4.90a

5.70b

3.90b

Note: Means for each characteristic followed by the same letter in each sample during a weekof storage are not significantly different at p < 0.05 by LSD test.

were packed separately and irradiated at 2 kGy and at 0.1 kGy for the basil
leaves. Regarding sensory quality, irradiated cooked rice had a longer shelf
life of around 4 weeks. The shelf life of irradiated spicy chicken packed
separately (>4 weeks) was much longer than the control sample (2 weeks).
However, there is a need to preserve basil leaf because it was microbiologically spoiled by the second week of storage. For the stir-fried rice noodles
with dried shrimp (pad Thai), irradiation at 3 kGy was not enough toeliminate L. monocytogenes entirely, which showed recovery after 2 weeks ofchilled storage. Therefore, a dose of 4 kGy was recommended because theproduct was free from pathogens, safe from microbial spoilage and had
acceptable sensory quality. After irradiation at 4 kGy, the shelf life of pad
Thai could be extended to more than 4 weeks when storing under chilledconditions compared with a normal chilled ready meal, which has a shelf lifeof 5–7 d. For steamed sticky rice, roasted chicken and papaya salad (kao neaw
som tom), a dose of 3 kGy was enough to control L. monocytogenes and E.
coli during chilled storage. After irradiation at 3 kGy or more, the productwas microbiologically safe when stored for more than 8 weeks, whereas the
non-irradiated sample was spoiled by the second week of storage.
Considering the sensory quality, panellists accepted irradiated steamed sticky
rice and roasted chicken stored for 8 weeks under chilled conditions, but theyrejected irradiated papaya salad owing to the soft texture and impaired taste.

306

NOOMHORM et al.

ACKNOWLEDGEMENTS
This study was financially supported by the IAEA. Technical assistance
was also provided by the Office of Atoms for Peace, Thailand.

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EFFECT OF GAMMA IRRADIATION ON THE
QUALITY OF READY MEALS AND THEIR MEATCOMPONENTS
E.M. STEWART
Agri-Food & Biosciences Institute,
Department of Food Science,
Queen’s University Belfast,
Belfast, United Kingdom

Abstract
The effects of gamma irradiation on the quality of a chicken masala ready meal,
minced red meat and salmon meat were studied in a series of experiments. Chicken
masala meals treated with a dose of 1–3 kGy and stored for up to 14 d at refrigeration
temperatures were analysed for vitamins E and B1, oxidative rancidity, microbiologicalquality and 2-alkylcyclobutanones. It was found that vitamin levels were significantly
reduced by a combination of irradiation, storage and reheating, while thiobarbituric acid
(TBA) values decreased upon irradiation, which was an unexpected result. The shelf lifeof the meals was extended by irradiation as levels of bacteria were significantly reducedin the prepared meals upon treatment. Both 2-dodecylcyclobutanone and 2-tetradecylcyclobutanone were detected in the irradiated samples, thereby showing that thesecompounds can be used as markers of irradiation treatment for such food products. In
order to study potential components for ready meals, freshly minced beef was used toprepare beef patties, which were vacuum packed and treated with doses from 2.5 to
10 kGy. Following irradiation, half the samples were retained in vacuum packs while theremainder were transferred to sterile containers and overwrapped with cling film.
Samples were stored for up to 21 d at refrigeration temperature with TBA values andmicrobiological quality being analysed at regular intervals. The TBA values of vacuum
packed samples were unaffected by irradiation although storage did result in an
increase. On the other hand, the TBA values of overwrapped patties increased upon
irradiation and storage. The microbiological quality of the irradiated patties uponstorage was significantly better than those of untreated patties. A further series ofexperiments were undertaken to determine the effect of adding antioxidants to beef andsalmon patties in order to improve lipid stability upon irradiation. In an initial experiment, minced beef patties were prepared with the antioxidants α-tocopherol, epicatechin, quercetin and resveratrol included at concentrations of 110 and 550 μmol/kg, after
which they were overwrapped and irradiated with 2.5 and 5 kGy. Following irradiation,
the patties were stored for up to 28 d at refrigeration temperature and TBA values
measured at intervals. Inclusion of the antioxidants reduced lipid oxidation, with thepatties containing resveratrol having the lowest TBA values. Samples containing
550 μmol/kg of antioxidant had lower TBA values than those with 110 μmol/kg. Further

313

STEWART

experiments were undertaken to study the effect of including the same antioxidants at
concentrations of 25, 50, 250, 500 and 700 μmol/kg in minced beef and salmon meat
patties irradiated at 2.5 kGy and stored for up to 14 d at refrigeration temperature. As
noted previously, resveratrol was the most effective antioxidant for improving lipid
stability in minced beef patties while the lowest TBA levels for salmon meat patties
were obtained for those containing epicatechin. Overall, concentration had a significant
effect on the TBA values with lower values being obtained for those samples containing
the higher inclusion levels.

1.

INTRODUCTION

The prepared convenience foods sector in Ireland is a significant part of
the Irish economy. In 2001, just under half of the sector’s total output wasexported for a value of €841 million, representing a 12% annual increase [1].
The sector’s strong growth, both in exports and in total sales, has made it one of
the fastest growing sectors of the food industry in Ireland [2]. Work carried out
by de Boer et al. [2] confirmed that perceived time pressures contributed
positively to the purchase of both ready meals and takeaway meals, which was
in line with previous findings of Verlegh and Candel [3] who found that timepressure had a positive effect on the frequency of consumption of TV dinners
and prepared dinners, meal centres and takeaways. Other reasons which
contributed positively to the purchase of ready meals included not enjoying
cooking for oneself, value-for-money perception of convenience foods anddifferent eating times of family members [2]. As a consequence of the increased
market for convenience foods, and particularly ready meals, the food industry
is interested in ways of producing meals which are safe to eat, nutritious andwith an acceptable shelf life. One technology investigated as a means ofachieving these objectives is food irradiation [4].
The results of previous research carried out in Belfast [5–8] concluded
that using an irradiation dose of 2 kGy would extend the shelf life of refrigerated ready meals, whole meals (e.g. roast pork, boiled potatoes, mixed
vegetables) and pureed meals (e.g. pureed chicken and gravy, boiled potatoes,
garden peas) for up to 14 d. However, the importance of storing the meals
under suitable refrigeration conditions (<3°C) was highlighted in order toobtain maximum benefit from the irradiation treatment. The researchshowed that vitamin losses due to treatment with ionizing irradiation werecomparable to those induced by cooking and storage. From a regulatory pointof view, results obtained in the experimental work showed that both the
2-alkylcyclobutanone (EN1785) and ESR spectroscopy (EN1787) standard
detection methods could be used to identify irradiated products, with EN1785

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STEWART

being carried out on the meat component of the meals and EN1787 using the
packaging as the radiation marker [9].
The following work is a further extension of that carried out to date. The
studies reported here focus primarily on the meat components of ready meals,such as minced beef and salmon meat. Some initial work was undertaken on
ready meals, but as sourcing of these meals proved difficult extensive studies
could not be undertaken. The experimental work studied the effects of ionizing
radiation on the quality attributes of the meals important to the consumer, suchas microbiological quality and off flavours as measured in terms of oxidative
rancidity and nutritional quality.

2.

MATERIALS AND METHODS

2.1. Effect of irradiation on the quality of a chilled chicken masala ready meal
2.1.1. Experimental protocol
A batch of chilled chicken masala ready meals was obtained from a local
manufacturer in Northern Ireland. The meals were obtained from theprocessor within 2 h of production and brought back to the laboratory where
they were stored at 3 ± 1°C until irradiated (Section 2.5.1). The samples wereanalysed for thiamine (Section 2.5.2) and α-tocopherol (Section 2.5.3),
oxidative rancidity (Section 2.5.4), microbiological quality and 2-alkylcyclobutanones (Section 2.5.5) in order to determine if irradiation treatment could be
confirmed.
The vitamin and oxidative rancidity analyses were carried out on thesame samples. A total of 72 meals were given doses of 1, 2 or 3 kGy or left nonirradiated to serve as controls, thereby giving 18 meals per treatment. Of the 18
meals within each batch, six were analysed immediately while six were stored
for 7 d and six for 14 d at 3 ± 1°C. Upon analysis, three meals at each dose level
were analysed in the fresh state while the other three meals were reheated in aconvection oven at 180°C for 20 min to give an internal temperature of 80°C.
The meals were allowed to cool to ambient temperature prior to being
homogenized by a food processor and analysed.
For the microbiological analysis, a total of 64 samples from the samebatch of meals were given the same irradiation doses as those described
previously, with 16 meals being treated per dose. Within each batch of 16, four
meals were analysed at each storage time of 0, 7, 11 and 14 d, two being stored
at 3 ± 1°C and two at 10 ± 1°C. These meals were not reheated prior to analysis.
The samples were homogenized in a stomacher for 2 min prior to sampling. On

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each sampling day, the meals were assessed as follows: total bacteria count(TBC) (30°C for 48 h) on typtone soya agar containing 0.6% yeast extract(TSAYE); coliform count (37°C for 18–24 h) on McConkey No. 3 agar; andpsychrotrophic count of TSAYE (7°C for 10 d).
2.2. Effect of irradiation on the quality of minced beef patties
2.2.1. Effect of irradiation on the oxidative rancidity and microbiologicalquality of vacuum packed and overwrapped minced beef patties stored for21 d at 3°C
On each of three separate occasions, freshly minced beef (15% lipid) was
obtained from a local butcher in Belfast. Under aseptic conditions 65 patties,
each weighing 50 g, were produced and vacuum packed. The samples were
irradiated with doses of 2.5, 5, 7.5 and 10 kGy (Section 2.5.1) or left nonirradiated to serve as controls, thereby giving 13 samples at each dose.
Following irradiation, 35 samples were retained within the vacuum packs while
the other 30 were removed aseptically from the packaging in a laminar flow
cabinet, placed in sterile cartons and covered in cling film in order to give 30
overwrapped samples. Five samples were either analysed immediately (day 0)
and five at each treatment after 1, 2, 5, 7, 14 and 21 d at 3 ± 1°C for microbiological quality, or after 1, 2, 5, 7, 14 and 21 d at 3 ± 1°C for oxidative rancidity,
thereby giving two samples per treatment.
The same patties were used for both the oxidative rancidity and microbiological assessment, the samples for microbiological analysis being taken underaseptic conditions prior to the patties being analysed for oxidative rancidity(Section 2.5.4).
For microbiological quality, on each sampling day, the vacuum packed
samples were assessed as follows: TBC (30°C for 48 h) on TSAYE; anaerobic
count (35°C for 48 h) on TSAYE; coliform count (37°C for 18–24 h) on
McConkey No. 3 agar; psychrotrophic count (7°C for 10 d) on TSAYE;
Pseudomona spp. (25°C for 48 h) on pseudomonad selective agar (PSA) to
CFC formulation; and lactic acid count (30°C for 48 h) on deMan, Rogosa,
Sharpe (MRS) agar using pour plates with an overlay. In the case of theoverwrapped samples, total viable, psychrotrophic, pseudomona and coliform
counts were carried out.

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2.3. Effect of ionizing radiation and storage on the oxidative rancidity ofminced beef patties containing natural antioxidants at different
concentrations
2.3.1. Experimental protocol 1
Freshly minced beef (6% lipid) was purchased from a local supplier in
Belfast and transferred to the laboratory where it was thoroughly mixed toprovide a homogenous bulk sample. This was used to prepare a total of 120
patties, each weighing 50 g, containing the antioxidants α-tocopherol,
epicatechin, quercetin and resveratrol at concentrations of 110 and 550 μmol/kg
or with no antioxidant added to serve as controls. Following preparation, eachpattie was placed in a plastic container, which was double wrapped with cling
film. The samples were irradiated at doses of 2.5 and 5 kGy or left non-irradiated.
The samples were stored for periods of 1, 7, 14, 21 and 28 d at 4 ± 1ºC, after which
they were analysed for oxidative rancidity using the thiobarbituric acid (TBA)
method (Section 2.5.4). The experiment was repeated on three separate
occasions.
2.3.2. Experimental protocol 2
As previously, fresh minced beef (8% lipid) was purchased and mixed toprovide a homogenous bulk sample. On this occasion 100 patties, eachweighing 50 g, were prepared. The antioxidants α-tocopherol, epicatechin,quercetin and resveratrol were included at concentrations of 25, 50, 100, 250,
500 and 700 µmol/kg whilst other patties were prepared with no antioxidant.
The samples were packed as before and treated with an irradiation dose of
2.5 kGy or left non-irradiated. They were then stored for 1 and 14 d at 4 ± 1ºC,
pending oxidative rancidity analysis (Section 2.5.4). The experiment was
repeated on three separate occasions.
2.4. Effect of ionizing radiation and storage on the oxidative rancidity ofsalmon meat patties containing natural antioxidants at different
concentrations
2.4.1. Experimental protocol
On each of three separate occasions, fresh skinless sides of salmon (15%lipid) were obtained from a local supplier in Belfast and transferred to thelaboratory. The salmon was passed through a mincer and the resultant puree
was thoroughly mixed to provide a single homogenous bulk sample. This was

