J. Pack. ScL Technol. Vol.6 No.1 (1997)

日 本 包 装 学 会 国 際 包 装 セ ミ ナ ー (IPS'96)要 旨
Stable Hurdle Technology Foods and Packaging- W o r l d w i d e
Dr. Lothar Leistner
International Food Consultant
An den Weinbergen 20, D-95326
Kulmbach, Germany

The stability and safet y of most f oods is ba sed on a co mbination of preser vative factors(hurdles) which the microorganisms present cannot overcome. This is true fortraditional foods w i t h i n h e r e n t e m p i r i c h u r d l e s , a s w e l l a s f o r n o v e lp r o d u c t s f o r w h i c h h u r d l e s a r e i n t e l l i g e n t l y selected and intentionallyapplied (Leistner, 1 995a). The most important hurdles in foods are t e m p e r a t u r e(high or low), water activity, acidity, redox potential, somep r e s e r v a t i v e s , a n d competitive microorganisms. However, in a recent Europeanr e s e a r c h p r o j e c t m o r e t h a n 5 0 potential hurdles which influence the preservation or qualityof foods have been identified and d e s c r i b e d ( B o r g - S o r e n s e n , 1 9 9 4 ) , a n d t h e l i s t o fpossible hurdles for food preservation is by no m e a n s c l o s e d . A t p r e s e n t
especially non-thermal processes are of interest, since they may be
used in combination with other hurdles for minimally processed,
f r e s h - l i k e f o o d p r o d u c t s w i t h little induced degradation of nutritional ands e n s o r y pr o p e r t i es ( B a r b o s a- C a n o v a s c t a l . , 1 9 9 5 ) . P a c k a g i n g ( e . g . v a c u u m o r
modified atmosphere packaging, active packaging, scavengers,
absorbers, antimicrobial packaging material, edible food coatings andfilms, aseptic packaging)is important for most hurdle technology
foods, however, again it has to be used in combination with otherhurdles.
The hurdle technology approach is applicable not only to safety, but
a l s o t o q u a l i t y a s p e c t s o f foods. In order to secure an optimal total qualityof a food the preservation and quality hurdles m u s t b e a d j u s t e d t o a n o p t i m a l r a n g e( L e i s t n e r , 1 9 9 4 a ) . S o m e h u r d l e s ( e . g . M a i l l a r d r e a c t i o n products) influence thesafety as well as the quality of foods, because they have antimicrobial p r op e r t i e s a n d a tt h e s am e ti m e i mp r ov e t h e f l av o r o f t h e p r o d u c t . M o r e o v e r , t h e s a m e h u r d l e c o u l d h a v e
a positive as well as a negative effect on foods, depending on its intensity. For
instance, chilling to an unsuitable low temperature will be detrimental to
fruit quality ("chilling injury"), whereas moderate chilling is beneficial(Leistner, 1995a).
The hurdle effect was introduced be Leistner (1978), and from an
u n d e r s t a n d i n g o f t h e h u r d l e effect the hurdle technology has been derived(Leistner, 1985). More recently out of the comprehension of the hurdle technology
new concepts for food safety have emerged (Leistncr, 1 9 9 5 b ) . T h e l a t t e r f o c u sonhomeostasis,
metabolicexhaustion
andstressreactionsofmicroorganisms and the multi-target preservation of foods.
Homeostasis is the tendency to uniformity and stab山 吋 in the normal status (internal
environment) within organisms. For instance, the maintenance of ad e f i n e d p H i n n a r r o w l i m i t s is prerequisite to all living cells. If thehomeostasis of microorganisms, i.e. their internal equilibrium, has been
disturbed by hurdles in a food, they will not multiply, i.e. they remain
in
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S t a b l e H u r d l e T e c h n o l o g y Fo o d s a n d P a c k a g i n g - W o r l d wi d e

