processing fruits science and technology second … processing fruits: science and technology,...

Part I

Biology, Principles, and Applications

1478_SD01.fm Wednesday, July 7, 2004 8:06 AM

Copyright 2005 by CRC Press LLC

1

Classification, Composition of Fruits, and Postharvest Maintenance of Quality

Adel A. Kader and Diane M. Barrett

CONTENTS

1.1 Classification of Fruits1.1.1 Temperate-Zone Fruits1.1.2 Subtropical Fruits 1.1.3 Tropical Fruits

1.2 Contribution of Fruits to Human Nutrition1.2.1 Energy (Calories)1.2.2 Vitamins1.2.3 Minerals1.2.4 Dietary Fiber1.2.5 Antioxidants

1.3 Factors Influencing Composition and Quality of Fruits1.3.1 Preharvest Factors1.3.2 Maturity at Harvest and Harvesting Method 1.3.3 Postharvest Factors

1.4 Fruit Maturity, Ripening, and Quality Relationships1.5 Composition and Compositional Changes

1.5.1 Carbohydrates1.5.2 Proteins 1.5.3 Lipids 1.5.4 Organic Acids 1.5.5 Pigments1.5.6 Phenolic Compounds1.5.7 Volatiles1.5.8 Vitamins1.5.9 Minerals

1.6 Biological Factors Involved in Postharvest Deterioration of Fruits1.6.1 Respiration1.6.2 Ethylene Production1.6.3 Transpiration or Water Loss1.6.4 Physiological Disorders1.6.5 Physical Damage1.6.6 Pathological Breakdown.

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Processing Fruits: Science and Technology, Second Edition

1.7 Environmental Factors Influencing Deterioration of Fruits 1.7.1 Temperature1.7.2 Relative Humidity1.7.3 Air Movement1.7.4 Atmospheric Composition1.7.5 Ethylene

1.8 Harvesting Procedures1.9 Postharvest Handling Procedures

1.9.1 Dumping 1.9.2 Washing1.9.3 Sorting1.9.4 Sizing 1.9.5 Ripening1.9.6 Inhibiting Ethylene Action 1.9.7 Cooling1.9.8 Storage1.9.9 Food Safety Guidelines1.9.10 Food Security Guidelines

1.10 Summary: Keys to Successful Handling of Fresh Fruits1.10.1 Maturity and Quality1.10.2 Temperature and Humidity Management Procedures1.10.3 Physical Damage1.10.4 Sanitation Procedures 1.10.5 Expedited Handling

References Internet Sites

The quality of processed fruit products depends on their quality at the start of processing; therefore,it is essential to understand how maturity at harvest, harvesting methods, and postharvest handlingprocedures influence quality and its maintenance in fresh fruits between harvest and processinitiation. Using such information, an appropriate system for harvesting and handling each kind offruit can be selected and used in conjunction with an effective quality control program to ensurethe best quality possible for fresh fruits when processed.

Quality attributes of fresh fruits include appearance, texture, flavor, and nutritive value. Appear-ance factors include size, shape, color, and freedom from defects and decay. Texture factors includefirmness, crispness, and juiciness. Flavor components incorporate sweetness, sourness (acidity),astringency, bitterness, aroma, and off-flavors. Nutritional quality is determined by a fruit’s contentof vitamins (A and C are the most important in fruits), minerals, dietary fiber, carbohydrates,proteins, and antioxidant phytochemicals (carotenoids, flavonoids, and other phenolic compounds).Safety factors that may influence the quality of fresh fruits include residues of pesticides, presenceof heavy metals, mycotoxins produced by certain species of fungi, and microbial contamination.