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used to prepare 100 salmon patties, each weighing 50 g. As previously carriedout for minced beef (Section 2.3.2), the antioxidants α-tocopherol, epicatechin,quercetin and resveratrol were included at concentrations of 25, 50, 100, 250,
500 and 700 µmol/kg or no antioxidant was added to serve as controls, after
which they were packed, irradiated and analysed as described previously.
2.5. Irradiation treatment and analytical methods
2.5.1. Irradiation treatment
Irradiation was carried out using 60Co as the source of ionizing radiation(Gammabeam-650, MDS Nordion, Kanata, Canada). Gammachrome YR
dosimeters (AEA Technology, Harwell, United Kingdom) were placed on
samples receiving a dose of 2 kGy or less while amber dosimeters (AEA
Technology, Harwell, UK) were placed on those samples receiving 2.5 kGy or
greater. Following irradiation, the change in absorbance of the dosimeters wasmeasured using a Unicam SP-8 uv/vis spectrophotometer (Unicam,
Cambridge, UK). Thickness of dosimeters was measured using a digitalelectronic micrometer (RS Components, Corby, UK) and the recorded
absorbances were corrected to a standard thickness of 3 mm. The corresponding dose received was obtained from a calibration graph provided by the
National Physical Laboratory (Teddington, UK).
2.5.2. Thiamine (vitamin B1) determination
Thiamine concentration of the ready meals was measured using a modification of the HPLC method of Finglas and Faulks [10], as outlined by Graham
et al. [11]. Each sample was analysed in duplicate.
2.5.3. α-tocopherol (vitamin E) determination
Determination of a-tocopherol was achieved using HPLC after saponification and extraction from the ready meal samples into n-hexane according to
the method of McMurray and Blanchflower [12] and McMurray et al. [13] withslight modifications. To a 1 g aliquot of extracted oil, 1 mL of 60% potassiumhydroxide and 5 mL of 50% pyrogallol in ethanol were added, the mixture
flushed with nitrogen gas, heated to boiling and allowed to simmer for 20 min.
After cooling, 2 mL water was added and the tubes shaken, followed by theaddition of 3 mL hexane and vigorous shaking for 1 min. The mixture was thencentrifuged at 2500g for 30 min. The top solvent layer containing the vitaminwas removed and evaporated to dryness under nitrogen and reconstituted in

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200 μL of acetone prior to HPLC analysis. The HPLC equipment used foranalysis consisted of a Hewlett Packard HP 1090 M liquid chromatograph withintegral fluorescence detector, autosampler and autoinjector along with a
Hewlett Packard 9000 series 320 data station (Winnersh, Wokingham, UK).
The HPLC column used was 250 mm × 4.6 mm i.d. packed with 10 μm
spherisorb ODS 2 (Phase Separations, UK). The mobile phase wasmethanol:water in a 97:3 ratio, the flow rate was 1.8 mL/min while the injection
volume was 20 μL. The column temperature was maintained at ambient.
Fluorescence detection was performed with an excitation wavelength of
289 nm and an emission wavelength of 335 nm. Identification and quantification of α-tocopherol was performed by comparing the sample retention
times and peak areas with those of external standards. The concentration of
α-tocopherol was expressed as milligrams per gram of sample on a fresh weightbasis. Recoveries of α-tocopherol were checked by spiking samples withstandard solutions of α-tocopherol and treating as for the meal samples.
2.5.4. Oxidative rancidity measurement (TBA method)
Oxidative rancidity of the samples was determined by measuring their
TBA values according to the method of Pikul et al. [14], but using trichloroacetic acid (TCA) in place of perchloric acid owing to the hazards associatedwith perchloric acid. A 10 g portion of sample was homogenized along with
35 mL of 5% TCA and 1 mL of 7.2% butylated hydroxyanisole in ethanol for
3 min using a Polytron PT 2000 homogenizer (Kinematica, Lucerne,
Switzerland). The resultant extract was filtered through a Whatman No. 541
filter paper (Whatman International, Maidstone, UK), collected in a 50 mL
volumetric flask and made to volume with 5% TCA. A 5 mL aliquot of extract
was pipetted into a glass tube followed by 5 mL of TBA, which had been freshly
prepared by dissolving 0.2883 g of 2-thiobarbituric acid (Sigma Chemical,
Poole, UK) in 100 mL of distilled water. The tubes were stoppered and thecontents well mixed prior to heating for 60 min in a boiling water bath (Grant
Instruments, Royston, UK). A blank was prepared in a similar manner using
5 mL of TCA and 5 mL of TBA. The tubes were removed from the water bath,cooled in water for 10 min and the absorbance (D) of their contents measured
in a UV500 spectrophotometer (Unicam, Cambridge, UK) at 538 nm using
1 cm cells. The TBA value was calculated as:
TBA value (as milligrams of malonaldehyde per kilogram of sample) =(Dsample – Dblank) × K
where K is a constant coefficient specifically calculated for individual products.

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2.5.5. 2-alkylcyclobutanone identification
The cyclobutanones, dodecylcyclobutanone (DCB) and tetradecylcyclobutanone (TCB) were determined according to European Standard
EN1785:2003 [9].
2.6. Statistical analysis
The results for all the experimental protocols were subjected to analysis
of variance using Genstat 5.

3.

RESULTS3.1. Effect of irradiation on the quality of a chicken masala chilled ready meal
3.1.1. Oxidative rancidity
Figure 1 shows the results of gamma irradiation on the oxidative rancidityof the ready meals as measured by the TBA method. Statistically, it was foundthat the irradiation dose had a highly significant (p < 0.01) effect on the TBA

0.5

Day 0
Day 7

0.45

Day 14

0.4

TBA values (mg/kg)

0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0 kGy

1 kGy

2 kGy

Uncooked

3 kGy

0 kGy

1 kGy

2 kGy

3 kGy

CookedFIG. 1. Effect of irradiation on the TBA values (mg malonaldehyde/kg) of a chicken
masala ready meal stored for up to 14 d at 3 ± 1°C (SEM = 0.0214, n = 3).

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values of the meals. However, it can be seen that the actual values decreased
with increasing irradiation dose over the range 0–3 kGy. The values obtained
from the non-irradiated and 1 kGy samples were similar, with larger decreases
being observed between 1 and 3 kGy. Overall, there was only a decrease of
13% in the TBA values between 0 and 3 kGy. This is not surprising as the meals
contained only 5.2% lipid. Storage had a significant effect (p < 0.001), the TBA
values with the most significant increase occurring between day 0 and day 7 ofstorage with little change taking place between days 7 and 14. Overall,reheating (cooked) the meals resulted in a 9% decrease in the TBA values. It is
important to note that the values obtained were all less than unity, thereby
indicating that irradiation of the meals would not contain off flavours due tooxidative rancidity.
The results obtained for oxidative rancidity were surprising as it was
expected that the TBA values would increase on irradiation, storage andcooking. One possibility for this result is the presence of antioxidants in themeals, which were quenching the free radicals produced by the ionizing
radiation. The meals proved to be a good source of α-tocopherol (Fig. 2) andcontained a range of ingredients such as onion, tomato, red pepper and spices,which are known for their antioxidant activity. Another explanation could bethat there is a preferential attack mechanism employed by the free radicals on
the α-tocopherol and thiamine present in the meals, thereby reducing the

25
Day 0
Day 7
Day 14

Vitamin E concentration (μg/g)

20

15

10

5

0
0 kGy

1 kGy

2 kGy

Uncooked

3 kGy

0 kGy

1 kGy

2 kGy

3 kGy

CookedFIG. 2. Effect of irradiation on the α-tocopherol content (μg/g) of a chicken masala readymeal stored for up to 14 d at 3 ± 1°C (SEM = 1.110, n = 3).

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concentration of these vitamins. This consequently resulted in a decrease in the
TBA values with an increase being observed in the amounts of α-tocopherol
and thiamine destroyed.
3.1.2. α-tocopherol (vitamin E)
An α-tocopherol level of 23.1 μg/g was measured in the chicken masalameals prior to being irradiated, reheated or stored. It was found that theconcentration of this fat soluble vitamin decreased linearly with increasing
irradiation dose (p < 0.001). Taking an average value over all the treatments,
vitamin E concentration in the meals decreased by 5, 14 and 17%, respectively,
when treated with doses of 1, 2 and 3 kGy, compared with their non-irradiatedcounterparts (Fig. 2). The decreases observed were not unexpected as it is
known that α-tocopherol is radiation labile, being the most sensitive of the fatsoluble vitamins [15, 16]. Reheating the meals resulted in a further reduction in
α-tocopherol concentration, with an overall decrease of 11% being observed.
Storage also resulted in a very highly significant (p < 0.001) reduction in
the α-tocopherol content of the meals (Fig. 2), with the greatest diminution
being found for the non-irradiated samples, where a 21% decrease between
days 0 and 14 was observed. Reductions of 11, 5 and 7% were observed for themeals treated with 1, 2 and 3 kGy, respectively, between days 0 and 14.
Generally, the greatest decrease in vitamin levels occurred between days 0 and
7, with the exception of the 2 kGy samples, in which case a reduction of 5%
occurred between days 7 and 14.
3.1.3. Thiamine (vitamin B1)
For thiamine (Fig. 3), an average concentration of 6.65 μg/g was measured
in the non-irradiated chicken masala ready meal at day 0 of storage and prior toreheating, with average values in the non-irradiated samples after 7 and 14 d
storage at refrigeration temperature being 5.72 and 5.64 μg/g, respectively.
Irradiation of the meals with 1 kGy resulted in an overall decrease in thiaminelevels of 16% compared with non-irradiated meals, with reductions of 21% and
31% being observed at dose levels of 2 and 3 kGy, respectively, in comparison
to their non-irradiated counterparts.
Reheating the meals resulted in an overall reduction in thiamine content(Fig. 3) from 5.13 to 4.80 μg/g, which represented a decrease of only 6%. At the
3 kGy dose level, the thiamine content was the same for both the reheated andchilled meals. The results obtained were similar to those of other studies where
irradiation and cooking have been shown to reduce thiamine levels [11, 17].

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7
Day 0
Day 7

6
Thiamin concentration (Pg/g)

Day 14
5

4

3

2

1

0
0 kGy

1 kGy

2 kGy

3 kGy

Uncooked

0 kGy

1 kGy

2 kGy

3 kGy

CookedFIG. 3. Effect of irradiation on the thiamine content (μg/g) of a chicken masala readymeal stored for up to 14 d at 3 ± 1°C (SEM = 0.0997, n = 3).

The thiamine content of the meals decreased with increasing storage time
(Fig. 3). The greatest decrease in thiamine concentration was observed for the
non-irradiated meals, where an overall decrease of 13% occurred between days
0 and 7, the levels decreasing only 1% further between days 7 and 14. The
thiamine content of the meals given 1, 2 and 3 kGy decreased similarly byapproximately 7% between days 0 and 14.
3.1.4. Alkylcyclobutanone identification
Both DCB and TCB were detected in the irradiated meals, although ionsm/z 98 and 112 were not detected in all of the samples analysed. As expectedfrom previous work [18, 19], irradiation had a very significant effect (p < 0.001)
on the concentration of both DCB and TCB in the chilled meals, with higher
levels of 2-DCB being detected compared with TCB. Levels of 0.071, 0.117 and
0.172 μg DCB/g lipid were detected in the chilled (non-reheated) meals for the
1, 2 and 3 kGy doses, respectively, while TCB concentrations of 0.014, 0.034 and0.053 μg/g lipid were detected. Cooking or storage did not have a significant
effect on the levels of the cyclobutanones as similar levels of cyclobutanones
were measured for DCB in the cooked and uncooked meals (Fig. 4). Detectionof both cyclobutanones proved possible for the chicken masala meals but the323

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0.2
Day 0
0.175

Day 7
Day 14

DCB concentration (Pg/g)

0.15
0.125
0.1
0.075
0.05
0.025
0
1 kGy

2 kGy
Uncooked

3 kGy

1 kGy

2 kGy

3 kGy

CookedFIG. 4. Effect of irradiation on the 2-DCB content (μg/g lipid) of a chicken masala readymeal stored for up to 14 d at 3 ± 1°C (SEM = 0.0114, n = 3).

method would need to be developed in order that ions m/z 98 and 112 can bedetected for each sample in the correct ratios. It should also be borne in mind
that as the meals had a lipid content of only 5%, detection of these compounds
is more difficult than if the meals contained a higher amount of lipid.
3.1.5. Microbiological quality
The effects of irradiation on the microbiological quality of the chilledmeals are illustrated in Figs 5 and 6. In all cases, irradiation significantly
reduced the levels of bacteria in the chicken masala ready meals. Figure 5
shows the effect of irradiation and storage on the TBCs of the meals stored at 3
and 10°C. For the 3°C samples (Fig. 5(a)), all three doses reduced the viablebacteria levels in a similar manner, with numbers being significantly lower thanthe 0 kGy meals even after 14 d of storage. At 10°C storage (Fig. 5(b)), similar
TBCs were observed for the non-irradiated, 1 and 2 kGy meals, with the 3 kGydose significantly reducing levels over the 14 d storage period. The bacterialloads in the meals stored at 10°C were significantly higher than those stored at
refrigeration temperature.
Figure 6 demonstrates the effects of irradiation and storage on thepsychrotrophic counts for meals retained at the two storage temperatures. For
meals stored at 3°C (Fig. 6(a)), similar levels of bacteria were found at the 0324

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(a)
10

0 kGy

1 kGy

2

4

2 kGy

3 kGy

L.O.D

6

8

10

12

3 kGy

L.O.D

Log10 cfu/g

8
6
4
2
0
0

14

Storage (days)

(b)
10

0 kGy

1 kGy

2 kGy

Log10 cfu/g

8
6
4
2
0
0

2

4

6
8
Storage (days)

10

12

14

FIG. 5. Effect of irradiation and storage on the TBCs of a chicken masala ready meal
stored at 3 ± 1°C (a) and 10 ± 1°C (b). LOD = limit of detection (1.70 ln CFU/g).

and 1 kGy dose levels while no bacteria were detected at 2 and 3 kGy, being
below the LOD of 1.70 ln CFU/g. For the meals stored at 10°C (Fig. 6(b)),
similar bacterial loads were observed for the non-irradiated samples and for
those given doses of 1 and 2 kGy. Irradiation at 3 kGy had the most significant
effect on the numbers of psychrotrophic bacteria, although it was noted thatnone were detected at day 0 of storage. Coliforms were not detected in any of
the ready meals during storage.

