Restructured fruit and vegetable products and processing methods

Value-added, restructured fruit and vegetable products made from bulk-processed ingredients are taught. The restructured fruit and vegetable products are to be eaten out-of-hand as confectionery items or incorporated into baked, canned and/or frozen foods, such as cereals, cookies, cakes, fruit cocktails and ice creams. Processing methods involving twin-screw extrusion used to obtain the restructured fruit and vegetable products are also taught.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to methods of restructuring bulk-processed fruits and 
vegetables utilizing drum drying and extrusion, and products made by such 
methods. 
2. Description of the Art 
Research on structured fruit products began in the 1940's with a process 
using alginates for the formation of structured cherries. Droplets, 
containing cherry puree and alginate, were dropped into a bath of calcium 
salt to form a skin. Alginate based structured fruits offer the advantage 
that they are not affected by heat; therefore, these cherries could be 
used in baked goods (Peschardt, U.S. Pat. No. 2,403,547 1942). 
During the 1960's and early 1970's the USDA began to develop structured 
fruit products. Gelled applesauce, similar to cranberry sauce, was 
produced in an effort to increase utilization of process-grade apples. 
Gelled applesauce contained golden delicious apples, sucrose, low-methoxyl 
pectin, citric acid, calcium lactate and water. The product was marketed 
mainly as an adjunct to pork, as cranberry is to turkey (Lazar and Morgan, 
Food Technology March: 52-53, 1964). Several years later, prunes and other 
dried fruits were gelled using low-methoxyl pectin. These gelled sauces 
could then be used in bakery goods, cereals, mixes, etc. (Bolin and Nury, 
Canner/Packer May, 1967). In another study, apricot concentrate was formed 
into fruit "sheets of cloth" using a drum drier. The cloth was pressed 
into cubes, artificial halves and bars for use in a variety of food 
products. Consumers recommended increasing product moisture content and 
sweetness to improve acceptability (Bolin, Fuller et al., The Bakers 
Digest March: 30-32, 1973; Bolin, Turnbaugh et al., The Bakers Digest 
August: 24-25, 1974). 
The properties of structured fruits were studied in the late 1970's and 
early 1980's. These gels simulated fruit texture, but did not contain any 
fruit. Simulated fruit gels suitable for freeze dehydration were produced. 
Freeze dried gels were formed using a two step process in which a gelatin 
containing sodium alginate gel was cooled, sliced and placed in a calcium 
lactate solution for crosslinkage. When evaluated in yogurt and jello, 
rehydrated gels scored as well organoleptically as most fresh fruits, with 
the exceptions of banana and pineapple (Luh, Karel et al., Journal of Food 
Science 41:89-93, 1976). Later Karel correlated the compressive break 
strength and fracture energy density of calcium alginate gels with sensory 
properties. The effects of pectin, gelatin and sucrose on textural 
properties were also evaluated. The Instron Universal Testing Machine was 
capable of detecting smaller differences in sample mechanical properties 
than sensory panelists. Results indicated that pectin improved the sensory 
acceptability of simulated fruits. The two step method for formation of 
simulated fruit gels was later improved to increase retention of water 
soluble components such as ascorbic acid (Luh, Flink et al., Journal of 
Food Science 42(4):976-981, 1977). A one step procedure using 
glucono-delta-lactone and dicalcium phosphate dihydrate was developed, 
eliminating residence in the crosslinking bath (Pelaez and Karel, Journal 
of Food Processing and Preservation 5:63-81, 1981). 
In the 1980's, the three processing methods for the formation of structured 
fruits from alginates were defined as internal setting, diffusion setting 
and setting by cooling. Internal setting involves calcium ion release from 
within the system at room temperature and produces structured fruits with 
uniform texture. Diffusion setting allows calcium ions to diffuse into the 
alginate matrix and produces structured fruits with an outer skin and a 
liquid center. Co-extrusion may also be used to accomplish diffusion 
setting. The third method involves setting by cooling where gelled 
ingredients are dissolved in hot water and later set by cooling (Hannigan, 
Food Engineering March: 48-49, 1983). 
Novel expanded snacks were formed in the late 1980's by co-extrusion of 
rice flour with dried fruits and fruit juice concentrates. A Brabender 
laboratory extruder was used in this study. Extruded snacks exhibited 
comparable yield and sensory properties compared to extrudate made 
exclusively from rice. The juices performed better than the dried fruit in 
regards to expansion. Citric acid addition did not significantly improve 
extrudate properties with the exception of improved color retention (Maga 
and Kim, Lebensm.-Wiss. U.-Technol. 22(4):182-187, 1989). 