Losses in fresh fruits between harvest and processing may be quantitative (e.g., water loss,physical injuries, physiological breakdown, and decay) or qualitative (e.g., loss of acidity, flavor,color, and nutritive value). Many factors influence fruit quality and the extent of postharvest lossesthat can occur in the orchard, during transportation, and throughout the handling system (sorting,sizing, ripening, cooling, and storage). The total time between harvesting and processing may alsobe an important factor in maintaining the quality and freshness of fruit. Minimizing the delaysthroughout the postharvest handling system greatly reduces quality loss, especially in highlyperishable fruits such as strawberries, raspberries, blackberries, apricots, and cherries.




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1.1 CLASSIFICATION OF FRUITS

Fruit are commonly classified by growing region as follows: temperate-zone, subtropical, andtropical. Growing region and environmental conditions specific to each region significantly affectfruit quality. Examples of fruit grown in each region are listed below.

1.1.1 T

EMPERATE

-Z

ONE

F

RUITS

1. Pome fruits: apple, Asian pear (nashi), European pear, quince2. Stone fruits: apricot, cherry, nectarine, peach, plum3. Small fruits and berries: grape (European and American types), strawberry, raspberry,

blueberry, blackberry, cranberry

1.1.2 S

UBTROPICAL

F

RUITS

1. Citrus fruits: grapefruit, lemon, lime, orange, pummelo, tangerine, and mandarin2. Noncitrus fruits: avocado, cherimoya, fig, kiwifruit, olive, pomegranate

1.1.3 T

ROPICAL

F

RUITS

1. Major tropical fruits: banana, mango, papaya, pineapple2. Minor tropical fruits: carambola, cashew apple, durian, guava, longan, lychee, mangos-

teen, passion fruit, rambutan, sapota, tamarind

1.2 CONTRIBUTION OF FRUITS TO HUMAN NUTRITION

Fruits are not only colorful and flavorful components of our diet, but they also serve as a sourceof energy, vitamins, minerals, and dietary fiber. The U.S. Department of Agriculture DietaryGuidelines encourage consumers to enjoy “five a day,” i.e., eat at least two servings of fruit andthree servings of vegetables each day and to choose fresh, frozen, dried, or canned forms of avariety of colors and kinds of fruits and vegetables. In some countries, consumers are encouragedto eat up to 10 servings of fruits and vegetables per day. For more information access one or moreof the following Websites: www.nutrition.gov, www.5aday.gov, and www.5aday.org.

1.2.1 E

NERGY

(C

ALORIES

)

1. Carbohydrates: banana, breadfruit, jackfruit, plantain, dates, prunes, raisin2. Proteins and amino acids: nuts, dried apricot, fig3. Fats: avocado, olive, nuts

1.2.2 V

ITAMINS

1. Fresh fruits and vegetables contribute about 91% of vitamin C, 48% of vitamin A, 27%of vitamin B

6

, 17% of thiamin, and 15% of niacin to the U.S. diet.2. The following fruits are important contributors (based on their vitamin content and the

amount consumed) to the supply of indicated vitamins in the U.S. diet:Vitamin A: apricot, peach, cherry, orange, mango, papaya, persimmon, pineapple, can-

taloupe, watermelonVitamin C: strawberry, orange, grapefruit, kiwifruit, pineapple, banana, apple, cantaloupeNiacin: peach, banana, orange, apricotRiboflavin: banana, peach, orange, apple, avocadoThiamin: orange, banana, grapefruit, apple



www.nutrition.gov

www.5aday.gov

www.5aday.org

6


1.2.3 M

INERALS

1. Fresh fruits and vegetables contribute about 26% of the magnesium and 19% of the ironto the U.S. diet.

2. The following fruits are important contributors to the supply of indicated minerals in theU.S. diet:Potassium: banana, peach, orange, apple, dried fruits such as apricot and prunePhosphorus: banana, orange, peach, fig, raisinCalcium: tangerine, grapefruit, orangeIron: strawberry, banana, apple, orange

1.2.4 D

IETARY

F

IBER

1. All fruits and nuts contribute to dietary fiber. Dietary fiber consists of cellulose, hemi-cellulose, lignin, and pectic substances, which are derived primarily from fruit cell wallsand skin.