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(a)
10

0 kGy

1 kGy

2

4

2 kGy

3 kGy

L.O.D

6

8

10

Log10 cfu/g

8
6
4
2
0
0

12

14

12

14

Storage (days)

(b)
10

0 kGy

1 kGy

2

4

2 kGy

3 kGy

L.O.D

6

8

10

Log10 cfu/g

8
6
4
2
0
0

Storage (days)

FIG. 6. Effect of irradiation and storage on the psychrotrophic counts of a chicken masala
ready meal stored at 3 ± 1°C (a) and 10 ± 1°C (b). LOD = limit of detection (1.70 ln CFU/g).

3.2. Effect of irradiation on the quality of minced beef patties
3.2.1. Effects of irradiation on the oxidative rancidity and microbiologicalquality of vacuum packed and overwrapped minced beef patties stored for21 d at 3°C
3.2.1.1. Oxidative rancidity
When the results for the vacuum packed samples were analysed statistically, it was found that irradiation dose did not have a significant effect on the
TBA values. In comparison to the results obtained for the previous

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experiments, it was found that there was an increase in the TBA values withincreasing dose (Fig. 7). However, it was also found that the increase between
the non-irradiated samples and those given 2.5, 5, 7.5 and 10 kGy was 13, 3, 6
and 14%, respectively, thereby indicating that the changes with dose were notconsistent. Similar values were obtained for the 2.5 and 10 kGy samples.
Storage had a highly significant effect (p < 0.001) on the TBA values ofthe beef patties over the 21 d of storage. As can be seen from Fig. 7, the TBA
values were similar from day 0 to 7 for 0 kGy and the 2.5 kGy patties increased
from day 7 to 21. However, for the other doses, there was no particular trend in
the values from day 0 to 21.
Figure 8 shows a comparison of the TBA values obtained for minced beef
patties irradiated in vacuum packages followed by subsequent storage for 21 d,remaining in the vacuum packs or after being transferred to overwrappedpackages. Overall, there was a significant increase in the TBA values withincreasing irradiation dose and this was due to the increases that occurred in
the overwrapped beef patties. A 39% increase in TBA values was observed
between the overwrapped non-irradiated patties and those given 2.5 kGy, withincreases of 57% and 70% being found in the non-irradiated samples and thosegiven 5 and 7.5 kGy, respectively. The values obtained for the 7.5 and 10 kGy
overwrapped samples were similar.

0.6

0 kGy
2.5 kGy

0.5

5.0 kGy
7.5 kGy

TBA values (mg/kg)

10 kGy
0.4

0.3

0.2

0.1

0
Da y 1Da y 2Da y 5Da y 7Da y 14

Da y 21

FIG. 7. Effect of irradiation on the TBA values (mg malonaldehyde/kg) of vacuum
packed minced beef patties stored for up to 21 d at 3 ± 1° C (SEM = 0.0476, n = 3).

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4.5

Day 1
Day 2

4

Day 5

TBA values (mg/kg)

3.5

Day 7
Day 143

Day 21
2.5
2
1.5
1
0.5
0
0 kGy

2.5 kGy

5.0 kGy
Overwrapped

7.5 kGy

10 kGy0 kGy

2.5 kGy

5.0 kGy

7.5 kGy

10 kGyVacuum packed

FIG. 8. Effect of irradiation on the TBA values (mg malonaldehyde/kg) of overwrappedand vacuum packed minced beef patties stored up to 21 d at 3 ± 1°C (SEM = 0.1389, n = 3).

The TBA values of the overwrapped samples increased with storage,
although it was noted that little change occurred over the first two days ofstorage. If a value of unity is taken as the TBA value above which the meat
would be deemed unacceptable from an organoleptic point of view, only the
non-irradiated samples were acceptable over the 21 d storage period. The 2.5
and 5 kGy samples were acceptable up to 7 d, while the 7.5 and 10.0 kGy
samples were acceptable for less than 5 d.
According to work reported by Ahn et al. [20] and Kim et al. [21], despite
the intrinsic antioxidant activities of fresh meat, irradiation was found toaccelerate lipid oxidation in raw pork and beef patties under aerobic
conditions. Therefore, in order to extend the shelf life of products such as
minced beef patties when stored in overwrapped packages, it may be beneficial
to add antioxidants to the meat prior to irradiation in order to prevent or slow
down the process of oxidative rancidity. On the other hand, the patties could be
irradiated and stored in vacuum packs in order to prevent the occurrence ofoxidative rancidity as noted previously. Results of this work show that the
average TBA value obtained for the overwrapped samples was 1.34 mg
malonaldehyde/kg compared with a value of 0.37 mg/kg for the vacuum packed
samples.

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3.2.1.2. Microbiological quality
Both irradiation and storage significantly affected the microbiologicalquality of both the overwrapped and vacuum packed beef patties. Figure 9
clearly shows that irradiation reduced the TBCs in samples stored in both typesof packaging, although it should be noted that higher counts were obtained forthe overwrapped samples (Fig. 9(b)) compared with those stored in vacuum
packages (Fig. 9(a)). Irradiation doses greater than 2.5 kGy reduced thebacterial levels to below the LOD in the vacuum packed samples, with all doses
reducing detectable numbers in the overwrapped patties.
There was little change in the TBCs over the 21 d storage period in thevacuum packed samples, with numbers increasing steadily in the non-irradiatedoverwrapped samples. Similar results were obtained for the pseudomonds
(a)
12
0 kGy

2.5 kGy

3

6

L.O.D

Log10 cfu/g

10
8
6
4
2
0
0

9

12

15

18

21

15

18

21

Storage (days)
(b)
12

0 kGy

L.O.D

3

6

Log10 cfu/g

10
8
6
4
2
0
0

9

12

Storage (days)

FIG. 9. Effects of irradiation treatment and storage on the TBCs of vacuum packed (a) andoverwrapped (b) minced beef patties stored at 3 ± 1° C. LOD = limit of detection (1.7 ln CFU/g).

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counts. The levels of psychrotrophic bacteria counted in the beef patties arepresented in Fig. 10. Irradiation significantly reduced the numbers of psychrotrophs in both types of packaging, although the bacteria appeared to be moresensitive in the overwrapped packs (Fig. 10(b)) owing to the availability ofoxygen. Similar bacterial numbers were detected at the 2.5 and 5 kGy doses inthe vacuum packages (Fig. 10(a)), while bacteria were only detectable at the
2.5 kGy dose in the overwrapped samples. As for the TBCs, the levels ofbacteria were constant over the 21 d of storage in the vacuum packed patties,
while a steady increase was observed in the overwrapped samples.
Anaerobic bacteria (Fig. 11) were detected only in the non-irradiated and2.5 kGy beef patties, with similar levels being detected over the storage period
at 3°C. The irradiation doses of 5–10 kGy reduced the levels of these bacteria to

(a)
12

0 kGy

2.5 kGy

3

6

5.0 kGy

L.O.D

Log10 cfu/g

10
8
6
4
2
0
0

9

12

15

18

21

Storage (days)

(b)
12

0 kGy

2.5 kGy

3

6

L.O.D

Log10 cfu/g

10
8
6
4
2
0
0

9

12

15

18

21

Storage (days)

FIG. 10. Effects of irradiation treatment and storage on the psychrotrophic counts ofvacuum packed (a) and overwrapped (b) minced beef patties stored at 3 ± 1° C. LOD =limit of detection (1.7 ln CFU/g).

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80 kGy

2.5 kGy

L.O.D

7

Log10 cfu/g

6
5
4
3
2
1
0
0

3

6

9

12

15

18

21

Storage (days)

FIG. 11. Effects of irradiation and storage on the anaerobic bacteria in vacuum packed
minced beef patties stored at 3 ± 1° C. LOD = limit of detection (0.70 ln CFU/g).

below the limit of detection. Irradiation significantly reduced the numbers oflactic acid bacteria (Fig. 12) in the vacuum packed patties, with 7.5 and 10 kGy
reducing levels to below the detectable limit. Similar numbers were observed
for the 2.5 and 5 kGy irradiation treatments. The levels of bacteria detected in
the non-irradiated and irradiated samples remained similar over the 21 d ofstorage at 3°C.
8

0 kGy

2.5 kGy

5.0 kGy

L.O.D

7
6

Log10 cfu/g

5
4
3
2
1
0
0

3

6

9

12

15

18

21

Storage (days)

FIG. 12. Effects of irradiation and storage on the lactic acid bacteria in vacuum packed
minced beef patties stored at 3 ± 1° C. LOD = limit of detection (0.70 ln CFU/g).

331

STEWART

3.3. Effect of ionizing radiation and storage on the oxidative rancidity ofminced beef patties containing antioxidants at different concentrations
3.3.1. Experimental protocol 1
Data from this experiment showed that inclusion of antioxidants into thepatties significantly (p < 0.001) reduced oxidation of the product (Figs 13–15) with
TBA values being half of those in control samples without antioxidant added.
Resveratrol was found to be the most effective antioxidant (Fig. 14) with theaverage TBA values of samples containing it being almost three times lower thanthose for control samples. Quercetin and epicatechin produced similar effects(Fig. 16) as oxidation levels were significantly lower than those of the controls.
The least effective antioxidant was α-tocopherol, as the TBA values ofsamples treated with ionizing radiation were not significantly reduced
compared with those of control samples and were significantly higher than theother antioxidants tested (Fig. 14).
It was found that there was a significant difference (p < 0.001) in TBA
values between the two concentrations of antioxidant used with lower values
being obtained at the higher concentration of 550 μmol/kg compared with110 μmol/kg. This effect was most noticeable in the irradiated samples, withlittle effect being observed in the non-irradiated meat patties (Fig. 15).
1.6

Antioxidants included

TBA Value (mg/kg)

Antioxidants not included
1.2

0.8

0.4

0
0

1

2

3

4

5

Irradiation dose (kGy)
FIG. 13. Effect of irradiation treatment on the TBA values (mg malonaldehyde/kg) of
minced beef patties with and without antioxidants included (for antioxidants not included
SEM = 0.0595, n = 15; for antioxidants included SEM = 0.021, n = 120).

332

TBA Value (mg/kg)

STEWART

1.6

T ocopherol

1.4

Quercetin
Epicatechin

1.2

Resveratrol1

Control

0.8
0.6
0.4
0.2
0
0

1

2

3

4

5

Irradiation dose (kGy)
FIG. 14. Effect of including antioxidants on the TBA values (mg malonaldehyde/kg) of
irradiated and non-irradiated minced beef patties with and without antioxidants included(for antioxidants not included SEM = 0.0595, n = 15; for antioxidants included SEM =0.0421, n = 30).

1.6

TBA Value (mg/kg)

1.4
1.2

0 micromol/kg
110 micromol/kg
550 micromol/kg

1
0.8
0.6
0.4
0.2
0
0 kGy

2.5 kGy

5 kGy

FIG. 15. Effect of including antioxidants at different concentrations on the TBA values(mg malonaldehyde/kg) of irradiated and non-irradiated minced beef patties with andwithout antioxidants included (for 0 μmol/kg SEM = 0.0595, n = 15; for 110 and
550 μmol/kg SEM = 0.0298, n = 60).

333

STEWARTAs expected, TBA values increased significantly (p < 0.001) whensamples were treated with ionizing radiation, the increase being linear over the
0–5 kGy dose range (Figs 13 and 14). It was also found that TBA values
increased significantly upon storage, with values at day 28 being approximately
double those on day 1 of storage (Fig. 16). Figure 16 shows that for resveratrol,
quercetin and epicatechin, similar TBA values were obtained during the first
14 d of storage, after which the rate of oxidation started to increase. In the caseof α-tocopherol, there was a linear increase in values from day 1 to day 28 ofstorage similar to that of the control samples without antioxidant added(Fig. 16).
3.3.2. Experimental protocol 2

TBA Value (mg/kg)

As a result of the findings discussed above, another experiment wasundertaken to study a range of concentrations of the four antioxidants todetermine the most effective level for reducing the oxidation of minced beef
patties. As found previously, resveratrol proved to be the most effective
antioxidant with α-tocopherol being least effective (Fig. 17). The concentrationof antioxidant had a significant effect (p < 0.001) on the TBA values with a
gradual decrease in oxidation being observed over the concentration range of

1.6

T ocopherol

1.4

Quercetin
Epicatechin

1.2

Resveratrol1

Control

0.8
0.6
0.4
0.2
0
0

7

14

21

28

Storage (days)
FIG. 16. Effect of storage at 3 ± 1° C on the TBA values (mg malonaldehyde/kg) of minced
beef patties with and without antioxidants included (control: antioxidants not included
SEM = 0.0710, n = 9; antioxidants included SEM = 0.050, n = 18).