In the past few years, A. Nussinovitsch has performed several studies on 
the formation and properties of structured fruits. In the first study, 
apple pulp and reconstituted grapefruit juice were added to calcium 
alginate gels at concentrations of 5-96% (Kaletunc, Nussinovitsch et al., 
Journal of Food Science 55(6):1759-1761, 1990). The mechanical properties 
of the resultant gels were characterized. This work was the first to 
incorporate such high concentrations of fruit pulp to gels. In another 
study, raspberry pulp was added to calcium alginate gels with and without 
the addition of agar (Nussinovitsch and Peleg, Journal of Food Processing 
and Preservation 14:267-278, 1990). Agar did not improve product strength, 
but did increase brittleness and stiffness. Nussinovitsch also 
investigated the mechanical properties of gel-pulp-sugar composite 
products formed from various hydrocolloids (agar, carrageenan and 
alginate), a wide range of sugar concentrations, and various fruit pulps 
(orange, banana, and apricot) in order to identify means of producing 
structured fruits with a desired consistency (Nussinovitsch, Kopelman et 
al., Lebensm-Wiss. U.-Technol. 24:513-517, 1991). Sugar addition 
strengthened gels up to a maximum point after which gel strength was 
reduced. Fruit pulp, on the other hand, weakened gel strength down to a 
minimum point after which the gel system regained strength. Size reduction 
increased strength. Models were later developed to quantitate the combined 
effect of fruit pulp, sugar and gum on the mechanical properties of agar 
and alginate gels (Nussinovitsch, Kopelman et al., supra, 1991). 
Recently, two studies concerning structured fruit products were published. 
Response surface methodology was used to optimize the texture of a 
sweetened mango pulp-alginate structured fruit product. Structured mango 
was formed with 90% fruit pulp. This study also developed a method for 
evaluating the thermostability of textured fruits (Mouquet, Dumas et al., 
Journal of Food Science 57(6):1395-1400, 1992). A group from Saudi Arabia 
formed prickly pear sheets from fruit pulp, sucrose, citric acid, sodium 
metabisulphite and olive oil. These sheets were highly acceptable to a 
small sensory panel and could be marketed as an alternative to apricot 
sheets (Ewaidah and Hassan, International Journal of Food Science and 
Technology 27:353-358, 1992). 
In the past, the formation and properties of restructured vegetable 
products have not been investigated. However, recent research projects 
have evaluated the formation and properties of restructured sweet potato 
products. Collins et al., Journal of Food Science 60(3):465-467, (1995) 
formed sweet potato pieces by stuffing baked sweet potato into cellulose 
casings and subsequently freezing the product. Troung et al., Journal of 
Food Science 60(5):1054-1059, (1995) formed restructured sweet potato 
products in a similar fashion, with the addition of alginate and various 
salts. Products from both studies exhibited acceptable color, flavor and 
texture. Kim and Maga, IFT 95 Book of Abstracts 25H-7, (1995) recently 
produced a snack containing squash and pinto beans. 
Most current commercial products and processes utilize only a small 
percentage of dried fruit, fruit juice concentrate, fruit powder or fruit 
puree in the final product. The major ingredients are sugars, starches, 
gels and gums. Molded fruit pieces made with dried plum paste, glycerin, 
oat fiber and citrus fiber are available commercially. Extruded fruit 
pieces made from sugar, soybean oil, soy protein, cellulose gum, and 
natural and artificial colors and flavors are also available commercially. 
Restructured vegetable products are not available in the current 
marketplace. 
SUMMARY OF THE INVENTION 
It is the prime objective of the invention to provide value-added, 
restructured fruit and vegetable products made from bulk-processed 
ingredients, to be eaten out-of-hand as confectionery items or 
incorporated into baked, canned and/or frozen foods, such as cereals, 
cookies, cakes, fruit cocktails and ice creams. 
The USDA Food Guide Pyramid advises mature adults to consume 3-5 servings 
of vegetables and 2-4 servings of fruit per day. Because consumers wish 
convenience and variety in their food products, there is a need to provide 
fruit and vegetable products in different forms so that the dietary goals 
are more likely to be attained. The use of value-added, restructured fruit 
or vegetable products would increase utilization and consumption of fruits 
and vegetables. 
Often fruit and vegetable crops have short harvest seasons, so that large 
amounts of material must be processed during a short period, further 
limiting the kinds of products that may be made. There is a need to 
develop processing systems in which large amounts of materials may be 
partially processed into a stable forms within a short harvest season, and 
subsequently made into a variety of desirable final products throughout 
the remainder of the year. Various systems already exist for partially 
processing fruits and vegetables in bulk. These include aseptically 
processed fruit and vegetable purees, aseptically processed piece-form 
products, such as slices, and dehydrated and dehydrofrozen materials. Of 
these, aseptically processed concentrated purees are the least costly to 
produce. However, at present the market for concentrated purees is very 
limited. Typically, off-grade fruits and vegetables or high quality fruits 
and vegetables that are in excess of that needed for canning, freezing, or 
other processing is made into concentrated puree. It is often a salvage 
operation. Concentrated purees are utilized in juice drinks, nectars, baby 
food, and some sauces. 