the lag-phase or even die, before their homeostasis is re-established ("repaired"). Therefore,food preservation is achieved by disturbing the homeostasis of microorganisms in foods
temporarily or permanently (Gould, 1988, 1995; Leistner, 1995a). Repair of a disturbed
homeostasis, e.g. the osmoregulation of bacterial cells in foods of low water activity, demands
mu c h en e rg y o f th e mi c r o o rg a n i s ms , a n d t h e re fo r e re s tr ic tio n o f th e en er g y su p p l y i nhib it s
repair mechanisms of the microbial cells and leads to a synergistic effect of hurdles. Energy
restrictions for the present microorganisms are e.g. caused by anaerobic conditions, such as inmodified atmosphere or in vacuum packaging of foods.
In general microorganisms which cannot grow will die, and they die more quickly if the stabilityof a food is close to the threshold for microbial growth, the storage temperature is elevated,
antimicrobial substances are present, and the organisms are sublethally injured (e.g. by heat).
A p p a r e n t l y , mi c r o o r g a n i s ms i n s t a b l e h u r d l e t e c h n o l o g y f o o d s s t r a i n e v e r y p o s s i b l e r e p a i rmechanism to overcome the hostile environ ment, b y doing this they co mpletely use up theirenergy and die, if they become metabolicly exhausted. This leads to an autosterilization of such
foods (Leistner, 1995a; Alzamora et al., 1993, 1995). Due to autosterilization hurdle technology
f o o d s , w h i c h a r e mi c r o b i o l o g i c a l l y s t a b l e , b e c o me m o r e s a f e d u r i n g s t o r a g e , e s p e c i a l l y a tambient temperatures. For example, salmonellae which survived the ripening process infermented sausages, will vanish more quickly if the products are stored at ambient temperature,and they will survive longer in products stored under refrigeration (Leistner, 1995a).
Some bacteria beco me mo re resistant (e.g. toward heat) or ev en mo re virulent under stress,
since they generate their "safety net" (Booth, 1996). Synthesis of protective stress shockproteins is induced by heat, pH, aw, ethanol, etc. as well as by starvation. These responses ofmi c roo rg anisms u n d er s tr es s co u ld tu r n o u t t o b e p ro b l e ma t i c f o r t h e a p p l i c a t i o n o f h u r d l etechnology. However, the switch on of genes for the synthesis of stress shock proteins should
become more difficult if different stresses arc received at the same time, because to counter
different stresses will ask for the energy consuming synthesis of several or at least much more
protective stress proteins, which the microorganisms cannot deliver since they become
metabolicly exhausted (Leistner, 1995b).
For foods preserved by hurdle technology, it has been suspected for some time that different
hurdles in a food could not just have an additive effect on stability but act synerg istically(Leistner, 1978). A synergistic effect could become true if the hurdles in a food hit, at the samet i me , d i f fe r e n t t a r g e t s ( e . g . c e l l me mb r a n e , D N A , e n z y me s y s t e m s , p H, a w , E h ) w i t h i n t h e
microbial cell, because then the repair of the homeostasis of the microorganisms should be moredifficult. In practical terms this could mean that it would be more effective to use different
preservatives in small amounts in a food than only one preservative in larger amounts, because
different hurdles might hit different targets within the microbial cell, and thus act synergistically(Leistner, 1994a, 19 95 a). This mu lti-target preservation of food s might beco me a pro misingresearch area. It is now anticipated that the targets in microorganisms of different preservative
factors (hurdles) for foods will be elucidated, and then the hurdles could be grouped in classes
according to their targets within the microbial cells. A mild and effective preservation of foods,
i.e. a syngergistic effect of hurdles, is likely if the preservation measures are based on an
intelligent selection and mix of hurdles taken from different "target classes" (Leistner, 1996).