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STEWART

0.5

TBA Value (mg/kg)

0.45
0.4
0.35
0.3
0.25
0.2
0.15

T ocopherol

0.1
0.05

Epicatechin

Quercetin

Resveratrol

0
0

100

200

300

400

500

600

700

Antioxidant concentration (Pmol/kg)
FIG. 17. Effect of different concentrations of antioxidant on the TBA values (mg malonaldehyde/kg) of minced beef patties (SEM = 0.0389, n = 12).

25–700 μmol/kg. The decrease in TBA values with increasing concentration of
resveratrol did not appear to be significant as similar values were obtained ateach concentration. A more noticeable decrease in oxidation values was notedfor quercetin and epicatechin between levels of 25 and 100 μmol/kg, with aslight increase being observed at these concentrations for α-tocopherol, after
which the values decreased. Thus, it would appear that inclusion levels as low as
25 μmol/kg would effectively reduce oxidation in meat purees, particularly if
resveratrol was used as the antioxidant.
As for experiment 1, beef patties treated with ionizing radiation exhibited
higher TBA values than non-irradiated samples (Fig. 18), although it wasobserved that there was no significant difference between values for theirradiated and non-irradiated samples containing resveratrol. Similar TBA
values were measured for samples containing quercetin and epicatechin, bothfor irradiated and non-irradiated samples. Storage (Fig. 19) also resulted in asignificant increase in TBA values.
The results obtained for the addition of antioxidants to minced beef are inagreement with studies carried out by other workers. Work by Bekhit et al. [22]on beef patties showed that resveratrol gave the highest protective effectagainst lipid peroxidation, with quercetin, carnosine and rutin also slowing
down the process compared with the control. These workers did note that theeffect of resveratrol is dependent on its concentration and method of
application to meat, being more effective when applied in solution rather than335

STEWART

0.6

0 kGy
2.5 kGy

TBA Value (mg/kg)

0.5
0.4
0.3
0.2
0.1
0
Control

Tocopherol

Quercetin

Epicatechin

Resveratrol

FIG. 18. Effect of ionizing radiation on the TBA values (mg malonaldehyde/kg) of
minced beef patties with and without antioxidants included (control: no antioxidants
included, SEM = 0.0551, n = 6; antioxidants included, SEM = 0.0225, n = 36).

in the dry form. It was found that the effect was also dependent on concentration which was also the case for the work reported here. The results obtainedfor α-tocopherol were somewhat surprising as this vitamin is well known for its
antioxidant properties. It may be the case that as α-tocopherol is radiation
0.7

Day 1
Day 14TBA Value (mg/kg)

0.6
0.5
0.4
0.3
0.2
0.1
0
Control

Tocopherol

Quercetin

Epicatechin

Resveratrol

FIG. 19. Effect of storage at 3 ± 1° C on the TBA values (mg malonaldehyde/kg) of minced
beef patties with and without antioxidants included (control: no antioxidants included,
SEM = 0.0551, n = 6; antioxidants included, SEM = 0.0225, n = 36).

336

STEWARTsensitive, the level of the vitamin in the patties decreased upon irradiation
resulting in its antioxidant activity being reduced and thus it being less effective
than the other antioxidants. However, it was noted in work carried out by Ahn
and Nam [23] that a combination for sesamol and tocopherol was highly
effective for reducing lipid oxidation.
3.4. Effects of ionizing radiation and storage on the oxidative rancidity ofsalmon meat patties containing antioxidants at different concentrations
As for minced beef patties inclusion of antioxidants significantly (p <0.001) reduced the levels of oxidative rancidity in the salmon patties. Data fromthis study showed that epicatechin was the most effective antioxidant (Fig. 20)
for reducing oxidative rancidity, with TBA levels approximately 53% of thosesamples with no antioxidant included. This is in contrast to the results obtained
for the beef patties where resveratrol proved most effective. Quercetin was thenext most effective antioxidant for reducing rancidity, followed by resveratrol.
As for the beef patties, α-tocopherol was the most ineffectual antioxidant, with
TBA levels 5% less than those of the control samples. Work by Tang et al. [24]on the antioxidant activity of added tea catechins on lipid oxidation of raw
minced red meat, poultry and fish muscle reported that tea catechins added at
a level of 300 mg/kg reduced lipid oxidation, the antioxidant potential being
two to fourfold greater than α-tocopherol, depending on the species.

1.4

TBA Value (mg/kg)

1.2
1
0.8
0.6
0.4
0.2
0
Control

Tocopherol

Quercetin

Epicatechin

Resveratrol

FIG. 20. Effect of including different antioxidants on the TBA values (mg malonaldehyde/kg) of salmon meat patties (SEM = 0.116, n = 12 for control, n = 72 for antioxidants).

337

STEWART

Tang et al. [24] found that when α-tocopherol was added at a level of
300 mg/kg to minced muscle, it showed limited effects in inhibiting lipidoxidation for pig, chicken, duck and whiting. These workers suggested thatchelating iron in raw minced muscle may be a possible mechanism forinhibition of lipid oxidation.
Antioxidant concentration had a significant effect (p < 0.001) on
oxidative rancidity (Fig. 21) with overall reduction in TBA values of 31% being
observed for the irradiated samples between concentrations of 25 and700 μmol/kg. As expected, the irradiation dose significantly affected TBA
levels as can be seen from Fig. 22, which also shows the effect of storage on the
TBA values of the salmon purees for each of the different antioxidants andcontrols when irradiated or left non-irradiated. For the non-irradiated samples,
similar TBA values were measured for quercetin, epicatechin and resveratrolon days 1 and 14, while the values for samples containing α-tocopherol or noantioxidant showed an increase of over 50% in both cases. A significant
increase in oxidative rancidity can be clearly seen when irradiated samples
were stored over the 14 d storage period. The salmon patties containing αtocopherol showed the greatest increase in TBA values upon storage.

TBA Value (mg/kg)

2
1.8

0 kGy
2.5 kGy

1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0

100

200

300

400

500

600

700

Antioxidant concentration (Pmol/kg)
FIG. 21. Effect of concentration of antioxidant on the TBA values (mg malonaldehyde/kg)
of salmon meat patties, non-irradiated and treated with 2.5 kGy (SEM = 0.088, n = 36).

338

STEWART

3.5

Day 1
Day 14TBA Value (mg/kg)

3.0
2.5
2.0
1.5
1.0
0.5
0.0
Co

ntr

ol

To
Qu
Ep
Re
To
Qu
Ep
Re
Co
cop
ica
sve
c op
sve
ica
erc
erc
ntr
tec
tec
etin
rat
etin
rat
ol
her
he r
hin
hi n
rol
rol
ol
ol

0 kGy

2.5 kGy

FIG. 22. Effect of storage on the TBA values (mg malonaldehyde/kg) of salmon meat
patties with and without antioxidants, non-irradiated and treated with 2.5 kGy (SEM =0.023, n = 36 for control, n = 18 for antioxidants).

4.

CONCLUSIONS
The work undertaken demonstrated that:• Irradiation doses of 2–3 kGy can extend the shelf life of ready meals andminced beef for at least 14 d at refrigeration temperatures.
• Irradiation under vacuum packaging will significantly enhance shelf life,
as numbers of bacteria are significantly reduced for up to 21 d without theoccurrence of unacceptable levels of oxidative rancidity.
• Storing irradiated meals or minced beef in overwrapped packages will
significantly increase the microbial numbers present and result in an
increase of oxidative rancidity, thereby resulting in a decrease in overall
quality and acceptability.
• Irradiation will reduce the levels of vitamins in ready meals although thediminution would not have a significant impact on nutritional value.
• Addition of antioxidants to meat and fish purees prior to irradiation cansignificantly reduce oxidative rancidity, with the phytochemicals
epicatechin, quercetin and resveratrol being more effective than αtocopherol.

339

STEWART• The 2-alkylcyclobutanone (EN1785) standard method can be used todetect irradiation treatment of the meals analysed and, from previous
work, has been demonstrated to be capable of detecting irradiatedminced beef [25] and salmon meat [26].

ACKNOWLEDGEMENTS
The author wishes to thank W. Graham, S. Wilson and M. Linton fortechnical assistance during the course of this work and A. Gordon and
S. Dawson for carrying out the statistical analysis.

REFERENCES
[1]
[2]

[3]

[4]

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[6]

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VERLEGH, P.W.J., CANDEL, M.J.J.M., The consumption of convenience foods:
reference groups and eating situations, Journal of Food Quality and Preference 10
6 (1999) 457–464.
INTERNATIONAL ATOMIC ENERGY AGENCY, Radiation Processing for
Safe, Shelf-stable and Ready-to-eat Food, IAEA-TECDOC-1337, IAEA, Vienna(2003).
McATEER, N.J., GRANT, I.R., PATTERSON, M.F., STEVENSON, M.H.,
WEATHERUP, S.T., Effect of irradiation and chilled storage on the microbiological and sensory quality of a ready meal, International Journal of Food
Science and Technology 30 (1995) 757–771.
PATTERSON, M.F., STEVENSON, M.H., GRANT, I.R., McATEER, N.J.,
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STEVENSON, M.H., STEWART, E.M., McATEER, N.J., A consumer trial toassess the acceptability of an irradiated chilled ready meal, Radiation Physics andChemistry 46 4–6 (1995) 785–788.

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food/food/biosafety/irradiation/anal_methods_en.htm (2006).
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CONSUMERS’ WILLINGNESS TO PAY FORIRRADIATED PREPARED GROUND BEEF
R.M. NAYGA, Jr., R. WOODWARD
Department of Agricultural Economics,
Texas A&M University,
College Station, Texas,
United States of America
W. AIEW
CP Group,
Bangkok, Thailand

Abstract
This paper focuses on estimating willingness to pay for reducing the risk ofcontracting foodborne illness using a non-hypothetical experiment utilizing real foodproducts (i.e. prepared ground beef), real cash and actual exchange in a market setting.
Respondents were given positive information about the nature of food irradiation.
Single bounded and one and one-half bounded models are developed using dichotomous choice experiments. The results indicate that individuals are willing to pay for a
reduction in the risk of foodborne illness once informed about the nature of food irradiation. Respondents are willing to pay a premium of about US $0.77 for 450 g (1 pound)of irradiated ground beef, which is higher than the cost of irradiating the product.

1.

INTRODUCTION

Despite the fact that food has never been as safe as it is today, food safety
remains a major issue. The Centers for Disease Control and Prevention
estimated that in the United States of America, 76 million people fall sick,more than 300 000 are hospitalized and 5000 people die each year fromfoodborne illness [1]. There were also 66 recalls for Listeria or Escherichia colicontaminated beef, pork and poultry in 2002, totalling approximately 27 ×
106 kg of meat — nearly three times as much as in 2001. The largest of theserecalls involved about 12 × 106 kg of food product and cost US $81 million, notincluding litigation costs [2]. Although the developments related to theadoption of hazard analysis critical control point (HACCP) and other safety
standards may have helped reduce the incidence of foodborne illness in theUSA, infections with Salmonella, E. coli O157:H7, Campylobacter and Listeria

343

NAYGA et al.

remain and, alarmingly, continue to be an ever present phenomenon. The
HACCP standard for all meat and poultry plants currently in place requiresthat certain standards be met throughout the industry, but it does not explicitly
promote any particular antibacterial intervention and thus allows the plant
some flexibility in its compliance decisions.
To really make a difference, new approaches for prevention are needed.
One such approach is the use of food irradiation technology. Food irradiation isa food safety technology that can eliminate disease-causing germs from foods.
As with pasteurization of milk and pressure cooking of canned foods, treating
food with ionizing radiation can kill bacteria and parasites that would
otherwise cause foodborne disease. Food is irradiated in a special processing
facility where it is exposed to an electron beam or X ray, generated fromelectricity or gamma rays produced by 60Co. Careful monitoring ensures thatthe food receives the prescribed amount of irradiation needed to destroy
harmful bacteria. On the basis of decades of studies, the World Health Organization, the Food and Drug Administration (FDA), the US Department ofAgriculture and the Centers for Disease Control and Prevention haveendorsed the safety of irradiated food. The last organization conducted a studyof the potential benefit of irradiating meat and poultry in the USA andestimated that irradiating 50% of meat and poultry will result in the preventionof nearly 900 000 cases of infection, 8500 hospitalizations and 350 deaths eachyear [3].
Despite these benefits, the use of this technology as an important healthand food safety tool that could complement rigorous safety programmes is still
limited. This paper focuses on an important component of its acceptance —consumers’ willingness to pay (WTP) for irradiated food after they have been
given positive information about the nature of food irradiation. The authors
estimate this WTP using a non-hypothetical market experiment with real
products (i.e. irradiated prepared ground beef), cash and actual exchange. A
number of papers in the economics literature, including Shogren et al. [4] andList [5], have also used real products, cash and actual exchange in a market
setting. Using data from their dichotomous choice experiments, the authors
estimate the WTP for irradiated food using the traditional single bounded (SB)approach and a one and one-half bounded (OOHB) approach, based on
Cooper et al. [6]. The authors’ results suggest that individuals are willing to pay
for reducing the risk of foodborne illness once informed about the nature offood irradiation with the WTP estimates varying little between the SB andOOHB estimates. Their study, however, does not provide anti-food-irradiation
information to consumers, so it is possible that the results reflect the absolute
maximum consumers would pay for irradiated prepared ground beef.

