1478 c03.fm page 53 wednesday, july 7, 2004 8:18 am fresh-cut fruits · 2015. 7. 22. · 3.4...

3

Fresh-Cut Fruits

Elisabeth Garcia and Diane M. Barrett

CONTENTS

3.1 Introduction 3.2 Effects of Fresh-Cut Processing on Produce Physiology3.3 Unit Operations in Fresh-Cut Fruit Preparation

3.3.1 Receiving, Inspection, and Storage of Raw Material3.3.2 Cleaning and Disinfection3.3.3 Peeling, Deseeding, Trimming, Coring, and Cutting3.3.4 Washing and Cooling3.3.5 Dewatering3.3.6 Packaging and Distribution

3.4 Quality Aspects of Fresh-Cut Fruits3.4.1 Importance of Cultivar Selection 3.4.2 Optimum Degree of Ripeness for Processing3.4.3 Microbial Spoilage3.4.4 Browning Control3.4.5 Prevention of Textural Losses3.4.6 Appearance and Sensory Quality3.4.7 Nutritional Aspects

3.5 Shelf Life Extension of Fresh-Cut Fruit 3.5.1 Temperature Management3.5.2 Modified Atmosphere Packaging 3.5.3 Humidity3.5.4 Edible Coatings

References

3.1 INTRODUCTION

Over the past 25 years the consumption of

fresh

fruit in the U.S. was reported to have grown byabout 26%, according to the Economic Research Service-U.S. Department of Agriculture (Pollack,2001). However, this does not reflect all fruit because the report does not include melon consump-tion, which was part of the vegetable category statistics. Over the same period, the U.S. consumptionof fresh vegetables and melon has increased by 33%. In addition to awareness of the health benefitsof a diet rich in fruits and vegetables, several factors are attributed to these changes, such as risingincome, increased production, greater diversity and availability (of domestic and imported produce,on and off season), product convenience, storage, and transportation, among others (Pollack, 2001).Nevertheless, according to a USDA survey (1994 to 1996), the recommended number of at leasttwo daily fruit servings is currently met by only 23% of the American population (USDA, 1998).

Frequently, convenience is an important factor in a consumer’s selection of produce, and fruitare no exception. From 1997 to 1999, over 40% of the total fruit intake was consumed as juice,

1478_C03.fm Page 53 Wednesday, July 7, 2004 8:18 AM

Copyright 2005 by CRC Press LLC

54

Processing Fruits: Science and Technology, Second Edition

63% of which was solely orange juice (accounting for 86% of orange consumption). Another trendobserved since the mid-1970s is that Americans are eating less canned produce, and more freshand frozen items. Although over the past two decades the consumption of frozen fruit increased36%, this constitutes a small fraction of all fruit consumed in the U.S. During the last two decades,another category of fruit product has been introduced in the market: fresh-cut fruit. Fresh-cutproducts have also been referred to as “lightly processed,” “minimally processed,” “fresh-pro-cessed,” “partially processed,” or “preprepared” products. According to the International Fresh-CutProduce Association (IFPA),

Fresh-cut produce is defined as any fresh fruit or vegetable or any combination thereof that has beenphysically altered from its original form, but remains in a fresh state. These fruits and vegetables havebeen trimmed, peeled, washed, and cut into 100% usable product that is largely bagged or prepackagedto offer consumers high nutrition, convenience, and value while still maintaining freshness

(IFPA, 2002).

The idea of minimal processing of fruit has been around in different parts of the world forsome time, but at a different scale. Consumers could find convenient produce items already washedand peeled or either, cut on site at a local market or street stall. No special packaging or refrigerationwas used; these products were directed toward immediate consumption. In the U.S., fresh-cutproduce first appeared in retail markets in the 1940s, but second-quality, misshapen produce wasused; quality was unpredictable and shelf life was limited. In the mid-1970s, fast-food chains wereusing shredded fresh-cut lettuce and chopped onions; in the mid 1980s, salad bars opened, andfresh-cut produce start replacing canned products (Garrett, 2002). Today, vegetables (mainly salads)constitute the main segment (~70%) of fresh-cut products. In addition to the convenience, thereare other reasons for the success of fresh-cut produce, such as the absence of waste material. Whenutilizing fresh-cut produce, 100% is consumable, and there is also a substantial decrease in laborrequired for home produce preparation (e.g., no need for washing, trimming, etc.) and wastedisposal. The amount of waste in peeling and coring fruit can be quite elevated; in pineapple itfrequently exceeds 50% of the fresh fruit

weight (including the crown). These advantages makefresh-cut produce well accepted items in the foodservice sector, commercial salad bars, and fast-food outlets (Price and Floros, 1993).

Examples of fresh-cut fruit available in the U.S. for retail and foodservice distribution are slicedapples, peaches, strawberries, oranges, grapefruit, mangoes, melons, watermelons, pineapple, citrussegments, and fruit salads. Fresh-cut fruit tend to be more perishable than the commodity fromwhich they were prepared. The expected shelf life of fresh-cut fruit is around 7 to 8 d, in contrastto 10 to 14 d for fresh-cut vegetables (Kader, 2002). The limited commercial success of fresh-cutfruit is related to their perishability and consequently short shelf life.

3.2 EFFECTS OF FRESH-CUT PROCESSING ON PRODUCE PHYSIOLOGY

Whereas the processing of fruits generally extends their shelf life, as seen in the case of canning,freezing, and drying, fresh-cut processing increases the perishability of fruits (Cantwell and Suslow,1999). The physical wounding of tissue caused by the preparation (peeling, cutting, slicing, dicing,etc.) of the fresh-cut products leads to many physical and physiological responses (Brecht, 1995;Saltveit, 1997). There is an increase in respiration rate and ethylene production, which impactsfruit quality and shelf life. Increased respiration rate is related to elevated cellular metabolism,which contributes to faster quality deterioration. Table 3.1 shows examples of respiration rates offresh-cut fruit as compared to intact fruit. Respiration rates increase with the degree of injury orprocessing and with storage temperature. In a study with papayas (Paull and Chen, 1997), fruitwere longitudinally halved, one half fruit was kept with seeds, and the other half was deseeded.



Fresh-Cut Fruits

55

Opposite halves of the same fruit were used. The wound caused by slicing and deseeding led toincreases in ethylene production five- and ninefold higher in the halves with seeds and in thedeseeded halves, respectively, as compared to the intact fruit. The injury caused by woundingthrough slicing and deseeding of papaya fruit also led to yellowing of the fruit skin and softeningof the mesocarp.

Wound-related production of ethylene is higher in fruit at the preclimacteric and climactericstages than in postclimacteric period (Abeles et al., 1992). The response to injury may also beaffected by the maturity stage of fruit. In a study by Cantwell and Suslow (1999), cantaloupe melonpieces processed from fruit at different maturity stages had similar respiration rates, but ethyleneproduction was much higher in pieces from riper fruits.