2. The dietary fiber content of fruits ranges from 0.5 to 1.5% (fresh weight basis).3. Dietary fiber plays an important role in relieving constipation by increasing water-holding

capacity of feces. Its consumption is also linked to decreased incidence of cardiovasculardisease, diverticulosis, and colon cancer.

1.2.5 A

NTIOXIDANTS

1. Fruits, nuts, and vegetables in the daily diet have been strongly associated with reducedrisk for some forms of cancer, heart disease, stroke, and other chronic diseases. This isattributed, in part, to their content of antioxidant phytochemicals.

2. Red, blue, and purple fruits (such as apple, blackberry, blueberry, blood orange, cranberry,grape, nectarine, peach, plum, prune, pomegranate, raspberry, and strawberry) are goodsources of flavonoids and other phenolic compounds that are positively correlated withantioxidant capacity of the fruit.

3. Orange-flesh fruits (such as apricot, cantaloupe, mango, nectarine, orange, papaya, peach,persimmon, and pineapple) and some red-flesh fruits (such as tomato, watermelon, andpink grapefruit) are good sources of carotenoids. Availability of lycopene to humans isincreased during tomato processing.

1.3 FACTORS INFLUENCING COMPOSITION AND QUALITY OF FRUITS

1.3.1 P

REHARVEST

F

ACTORS

1. Genetic: selection of cultivars, rootstocks. Cultivar and rootstock selection are importantbecause there are often differences in raw fruit composition, postharvest-life potential,and response to processing. In many cases, fruit cultivars grown for fresh market saleare not optimal cultivars for processing.

2. Climatic: temperature, light, wind. Climatic factors may have a strong influence onnutritional quality of fruits. Light intensity significantly affects vitamin concentration, andtemperature influences transpiration rate, which will affect mineral uptake and metabolism.

3. Cultural practices: soil type, soil nutrient and water supply, pruning, thinning, pestcontrol. Fertilizer addition may significantly affect the mineral content of fruit, whileother cultural practices such as pruning and thinning may influence nutritional compo-sition by changing fruit crop load and size.




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1.3.2 M

ATURITY

AT

H

ARVEST

AND

H

ARVESTING

M

ETHOD

Maturity at harvest is one of the primary factors affecting fruit composition, quality, and storagelife. Although most fruits reach peak eating quality when harvested fully ripe, they are usuallypicked mature, but not ripe to decrease mechanical damage during postharvest handling. Harvestingmay also mechanically damage fruit; therefore, choice of harvest method should allow for main-tenance of quality.

1.3.3 P

OSTHARVEST

F

ACTORS

1. Environmental: temperature, relative humidity, atmospheric composition. Temperaturemanagement is the most important tool for extension of shelf life and maintenance ofthe quality of fresh fruit. Relative humidity influences water loss, decay development,incidence of some physiological disorders, and uniformity of fruit ripening. Optimalrelative humidity for storage of fruits is 85 to 90%. Finally, atmospheric composition(O

2

, CO

2

, and C

2

H

4

, in particular) can greatly affect respiration rate and storage life.2. Handling methods: Postharvest handling systems involve the channels through which

harvested fruit reaches the processing facility or consumer. Handling methods should bechosen such that they maintain fruit quality and avoid delays.

3. Time period between harvesting and consumption: Delays between harvesting and cool-ing or processing may result in direct losses (due to water loss and decay) and indirectlosses (decrease in flavor and nutritional quality).

1.4 FRUIT MATURITY, RIPENING, AND QUALITY RELATIONSHIPS

Maturity at harvest is the most important factor that determines storage life and final fruit quality.Immature fruits are more subject to shriveling and mechanical damage, and are of inferior qualitywhen ripened. Overripe fruits are likely to become soft and mealy with insipid flavor soon afterharvest. Fruits picked either too early or too late in the season are more susceptible to physiologicaldisorders and have a shorter storage life than those picked at mid-season.