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NAYGA et al.

2.

LITERATURE REVIEWThe early efforts of Bishop and Heberlein [7] found that hypotheticalquestions can yield responses that are similar in magnitude to those representing true market behaviour and, although there is still some debate about
the method, many studies have found that elicited values can be realistic
measures of WTP. Two of the main areas of concern in the WTP literature areconstruct validity, whether the results are consistent with economic theory, andcontent validity, how well the survey instrument presents the problem andcaptures true preferences. A source of bias that has been of particular concern
in the literature is the tendency to “yea say”, leading to greater estimates of
WTP than is probably realistic. Evidence of this ‘hypothetical bias’ iswidespread [8–11]. To counter such problems, some studies have investigatedthe means of calibrating hypothetical WTP to non-hypothetical results
obtained in an experimental setting [12–15]. In general, the consistent lesson in
the literature is that the more realistic the setting, the less the hypothetical bias
the more valid the results will be. To the extent that real payment can be used,confidence in the results will increase [16].
A number of studies have elicited WTP for irradiated meat [17–20]. One
such study, by Shogren et al. [19], is an empirical study composed of a mailsurvey, a laboratory experiment and a retail store semicontrolled experiment.
In each case, individuals are confronted with a choice between conventional
and irradiated chicken breast. They concluded that consumer choices weresimilar across market settings at a price premium for irradiation. Their findings
also suggest that individuals are initially sceptical of irradiated food but theirconcerns can easily be allayed through simple educational devices. They also
noted that the premium their respondents were willing to pay for irradiatedchicken breasts easily covers the additional costs for commercial scale irradiation. Another study by Nayga et al. [20] ‘revisited’ the WTP and willingness toaccept (WTA) divergence issue using irradiated ground beef and the same nonhypothetical market experiment utilized in the current paper. They found
WTA/WTP ratios that are significantly lower than most such studies. Other
studies have also found that consumer preferences and acceptance of theirradiation technology can be influenced by knowledge and information about
the technology [17, 20–24]. For instance, Nayga et al. [24] revealed that
information about the nature and benefits of food irradiation positively affects
consumers’ willingness to buy irradiated foods. Their study does not focus on
the information effects on consumers’ willingness to buy (c.f. Ref. [24]) or on
the WTP–WTA divergence issue (c.f. Ref. [20]). Rather, the focus of this study
is on the WTP for irradiated ground beef in Texas using data from anartefactual field experiment [25] in which respondents demonstrate their values

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NAYGA et al.

by exchanging money for real products. Similar elicitation approaches havebeen used in the past by a few studies [26, 27]. The study was conducted in
Texas because no irradiated ground beef has yet been sold in Texas supermarkets and because of the relative importance of beef consumption andproduction in Texas. The south region that includes Texas consumes close to
40% of the total ground beef consumption in the USA [28]. Texas is also thenation’s leading beef producer.

3.

EXPERIMENTAL METHOD

To date, most valuation experiments have been conducted in laboratory
settings and values are typically elicited using an auction mechanism [27]. In
the present study, the authors conducted the WTP experiments in a morefamiliar setting for the consumers by carrying out the experiment in supermarkets with individual shoppers rather than in a laboratory with randomly
selected groups of participants. Lusk et al. [27] argued that in store valuation
has demonstrable and potential advantages for the experimenter comparedwith a laboratory setting, in terms of subject selection and reduced cost. Insteadof using an auction elicitation mechanism, the authors conducted face-to-face
WTP dichotomous choice artefactual field experiments at selected stores of theregional supermarket chain in Austin, Houston, San Antonio and Waco, Texas,from March to June 2002, using real products (i.e. ground beef), cash and actual
product exchange in a supermarket setting. The sample size was determined
partly as a function of the budget for the study. The study was undertaken infour cities in Texas in order to achieve a good representation of consumers inthe state.
STATEMENT 1 (Info I):
General statement about food irradiation excerpted from United States
General Accounting Office (GAO), Washington, D.C.
“Food irradiation is the process of exposing food to controlled levels of
ionizing radiation. Ionizing radiation is a type of energy similar to radio
and television waves, microwaves, and infrared radiation. The highenergy produced allows it to penetrate deeply into food, killing microorganisms without significantly raising the food’s temperature.
Irradiation, within approved dosages, has been shown to destroy at least
99.9 percent of common foodborne pathogens, such as Salmonella346

NAYGA et al.

(various species), E.coli O157:H7, and Listeria monocytogenes, which areassociated with meat and poultry. Irradiation can also prolong shelf life,
decontaminate spices, and control insect infestation.”
STATEMENT 2 (Info II):“The FDA mandates that all foods treated with ionizing energy belabeled as having been irradiated. Note that ionizing radiation has thesame effect on food, but its source of energy is different. In the UnitedStates, gamma rays and electron beam are used for food irradiation.
1. Gamma rays process
The source of gamma rays is cobalt-60. The cobalt is held in thin stainlesssteel rods that are placed on a rack in an irradiation facility. The rackholding the cobalt containing rods is stored in a deep pool of water in theirradiation facility. When products are to be irradiated, the rack is raised
from the pool and products are conveyed past the rack to absorb the
gamma rays being emitted from the cobalt rods. Gamma rays are also
produced from cesium-137, but those from cesium are not used for foodirradiation.
2. Electron beam process
The source of electron beam is a machine, much like a television set,
which utilizes electricity to generate electrons and accelerates theelectrons to nearly the speed of light. When products are to be irradiated,the electron beam accelerator is switched on and products are conveyed
through the stream of electrons. The electron beam process is also called
electronic pasteurization.”
The WTP experiments were carried out in 13 supermarkets. About 13–15
respondents per store were selected for the WTP experiments for a total
sample size of 256.1 The respondents were randomly selected as they entered
the supermarket. The selected individuals were asked if they purchase and1

A total of 484 respondents were interviewed but only 471 of these were usefulowing to incompleteness in some of the data. Of the 471 subjects, 256 were given the
WTP experiments and 215 were given the WTA experiments (see Ref. [20] for results
related to the WTP–WTA divergence issue).

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consume ground beef and, if so, were invited to participate in a survey. If theselected individual was not eligible or refused to participate, another individual
was randomly chosen. The respondents were first provided information aboutfood irradiation as presented in statements 1 and 2. After information aboutfood irradiation was provided, each respondent was given a pound (450 g) of
non-irradiated ground beef and a randomly chosen amount of cash.2 The
respondents were told that the meat and cash were gifts for participating in the
study. The respondent was then asked whether he or she would be willing to
exchange the non-irradiated ground beef and the cash for the same quantity ofirradiated ground beef. If the respondent accepted the bid, the cash amount
was recorded as his/her WTP first bid value and the exchange was made.
However, if the respondent rejected the bid, he/she was again asked his/herwillingness to exchange the non-irradiated ground beef and a half value of the
cash (representing second bid value for the OOHB specification) for the same
quantity of irradiated ground beef. If the answer was “yes”, the cash amount
was recorded as his/her WTP second bid value and the exchange was made.3
In developing the experiment, a two day pretest was carried out in a local
supermarket in College Station, Texas. The objective of the first pretest day was
to use open ended WTP questions to help determine the bid values to be usedin the dichotomous choice experiments. The open ended responses from thesepretests were then used to select the bid values and sample sizes to be used in
the dichotomous choice questions in the main experiment using the DWEABSmodel [29]. The DWEABS model uses an iterative procedure to select the
optimal bid values as well as the sample sizes corresponding to each bid thatminimize the mean square error of the welfare measure. Pretest data and total
sample sizes are required as inputs for the DWEABS model to calculate
optimal bid values and sample sizes corresponding to each bid. On the second
day of the pretest, the dichotomous choice with follow-up experimental design
was tested with the specific bid values calculated from the DWEABS model.
The experiment was designed to achieve the highest degree of realism
possible. Real meat products were used in order to give the respondent anexperience similar to standing at the meat counter and making choices. Real
cash was used to make it clear that the respondent was making actual sacrifices

2

Cash amounts were randomly chosen, based on values calculated from the
distribution with equal area bid selection (DWEABS) model as discussed below.
3
A reviewer expressed concerns over offering a higher incentive if the participant refused the offer the first time. The participants were not informed initially that
there would be a follow-up question. However, it is possible that a participant might
strategically refuse the second time, thinking there might be a third offer.

348

NAYGA et al.

if he or she chose to pay for the irradiated meat. Although it is possible that
respondents treated the gift given to them in the experiment differently than
the rest of their budget, efforts were made to diminish this possibility byemphasizing that the meat and money were a gift and that they could keepthese at the end of the interview. They were also told that they could stop or
walk away at any time during the interview if they so desired and still keep thegift given to them. A similar method was employed by Shogren et al. [19],although in that study a payment of US $30 was given to the respondent, andthey were informed that they would be offered an opportunity to purchase agood for up to US $5.

4.

THE EMPIRICAL FRAMEWORK

Although statistical information could be maximized using an open
ended WTP question, this ignores considerations of an individual’s cognitive
capacity [30]. Individuals often cannot simply state their WTP ‘off the top of
their heads’. The closed ended dichotomous choice format comes closest toreflecting how individuals think and what they can answer. Consequently, theauthors used the dichotomous choice with follow-up experimental
methodology described in this paper and estimated SB and OOHB models.
The following sections discuss these models.
4.1. SB model
Assume that an individual’s utility function is well behaved and definedover the commodity of interest, q, and x, a bundle of commodities other thanq. The individual’s optimization problem is also affected by their income, y,their characteristics, s, and the stochastic component of preference, ε. Define
an indirect utility function for the individual as v(p,q,y,s,ε), which implicitly
assumes that optimal choices over x have already been made. Suppose theindividual is confronted with the possibility of securing a change from q0(non-irradiated ground beef) to q1 (irradiated ground beef) and this change
costs US $A. If they regard this change as an improvement, then v(p,q1,y–A,s,ε) ≥ v(p,q0,y,s,ε). The probability that an individual would accept thechange at cost US $A is, therefore:{}

Pr {response is yes } = Pr v( p, q 1 , y - A, s, e ) ≥ v( p, q 0 , y, s, e )(1)

An equivalent way to express this same outcome uses the compensating
variation measure, which is the quantity C that satisfies:349

NAYGA et al.

v( p, q 1 , y - C , s, e ) = v( p, q 0 , y, s, e )(2)Thus, C = C(p,q0,q1,y,s,ε) is the individual’s maximum WTP for the change
from q0 to q1. In general, it is assumed that the respondent knows C, but it isunknown to the analyst. The respondent will answer “no” if their maximum
WTP value is smaller than the cost of the change, i.e. C < Α. Therefore, anequivalent condition to Eq. (1) is:{}

Pr {response is no } = Pr C ( p, q 0 , q 1 , y, s, e ) < A(3)

The analyst treats C as a random variable, with an assumed cumulative
distribution function, GC(·), and probability density function, gC(·). By
construction, it is interpreted that GC (◊) = Pr {response is no }, and theprobability of a “yes” response is:

Pr {response is yes } = 1 - GC ( A)(4)

An individual’s random WTP can be formulated by assuming that C is
A- mnormally distributed with E {C } = m = X b , and Var(C )=s 2 . Hence, z =sis a standard normal variable and Eq. (4) can be rewritten:

Pr {response is yes } = 1 - F (z)(5)

where Φ(⋅) is the standard normal distribution. Hence, the model equates to amprobit model with an intercept term ofand a bid coefficient of 1 :ss

Ê m Aˆ
Pr {response is yes } = F Á - ˜ ∫ F (a - b A)
Ës s ¯(6)Note that the right hand side of Eq. (1) can be rewritten as follows:

{

} (7)

Pr {response is yes } = Pr v( p, q 1 , y - A, s, e ) - v( p, q 0 , y, s, e ) ≥ 0{}

Pr {response is yes } = Pr Dv( p, q 0 , q 1 , y, A, s, e ) ≥ 0

350

(8)

NAYGA et al.