The restructured fruit or vegetable products of the invention are made with 
concentrated fruit and/or vegetable puree as the primary starting 
material. Further bulk-processed products such as clarified syrups, highly 
concentrated purees, drum dried films, spray dried purees, and piece-form 
materials, such as dried, dehydrofrozen, and aseptically processed dices 
and slices are incorporated into the products to provide unique textural 
and flavor qualities. 
It is a further object of the invention to provide a convenient and 
efficient method for preparing such fruit or vegetable products. The 
method incorporates extrusion technology, which is primarily used for the 
production of breakfast cereals, snack foods, pet foods and the production 
of synthetic polymers. Advantages of extrusion include continuous 
processing, enhanced hygiene, lower energy needs, and enhanced control. 
The combination of drum drying and twin-screw extrusion allows for the 
production of 100% fruit products.

DETAILED DESCRIPTION OF THE INVENTION 
The invention comprises restructured fruit and vegetable products produced 
from bulk-processed ingredients. The invention will be described for fruit 
products with the understanding that the invention applies equally to 
vegetables. 
One hundred percent fruit puree products were formed using twin-screw 
extrusion. Fruit puree was drum dried prior to extrusion to enable the 
formation of 100% fruit products. Various gelling agents such as starch, 
gelatin, alginate, pectin and gellan gum may be incorporated to provide 
the desired structure in the final product. Using different dies, the 
fruit products can be formed in a variety of shapes and sizes. 
A Haake-Leistritz co-rotating, twin screw extruder rheometer was used for 
the continuous production of restructured fruit. The temperature profile 
within the extruder barrel was manipulated and monitored to achieve the 
desired results. The characteristics of the final product can be 
manipulated by varying the temperature of the extrudate. At lower 
temperatures, added starch remains ungelatinized, resulting in a more 
dense product. As the temperature increases, adhesiveness and cohesiveness 
of the product increases. As the product temperature increases, the 
texture changes from soft and dense to a light, puffed state. Product 
temperatures above 100.degree. C. result in crisp, puffed restructured 
fruit and vegetable products, whereas product temperatures below 
100.degree. C. result in softer, denser products. The pressure build-up 
within the barrel was monitored. Ingredients can be added to the extruder 
using a gravimetric feeder or through the use of pumps into any point 
within the extruder barrel. Haake's computer-controlled torque rheometer 
was employed for complete characterization of the flow properties and 
processing characteristics of the food for final product optimization. 
Final restructured fruit and vegetable product properties were determined 
in the following manner. The water activities of the final fruit and 
vegetable pieces were tested using an AquaLab CX2 water activity meter. 
Moisture contents were determined either by vacuum oven drying or using a 
Karl Fisher titrator. Color was monitored through the use of a Minolta 
colorimeter. Texture profile parameters such as hardness, springiness, 
adhesiveness and cohesiveness were determined using a cyclic method 
developed on an Instron Universal Testing machine. 
Sensory evaluations may be employed to evaluate the color, flavor and odor 
of the final restructured pieces. Fruit and vegetable piece flavor and 
odor compounds may be further characterized using a HP-6890 gas 
chromatograph-mass spectrometer. Scanning electron microscopy may be 
employed to examine the microstructure of the restructured pieces. Rapid 
methods of analysis, such as Near Infrared Analysis (NIRA), may provide 
potential users with methods to monitor the processes and apply advanced 
processing control, such as Statistical Process Control (SPC), in 
manufacturing operations. Neural Network theory may be applied for data 
analysis and model development. 
Any fruits and vegetables, either alone or in combination, may be used in 
the invention. Possible combinations include, but are not limited to, 
carrot and sweet corn, cranberry and raspberry, banana and strawberry, 
pear and broccoli, pear and celery, and mango and red bell pepper. 
EXAMPLE 1 
Materials. 
This example describes the production of restructured peaches containing 
100% fruit other than added water. Yellow cling peach puree concentrate 
was used in liquid and dried forms. The dried form was dried in a double 
drum drier to approximately 6% moisture content. Drum dried puree was 
ground in a food processor. 
Extrusion conditions. 
A Haake-Leistritz co-rotating twin screw extruder equipped with a 18 mm 
barrel diameter and a barrel length to diameter ratio of 30:1, with six 
barrel sections, was used. The extruder was driven by a torque rheometer. 
Barrel temperature profiles ranged from 60,65,65,65,50,30.degree. C. to 
60,95,105,95,40,40.degree. C. for the six sections. Dry ingredients were 
fed into the first section and liquid ingredients such as water, sugar 
solutions or fruit juice concentrates were fed into the second section. 