J. Pack. Sci. Technol. Vol.6 No.l (1997)

Over the years the insight into the hurdle effect has been broadened and the application of thehurdle technology extended. In industrialized countries hurdle technology is of particular interest
for minimally processed foods, whereas in developing countries now high-moisture foods
storable without refrigeration, due to stabilization by hurdle technology, are of paramountimportance. The application of hurdle technology advances worldwide, even though this concept
is synonymously called combined methods, combination preservation or Hurden-Technologie in
German, Technologic des Barrieres in French, Tecnologia degli Ostacoli in Italian, Tecnologia
de Obstaculos in Spanish, and Zanglangishu in Chinese. In numerous publications traditionaland novel hurdle technology foods have been described, e.g. meat products of Germany(Leistner, 1994b), Taiwan (Kuo et al., 1994), and China (Wang and Leistner, 1993, 1994,
1995), dairy products of India (Rao, 1993; Hossain, 1994), as well as high-moisture fruit
products from Latin America (Alzamora et al., 1995; Argaiz et al., 1995). The application of
hurdle technology in Europe was fostered by a three-year project of the European Commission
on "Food preservation by combined processes", to which scientists of 11 European countries
have contributed. More than 2000 copies of the final report (Leistner and Gorris, 1994) wererequested by scientists and industrialists. Furthermore, hurdle technology was featured in
Trends in Food Science & Technology (Leistner and Gorris, 1995), and indeed this concept is
now worldwide in the trend.
Little research has been done towards the packaging of hurdle technology foods as a group.
Because for the various types of hurdle technology foods known, the appropriate packaging
materials and procedures must be selected and applied individually. However, for some types ofthese foods already much information is available e.g. on the suitable packaging of fresh-likeand minimally processed foods, which all are based on hurdle technology (Zagory, 1995;
Swanson et al., 1995; Yang, 1995). Such foods (e.g. MAP, CAP, vacuum packaged or sousvide products) need rigorous refrigeration as the main hurdle and therefore they are prevalent
primarily in industrialized countries. Furthermore, already extensive information on theappropriate packaging of hurdle technology foods which are mildly heated or dried or fermented
is available (Leistner, 1994b). In these instances packaging procedures which are in general use
are suitable for such hurdle technology foods too, if they are intelligently selected for packagingof the various food items. The stable hurdle technology foods have an improved microbial
stability, nevertheless their microbial recontamination after processing must be excluded,
however a complete integrity of the seal is not essential, i.e. clipped casings are sufficient. For
the packaging of hurdle technology foods casings and pouches are more suitable than cans,since condensation of water vapor inside of the package (i.e. formation of water droplets in theheadspace of cans) might unbalance the adjusted water activity, and this will be detrimental tothe product stability (Hechelmann et al., 1985). For hurdle technology foods in the intermediatemoisture rage, which are prevalent in developing countries, reabsorption of water is a problem
and must be avoided, and this is achieved by simple packaging devices (e.g. metal cans, glassjars). For stable high-moisture foods, based on hurdle technology, which are of current interestin developing countries (e.g. high moisture fruit products in Latin America) appropriate
packaging procedures have not yet developed. Generally, there is a lack of knowledge related tot h e p a c k a g i n g o f h u r d l e t e c h n o l o g y f o o d s i n d ev el o p i n g c o u n t r i e s , a n d o n l y s p o ra d i cinformation (e.g. Argaiz et al. 1995) has been published on this subject. However, further

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Stable Hurdle Technology Foods and Packaging - Worldwide

exploration into the application of easy to use, cheap and efficient packaging for hurdle
technology foods of developing countries, which are stored in small consumer packages or large
containers in bulk, should be a challenging and even lucrative approach.