If Δv(·) equals zero, then an individual will be indifferent to the proposed
improvement. From Eqs (2, 6), suppress A with C and obtain a – bC = 0, where
C is the expected compensating variation. Hence, given an estimate of theparameters α and β, an estimate of the individual’s maximum WTP is obtained:

WTP = -ab

(9)

The parameters of both the SB and OOHB models are estimated using
maximum likelihood. For the SB model, the log likelihood function is:ln Ls (a , b ) =Â {d ln (F (a - b A )) + d ln (1 - F (a - b A ))}
n

i =1

Y
i

i

N
i

i

(10)

where d iY = 1 if the ith response is “yes” and 0 otherwise, while d iN = 1 if the
ith response is “no” and 0 otherwise. The maximum likelihood estimator,ŸŸŸ∂ ln L(q)denoted q ∫ (a , b ), is the solution to the equation= 0. The asymptotic∂q
variance–covariance matrix of q is given by the Cramer–Rao lower bound:
Ÿ ˆ˘
È
Ê 2
∂
ln
(
)˜ ˙
L
q
Í
V Áq ˜ = - E ÁÍË ¯Á ∂q ∂q ¢ ˜ ˙
Ë
¯ ˙˚
ÍÎ

Ê Ÿˆ

-1

(11)

4.2. OOHB model
In recent years, it has been recognized that the econometric efficiency of
the SB approach is limited. Various approaches have been proposed to gather
more data from each respondent and there is no consensus that one method isalways to be preferred to others [31]. One approach that is now widely used isthe double bounded (DB) dichotomous choice framework [32, 33]. In the DB
approach, a second WTP question is asked in which the bid is increased for
those who responded “yes” and decreased for those who responded “no”.4
Despite the increased econometric efficiency [32], however, Hanemann and

4Note that the DB approach is distinct from a bidding game specification inwhich the questions are repeated until a maximum WTP is identified. The bidding gameapproach has been rejected because its results are biased from the point at which
bidding starts.

351

NAYGA et al.

Kanninen [30] argued that there is evidence that some of the responses to thesecond bid are inconsistent with the responses to the first bid owing to the factthat two separate overlapping sets of bids are being requested. For example,
the following scenarios can be considered: (a) the respondent answers “no” toa US $0.80 bid but answers “yes” to a US $0.40 bid, (b) the respondent answers“yes” to US $0.20 bid and answers “yes” to a US $0.40 bid. Seeing that theprobability of accepting US $0.40 bid is conditioned by the first bid question,
the calculated probability of accepting the US $0.40 offer from the two
scenarios differs. This finding is supported by the McFadden and Leonard study[34].
A second inconsistency in the DB approach arises from what is known as
the response effect. Altaf and Deshazo [35] argued that even if the respondent
answers the first bid question in a neutral manner, when asked a follow-up
question with a lower or a higher bid, they might not react to the second
question in a neutral manner because the second question is seen as an attempt
to bargain. Therefore, the response to the second bid can be biased.
Cooper et al. [6] responded to these concerns by developing an approachin which respondents are only asked a follow-up question some of the time.
Their OOHB approach first involves providing a respondent with two initialvalues into which the true price of the good might be found. Choosing one ofthese two extremes at random, a first WTP question is asked. A follow-up is
asked only if the respondent might rationally change their answer when asked
about the second extreme. For example, a “yes” to a US $2 question might befollowed by a “no” to a US $4 question. The authors show analytically that the
OOHB method achieves a large portion of the efficiency gain achieved throughthe DB.5
Hence, the OOHB approach may offer most of the statistical advantagesof the DB format without the problematic response effects.
The OOHB approach used here is similar to that used by Cooper et al. [6]except that a single price is first given, and then a follow-up question is asked
only if a response of “no” is given to the first question. In the authors’ OOHB
model, therefore, there are three possible outcomes: (1) the individual
responds “yes” and is given the product; (2) the individual responds “no” on thefirst bid but “yes” on the second, lower, offer; and (3) the individual responds“no” on both the first and second offers. Given an initial bid of US $A1, andusing the same functional form assumptions as above, the probability of the5

Although, as noted, the anticipated efficiency gain does not materialize in theirempirical application.

352

NAYGA et al.

mA

first event is 1 – Φ(z1), where, as above, z1 = - 1 = a - b A1. Those that rejects s
the first bid are offered a second bid, A2 < A1, and the probability of acceptingthat bid, conditional on the fact that the first bid has already been rejected, isg(z1, z2), where g(⋅) is the density function of z2 = α − βA2.
The log likelihood of the OOHB model is:

ln L =

È

È

˘

˘

•

Â {(I ) log ÍÎ Ú F(z )dz ˙˚ + (1 - I )(I ) log ÍÎ Ú Ú g (z , z ) dz dz ˙˚
N

i =1

1

z1

-•

1

1

1

2

z1

-• z 21

2

1

2

È z1 z 2˘+ (1 - I 1 )(1 - I 2 ) log Íg (z1 , z 2 ) dz1dz 2 ˙Î -• -•
˚

Ú Ú

(12)

where I1 = 1 if the answer to the first bid is “yes”, and 0 otherwise, and I2 = 1 if
the answer to the second bid is “yes”, and 0 otherwise. Equation (10) is treatedas a bivariate function.

5.

RESULTS

Table 1 presents the profile of the sample compared with the population
profiles of Texas and the USA. About 57% of individuals in the sample arefemale, 54% are white and 45% have incomes between US $30 000 and
US $75 000 per year. The sample is representative of the Texas and US
populations in terms of income, employment status and marital status.
Compared with the state averages, however, the sample includes more womenand members of other ethnic groups (i.e. Hispanics). This was expected since
the study targets shoppers in the family, who tend to be female in cities with arelatively high Hispanic population.
Table 2 exhibits the parameter estimates of the WTP models. These were
estimated using Eqs (8, 10) above. The bid1 and income1 variables refer to thebid (measured in cents) and income (measured in thousands of dollars), using
only the first bid values while the bid2 and income2 variables refer to the bid andincome variables using follow-up bids in the OOHB model. Hence, there are nobid2 and income2 variables in the SB model because this model only uses the firstbid values. Results indicate that the expected WTP equals 76.96 cents for the SBmodel and 76.98 cents for the OOHB model. Using Krinsky and Robb’s [36]approach, the 90% confidence bounds are between 62.42 and 99.10 and between
58.90 and 153.03, respectively.

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NAYGA et al.

TABLE 1. RESPONDENT PROFILE COMPARED WITH TEXAS AND
US POPULATION PROFILES
Variable

Survey sample

TexasaUSAa

Female

0.57

0.50

0.51

Whites

0.54

0.71

0.75

African American

0.14

0.12

0.12

Other ethnic groups

0.32

0.17

0.13

Age less than 30 years

0.17

0.46

0.42

Age between 30 and 50 years

0.50

0.30

0.30

Age greater than 50 years

0.33

0.24

0.28

Married

0.63

0.67

0.64

Employed full-time

0.55

0.59

0.60

Annual household income lower than US $30 000

0.37

0.37

0.35

Annual household income between US $30 000 and
US $75 000

0.45

0.42

0.42

Annual household income greater than US $75 000

0.18

0.21

0.23

a

Source: http://www.census.gov/main/www/cen2000.html as of 4 June 2003.

TABLE 2. ESTIMATION RESULTS
SB
Variable

Coefficient

OOHB
p value

Coefficient

p valueConstant1

0.72160.00070.78310.0001

Bid1–0.00940.0002–0.01030.0001

Income10.00010.97420.00010.9059Constant2

0.91630.0001

Bid2–0.01190.0300

Income20.00010.7285

Rho

0.99890.0001

Estimated WTP
90% confidence interval
Number of observations
a

a

76.97

76.98

62.43–99.10

58.90–153.03

256

256

Calculated using Krinsky and Robb’s (1986) Monte Carlo simulation technique [36].
Bids or prices used are $0.10, $0.40, $0.60, $0.80 and $1.20 for first bid values and halfeach of these prices for the second bid values.

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NAYGA et al.

It is not surprising that the OOHB results do not differ from the SB ones
since both should be capturing the same underlying preferences. However, it isinteresting that the efficiency gains hoped for in the OOHB approach do notmaterialize — the confidence interval actually increases relative to that in the
SB model. Such results are not, however, without precedent. Cooper et al. [6]found very similar results in their empirical application. Their OOHB approach
did not significantly change the mean predicted value, and the confidence
interval actually increased.6
As the mean WTP values indicate, there is no statistical difference
between the SB model and OOHB model WTP values. Consequently, one
could conceivably use just the data from the first bids and ignore data from thefollow-up questions. Herriges and Shogren [37] suggest that there are also costs
associated with the use of follow-up questions. For instance, it is possible that if
the individual anchors their prior WTP to the initial bid then the efficiency
gains from follow-up questioning are likely to be reduced since the effective
information content of the follow-up questioning is diluted by the anchoring
phenomenon. The issue of anchoring was not evaluated, however, because it
was beyond the scope of the current paper.
Figure 1 presents a pseudo-demand function of the predicted percentage
of individuals that would accept bids from US $0 to US $2.50. The circular dots

FIG. 1. Predicted probability that a bid is accepted (evaluated at an average income of
US $48 175) and the actual percentage of bids accepted in the first and second rounds.

6

It is not clear why there is a loss of precision with the OOHB approach. It is
possible that this is related to the issue discussed in footnote 3. Further research on thisarea is warranted.

355

NAYGA et al.

indicate the proportion of the respondents that answered affirmatively to thefirst bid question and the square dots indicate the responses to the second bid
question. As can be seen in this case, the SB and OOHB specifications yieldessentially the same WTP estimate. The main difference between the predictedacceptance rates is that the OOHB line is somewhat steeper than the SB line.
This change in the slope is due to the low acceptance rates for the second bid.
The steeper slopes mean that the OOHB estimate of the probability of a bid
being accepted is ‘tighter’, which is the advantage of the OOHB specification.
However, as noted above, this increase in precision is offset in this case by thegreater variation in the estimated coefficients, leading to an increase in theconfidence interval for the expected WTP.
Consistent with findings from other studies mentioned previously [17–19], the current findings suggest that consumers are willing to pay for irradiatedfood to reduce the risk of contracting foodborne illness. The USDA estimatesthat irradiated ground beef will cost 13–20 cents more per 450 g than nonirradiated ground beef because of the additional handling and packaging, thecost of irradiation itself, and post-irradiation testing for pathogens [2]. At thesecost estimates, similar to the findings of Shogren et al. [19], the authors’ WTP
estimates will cover the additional costs of commercial scale irradiation. Moreeffort is still needed though, in educating consumers about the irradiation
process in order to increase their acceptance of this technology.

6.

VALIDITY TESTS

Owing to the nature of WTP studies, it is important to assess the validityof the results. As noted above, the experiment was designed to achieve a highlevel of hypothetical validity. Construct validity is a form of validity used toassess whether hypothesized theoretical relationships between the elicited
WTP and its explanatory variables are supported by the data [38]. Hence, if theresults are construct valid, the estimated parameters should normally beconsistent with prior expectations [39]. In the current case, two characteristics
are tested: (1) is the demand curve downward sloping, and (2) whether theincome effect is positive. The negative coefficients on the bid are statisticallysignificant at the 5% level, consistent with a downward sloping demand curve.
The income variable, however, is not statistically significant, suggesting that
income does not have an important effect on the WTP for food safety. It is notclear, however, what feature of the authors’ data or model leads to this finding.
To strengthen their analysis, the authors also tried to incorporate
additional variables (i.e. demographics) to their model. Unfortunately, theeconometric model did not converge when demographic variables were356

NAYGA et al.

included. This is not unusual. As shown by Hanemann [40], WTP is estimatedon the basis of a discrete choice between two alternatives that results from autility maximizing choice; demographic variables often have little influence onthese outcomes. This condition is the analogue of the integrability conditions inconventional demand theory, which provides a criterion for determining
whether a given statistical model is compatible with the economic hypothesis ofutility maximization [40]. Also, it should be noted that if the indirect utility
function is linear in arguments and the values a variable (e.g. demographic
variable) takes for two alternatives being evaluated is constant, then thevariable of potential interest essentially drops out of the comparison (i.e. it has
no importance in determining an individual’s choice between these two alternatives) [41]. This seriously hinders the model’s capability to estimateparameters on these variables. Hence, the authors’ tests of construct validity
were limited to the standard economic variables of price and income.
A second type of validity test is criterion validity. Criterion validity
compares WTP values either with identical markets in which the same good isbought and sold, or with an experimental market, which creates or simulates amarket in which the good is actually bought or sold [39, 42]. At the time thestudy was conducted, irradiated ground beef was not available at any
supermarket in the study locations. However, recent information about
premiums of irradiated ground beef now being sold in supermarkets appear to
be consistent with the authors’ findings [2]; their results also appear to beconsistent with findings in similar studies of WTP for food safety [17–19].

7.

CONCLUDING REMARKS AND AREAS OF FUTURE
RESEARCH

The realization of the benefits of food irradiation will depend on
consumers’ acceptance of the technology. The results of this study suggest thatmany individuals are willing to pay for irradiated foods once they are informed
about the nature of food irradiation technology and its capability to reduce therisk of foodborne illness. Given the subject pool, the next step should be to
apply the authors’ methodology across a larger cross-section of the US
population, both geographically and socioeconomically. In addition, the Le
Chatelier principle suggests that their WTP estimates represent a measure of
the upper end of the distribution of food safety preferences [43]. Hence, future
research should explore other design features or alternative elicitation methods
to test further the robustness of the findings. For example, future researchshould assess whether the results can be confirmed with experimentallaboratory auction exercises or actual supermarket trials. Future research357

NAYGA et al.

should also further evaluate the possible effect of the ‘novelty’ of the producton consumers’ WTP. In the current study, some subjects may have been willingto pay more for irradiated ground beef because it is new and they would like totry it. This is sometimes referred to in the literature as ‘preference learning’.
Preference learning or novelty effects exist if subjects are willing to pay a highpremium for a good because they wanted to learn about an unfamiliar goodthey had not previously consumed. If this is the motive, then the authors
hypothesize that the WTP will likely decline as the novelty wears off. It is also
possible that some consumers have a negative WTP for irradiated foods. Veryfew respondents in the sample indicated a negative WTP, but future studies
should not neglect this possibility. Another area of future research is assessing
the effect of not only positive but also negative information (i.e., antiirradiation information) about food irradiation on consumers’ WTP, similar to
the work conducted by Fox et al. [17]. Since the current study did not provide
anti-food-irradiation information to consumers, it is possible that the results
reflect the absolute maximum consumers would pay for irradiated ground beef.