The removal of protective epidermis or skin of the fruit leads to changes in gas diffusion,accelerates water loss, and favors microbial contamination. It is important to prevent cut-surfacedesiccation, which negatively impacts product appearance. Another consequence of fresh-cut fruitprocessing is cell disruption, which allows previously compartmentalized enzymes to come incontact with their substrates, leading to undesirable reactions such as development of enzymaticbrowning and accelerated softening.

3.3 UNIT OPERATIONS IN FRESH-CUT FRUIT PREPARATION

In order to maintain the highest possible quality of a fresh-cut fruit, it is important to observeadequate handling of the produce before preparation. It is necessary to keep produce under adequatestorage conditions (temperature and relative humidity) and use gentle handling to minimize bruisingand other physical injuries. Strict temperature control is the single most important factor in main-taining quality throughout the fresh-cut preparation and distribution. All unit operations should becarried out in cold processing rooms (

£

5

∞

C), and cleanliness is very important to ensure a high-quality and safe product. It is of utmost importance to use sanitary equipment and adopt GoodManufacturing Practices (GMP) in combination with Hazard Analysis Critical Control Point(HACCP) (IFPA, 1996a

,

1997; Beuchat, 2000). The overall steps involved in the preparation offresh-cut fruit follow.

TABLE 3.1Respiration Rates of Fresh-Cut Fruit and Whole Fruits Stored at Different Temperatures

Fruit

Respiration (mg CO

2

/kg/h)

0

∞

C 5

∞

C 10

∞

C

Kiwi wholeslices

3.27.2

4.611.6

8.623.3

Peach wholeslices

4.06.0

8.110.0

15.018.6

Muskmelon large, wholelarge, slicessmall, wholesmall, slices

4.83.73.12.7

8.67.06.34.2

14.712.213.6

9.8Honeydew whole

slices1.42.3

4.63.0

5.28.3

Source:

From Watada, A.E., Ko, N.P., Minott, D.A. 1996.Factors affecting quality of fresh-cut horticultural products.

Postharvest Biol. Technol.

9: 115–125.



56


3.3.1 R

ECEIVING

, I

NSPECTION

,

AND

S

TORAGE

OF

R

AW

M

ATERIAL

Fruit has to be inspected and evaluated according to high standards of safety and quality. It is wellknown that no processing can increase the quality of a diseased or misshapen ingredient. Therefore,it is very important that while awaiting processing, fruit should be kept under refrigeration (ingeneral, 1 to 5

∞

C) according to produce specifications. If a commodity is sensitive to chilling injury,it requires appropriate storage conditions, separate from nonsensitive fruit. For example, symptomsof chilling injury are seen in pineapple stored for prolonged periods at temperatures below 12

∞

C(Paull and Rohrbach, 1985). Whereas some fruits, such as pears and apples, can be stored forextended periods of time while waiting to undergo processing, the effects of such storage on fresh-cut products may be undesirable. Gorny and coworkers (2000) observed significant shelf-lifereduction in fresh-cut pears prepared from fruit that had been kept for increased storage periods at1

∞

C in air or controlled atmosphere (2% O

2

+ 98% N

2

).

3.3.2 C

LEANING

AND

D

ISINFECTION

With many fruit that have a smooth surface, such as apples and pears, the use of cold clean watermay be enough for a first wash. However, some fruit may harbor a high microbial population ontheir external surface. Cantaloupes were one of three imported produce with the greatest incidenceof pathogen contamination in a survey carried out by the Food and Drug Administration (FDA,2002). Such fruit should be washed, scrubbed, and dipped in solutions of disinfectants. The mostcommonly used sanitizer is chlorinated water, but other possible chemicals for disinfection arehydrogen peroxide, surfactants, peroxyacetic acid, trisodium phosphate, and ozone, among others(Heard, 2002; Beuchat, 2000; Cherry, 1999; Sapers and Simmons, 1998). The efficacy of chlorineand hydrogen peroxide treatment on the native microflora of cantaloupes, as well as on

Escherichiacoli

population, was compared by Ukuku and coworkers (2001). Hydrogen peroxide proved to bemore efficient against the surface microflora of cantaloupe, while chlorine was more effectiveagainst

E. coli

ATCC 25922.

3.3.3 P

EELING

, D

ESEEDING

, T

RIMMING

, C

ORING

,

AND

C

UTTING

In contrast to vegetables, which in many instances can be peeled and cut mechanically (such ascarrots), for most fruit whose texture is soft, the removal of skins and rinds is carried out by hand.It is very important to use clean and sharp knives during this operation. The use of blunt bladescauses excessive physical injury (tissue crushing) to the fruit tissue adjacent to the cut, acceleratingquality deterioration. Fresh-cut cantaloupe melon prepared with sharp and blunt knives werecompared (Portela and Cantwell, 2001). Melon pieces prepared using blunt knives had increasedethanol levels, off-odors, and electrolyte leakage compared to sharp-cut pieces. The marketablevisual quality of sharp-cut melon lasted much longer; blunt-cut pieces developed a translucency,which is a common visual defect that indicates cell disruption in commercially prepared fresh-cut cantaloupe.

With citrus, enzymatic peeling has been reported as an alternative to hand peeling (Bruemmer etal., 1978; Pretel et al., 1996, 1998). Whole citrus fruit can be vacuum infused with solutions of pecticenzymes that will eliminate flavedo and albedo, with limited damage to the juice vesicles. After thistreatment, peeled fruit have to be rinsed by immersion in water for removal of the enzyme solution.

3.3.4 W

ASHING

AND

C

OOLING

During the cutting steps there is release of tissue fluids that should be removed to avoid undesirablemicrobiological or chemical reactions. It is imperative to rinse the cut surfaces of the fruit. At thisstage the use of cold water (~0

∞

C) accomplishes the washing of the cut surfaces as well as coolingof the fruit pieces. For safety reasons, chlorinated water (usually 50 to 100 ppm) is frequently used.



Fresh-Cut Fruits

57

All the equipment used in the processing (cutting tools and mats) are a potential source ofcontamination and require adequate sanitation.

In some cases it is necessary to use dipping solutions containing processing aids that will helpprevent nonmicrobial quality deterioration such as surface browning and softening (Garcia andBarrett, 2002).

3.3.5 D

EWATERING

Excess moisture picked up during the washing operation should be removed prior to packaging.This step helps to prevent growth of microorganisms that remained after produce disinfection. Dueto their delicate texture, fresh-cut fruit require passage through semi-fluidized beds with forced airto remove moisture.

3.3.6 P

ACKAGING

AND

D

ISTRIBUTION

In order to ensure the longest possible shelf life for fresh-cut fruit, it is important to chooseappropriate packaging materials and storage conditions.