References.
A l z a mo r a , S . M . , T ap ia , M . S . , Ar g a i z, A . an d W e lt i , J . ( 1 9 9 3 ) : A p p li c at io n o f co mb i n ed
methods technology. Food Res. Internat. 26: 125-130.
A l z a mo r a , S . M . , Ce n it t i, P. , Gu e r r e r o , S . a n d Lop c z -M a lo , A . (1 9 9 5 ):Minimally processed fruits by combined methods. In: "Food Preservation by Moisture Control"(G.V. Barbosa-Canovas and J. Welti-Chanes, eds.). Technomic Publishing Co., Lancaster &B a s e l ,p .
4 6 3 - 4 9 2 .
Argaiz, A., Lopez-Malo, A. and Welti-Chanes, J. (1995): Considerations for the development
and the stability of high moisture fruit products during storage. In: "Food Preservation by
Moisture Control" (G.V. Barbosa-Canovas and J. Welti-Chanes, eds.). Technomic PublishingCo., Lancaster & Basel, p.729-760.
B a r b o s a - C a n o v a s , G . V . , P o t h a k a mu r y , U . R . a n d S w a n s o n , B . G . ( 1 9 9 5 ) : S t a t e o f t h e a r ttechnologies for the stabilization of foods by non-thermal processes: physical methods. In:"Food Preservation by Moisture Control" (G.V. Barbosa-Ca'novas and J. Welt-Chanes, eds.).
Technomic Publishing Co., Lancaster & Basel, p. 493-532.
B o g h - S o r e n s e n , L . ( 1 9 9 4 ) : D e s c r i p t i o n o f h u r d l e s . I n : " F o o d P r e s e r v a t i o n b y C o m b i ne dProcesses" (L. Leistner and L.G.M. Gorris, eds.). FLAIR Final Report, EUR 15776 EN,
ISBN 90-900-7303-5, p. 7-24.
Booth, I.R. (1996): Adaptation to extreme environments. In: "Biology of the Prokaryotes: aPhysiological and Functional Approach". OUP, in press.
Gould, G,W. (1988): Interference with homeostasis - food. In: "Homeostatic Mechanisms in
Micro-organisms" (R. Whittenbury, G.W. Gould, J.G. Banks and R.G. Board, eds.). Bath
University Press, Bath, p. 220-228.
Gould, G.W. (1995): Homeostatic mechanisms during food preservation by combined
methods. In: "Food Preservation by Moisture Control" (G.V. Barbosa-Ca'novas and J. WeltiChanes, eds.). Techn omic Pu blishing Co., Lancaster & Basel, p. 397-410.
Hechelmann, H., Leistner, L. and Albertz, R. (1985): UngleichmaBiger aw-Wert als Ursache
fur mangelhafte Stabilitat von F-SSP. Jahresbericht Bundesanstalt Fleischforschung,
Kulmbach, C27.
Hossain, Sk.A. (199 4): "Technological Inno vation in Manu factu ring Dudh Chu rp i". Ph .D.

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Thesis, Un iversit y o f North Be ngal, Silig uri, India, 122 pp.
Kuo, J.C., Dresel, J. and Leistner, L. (1994). Effects of sodium lactate and storage temperatureon growth and survival of Staphylococcus aureus , Listeria monocytogenes and Salmonella inChinese sausage. Chinese Food Science 21: 182-196.
Leistner, L. (1978): Hurdle effect and energy saving. In: "Food Quality and Nutrition" (W.K.
D o w n e y, e d . ) . A p p li ed S c i en c e P u b l i s h e r s , L o n d o n , p . 5 5 3 - 5 5 7 .
Leistner, L. (1985): Hurdle technology applied to meat products of the shelf stable product andintermediate moisture food types. In: "Properties of Water in Foods in Relation to Quality andStability" (D. Simatos and J.L. Multon, eds.). Martinus Nijhoff Publishers, Dordrecht, p. 309329.
Leistner, L. (1994a): Further developments in the utilization of hurdle technology for foodpreservation. J. Food Engineering 22: 421-432.
Leistner, L. (1994b): "Food Design by Hurdle Technology and HACCP".
Printed and distributed by the Adalbert-Raps-Foundation, Kulmbach, Germany, 62 pp.
Leistner, L. and Gorris, L.G.M. (1994): "Food Preservation by Combined Processes". FLAIR
Final Report, EUR 15776 EN, ISBN 90-900-7303-5, 100 pp.
Leistner, L. and Gorris, L.G.M. (1995): Food preservation by hurdle technology. Trends inFood Science & Technology 6: 41-46.
Leistner, L. (1995a): Principles and applications of hurdle technology. In: "New Methods ofFood Preservation" (G.W. Gould, ed.). Blackie Academic & Professional, London, p. 1-21.
Leistner, L. (1995b): Emerging concepts for food safety. Proc. 41st ICoMST, held August 2025, 1995, at San Antonio, USA, p. 321-322.
Leistner, L. (1996): Water activity and hurdle technology. In: "Production of Processed Meats
and Convenience Foods" (C. Genigeorgis, ed.). ECCEAMST Publication, in press.
Rao, K.J. (1993): "Application of Hurdle Technology in the Development of Long life Paneerbased Convenience Food". Ph.D. Thesis. National Dairy Research Institute, Karnal, India, 193
pp.
Swanson, G.B., Berrios, J. de J. and Patterson, M.E. (1995): Selection of packaging materials
for minimally processed foods: safety considerations. In: "Food Preservation by MoistureControl" (G.V. Barbo sa-Canovas and J. Welt-Chanes, eds.). Technomic Publishing Co.,
Lancaster & Basel, p. 807-819.
Wang, W. and Leistner, L. (1993): Shafu: a novel dried meat product of China based on hurdle