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Annex I*
BIBLIOGRAPHY
AIEW, W., NAYGA, R.M., Jr., NICHOLS, J.P., The promise of food irradiation: Will
consumers accept it”, Choices, Third Quarter, pp. 31–34, (2003).
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ANDRÁSSY, É., et al., Changes of hen eggs and their components caused by nonthermal pasteurizing treatments. II. Some non-microbiological effects of gamma
irradiation or hydrotatic pressure processing on liquid egg white and egg yolk.
Acta Alimentaria, 35 (3) (2006) (accepted)
BALLA, C., FARKAS, J., Minimally processed fruits and fruit products and their microbiological safety. In: Y. H. Hui (ed.) Handbook of Fruits and Fruit Processing,Blackwell Publishing, Ames, Iowa, USA (2006) pp. 115–128.
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for inactivation of pathogens inoculated into Kimbab, steamed rice rolled bydried laver, Food Control (2006) In Press.
FARKAS, J., ANDRÁSSY, É., POLYÁK-FEHÉR, K., Improvement of the microbiological safety of two chilled semi-prepared meals by gamma irradiation. Food
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FARKAS, J., ANDRÁSSY, É., BECZNER, J., POLYÁK-FEHÉR, K., MOHÁCSIFARKAS, C.S., Comparing observed growth of selected test organisms in foodirradiation studies with growth predictions calculated by Combase software. In:
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FARKAS, J., ANDRÁSSY, É., POLYÁK-FEHÉR, K., Improvement of the microbiological safety of two chilled semi-prepared meals by gamma irradiation. In: Book
of Abstracts, The 19th International ICFMH Symposium, Food Micro 2004: New
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*

Annex I remains unedited.

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ANNEX I

FARKAS, J., Elimination of foodborne pathogens by ionising radiation. In: F. J. M.
Smulders and J. D. Collins (eds.) Food Safety Assurance and Veterinary Public
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Particle and Photon Interactions with Matter. Chemical, Physicochemical, andBiological Consequences with Applications. Marcel Dekker, Inc, New York,Basel (2004) pp. 785–812.
FARKAS, J., “Improvement of the microbiological safety and shelf-life of selectedchilled meals by gamma irradiation”, Irradiation to Ensure the Safety and Qualityof Prepared Meals (Proc. FAO/IAEA 2nd Res. Coord. Mtg Pretoria, 2004),
IAEA, Vienna (2004) 32–37.
FARKAS, J., Irradiation for better foods. O.2.1. In: Delegate Manual,. EFFOST
Symposium on Food Innovations for an Expanded Europe, Oct. 2004, Warsaw,
Poland.
FARKAS, J., Irradiation for better foods, Trends in Food Science and Technology, 17 (4)148–152 (2006).
FARKAS, J., Irradiation of poultry meat. Chapter 19. In: G.C. Mead (ed.), Food Safety
Control in the Poultry Industry. CRC Press, Boca Raton, Fla., and Woodhead
Publ. Ltd., Cambridge, England (2005) pp. 433 – 453.
FARKAS, J., Physical methods of food preservation. Chapter 32. In: L. Beuchat, M.
Doyle (eds.) Food Microbiology: Fundamentals and Frontiers. 3rd, revised andextended edition. ASM Press, Washington, D. C. (2006) (accepted).
FARKAS, J., The potential of new physical preservation methods in improving microbiological safety of minimally processed foods. In: Proceedings of „Food Safety”,
22nd Food Technology Days, organized by the University of Ljubljana,
Department of Food Science and Technology, held in Radenci, 18–19 March 2004
(eds. L. Gasperlin and B. Zlender), Ljubljana, 2004, pp. 15–28.
FARKAS, J., World-wide status of food irradiation. Keynote paper. In: Programme andBook of Abstracts, 2nd Central European Congress on Food, Budapest, 26–28
April 2004. pp.43.
GUO, Y., JON, Y., SUN, B., The Effects of irradiation on the physicochemical characteristics of boiled dumplings, Chinese Food Science and Technology, 5, 107–110(2005).
GUO, Y., SUN, B., The situation and prospect of irradiation to ensure the safety andquality of prepared meal. Acta Agriculturae Nucleatae Sinica, 19(3) 197–201(2005).
JIA, C., JIA, Y., SUN, B., Effect of irradiation on the microbiological safety of chilledcooked dumpling Acta Agriculturae Nucleatae Sinica, 19(5), 367–370 (2005).

364

ANNEX I

JO, C., HAN, C.D., CHUNG, K.H., BYUN, M.W., Gamma irradiation of ready-to-cookbulgogi improves safety and extends shelf-life without compromising organoleptic
quality. Nutraceuticals and Foods. 8(2), 191–195 (2003).
JO, C., KIM, D.H., SHIN, M.G., KANG, I.J., BYUN, M.W., Irradiation effect of bulgogi
sauce for manufacturing Korean traditional meat products, bulgogi, Radiation
and Physics and Chemistry 68(5), 851–856 (2003).
JO, C., LEE, N.Y., HONG, S.P., KIM, Y.H., BYUN, M.W.: Microbial contamination offood materials for manufacturing Korean laver roll (Kimbab) and effect of
gamma irradiation. Journal of Food Science and Nutrition 9(3), 236–239 (2004).
JO, C., et al., Radio-sensitivity of pathogens in inoculated into prepared foods fromanimal origin. Food Microbiology, 22(4), 329–336 (2005).
JO, C., et al., Inactivation of pathogens inoculated into prepared seafood products for
manufacturing Kimbab, a steamed rice rolled by dried seaweed, by gamma irradiation. Journal of Food Protection, 68(2), 396–402 (2005).
JO, C., LEE, N.Y., KANG, H.J., SHIN, D.H., BYUN, M.W., Inactivation of food-borne
pathogens in marinated beef rib by ionizing radiation. Food Microbiology 21(5),543–548 (2004).
KANG, H.J., JO, C., LEE, N.Y., BYUN, M.W., Effect of gamma irradiation on microbial
growth, electron donating ability, and lipid oxidation of marinated beef rib(Galbi) with different packaging methods during storage, Journal of Korean
Society of Food Science and Nutrition 33(5) (2004) 888–893.
LEBOVICS, V.K., et al., Effects of gamma irradiation or high hydrostatic pressure oncholesterol oxidation and sensorial quality in chicken liver and mechanicallydeboned turkey meat. M8OP41. In: Book of Abstracts, XIIth European
Symposium on the Quality of Poultry Meat, Doorwerth, Netherlands, 23–26 May
2005, pp. 218.
LEBOVICS, V.K., et al., Effects of gamma irradiation or high hydrostatic pressure oncholesterol oxidation and sensrorial quality in chicken liver and mechnicallydeboned turkey meat. In: Proceedings of the XVIIth European Symposium on
the Quality of Poultry Meat, Doorwerth, Netherlands, 2005. pp. 124–132.
LEE, N.Y., et al., The prediction of origin of microbial contamination in Kimbab andimprovement of microbial safety by gamma irradiation. Korean Journal of Food
Science and Technology 37(2), 279–286 (2005).
LEE, N.Y., et al., Microbiological and mutagenical safety of gamma irradiated ready-toeat foods of animal origin contaminated with pathogens, Korean Society of Food
Science of Animal Resources, 25(1), 13–19 (2005).
LEE, N.Y., JO, C., KANG, H.J., KIM, D.S., BYUN, M.W., Radio-sensitivity ofpathogens in gamma irradiated marinated beef rib (Galbi) and its sensory
property, Korean Journal of Food Science and Technology 36(1),168–173 (2004).

365

ANNEX I

LEE, N.Y., JO, C., SHIN, D.W., KIM, W.K, BYUN, M.W., Control of pathogen s
inoculated into ready-to-use vegetables by gamma-irradiation, Food Microbiology 23(7), 649–656 (2006).
MÉSZÁROS, L., HORTI, K., FARKAS, J., Changes of hen eggs and their components
caused by non-thermal pasteurizing treatments. I. Gamma irradiation of shelleggs, Acta Alimentaria, 35 (2) 2006 (in print)
NAYGA, R.M., Jr., AIEW, W., NICHOLS, J., Information effects on consumers’
willingness to purchase irradiated food products, Review of Agricultural
Economics 27(1), 37–48 (2005).
NAYGA, R.M., Jr., WOODWARD, R., AIEW, W., Willingness to pay for reducing riskof food-borne illness, Canadian Journal of Agricultural Economics, 54(3) (2006)
In Press.
NAYGA, R.M., Jr., WOODWARD, R., AIEW, W., Experiments on the divergence
between willingess to pay and willingness to accept: The issue revisited,
Economics Bulletin, 17(4), 1–5. (2005)
NAYGA, R.M., Jr., Food safety through food irradiation: Should it be adopted more by
the EU?”, EuroChoices, 2(3), 36–39 (2003).
NAYGA, R.M., Jr., POGHOSYAN, A., NICHOLS, J., Will consumers accept irradiatedfood products? International Journal of Consumer Studies, 28(2), 178–185, 2004.
NORTJE, K., Combined edible coating and irradiation treatment on quality of moist
beef biltong. MSc (Agric) Food Science and Technology Dissertation. Universityof Pretoria, Pretoria, South Africa (2004).
NORTJE, K., BUYS, E.M., MINNAAR, A., Effect of γ-irradiation on the sensory
quality of moist beef biltong, Meat Science 71, 603–611 (2005).
NORTJE, K., BUYS, E.M., MINNAAR, A., Use of γ-irradiation to reduce high levels of
Staphylococcus aureus on casein-whey protein coated moist beef biltong, Food
Microbiology (2006) In Press.
SEREGÉLY, Z.S., FARKAS, J., TUBOLY, E., DALMADI, I., KAFFKA, K.,
Monitoring the properties of egg white pasteurised by high hydrostatic pressureand gamma irradiation by evaluating their NIR spectra and chemosensor arraysensor signal resonses using different methods of qualitative analysis. In: Abstract
Book, International Conference on Chemometrics and Bioinformatics in Asia
(CCBA2004), Shanghai 2004, pp. 108.
SEREGÉLY, Z.S., FARKAS, J., TUBOLY, E., DALMADI, I., Investigating theproperties of egg white pasteurized by ultra-high hydrostatic pressure and gamma
irradiation by evaluating their NIR spectra and chemosensor array sensor signal
responses using different methods of qualitative analysis. Chemometrics andIntelligent Laboratory Systems, 82, 115–121 (2006).
XU, Y., SUN, B., The effect of 60Co irradiation on the survival of bacteria of sauced chop.
Acta Agriculturae Nucleatae Sinica, 18(1), 33–35 (2004).

366

Annex II*
ADDITIONAL READING
Conference proceedings/invited talks
AIEW, M., NAYGA, R.M., Jr., NICHOLS, J., “Experimental Study on Willingness toPurchase Safer Foods: The Case of Irradiated Foods”, Quality Assurance, Risk
Management and Environmental Control in Agriculture and Food Supply
Networks, Proceedings of the 82nd Seminar of the European Association ofAgricultural Economists, G. Schiefer and U. Rickert, eds., University of BonnILB Press, Bonn, Germany (2004) pp. 405–412.
DE SAN MARTÍN, J., Food Irradiation and Immunocompromised Patients, Clinical
Hospital, Buenos Aires, August 10, 2004.
IRAWATI, Z., MATALIA, L., NURCAHYA, C.M., ANAS, F., The role of medium
irradiation dose on microbiological safety and shelf-life of some traditional soups.
International Meeting on Radiation Processing (IMRP), Kualalumpur, Malaysia
26th Feb3rd May, 2006.
JO, C., LEE, N.Y., KANG, H.J., KIM, D.S., BYUN, M.W., Radio-sensitivity ofpathogens inoculated into seasoned Galbi. The 54th Meeting of Korea Society ofFood Science and Nutrition. Chungbuk National University, Cheongju, Korea.
Nov. 11 (2003).
JO, C., et al., Inactivation of pathogens inoculated into prepared seafood products by
gamma irradiation. International Conference of Food Science and Nutrition. Nov.
11–17, Jeju, Korea (2004).
JO, C., LEE, N.Y., KANG, H.J., KIM, D.S., BYUN, M.W., Microbial contamination of
the ready-to-use food materials for Kimbab and effect of gamma irradiation.
Korea Society of Food Preservation. Oct. 29, Mokpo National University, Mokpo,
Korea (2004).
JO, C., New application of irradiation in food and non-food products. 2nd International
Symposium on New Frontiers for Irradiated Food and Non-food Products,
Bangkok, Thailand, Sept. 22, 2005.
LEE, N.Y., JO, C., KANG, H.J., BYUN, M.W., Microbiological safety and sensorial
quality of gamma irradiated marinated beef. The 54th Meeting of Korea Society ofFood Science and Nutrition. Chungbuk National University, Cheongju, Korea.
Nov. 11. 2003
LEE, N.Y., et al., Mcirobiological and mutagenic safety of animal originated foodmaterial for manufacturing ready-to-eat food by gamma irradiation. Conference*

Annex II remains unedited.