Temperature is always a critical factor in the shelf life of fresh-cut fruit. The importance oftemperature control is related to food safety and extension of fresh-cut life by slowing respirationrate and preventing quality deterioration. As an example, the shelf life of sliced pineapple is reportedto range from a few hours at 20

∞

C and to greater than 5 weeks at 1

∞

C (O’Hare, 1994). Throughoutthe unit operations involved in preparation and up to consumption, a cold chain should be main-tained; ideally temperatures should not exceed 5

∞

C, although preferably they should be closer to1

∞

C (IFPA, 1997). During the distribution of fresh-cut products, it is also important to avoid roughhandling. Very often products are subjected to shock and vibration stress, which cause injury,leading to more rapid quality loss. In a study of fresh-cut watermelon cubes, results showedincreased juice leakage and darkening of product vibrated in noncompartmentalized packages.Authors suggested that the placement of compartments that decrease movement of fruit piecesduring transit can improve overall quality by reducing vibration (Fonseca et al., 1999).

3.4 QUALITY ASPECTS OF FRESH-CUT FRUITS

Fresh-cut fruit combine the convenience of a 100% usable product with the fresh-like qualitycharacteristics of fresh fruit, e.g., appearance, flavor, and texture. The initial appeal of a convenientfresh-cut product will only be ensured of continued acceptability if the product quality meets theconsumer’s quality criteria including appearance, product shelf-life, and relationship between per-ceived value and cost. Moreover, the product value as food also depends on its nutritional qualityand its safety (Kader, 2002).

Several preharvest factors affect the quality of a commodity, such as genetic background,agronomic practices, environmental conditions during cultivation, and stage of maturity at harvest.Final product quality is influenced to a great degree by postharvest handling and fresh-cut prepa-ration, from the initial unit operations up to distribution. As a result of the injury (wound) broughtby cutting, cells are broken and undesirable reactions may result. Fresh-cut fruit may undergosurface browning, tissue softening, loss of flavor, and other deterioration reactions. Moreover, theleakage of nutrient-rich tissue fluids can potentially lead to microbial spoilage; peeling and removalof protective tissues lead to water loss and, consequently, quality defects such as surface drying,loss of gloss, and shrinkage are more noticeable.

3.4.1 I

MPORTANCE

OF

C

ULTIVAR

S

ELECTION

A high-quality fresh-cut product starts with fruit of superior raw material quality and the appropriateselection of fruit cultivars (cv.). In fact, cultivar selection is one of the most important considerations.

1478_C03.fm 7 Wednesday, July 7, 2004 8:18 AM


58


The most suitable cultivars should be selected, or developed, for compatibility with fresh-cutprocessing, packaging, and distribution. At this stage, many characteristics may be considered, suchas fruit shape or size, flesh thickness, susceptibility to pre- and postharvest pathogens, susceptibilityto browning, desiccation, texture loss, etc. (Romig, 1995).

Different fruit cultivars may vary in their respiration rates when cut for processing. A compar-ison of four pear cultivars commonly available in the U.S. (cv. Bosc, Bartlett, Anjou, and RedAnjou) showed that pears of the cv. Bartlett showed no difference in respiration rate when storedat 10

∞

C in air and 90 to 95% relative humidity. However, slices prepared from the cv. Bosc had a35% increase, cv. Anjou a 64% increase, and cv. Red Anjou a 232% increase in respiration inrelation to the intact fruit of the same cultivar. The evolution of carbon dioxide in all cultivars wasbetween two- and fourfold greater when temperature was increased from 0

∞

C to 10

∞

C (Gorny etal., 2000).

Varying composition of different cultivars will affect final product quality. The browningtendency of different fruit cultivars is exemplified for pears and apricots in Table 3.2. The pearcultivars evaluated in this study showed almost a fourfold range in their difference in lightness (DLvalue) between fresh and oxidized purees. Apricot cultivars showed a similar range of differencein browning tendency.

Bartlett pear slices had a large decrease (82%) in flesh firmness, in contrast with cultivar Anjou(12% decrease in firmness) after 6 d at 10

∞

C (Gorny et al., 2000). Variations in the shelf life (rangingfrom 2 to 12 d at 0

∞

C) of different cultivars of sliced peaches and nectarines are shown in Figure3.1. Evaluation of shelf life was based on appearance; products developed surface browning, pitcavity breakdown, and limited dehydration, resulting in loss of sheen and gloss at the cut surface(Gorny et al., 1999).

TABLE 3.2Enzymatic Browning of Pear

a

and Apricot

b

Purees Prepared from Different Fruit Cultivars Harvested at Commercial Maturity

Pear Cultivar DL

a

Apricot Cultivar DL

a

Abbe Fetel –16.2 Bebeco 5.3Comice –15.1 Cafona 11.8Conference –14.1 Canino 16.7Guyot –9.9 Henderson 26.3P 2198 –15.3 Moniqui 21.4Williams –13.3 Polonais 16.86.30.100 –4.8 P. Tyrinthe 3.7

R. Fournes 17.8R. Roussillon 17.8

a

Reflectance measurements expressed as DL, difference in light-ness between oxidized and nonoxidized purees.

Source:

From

a

Amiot, M.J., Tacchini, M., Aubert, S., Oleszek, W.1995. Influence of cultivar, maturity stage, and storage conditionson phenolic composition and enzymatic browning of pear fruits.

J. Agr. Food Chem

. 43(5): 1132–1137;

b

Radi, M., Mahrouz, M.,Jaouad, A., Tacchini, M., Aubert, S., Hughes, M., Amiot, M.J.1997. Phenolic composition, browning susceptibility, and caro-tenoid content of several apricot cultivars at maturity.

HortScience

32(6): 1087–1091.



Fresh-Cut Fruits

59

Many agronomic (soil type, fertilizer application, water supply, etc.) and environmental (climateand rainfall) factors also affect fruit quality. Sucrose is the main soluble sugar in muskmelon flesh,and adverse weather conditions in the weeks prior to harvest can have a negative effect on fruitsweetness. Short-term shading (5 d at ~ 50% reduced daylight) of muskmelon plants prior toharvesting promoted accumulation of acetaldehyde and ethanol and reduction of sucrose contentin melon flesh (Nishizawa et al., 1998). Cultivars may also respond differently to conditions adoptedin modified atmosphere packaging. Different cultivars of strawberries showed wide variation inresponse when exposed to 20% carbon dioxide for up to 9 d. Some cultivars (such as Honeoye andKent) accumulated large levels of fermentation products associated with off-flavor development,such as acetaldehyde and ethanol.

Depending on the commodity, different traits may be relevant in selecting cultivars for fresh-cut preparation. While tendency to brown is important in fresh-cut apples and pears, there may bemore interest in other quality attributes such as texture retention in sliced kiwifruit, absence ofseeds in watermelon for fresh-cut use, reduced off-flavor production in strawberries, and a balancebetween sweetness and acidity in pineapple.