Stable Hurdle Technology Foods and Packaging - Worldwide

technology. Fleischwirtschaft 73: 854-856.
Wang, W. and Leistner, L. (1994): Traditionclle Fleischerzeugnisse von China und deren
Optimierung durch Hurden-Technologic. Fleischwirtschaft 74: 1 1 35-1 145.
Wang, W. and Leistner, L. (1995): Traditional meat products and their optimization by means of
hurdle technology. Meat Research 1995(3), 8-ll, 35 (in Chinese).
Yang, T.C.S. (1995): The use of films as suitable packaging materials for minimally processed
foods - a review. In: "Food Preservation by Moisture Control" (G.V. Barbosa-Ca'novas and J.
Welti-Chanes, eds.). Techno mic Publishin g Co., Lancaster & Basel, p. 831-848.
Zagory, D. (1995): Selection of packaging materials for minimally processed foods: technicalconsiderations. In: "Food Preservation by Moisture Control" (G.V. Barbosa-Ca'novas and J.
Welti-Chanes, eds.). Techno mic Publishing Co., Lancaster & Basel, p. 793-806.

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J. Pack. Sci Tcchnol. Vol.6 No.l (1997)

日本包装学会国際包装セミナー（IPS‘９６）要旨
A p p l i c a t i o n o f I m m o b i l i ze d E n zy m e s
in Active Packaging
Dr. Joseph H. Hotchkiss
Institute of Food Science
Cornell University
Ithaca, NY 14853 USA

Ever since Appert discovered that food could be preserved by heating in sealed bottles,
improvement in food packaging has been a major research goal. The traditional role ofpackaging in food preservation has been to withstand thermal processing and to act as a barrier
to contamination. Modem food packaging influences the nutritional, quality, and convenience
attributes of foods, insures availability year round, and is an important tool for marketingproducts.
The major advancements in food packaging technology have been the development of newmaterials, combinations of materials, and containers with specific technical and economic
benefits. However, these new technologies are passive in that they act primarily as inactive
barriers separating the food from the environment. The next frontier is to develop packaging
which actively contributes to the preservation, quality, and safety of foods. Such packaging has
been called "interactive" or "active" packaging.
Active packaging applies the advances in chemistry, biotechnology, materials science, and/or
micro-electronics to food packaging. Examples of active packaging include antimicrobial films
which prevent growth of spoilage and/or disease causing microorganisms, shelf life andtemperature abuse indicators which warn of potential hazards, atmosphere modifiers (humidity
and gas composition) which help preserve foods, flavor enhancers which maintain desirable
flavor in products, off-odor absorbers which remove undesirable flavors, systems whichintercept oxygen, and biosensors which detect microorganisms and toxins. These technologies
promise to improve the safety and quality of many foods including non-sterile refrigerated
foods such as milk, cheeses, and minimally processed fruits and vegetables. These foods
represent one of the most rapidly growing segment of the food market in parts of the world.
The concept of using packaging in an active rather than passive sense is relatively new andlargely undeveloped. One of the earliest active packaging concepts incorporated vapor or gas
absorbers and emitters into packages after closure. This might be as simple as a desiccant (e.g.
,sodium or calcium chloride) which controls relative humidity, or more complex substances
which absorb ethylene (to inhibit ripening), absorb undesirable odors, or emit ethanol to control
molds in baked products. Some commercial absorbers remove both residual and ingress
oxygen after the package is scaled and have been termed an "oxygen interceptors". These
interceptors have been used commercially to remove trace amounts of oxygen from theheadspace of bottled beer, for example.