Melt temperatures were monitored in the final barrel section and in the 
die where melt pressure was also determined. Screw speeds ranged from 100 
to 150 rpm. 
EXAMPLE 2 
Materials. 
This example describes the production of restructured peaches with added 
starch. Yellow cling peach puree concentrate was used in liquid and dried 
forms. The dried form was dried in a double drum drier to approximately 6% 
moisture content. Drum dried puree was ground in a food processor. As 
desired, 0-30% high amylose corn starch and 0-65% corn syrup or cane sugar 
solution (0-65% of the liquid ingredient) was added and 0.25% water was 
sprayed into the mixture while stirring. Fruit juice concentrates may be 
used instead of sugar solutions. 
Extrusion conditions. 
The conditions described in EXAMPLE 1 were used with the barrel temperature 
profile of 60,95,105,95,40,40.degree. C. to achieve a product temperature 
of 80.degree. C. Under these conditions, the starch was gelatinized. 
EXAMPLE 3 
Materials. 
This example describes the production of restructured peaches with added 
starch under conditions in which the starch remains ungelatinized and acts 
as a filler in the final product. Yellow cling peach puree concentrate was 
used in liquid and dried forms. The dried form was dried in a double drum 
drier to approximately 6% moisture content. Drum dried puree was ground in 
a food processor. As desired, 0-30% high amylose corn starch, thereby 
producing restructured peaches containing 70-100% fruit other than added 
water 0-65% corn syrup or cane sugar solution (0-65% of the liquid 
ingredient) was added and 0.25% water was sprayed into the mixture while 
stirring. 
Extrusion conditions. 
The conditions described in EXAMPLE 1 were used with the barrel temperature 
profile of 60,65,65,65,50,30.degree. C. to achieve a product temperature 
of 55.degree. C., which resulted in the starch remaining ungelatinized. 
Measurements. 
The following measurements were performed on the products from each 
example. Moisture content was determined using traditional vacuum oven 
tests performed at 75.degree. C. (FIG. 1 and FIG. 2). Water activity was 
determined using a Decagon AquaLab CX2 meter. A Minolta calorimeter was 
employed to measure lightness (L), redness (a) and yellowness (b) values 
on ground extruded samples (FIG. 1). The Series XII Software and an 
Instron 4502 was utilized to analyze texture profile parameters. Sample 
dimensions were 10 mm diameter by 15 mm high. Samples were compressed at 
12 mm/min to 80% of their original height. Two compression cycles were 
performed and the data was analyzed for hardness, adhesiveness, 
cohesiveness and springiness values. Specific mechanical energy (SME) 
values were calculated on smoothed torque data. 
##EQU1## 
Moisture content exhibited a great effect on all product properties. For 
100% peach puree extruded gels, as moisture content decreased, product 
lightness (L), redness (a) and yellowness (b) values increased 
significantly. Moisture content reduction also resulted in significant 
decreases in water activity and significant increases in product hardness. 
Sugar addition, either corn syrup or cane sugar, resulted in increased L, a 
and b values when the moisture content was equivalent. Product color 
improved significantly as more sugar was added (FIG. 3). Sugar addition 
had no significant effect on product hardness, springiness or 
cohesiveness. Product adhesiveness decreased significantly with increasing 
sugar concentrations (FIG. 4). 
Tests were performed at two temperature ranges with added starch. At a 
product temperature of 55.degree. C. the starch remained ungelatinized and 
acted as a filler in the final product. At a product temperature of 
80.degree. C. the starch was fully gelatinized. Equivalent moisture 
content gels were compared. Peach puree/starch gels containing gelatinized 
starch exhibited significantly lower L, a and b values, due to their 
higher process temperatures (FIG. 5). Hardness was significantly greater 
in ungelatinized gels. Springiness was not significantly different. 
Adhesiveness and cohesiveness increased significantly as temperature 
increased (FIG. 6). 
Increasing concentrations of starch in the extruder feed led to more 
rapidly setting gels upon exiting the extruder. No significant change in 
color was observed as starch concentration varied (FIG. 7). Product 
hardness and adhesiveness increased with increasing concentrations of 
starch; whereas, product cohesiveness decreased (FIG. 8). 
As the specific mechanical energy (SME) during extrusion increased, product 
hardness increased. SME could be used as an initial indication of product 
hardness. 
Extruded fruit products were made of up to 100% fruit puree. Starch can be 
added to these gels to improve their functional properties. Extruded fruit 
and vegetable products such as these can be consumed as healthy 
alternatives to be eaten out of hand or as ingredients to be added to 
baked and frozen food products, such as muffins, cookies and ice cream. 
It is understood that the foregoing detailed description is given merely by 
way of illustration and that modification and variations may be made 
therein without departing from the spirit and scope of the invention.