3.4.2 O

PTIMUM

D

EGREE

OF

R

IPENESS

FOR

P

ROCESSING

Quality and shelf life of fresh-cut fruit are affected by maturity stage. While a fresh-cut fruit isexpected (by the consumer) to be at its optimum ripeness, with the best sensory attributes of flavor,taste, and firmness, this is usually not the best maturity stage for handling and processing. Oftena fully ripe fruit may be at an advanced stage of softening for fresh-cut preparation, whereas animmature fruit may not present adequate eating quality (Kader and Mitcham, 1998). Synthesis ofboth flavor and color compounds occur relatively late in fruit maturation; therefore an early harvestmay result in poor flavor and color. Shorter shelf life results from harvest of either immature oroverripe fruit that are more susceptible to physiological disorders than fruit harvested at the propermaturity (Kader, 2002). In a study of sliced pears (cv. Bartlett), ripe fruit had a shelf life of ~2 dat 0

∞

C, in contrast with partially ripe and mature-green slices with a shelf life of 8 d. However,the eating quality of mature-green fruit was compromised due to poor aroma and lack of juiciness(Gorny et al., 2000). Likewise, using quality scores based on appearance, firmness, and taste,honeydew melon cubes prepared from fruit at the immature to mature threshold stage (8.8% solublesolids) were rated as

poor

after storage of 3 d at 10

∞

C, and as

fair to poor

after 7 d at 5

∞

C. Melon

FIGURE 3.1

Genotypic differences in shelf life of fresh-cut peaches and nectarines kept in air at 0

∞

C and90 to 95% relative humidity. (From Gorny, J.R., Hess-Pierce, B., Kader, A.A. 1999. Quality changes in fresh-cut peach and nectarine slices as affected by cultivar, storage atmosphere and chemical treatments.

J. FoodSci

. 64(3): 429–432.)

0 2 4 6 8 10 12 14

Tra ZeeSummer Lady

Snow KingSnow Giant

Ryan SunRed SunRed Cal

O’HenryFlavorcrest

Elegant LadyCarnivalCal Red

August Lady

Marketable shelf-life (days)

Peaches

0 2 4 6 8 10 12 14

Zee Grand

Summer Grand

Summer Fire

Summer Diamond

Sparkling Red

September Red

August Red

Arctic Queen

Marketable shelf-life (days)

Nectarines



60


cubes from very mature fruit (13% soluble solids) were rated as

good to fair

after 7 d at 5

∞

C and

fair

after 3 d at 10

∞

C. Fresh-cut products from immature fruit did not have honeydew taste or aromaand deteriorated faster than product from mature fruit (Watada and Qi, 1999).

3.4.3 M

ICROBIAL

S

POILAGE

Although it is considered that whole fresh produce, for the most part, are among one of thesafest foods (Brackett, 1987), the safety of fresh-cut products requires a great deal of attention.The processing that fruit undergo turn them more vulnerable to microbiological risks, and thesensory quality is meaningless if the product is unsafe (Brackett, 1992). Along the chain of stepsinvolved in the production of fresh-cut products, from the growth of the raw material to theprocessing and distribution, there is potential for microbiological risk. Microbial contaminationmay (1) be of public health significance due to the presence of human pathogens, or (2) decreasethe shelf life of the fresh-cut fruit due to spoilage microorganisms, and in addition render amajor economic impact.

Appropriate care should start in the farm environment. Contamination may result from soil,poor agronomic practices such as use of raw or improperly treated animal manure as fertilizer,irrigation with contaminated water, animal contact, etc. During fruit picking and packing, contam-ination may occur through contact with food handlers who may be carriers of microbial pathogens.In general, all fruit arrive at the receiving section of the food processing plant with a microbialload. In the initial steps of processing, with peeling and cutting there is removal of protectivebarriers (skin, peel, rind) and release of nutrient-rich cellular fluids, conditions that provide increasedrisk for microbial contamination of the product. After some outbreaks occurred due to the con-sumption of cantaloupe from salad bars, scientists concluded that microorganisms present in themelon rind were most likely introduced into the fruit during cutting of the melons (Madden, 1992).

The normal microflora found on the surface of produce is diverse, but it generally includes avariety of fungi, mostly harmless bacteria and different species of yeasts. It is expected that differentmicroorganisms will be present in produce that grows on top of the soil vs. a tree-borne fruit. Fungiconstitute the majority of spoilage microorganisms found in fruits (Brackett, 1987). However,human pathogens may be present in the fruit microflora.

Clostridium botulinum

,

Clostridiumperfringens

, and

Bacillus cereus

can be isolated from soils free of fecal contamination.

Listeriamonocytogenes

can be found in decaying vegetation and soil, as can coliforms of nonfecal originsuch

as Enterobacter

spp. and

Klebsiella

spp. Enteric microorganisms, among them

E. coli

, arelinked to soils contaminated with feces, improperly composted manure or sewage, and contaminatedirrigation water. In agricultural environments, animals (domestic and wild) constitute another sourceof pathogenic bacteria. Salmonellae are found in the intestine of many animals and are abundantin fecal material and sewage (Francis et al., 1999). Birds that feed at sewage works can be a vectorfor

L. monocytogenes

and enteric bacteria into farm environment. Enteric bacteria can be transmittedto flowers during pollination by insects (NACMCF, 1999). Viruses such as the Hepatitis A andNorwalk can also be found in foods. Fresh-cut product contamination may also occur duringharvesting, processing and handling as a result of inadequate personal hygiene among employees,poor sanitation of the processing facilities, dirty cutting tools and work surfaces, and reuse of washwater or ice.

In addition, due to certain characteristics of the fresh-cut fruit processing and packaging, thereare additional risks. While one of the initial steps in the processing of fresh-cut products is sanitation,not all microorganisms are eliminated. After breaking the fruit surface integrity with peeling andcutting, rapid bacterial growth can take place. However, the low pH of most fruits does not supportthe growth of most pathogens (Brackett, 1987). For example, the pH of pineapple ranges between3.5 and 4 (Siriphanich, 1994). Nevertheless, high pH values are common in different types ofmelons (Lund, 1992), such as honeydew (pH 5.2 to 5.6), cantaloupe (pH 6.2 to 6.5), and watermelon(pH 6.3 to 6.7), and these fruit are particularly susceptible to microbial contamination and growth.