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Application of Immobilized Enzymes in Active Packaging

Active packaging may improve safety by indicating the condition or history of a product. One
available technology is the time-temperature indicator. These devices integrate the time andtemperature history of a product and give a visual indication if the combination has exceededsome standard or desirable amount. Such technology would be especially useful whencombined with other shelf life technologies modified atmosphere packaging and sub-sterilization
ionizing radiation.
In the future it may be possible to directly detect the presence of specific toxins or
microorganisms in packaged foods using biosensors. Immunologically-based sensors coupled
to packaging could find applications in food safety, food processing, and detection of
adulteration. Such sensors may, for example, detect the presence of bacterial toxins in packaged
foods. They could also be used to determine if a food had been properly pasteurized, contained
enzyme activity, or undesirable pesticides. Biosensors which combine electronics withbiological specificity and sensitivity may find use in packaging as a monitors of safety andquality. Reportedly, methods to quantify the presence of microorganisms on fresh meats arenear commercialization. Such systems could eventually be incorporated directly into foodpackaging.

ANTIMICROBIAL PACKAGING

Microbial contamination is the major factor in food spoilage and responsible for most foodborne disease outbreaks. Two approaches, heat sterilization and direct addition of antimicrobial
additives, have been used to control microbial growth. In conventional thermal processing,foods are sealed in a package and the combined product-package thermally processed. This isthe basis of the canning industry. More recently, the package and the product have beensterilized separately then filled and sealed aseptically. Foods can also be otherwise processed(e.g., dried) to reduce microbial growth.
The addition of antimicrobial additives directly to foods usually does not inhibit all growth but
is selective. The use of these additives is regulated and their use, in most cases, must be statedon the label. The incorporation of an antimicrobial additive into the package, rather than into thefood may have advantages in that less additive may be needed and the effect may be greater
because most spoilage occurs at the food surface. If the additive remains in the packaging
material and does not migrate, it is not considered a food additive and need not be labeled.
I n s o l i d o r s e mi - s o l i d f o o d s , mi c r o b i a l g r o wt h o c c u r s p r i ma r i l y a t t h e s u r f a c e . S u r f a c etreatment with antimicrobial agents for products such as cheeses, fruits, and vegetables has
been practiced for decades. Anti-mycotic agents have been incorporated into waxes and otheredible coatings used for produce items. More recently, the idea of incorporating anti-microbial
agents directly into polymeric packaging films which would contact the surface of the food has
been discussed.

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J. Pack. Scl Techno!. Vol.6 No.l (1997)

Anti-microbial films can be divided into two types: those containing an ntimicrobial agent which
migrates to the food and those that are effective against surface growth without migration to thefood. A few commercial antimicrobial films have been introduced. One widely discussed
commercial product is a synthetic zeolite which has had a portion of it's sodium ions replacedwith silver ions. Silver is anti-microbial under certain situations. These zeolites are incorporated
directly into a food contact film to allow for a slow release of silver ions to the food. This
material is not approved for use in the U.S. but is reported to be in commercial use in Japan.
Other synthetic and naturally occurring compounds have been proposed and/or tested for
antimicrobial activity in packaging. The anti-fungal agent, imazalil, is effective whenincorporated into waxes used to coat fruits and vegetables. We have demonstrated that the same
compound is effective at preventing mold growth on cheese surfaces when incorporated into
LDPE films. The growth of several species of molds were inhibited when imazalil wasincorporated into LDPE at levels of 500 to 2, 000 mg/kg. Although imazalil is not approved forcheese, this work established that anti-mycotic films could effectively control surface molds infoods.
Reports have appeared which demonstrated the effectiveness of adding food-grade anti-mycotic
agents to cellulose-based edible films. Unfortunately, cellulose-based films are not heat sealable
or good barriers in high humidity situations.
We overcame the incompatibility of simple anti-mycotic organic acids such as propionic,
benzoic, and sorbic acids with polymers such as LDPE by forming the anhydride of the acid
which removes the ionized acid function and decreases polarity. Anhydrides are stable when
dry yet hydrolyze in aqueous environments such as foods. Hydrolysis leads to formation of thefree acid which in turn leads to migration from the surface of the polymer to the food where
they can be effective anti-mycotics. This is an example of "switched on" packaging; the active
ingredient remains in the film until the film contacts a food at which point it is "switched on."
The activity is initiated by the moisture in the food. Others have proposed the incorporation ofnaturally occurring microbial inhibitors into packaging materials. Using naturally occurring
antimicrobial agents would have regulatory advantages in parts of the world were naturalcompounds receive less scrutiny than synthetic.