With very few exceptions (e.g., pears, avocados, and bananas), all fruits reach their best eatingquality when allowed to ripen on the tree or plant. In general, fruits become sweeter, more colorful,and softer as they mature. However, some fruits are usually picked mature but unripe so that theycan withstand the postharvest handling system when shipped long distances. Most currently usedmaturity indices are based on a compromise between those indices that would ensure the best eatingquality to the consumer and those that provide the needed flexibility in transportation and marketing.

Fruits can be divided into two groups: (1) nonclimacteric fruits that are not capable of continuingtheir ripening process once removed from the plant, and (2) climacteric fruits that can be harvestedmature and ripened off the plant. Following are examples of each group:

Group 1: Berries (e.g., blackberry, cranberry, raspberry, strawberry), grape, cherry, citrus (grape-fruit, lemon, lime, orange, mandarin, tangerine), pineapple, pomegranate, lychee, tama-rillo, loquat.

Group 2: Apples, pear, quince, persimmon, apricot, nectarine, peach, plum, kiwifruit, avocado,banana, plantain, mango, papaya, cherimoya, sapodilla, sapota, guava, passion fruit.

Fruits of the first group (nonclimacteric) produce very small quantities of ethylene and do notrespond to ethylene treatment except in terms of degreening (degradation of chlorophyll) in citrusfruits and pineapples. Fruits in Group 2 (climacteric) produce much larger quantities of ethylenein association with their ripening and exposure to ethylene treatment will result in faster and moreuniform ripening.



8


Maturity indices used vary among fruits and often among cultivars within a specific fruit, butgenerally include one or several (combination indices) of the following: fruit size and shape, overallcolor, ground color of the skin, flesh color, flesh firmness, soluble solids content, starch content,acidity, and internal ethylene concentration. Listed below are some examples of maturity indicesthat can be used for selected fruits:

1.5 COMPOSITION AND COMPOSITIONAL CHANGES

The flesh of young developing fruits contains very little sugar, and the large amounts of starch,acid, and tannins make them inedible. As the fruits approach maturity, flesh cells enlarge consid-erably, and sugar content increases while starch, acid, and tannin contents decrease. In addition,certain volatile compounds develop, giving the fruit its characteristic aroma. Chlorophyll degrada-tion (loss of green color) and synthesis of carotenoids (yellow and orange colors) and anthocyanins(red and blue colors) takes place both in the skin and the flesh with fruit ripening. All fruits softenas they ripen due to changes in cell wall composition and structure. In this section, we present anoverview of fruit constituents in relation to quality and changes after harvest.

1.5.1 C

ARBOHYDRATES

Carbohydrates are the most abundant and widely distributed food component derived from plants.Fresh fruits vary greatly in their carbohydrate content, with the general range between 10 to25%. The structural framework, texture, taste, and food value of a fresh fruit is related to itscarbohydrate content.

Sucrose, glucose, and fructose are the primary sugars found in fruits (Table 1.1), and theirrelative importance varies among commodities. Sugars are found primarily in the cytoplasm andrange from about 0.9% in limes to 16% in fresh figs. Sucrose content ranges from a trace in cherries,grapes, and pomegranate to more than 8% in ripe bananas and pineapple. Such variation influencestaste since fructose is sweeter than sucrose, and sucrose is sweeter than glucose.

Starch occurs as small granules within the cells of immature fruits. Starch is converted to sugaras the fruit matures and ripens. Other polysaccharides present in fruits include cellulose, hemicel-lulose, pectin, and lignin, which are found mainly (up to 50%) in cell walls and vary greatly amongcommodities. These large molecules are broken down into simpler and more soluble compoundsas a result of fruit softening. The transformation of insoluble pectins into soluble pectins iscontrolled, for the most part, by the enzymes pectinesterase and polygalacturonase. Reducedactivities of these two enzymes have been associated with reduced juiciness and poor texture inpeaches that were ripened after storage at 1

∞

C for more than 3 weeks.