Fresh-Cut Fruits

61

Storage temperature is a very important factor in controlling microbial growth. Although storageunder refrigeration temperatures deters the growth of many microorganisms, some can grow atthese conditions, as shown for

L. monocytogenes

(Nguyen-The and Carlin, 1994). With the use ofcertain types of packaging (such as in modified atmosphere packaging) and long periods of storage,some pathogenic microorganisms may attain numbers high enough to pose a health risk. This couldresult from the growth of a pathogen population under conditions where there is a suppression ofthe natural microflora that under normal circumstances would play a positive role in competingwith pathogens. The long storage periods allow time for available pathogens to grow, and significantmicrobial populations may develop. Additionally, if temperature abuse occurs, anaerobic atmo-spheres can develop inside packages during extended storage (Francis et al., 1999). While theseconditions do not favor the growth of some microorganisms,

C. botulinum

can grow under highCO

2

. Product appearance or sensory characteristics may not be affected and the potential healthrisk may not be perceived by the consumer (IFPA, 1996b

)

.Following the strict guidelines of GMP and a well-designed HACCP (Hazard Analysis Critical

Control Points) plan are fundamental recommendations of the International Fresh-Cut ProduceAssociation (1996a, 1997) in order to produce a microbiologically safe product.

3.4.4 B

ROWNING

C

ONTROL

Surface discoloration is probably the most common quality defect of fresh-cut fruit and the factormost limiting shelf life. During the peeling and cutting operations, cells are broken, and theircontents include previously compartmentalized enzymes that are suddenly freed to come in contactwith their substrates. A group of enzymes called polyphenol oxidases (PPO), which occur inparticularly high amounts in fruits such as banana, apple, pear, avocado, and peach, are responsiblefor the discoloration referred to as enzymatic browning.

Enzymatic browning may be controlled through the use of physical and chemical methods;often both are employed. Physical methods commonly used include reduction of temperature andoxygen, and use of modified atmosphere packaging or edible coatings. Chemical methods dependon either treatment with compounds that inhibit polyphenol oxidase, remove its substrates (oxygenand phenolics), or function as preferred substrates. Various antibrowning agents can be used inpostcutting dip solutions. An overview on preservative treatments for fresh-cut products was recentlypublished (Garcia and Barrett, 2002).

Ascorbic acid is probably the most common antibrowning agent selected for use in fresh-cutfruit. The drawback of ascorbic acid is that it confers only temporary protection because it isoxidized in the process of preventing browning. While the inhibitory effect of ascorbic acid onbrowning is due to its reductant action on quinones, other common types of antibrowning agentsavailable for use in fresh-cut fruits include acidulants (e.g., citric acid, malic acid) and chelators(e.g., EDTA), which are often used in combination in browning prevention. Antibrowning treatmentscommonly include ascorbic acid or its isomer erythorbic acid (

d

-isoascorbic acid), citric acid,EDTA, cysteine, and its derivatives. Research papers have presented results on 4-hexylresorcinol,which has shown effective control of enzymatic browning in fruits (Sapers, 1993); however, 4-hexylresorcinol is currently only approved for use in the prevention of shrimp discoloration(McEvily et al., 1991).

No single antibrowning treatment can control enzymatic browning of all fresh-cut fruit becausethere is not just one possible solution for a particular fruit product. This can be illustrated by theexamples shown in Table 3.3, where various antibrowning treatments selected by different authorsfor use in fresh-cut pears are presented. Although there has been commercial interest in thedevelopment of fresh-cut pear products, pear fruit presents some particular challenges, such as itshigh susceptibility to enzymatic browning and tissue softening. Fruit ripeness stage proved to bean important factor in the control of browning in pears. Overripe pears are generally prone to moresevere discoloration (Sapers and Miller, 1998; Dong et al., 2000); optimal flesh firmness for



62


TABLE 3.3Examples of Treatments Suggested for Controlling Enzymatic Browning in Fresh-Cut Pears

Pear Firmness Antibrowning Treatment Comments Reference

Bartlett 44.5 N

1% CaCl

2

+ 0.5% O

2

atmosphere Rosen and Kader (1989)Anjou 4.0 kg 4% Sodium erythorbate, 0.2%

CaCl

2

100 ppm 4-Hexylresorcinol1-min dip; storage at 4

∞

CModified Atmosphere Packaging (MAP)

Slightly underripe fruit. Use of 0.25% NaCl holding solution after cutting

With Anjou pears, neutral dip (pH 7.7) more effective than acidic (pH 3.3) dip

Less firm fruit browned more, and soft Bartlett pears developed tissue breakdown

Sapers and Miller (1998)

Bartlett 5.7 kg 4% Sodium erythorbate, and/or 0.2% CaCl

2

and/or 4-Hexylresorcinol MAP

Shelf life at least 14 d (Anjou and Bartlett)

Trials with 0.2% cysteine did not inhibit browning, and induced red or pink discoloration

4-Hexylresorcinol prevented core tissue browning

Bosc Treatment not effective on Bosc pears

Bartlett 27–45 N 2% Ascorbic acid1% Calcium lactate1-min dip

Product observed for 2 d at 20

∞

C; surface color was not significantly different from that at the start of experiment

Gorny et al.

(1998)

AnjouBartlettBosc

36–45 N45–67 N27–45 N

0.01% 4-Hexylresorcinol0.5% Ascorbic acid1% Calcium lactate2-min dipStorage at 2–5

∞

C in pouches partially vacuumed

Partially ripe fruit was peeledShelf life of 30 d for Bartlett and Bosc, and 15–20 d for Anjou pears

Sensory panelists detected difference in taste as compared with water-treated control

Dong et al. (2000)

AnjouBartlettBosc

Slices:22 N36 N22 N

0.01

M

4-Hexylresorcinol0.5

M

Isoascorbic acid0.05

M

Potassium sorbatepH 5.5 30-sec dipStorage at 5

∞

C, 14 d

Browning inhibitor of both cut surface and edges of the slices

Less inhibition in Bartlett pearsIn Anjou initial firmness (21–52 N) did not affect browning control

Buta and Abbott (2000)

Bartlett 45–58 N 2% Ascorbic acid1% Calcium lactate0.5% CysteinepH 7.05-min dip at 20

∞

C

When acidic (pH 3.7) dip was used, a pinkish-red discoloration was observed

Dip alone was unable to control browning at the edges of flesh beneath the skin

Sensory panelists did not perceive difference in taste

Gorny et al. (2002)

Note:

Unless indicated, firmness was measured in whole fruit, and fresh-cut products were prepared from unpeeled fruit.

N = Newtons.



Fresh-Cut Fruits

63

fresh-cut processing needs to be determined in order to obtain a product of high quality and longshelf life. In addition, fruit cultivar is a very important factor to consider; as discussed previously,the browning potential can vary greatly among cultivars (Amiot et al., 1995). Pear fruit size wasalso shown to affect surface discoloration in pears. Gorny and coworkers (2000) found that pearslices prepared from small-size fruit discolor more than slices cut from larger fruit. This mayindicate a difference in maturity and activity of the polyphenol oxidase enzyme.