PEPTIDES, PROTEINS, AND ENZYMES AS ACTIVE PACKAGING AGENTS

The major drawback to all of these technologies is the antimicrobial agent must migrate from thepackaging material to the food in order to be effective. The next generation of active packaging
films may use biologically-derived materials that may not need to migrate to the food to beeffective. For example, bacteriocins are proteins derived from microorganisms much in thesame way penicillin is derived from mold. Bacteriocins are effective against organisms such as
Clostridium botulism and one such compound, nisin, has been approved in the U.S. for fooduse. Several other anti-microbial short chain peptides have been isolated from natural sources .

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Application of Immobilized Enzymes in Active Packaging

For example, defensins, cecropins, and magainins have been isolated from mammalianphagocytes, frog skin, and insects, respectively. Each is a potent anti-bacterial agent of little orn o ma mma lian to xicity. The lo w toxicity is du e to th e b reak down o f the p rotein in th e
mammalian stomach. These peptides could theoretically, be attached to the surface of foodcontact films rendering them antimicrobial. A search of the world patent literature suggests thatthe use of anti-microbial peptides in polymer-based human implants in being investigated andperhaps used.
Enzymes have been immobilized on solid polymers including nylon, EVOH and cellulose
acetate. Anti-microbial enzymes might be effective even if bound to the inner surface of foodcontact films. These enzymes would produce microbial toxins or act directly on
microorganisms. Glucose oxidase which forms hydrogen peroxide is an example of one such
enzyme. Lysozyme is a common enzyme which attack the cell wall in many microorganisms.
Preliminary work in our lab has shown the feasibility of immobilizing lysozyme to an approved
food packaging polymer. Immobilized lysozyme is effective at inhibiting microbial growth indefined media when incorporated into the film. Immo bilization of the lysozyme prevents
migration to the media while maintain in g anti-bacterial activity.

FLAVOR ENHANCING ENZY MES
Flavor deterioration during processing and/or storage is likewise, a problem for most foods andoften the limiting factor in shelf life. Bitterness can develop in citrus juices due to the formationof compounds such as naringin. A fungal enzyme ( naringinase ) is available which hydrolyzes
the compound narigin and removes bitterness. Preliminary work in our lab has shown that thisenzyme can be immobilized to a food approved polymer substrate and that the bitterness of
citrus can be actively removed during storage. We have been successful at increasing theactivity of the immobilized enzyme ten-fold over that reported in the literature. This raises thepossibility that naringinase could be immobilized to the product contact surface of juice
packaging and thus improve the product during storage. This technology would be especiallyapplicable to aseptically filled juices.

CONCLUSIONS

Our preliminary experiments have convinced us that the use of immobilized peptides andenzymes on food-grade polymer substrates as interactive packaging materials bears moredetailed investigation. While our initial work has focused on lysozyme and naringinase, otherenzymes and peptides might be even more interesting. Naringin in grapefruit juice is decreased
by approximately 80% in 4 days when stored at AC when in contact with cellulose acetate
containing naringinase. Likewise, microbial suspensions of 10e4 CFU are rendered sterile in 24- 1 3 -

J. Pack. Scl Techno!. Vot.6 No.l (1997)

hours when in contact with cellulose acetate containing lysozymc. These preliminary results
indicate that the concept of interactive packaging using immobilized enzymes may be feasible.
What little literature that exists suggests that over the next few years, active packaging materials
which arc capable of direct interaction with foods could be developed. Advances inbiotechnology, micro-electronics, and materials science need to be applied to food packaging
technologies. Our general approach will be to seek out recent scientific developments in thefields of materials science, biotechnology, and micro-electronics and to apply them to thedevelopment of active packaging systems. It is our intent to be active in their development.

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