367

ANNEX II

of Korea Society of Food of Animal Resources. May 28, Konkuk University,
Seoul, Korea, 2004
LEE, N.Y., JO, C., KANG, H.J., KIM, H.J., BYUN, M.W., Microbiological safety of
gamma irradiated prepared foods contaminated with pathogens. Korea Society ofFood Preservation. Oct. 29, Mokpo National University, Mokpo, Korea, 2004.
LIENDO, G., NARVAIZ, P., Safer ready-to-eat foods by ionizing radiations: caneloni intomato sauce. Argentine Food Science and Technology Congress, Córdoba,
Córdoba province, November 26, 2004.
MENGONI, G., NARVAIZ, P., VERONESI, P., GÓMEZ, F., Control of Listeria
monocytogenes and other pathogenic bacteria by ionizing radiations in chickenpie. International Congress on Feeding and Society , Neuquén, Neuquén
province, April 7 – 9, 2005.
MENGONI, G., NARVAIZ, P., HOVSEPIAN, J., CAMPOS, M., Control of pathogenic
microorganisms in sandwiches by gamma irradiation. XIII Latinamerican and the
Caribbean Seminar on Food Science and Technology, Montevideo, Uruguay,
October 12– 16, 2004
NARVAIZ, P., et al., Poster presentation Safer prepared meals, for immunocompromised patients and the general public, by ionizing radiations. Texas A&M
University and USDA, College Station, Texas, USA, March 30– April 2 de abril,
2004.
NARVAIZ, P., VERONESI, P., LOUND, L., GASPAROVICH, A., COSSANI, E.X.,
Irradiated “empanadas” to attain higher microbiological safety. Argentine Microbiology Congress, and XVII Latinamerican Microbiology Congress, Buenos
Aires, November 17–23, 2004.
NARVAIZ, P., Argentine Experience on Food Irradiation. “Food Safety and
Irradiation”, seminar organized by IAEA, CNEA and INPPAZ, at INPPAZ(Panamerican Institute of Food and Zoonosis Protection, Martínez, Buenos Aires
province, November 23, 2004.
NARVAIZ, P., Argentine Experience on Food Irradiation. International Forum on
Irradiation Technology for the Industry, organized by the Uruguay Technological
Laboratory (LATU), Montevideo, Uruguay, May 24, 2004.
NARVAIZ, P., Bromatology Meetings, organized by Veterinary College of the Buenos
Aires province, La Plata, Buenos Aires province, Conference: "Present status offood irradiation in Argentina and the world” April 11 , 2003.
NARVAIZ, P., e-LEARNING: “Food Irradiation” course, at the Web page NUTRAR:
http://www.nutrar.com.ar. Professor: Nutritionist Paola Veronesi. June 13– July13, 2005; March 6– April 6, 2006.
NARVAIZ, P., Food Irradiation for Immunocompromised Patients. Nutrition andOncology Conference, Piñero Hospital, Buenos Aires, November 16, 2004.

368

ANNEX IINARVAIZ, P., Food Irradiation for immunocompromised persons. Second International Symposium on Food Development and Innovation, Montevideo, Uruguay
INNOVA 2005, September 28–30, 2005.
NARVAIZ, P., Food Irradiation, for advanced Food Engineering students, Azuay
University, Ecuador. At the Exact and Natural Sciences Faculty, Buenos Aires
University, October 10–14, 2005.
NARVAIZ, P., Food Irradiation, for students of the Southern Gastronomic Institute. At
the Ezeiza Atomic Center, October 19, 2005.
NARVAIZ, P., Food Irradiation, Medicine Faculty, National Buenos Aires University,
September 3, 2004.
NARVAIZ, P., Present status of food irradiation in Argentina and the world, Permanent
Forum on Ionizing Energy Applications, organized by CNEA, Buenos Aires,
Conference, July 17, 2003.
NARVAIZ, P., Present status of food irradiation in Argentina and the world, organizedby the Argentine Food Technologists Association (AATA), Argentine Enterprise
University (UADE), September 4, 2003.
NARVAIZ, P., Present status of food irradiation in Argentina and the world. Permanent
Forum on Ionizing Energy Applications, organized by CNEA and Cordoba
Science Agency, Córdoba, Córdoba province, October 2, 2003.
NARVAIZ, P., Present status of food irradiation in Argentina and the world , organizedby the Argentine Standardization Institute (IRAM) ,Buenos Aires, October 28,
2003.
NARVAIZ, P., Present status of food irradiation in Argentina and the world, organizedby the Health Ministry of the Buenos Aires province , National La Plata
University, La Plata, October 30, 2003.
NARVAIZ, P., Present status of food irradiation in Argentina and the world, organizedby the Argentine Biochemistry Foundation, Buenos Aires, June 16, 2004.
NARVAIZ, P., Present status of food irradiation in Argentina and the world. In
Colonies Feria (FECOL), Esperanza, Santa Fe province, September11, 2004.
NARVAIZ, P., Present status of food irradiation in Argentina and the world. “FirstInternational Symposium on New Technologies”, in parallel with the “X
Argentine Food Science and Technology Congress”, May 18 – 20, 2005.
NARVAIZ, P., Present status of food irradiation in Argentina. Radiology Technicians
Congress, at the Medicine Faculty, National Buenos Aires University , September
3, 2004.
NAYGA, R.M., Jr., Consumer acceptance and willingness to pay for irradiated foods.
Philippine Nuclear Research Institute and Department of Agriculture, Manila,
Philippines, June 14, 2005.

369

ANNEX IINAYGA, R.M., Jr., Consumers’ willingness to pay for irradiated foods International
Seminar on Production of Safe and Quality Meat Products, Kerala Agricultural
University India, Feb. 24, 2006.
NAYGA, R.M., Jr., Consumers’ willingness to pay for irradiated prepared beef. Beijing
Institute of Technology, China, May 23, 2006.
NAYGA, R.M., Jr., Food safety and food irradiation: Risk communication andconsumer acceptance issues. National Food Safety and Food Irradiation
Workshop, Ministry of Agriculture, Jakarta, Indonesia, Jan. 24. 2005.
NAYGA, R.M., Jr., Information effects on consumers’ willingness to purchaseirradiated food products. National Center for Electron Beam Food Research’s
Short Course on Food Irradiation, Texas A&M University, College Station, Texas,
Feb. 10, 2005.
NAYGA, R.M., Jr., Marketing and economics of irradiated foods. Indonesian National
Nuclear Agency, Jakarta, Indonesia, Jan. 25, 2005.
NAYGA, R.M., Jr., Marketing and public perception issues of food irradiation. 2nd
International Symposium on New Frontiers for Irradiated Food and Non-food
Products, Bangkok, Thailnad, Sept. 22, 2005.
NAYGA, R.M., Jr., Marketing of irradiated food products. INDOGAMMA, Cibitung,Bekasi, Indonesia, Jan. 20, 2005.
NAYGA, R.M., Jr., Marketing of irradiated foods in the U.S. Bhabha Atomic ResearchCenter, Mumbai, India, April 15, 2005.
NAYGA, R.M., Jr., Marketing of irradiated foods in the U.S. Kerala Agricultureal
University, Kochi, India, April 12, 2005.
NAYGA, R.M., Jr., Marketing of irradiated foods in the U.S. Venky Food Company,
Pune, India, April 14, 2005.
NAYGA, R.M., Jr., Willingness to pay for irradiated foods. Bogor Agricultural
University, Bogor, Indonesia, Jan. 22, 2005.
NAYGA, R.M., Jr., “Consumer acceptance of irradiated prepared and processed food”,
Irradiation to Ensure the Safety and Quality of Prepared Meals (Proc. FAO/
IAEA 2nd Res. Coord. Mtg Pretoria, 2004), IAEA, Vienna (2004) 93–97.
NAYGA, R.M., Jr., “Consumer Acceptance of Irradiated Prepared and Processed Food”.
NAYGA, R.M., Jr., POGHOSYAN, A., NICHOLS, J., “Consumer Willingness to Pay
for Irradiated Beef: Initial Phase”, Paradoxes in Food Chains and Networks, J.H.
Trienekens and S.W.F Omta (editors), Wageningen Academic Publishers, The
Netherlands, 2002, pp. 250–259.
NORTJE, K., BUYS, E.M., MINNAAR, A., Effect of g-irradiation on the sensory
quality of moist beef biltong. 17th International Congress and Exhibition,
Pretoria, Sept. 2003.
VERONESI, P., NARVAIZ, P., COSANNI, E., LOUND, L., GASPAROVICH, A.,
Microbiologically safe and nutritive meals, treated by gamma irradiation, for370

ANNEX II

immunocompromised patients. XI Annual Nutritionists Meeting of the Argentine
Association of Dietists and Nutritionists Dietists (AADYND), Buenos Aires,
November 1–3, 2004.
VERONESI, P., NARVAIZ, P., LOUND, L., GASPAROVICH, A., COSSANI, E.,
Microbial decontamination of a fruits and gelatin dessert by ionizing radiations.
XIII Latinamerican and the Caribbean Seminar on Food Science and Technology,
Montevideo, Uruguay, October 12–16, 2004.

Press articles“Food irradiation implementation is being studied”– La Nación newspaper, Buenos
Aires, April 5, 2004, Journalist: Daniel Arias.
“Polemic rays”–“Para Ti” magazine, Buenos Aires, July 16, 2004, Journalist: Daniela
Fajardo.

Radio interviews“Food Irradiation for Immunocompromised Patients” –Radio LRL 714 Class, FM 102.,7
MHz., Saenz Peña, Bs. As. Province, May 18, 2004, – Programme “Week News on
Science and Technology”, Journalist: Pedro Fernández.
“Public Knowledge” City Radio, National Buenos Aires University, June 2004,
Journalist: Gabriel Rocca.

Television interviews“Food Irradiation for Immunocompromised Patients”, In: “Scientifics, Argentine
Industry”, State Channel No. 7, July 26, 2004, Journalist: Adrián Paenza, (Videoavailable upon request).

371

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LIST OF PARTICIPANTS
Al-Bachir, M.

Food Irradiation Division,
Radiation Technology Department,
Syrian Atomic Energy Commission,
P.O. Box 6091,
Damascus,
Syrian Arab Republic
Fax: +61122289
Email: malbachir@aec.org.sy

Farkas, J.

Central Food Research Institute,
Herman Ottó 15,
H-1022 Budapest, Hungary
Fax: +3611653374
Email: jozef.farkas@uni-corvinus.hu

Haruvy, Y.F.

Department of Radiation Safety,
Soreq Nuclear Research Centre,
Yavne 81800, Israel
Fax: +97289434403
Email: haruvy@soreq.gov.il

Jo, Cheorun

Radiation Application Research Division,
KAERI,
1266, Sinjeong-Dong,
Jeogeng 580-185,
Republic of Korea
Fax: +82635703213
Email: cheorun@kaeri.re.kr

Koenari, Zubaidah Irawati

Centre for Application of
Isotopes and Radiation Technology,
P.O. Box 7002, JKSKL,
Jakarta 12070, Indonesia
Fax: +62217691607
Email: irakoenari@yahoo.com

Minnaar, A.

Department of Food Science,
University of Pretoria,
Lynnwood Road,
Pretoria 0002, South Africa
Fax: +27124202839
Email: Amanda.minnaar@up.ac.za

373

LIST OF PARTICIPANTS

Nayga, R.M., Jr.

Department of Agricultural Economics,
Texas A&M University,
College Station, Texas 77843-2124
United States of America
Fax: +19798623019
Email: rnayga@tamu.edu

Nketsia-Tabiri, J.

Department of Food Science & Radiation
Technology,
Biotechnology and Nuclear Agriculture
Research Institute,
Ghana Atomic Energy Commision,
P.O.Box 80, Legon-Accra, Ghana
Fax: +23321400807
Email: josephinetabiri@hotmail.com

Noomhorm, A.

Asian Institute of Technology,
Km. 42 Paholyothin Highway,
P.O. Box 4, Klong Luang,
Pathumthani 12120, Thailand
Fax: +6625246200
Email: athapol@ait.ac.th

Sharma, A.

Food Technology Division,
Bhabha Atomic Research Centre,
Trombay, Mumbai,
400 085 India
Fax: +91225505151
Email: ksarun@barc.gov.in

Stewart, E.

Agri-Food & Biosciences Institute,
Queen’s University Belfast,
Newforge Lane, Belfast,
BT9 5PX, United Kingdom
Fax: +442890255006
Email: eileen.stewart@afbini.gov.uk

Sun, Baozhong

Institute of Animal Science,
Chinese Academy of Agricultural Science,
Beijing,
100094 China
Fax: +861062895351
Email: sunbaozhong@yahoo.com.cn

374

LIST OF PARTICIPANTS

Rubio-Cabello, T.

Joint FAO/IAEA Division of
Nuclear Techniques in Food and Agriculture,
International Atomic Energy Agency,
Wagramer Strasse 5, P.O. Box 100,
A-1400 Vienna, Austria
Fax: +43126007
Email: T.Rubio-Cabello@iaea.org

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