3.4.5 P

REVENTION

OF

T

EXTURAL

L

OSSES

Fruit texture is perceived by the consumer prior to taste. When biting into a piece of apple,crunchiness is perceived before juiciness. Softening or loss of tissue firmness is a quality defectthat compromises the shelf life of many fresh-cut fruits. Examples of changes in the firmness ofsliced kiwifruit and banana during storage in various ethylene concentrations are shown in Figure3.2. Selection of appropriate fruit cultivars is important in avoiding apple fruit prone to mealiness,for instance, or choosing cv. with attractive characteristics of juiciness and crispness. However,textural defects may develop after preparation of the fresh-cut product. Figure 3.3 illustrates pear

FIGURE 3.2

Changes in firmness of sliced kiwifruit and bananas kept at 20

∞

C in atmosphere of 0, 2, or20 ppm of ethylene in air. (From Watada, A.E

.

, Ko, N.P., Minott, D.A. 1996. Factors affecting quality of fresh-cut horticultural products.

Postharvest Biol. Technol.

9: 115–125.)

FIGURE 3.3

Ripe fresh-cut pears (cv. Bartlett) a few minutes after cutting. Note the translucency at the edgesof the pear pieces.

0

1

2

3

4

5

6

0 2 20 0 202Ethylene in air (ppm)

Firm

ness

(N

)0

24 hr

48 hr

kiwi

banana



64


pieces prepared from ripe fruit, where translucent edges were noticeable just a few minutes aftercutting. Fruit had been selected based on its superior eating qualities (flavor, sweetness, juiciness,and texture), but it was evidently inadequate for fresh-cut processing. In fresh-cut kiwifruit, fleshsoftening is the most noticeable change after cutting (Varoquaux et al., 1990); the cut surfacedarkens not due to enzymatic browning, but rather to the appearance of a translucent water-soakedtissue (Agar et al.,

1999). The loss of firmness increases with storage temperature and time, whileremoval of ethylene from the storage atmosphere improves retention of slice texture.

The most common treatment used to improve texture retention is to dip fruit pieces in calciumsolutions, as described for strawberries (Main et al., 1986), and pears and strawberries (Rosen andKader, 1989). The firming effect of calcium is attributed to the formation of complexes withpolygalacturonic acid residues in the middle lamella and cell wall (Van-Buren, 1979). Both calciumchloride and calcium lactate are frequently used. However, trained sensory panels have judged thatcalcium chloride imparts a bitter flavor to fresh-cut cantaloupe (Luna-Guzmán and Barrett, 2000).Moreover, typical melon flavor was better detected in cantaloupe treated with 1% calcium lactateas compared with 1% calcium chloride. In this study, we found that the initial firming effect ofboth calcium chloride and calcium lactate on melon cylinders was the same; however calciumlactate–treated samples tended to maintain higher firmness during storage.

A combined treatment using low-temperature blanching prior to dipping in calcium solutionhas been associated with a decrease in pectin esterification by pectinmethylesterase, creatingpotential sites for cross-linking with calcium (Stanley et al., 1995). A study of the effect of combinedcalcium chloride dips and heat treatment on firmness of fresh-cut cantaloupe carried out in ourgroup showed improved firmness as compared with a calcium dip alone. However, it may be thatrather than pectinmethylesterase activation, the results observed could be related to a membraneor turgor pressure effect. No significant difference was observed in the amount of bound calciumbetween samples treated at 60, 40, or 20

∞

C (Luna-Guzmán et al., 1999).The texture of fresh-cut apples has been reported to improve with the application of heat

treatments to apples prior to slicing (Kim et al., 1994). Three apple cv. (Delicious, Golden Delicious,and McIntosh) that had been kept in cold storage (2

∞

C, 90% RH) for less than 2 months weretreated for 1.75 h in a water bath at 45

∞

C, then held overnight at 2

∞

C. Fruit were sliced and storedat 2

∞

C for 21 d in unsealed polyethylene bags. Whereas untreated control samples exhibited asteady loss of flesh firmness during storage, heat-treated samples showed an initial increase infirmness (up to 7 d for cv. Golden Delicious and up to 14 d for cv. Delicious), followed by adecrease in firmness. At 7 d of storage, the difference in firmness between heat-treated and controlsamples were 12% for cv. McIntosh, 34% for Golden Delicious, and 28% for Delicious. The greatestdifference observed was with cv. Delicious at 14 d of storage, where the heat-treated sample was~40% firmer than the untreated control.

3.4.6 A

PPEARANCE

AND

S

ENSORY

Q

UALITY

The most appealing attributes of fresh-cut products include their perception of freshness, taste andflavor, in addition to convenience. When assessing quality, consumers take product appearance intoconsideration as a primary criterion. Appearance can be characterized by size, shape, color, gloss,condition, and absence of defects. However, product color contributes more than any other singlefactor (Kays, 1999).

While appearance may have a major impact on consumers, sensory quality (taste, aroma,texture) is what will ensure consumers’ repeated acceptance of a fresh-cut product. Most of thequality indexes used by both academia and industry for these products are visual, based onappearance; little research has been done on sensory quality of fresh-cut produce (Beaulieu andBaldwin, 2002). General methods for determining quality characteristics of fresh produce aredescribed elsewhere (Mitcham and Kader, 1998).



Fresh-Cut Fruits

65

The relative importance of each quality characteristic depends on the commodity; for instance,gloss is relevant for peach slices but may not be for persimmon wedges. When the optimum ripenessstage for fresh-cut preparation occurs before full ripening and fruit flavor has yet to completelydevelop, even a fresh-cut product with very good appearance will lack the characteristic flavor ofa perfectly ripe fruit. In addition, some flavor components may disappear after processing, or inother cases off-flavors may develop due to either physiological changes in the fruit tissue ormicrobial spoilage after packaging. Nevertheless, it has been reported that when off-flavors ofmicrobial origin are detected, product appearance is likely to be compromised (Huxsoll et al., 1989).

3.4.7 N

UTRITIONAL

A

SPECTS

In addition to their sensory appeal, for nutritional reasons fruit should be an important part of ahealthy diet. Although it is generally low in calories due to its high moisture content, fruit suppliesvitamins, minerals, phytonutrients, and fiber to the diet. One of the most significant contributionsto our diet comes from the high content of vitamin C and precursors of vitamin A (carotenoids)found in fruits. While citrus fruits are well known as sources of vitamin C, kiwifruit, melons,tomatoes, and berries are also significant sources of this vitamin. Good sources of carotenoidsinclude yellow-fleshed peaches and nectarines, mangoes, papaya, and persimmons. Apples andpears are good sources of fiber, as are many berries (Margen et al., 1992).

While it has been assumed that fresh-cut products would have lowered nutrient content thanthe commodities they are derived from (Klein, 1987; McCarthy and Matthews, 1994), someexperimental data do not indicate this. The shelf life of fresh-cut persimmons and peaches waslimited before major losses of carotenoids were detected (Wright and Kader, 1997b). The samewas observed with the vitamin C content of strawberries and persimmons (Wright and Kader,1997a

)

. However, significant oxidation of ascorbic acid was determined when washing fruit sliceswith chlorinated water (100 ppm sodium hypochlorite) in comparison to washing with water. Anintermediate level of oxidized ascorbic acid, or dehydroascorbic acid, was obtained when washingthe whole fruit in chlorinated water before slicing it. Fresh-cut kiwifruit stored for 6 d at differenttemperatures showed a gradual decrease in total vitamin C content with increased temperature.While a loss of 8% in relation to initial vitamin C level in kiwifruit occurred at 0

∞

C, there was adecrease of 13 and 21% at 5 and 10

∞

C, respectively. In ethylene-free storage, ascorbic acid levelswere threefold higher than in control slices stored in air (Agar et al., 1999). Losses of ascorbicacid in whole pears stored under controlled atmosphere conditions (low O

2

and high CO

2

) revealedthat in the cv. Rocha, losses occurred mainly during long-term storage, while in the cv. Conference,most of the ascorbic acid decreased when pears were transferred to controlled atmosphere storage.It is a common practice to store apples and pears under controlled conditions for extended periodsof time prior to processing. Lowered levels of ascorbic acid in the fruit flesh will increase suscep-tibility to browning (Veltman et al., 2000).

In recent years there has been a great interest in phytochemicals due to a variety of potentialhealth benefits they may have. This is an emerging field of research, and very little information isavailable on concentrations of such compounds in different plant tissues, and even less on possibleeffects of cultivar, agronomic practices, maturity stage, and postharvest handling on the retentionof phytochemicals. In a study with whole apples stored at 1

∞

C for 2 months, the cv. Granny Smithand Delicious had increased antioxidant levels of up to 10-fold, but in longer storage substantialdecreases in antioxidants were reported (Curry, 1997).

3.5 SHELF LIFE EXTENSION OF FRESH-CUT FRUIT

Once the negative consequences brought about by injuries caused by fresh-cut processing arerecognized, it is important to search for means of extending the shelf life of fresh-cut fruits. The



66


objective is to maintain a fresh-like appearance, flavor, and nutritional quality of the product whileensuring its safety. Among the most common strategies used to extend the shelf life of fresh-cutfruits are temperature management and modified atmosphere packaging. Other benefits can befound with the application of edible coatings. It is important to consider that the consumer perceivesa fresh-cut product as fresh-like produce, just minimally prepared to be ready for eating. It is notexpected that many chemicals are added to such products or that they are treated in ways that arenot considered wholesome by the public. The perception of fresh-cut products as “natural” is partof its appeal. In a survey on the perception of convenience products, consumers revealed the desirethat such products maintain fresh characteristics longer without the use of food preservatives(Bruhn, 1994).

3.5.1 T

EMPERATURE

M

ANAGEMENT

Temperature control is very critical in prolonging the shelf life of fresh-cut products, serving tominimize losses due to wound-related responses and microbial spoilage. At low temperatures,respiration rates and enzymatic activities are reduced, and general metabolic rates are also lowered,extending product shelf life. The growth of some spoilage microorganisms and foodborne patho-gens is decreased under the low-temperature conditions recommended for fresh-cut fruit processingand storage.

The results presented in Table 3.1 show the effect of temperature on respiration rates in somefruits. Fresh-cut fruit ideally should be kept close to 0

∞

C, even for chilling-sensitive fruit, becausethe quality deterioration that results from storage at nonchilling temperatures is more damagingthan that resulting from chilling injury (Watada et al., 1996). Rapid cooling of fresh-cut producereduces respiration and deterioration rates, as well as microbial spoilage. However, it is of paramountimportance to maintain product under refrigeration throughout the processing and distribution, andup to consumption.

3.5.2 M

ODIFIED

A

TMOSPHERE

P

ACKAGING

Modified atmosphere packaging (MAP) can extend the shelf life of produce by minimizing waterloss, reducing respiration and ethylene production rates, decreasing metabolic activity, and reducingmicrobial growth and decay. The widely used MAP aims at the creation of an ideal gas compositioninside the package. The modification of the atmosphere surrounding the fresh-cut produce can beachieved either through the establishment of an active modified atmosphere (gas flushing) in thepackage or be generated over time by the fruit pieces respiring in the sealed package. Despiteadditional costs, active MAP has been preferred because of the limitations in regulating a passivelyestablished atmosphere (Kader and Watkins, 2000).

In modified atmospheres, O

2

levels are generally reduced and CO

2

is increased; high levels ofCO

2

lead to a decreased sensitivity of plant tissues to ethylene (Kader et al., 1989). When O

2

levelsare lowered, respiration of produce begin to decrease, and generally continues to decrease withlowering O

2

levels down to a level where anaerobic respiration takes place. Among the responsesof plant tissue to low O

2

levels include reduction in respiration, reduced ethylene synthesis andperception, reduced chlorophyll degradation, reduced cell wall degradation, and reduced phenolicsoxidation. Negative responses to low O

2

include induction of fermentation, accumulation of ace-taldehyde, ethanol and lactate, and reduced biosynthesis of aroma compounds (Beaudry, 2000). Inthe establishment of safe atmospheres it is important to determine product tolerance to low O

2

levels and high CO

2 levels.Watkins (2000) reviewed the effects of high CO2 on produce. In general, fruit tolerances for

high concentrations of CO2 and low O2 vary for the same commodity between fresh-cut productsand the intact fruit. It is important to experimentally determine the appropriate gas compositionfor each particular product, which extends the product shelf life and also prevents the damaging



Fresh-Cut Fruits 67

effects of low levels of O2 or high levels of CO2. These may lead to anaerobic respiration andincrease susceptibility to decay. An adequate MAP should help achieve a decrease in respirationwhile preventing anaerobic respiration. In the design of the optimal MAP, it is of utmost importanceto know the ideal atmosphere for each particular fresh-cut fruit product and its respiration rateunder a certain temperature. In addition, it is necessary to avoid temperature abuse during storage;otherwise the atmospheric composition inside the package changes, which negatively impacts theproduct. Recommended atmospheres for storage of selected fresh-cut fruits were reviewed byGorny (1997).

Another important aspect in the application of modified atmosphere packaging is the appropriateselection of packaging material. Common packages include flexible film pouches, rigid traysoverwrapped with flexible films, and rigid plastic containers with gas diffusion windows. The mostcommon polymeric film used in MAP is oriented polypropylene; other examples are low-densitypolyethylene (for bagged products), monolayer polyvinyl chloride (for overwrapped trays), andblends of low- and medium-density polyethylene with ethylene vinyl acetate; microperforated filmshave been studied as a way of overcoming anaerobic conditions in the package (Al-Ati andHotchkiss, 2002).

A comparison of different systems for storage of fresh-cut cantaloupe was carried out usingthe cv. Athena, considered adequate for fresh-cut processing (Bai et al., 2001). Cantaloupe cubeswere stored either in (1) pouches where they were allowed to develop a “natural” modifiedatmosphere (nMAP) through produce respiration, or (2) packages that were flushed with a gasmixture containing 4 kPa of O2 plus 10 kPa of CO2 (fMAP), or (3) packages where the packagefilm was perforated with a needle (PFP). In cantaloupe melons, quality deterioration is primarilyrelated to the development of tissue translucency; salable quality may be limited when the level oftranslucency is greater than 20%. Although shelf life of cantaloupe cubes (Figure 3.4) was prolongedunder both nMAP (9 d) and fMAP (12 d) conditions, a faint off-odor was detected in all samplesby day 12, with the exception of one of the three replicate trials for the fMAP.

Fresh-cut fruits do not respond to MAP as well as young vegetative fresh-cut tissues; the effectsof MAP on control of senescence rate have been only marginally effective. Many factors influencethe atmospheric composition at equilibrium inside the package. Film type, thickness, area, weight

FIGURE 3.4 Changes in tissue translucency of cantaloupe cubes stored in packages with overlap film per-forated with 10 holes of 1.5 mm (PFP), packages containing a naturally formed modified atmosphere (nMAP),and packages in which the internal atmosphere was flushed with a gas mixture of 4 kPa O2 plus 10 kPa CO2

prior to storage. (From Bai, J.-H., Saftner, A.E., Watada, A.E., Lee, Y.-S. 2001. Modified atmosphere maintainsquality of fresh-cut cantaloupe (cucumis melo L.). J. Food Sci. 66(8): 1207–1211.)

0

20

40

60

80

100

0 2 4 6 8 10 12

Storage (days)

Tra

nslu

cenc

y (%

)

PFP

nMAP

fMAP



68 Processing Fruits: Science and Technology, Second Edition

of fresh-cut fruit in the package, temperature, relative humidity, and product respiration rate areall important. In spite of the advances occurring in film technology, currently available films arenot considered as satisfying the requirements of fresh-cut fruit. Current films meet the needs ofeither CO2 or O2 because they allow permeability of CO2 at higher rates than O2, which constitutesa shortcoming of MAP for fresh-cut fruit application (Al-Ati and Hotchkiss, 2002). More researchis needed in establishing the most appropriate atmospheres for fresh-cut fruits, which are expectedto vary with cultivar, growing location, and duration of storage prior to processing (Gorny, 1997).

3.5.3 HUMIDITY

Humidity is another important factor that should be controlled in fresh-cut fruit product handlingand storage. Although water is the most abundant (80 to 90% of the fresh weight) component offruit tissues, even small changes (~5%) in the water content of fruit are detrimental to quality. Infresh-cut products the removal of skin or rind and cutting lead to exposure of a large surface asseen in fruit slices, cubes, and wedges, which are prone to great water loss. Surface dehydrationoccurs quickly and has a negative impact on product appearance, resulting in a product exhibitingless gloss, greater wrinkling, wilting, or flaccidness. However, poor appearance is not the onlypossible defect resulting from water loss; cellular metabolism may be affected, fruit ripening maybe accelerated, and ripening related softening significantly impacted (Paul, 1999). Desiccation mayalso favor the development of microorganisms that tolerate low moisture, such as fungi (Brackett,1987). In the dewatering operation, it is important to avoid excessive water loss. Moreover, reductionof moisture loss can be achieved by decreasing the capacity of the surrounding air to hold water.This is done by lowering the temperature, increasing the relative humidity, or creating a barrier towater loss. The last mentioned is commonly done through the use of polymeric films in packaging;moisture retention can also be attained with edible coatings, as exemplified with fresh-cut papaya,where desiccation is a major problem (Siriphanich, 1994). However, in film-packaged products,water is formed as a result of respiration, and it condenses inside the package and becomes availablefor microbial growth (Al-Ati and Hotchkiss, 2002). This is another point demonstrating the needto avoid product temperature abuse and maintain lower respiration rates.

3.5.4 EDIBLE COATINGS

The use of edible coatings is another method of extending the shelf life of fresh-cut fruit. Ediblecoatings consist of thin layers of protective materials applied to the surface of the fruit as areplacement for the natural protective tissue (epidermis, peel). Edible coatings are used as a semi-permeable barrier that help reduce respiration, retard water loss and color changes, improve textureand mechanical integrity, improve handling characteristics, help retain volatile flavor compounds,and reduce microbial growth. It is possible to create a modified atmosphere enrobing fresh-cutproduce in edible coating. (Baldwin et al., 1995; Baldwin et al., 1996; Nisperos and Baldwin, 1996).

Different food additives can be incorporated into coating formulation, such as coatings withantioxidants (Baldwin et al., 1995). Control of surface browning in apples by ascorbic acid wasimproved when it was incorporated into an edible coating formulation compared to dipping. Acarboxymethylcellulose-based coating did not control enzymatic browning of cut apples, but whensuch a coating was combined with additives (antioxidant, acidulant, and preservative), browningcontrol was superior to dipping the fresh-cut produce in solutions with the same additives (Baldwinet al., 1996).

Examples of browning inhibition in apple slices have been described for different edible coatings(Avena-Bustillos and Krochta, 1993; Kinzel, 1992). Edible coatings made from apple puree to whichlipids and beeswax were added helped control moisture loss and browning of fresh-cut apples(McHugh and Senesi, 2000). Coated and wrapped (“apple wraps”) fresh-cut apple products werecompared; apple pieces were either coated with (dipped in) a solution of 70% apple puree, 27%



Fresh-Cut Fruits 69

vegetable oil, 1.5% ascorbic acid, and 1.5% citric acid or wrapped in a film of the same composition.Moisture loss was significantly reduced in apple wraps during storage at 5∞C for 12 d. While coatingsinhibited browning by 80% over a period of 3 d, wraps showed a 100% inhibition of browning forup to 10 d at 5∞C, in addition to maintaining texture, fruity flavor, and odor.

It is important to understand the need for an integrated approach in the processing of fresh-cutfruits. In order to ensure prolonged shelf life, all steps should be carried out taking into considerationthe requirement for superior fruit quality of cultivars selected for fresh-cut, adoption of goodsanitation practices, gentle handling throughout processing, adequate temperature management, andappropriate choice of packaging and storage conditions. All these factors should be seen as a wayof ensuring not only extended shelf life, but also a convenient high quality product that is safe,nutritionally sound, and appealing to the senses.

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