Index Fruits

Elapsed days from full bloom to harvest Apple, pearSize Most fruitsShape (fullness of fruit shoulders and suture) Stone fruitsDry Weight Avocado, kiwifruitColor, external All fruitsColor, internal Stone fruits, mangoFirmness Pome and stone fruits, berriesCompositional factors

Starch content Apple, pearSoluble solids content Pome and stone fruits, grapes, kiwifruitAcid content PomegranateSugar/acid ratio Citrus fruits, grapeTannin content Persimmon




9

1.5.2 P

ROTEINS

Fruits contain less than 1% protein (vs. 9 to 20% protein in nuts such as almond, pistachio, andwalnut). Changes in the level and activity of proteins resulting from permeability changes in cellmembranes may be involved in chilling injury. Enzymes, which catalyze metabolic processes infruits, are proteins that are important in the reactions involved in fruit ripening and senescence. Someof the enzymes important to fruit quality include the following:

1.5.3 L

IPIDS

Lipids constitute only 0.1 to 0.2% of most fresh fruits, except for avocados, olives, and nuts.However, lipids are very important because they make up the surface wax that contributes to fruitappearance and the cuticle that protects the fruit against water loss and pathogens. Lipids are alsoimportant constituents of cell membranes. The degree of fatty acid saturation establishes membraneflexibility, with greater saturation resulting in less flexibility. Desaturation of fatty acids can occurupon chilling in chilling-sensitive fruits; in which case membranes undergo a phase change (liquidcrystalline to solid gel) at chilling temperatures resulting in disruption of normal metabolism.

1.5.4 O

RGANIC

A

CIDS

Organic acids are important intermediate products of metabolism. The Krebs (TCA) cycle is themain channel for the oxidation of organic acids in living cells and it provides the energy required

TABLE 1.1Sugar Composition of Selected Fruits

Fruit

Sugar (g/100 ml of Juice)

Sucrose Glucose Fructose Sorbitol

Apple 0.82 ± 0.13 2.14 ± 0.43 5.31 ± 0.94 0.20 ± 0.04Cherry 0.08 ± 0.02 7.50 ± 0.81 6.83 ± 0.74 2.95 ± 0.33Grape 0.29 ± 0.08 9.59 ± 1.03 10.53 ± 1.04 NDNectarine 8.38 ± 0.73 0.85

±

0.04 0.59 ± 0.02 0.27 ± 0.04Peach 5.68 ± 0.52 0.67 ± 0.06 0.49 ± 0.01 0.09 ± 0.02Pear 0.55 ± 0.12 1.68 ± 0.36 8.12 ± 1.56 4.08 ± 0.79Plum 0.51 ± 0.36 4.28 ± 1.18 4.86 ± 1.30 6.29 ± 1.97Kiwifruit 1.81 ± 0.72 6.94 ± 2.85 8.24 ± 3.43 NDStrawberry 0.17 ± 0.06 1.80 ± 0.16 2.18 ± 0.19 ND

Note:

ND = not detected (less than 0.05 g/100 ml).

Source:

Van Gorsel, H., C. Li, E.L. Kerbel, M. Smits, and A.A. Kader. 1992.Compositional characterization of prune juice.

J. Agric. Food Chem.,

40: 784–789.

Enzyme Action

Polyphenoloxidase Catalyzes oxidation of phenolics, resulting in formation of brown polymersPolygalacturonase Catalyzes hydrolysis of glycosidic bonds between adjacent polygalacturonic acid

residues in pectin; results in tissue softeningPectinesterase Catalyzes deesterification of galacturonans in pectin; may result in tissue firmingLipoxygenase Catalyzes oxidation of lipids; results in off-odor and off-flavor productionAscorbic acid oxidase Catalyzes oxidation of ascorbic acid; results in loss of nutritional qualityChlorophyllase Catalyzes removal of phytol ring from chlorophyll; results in loss of green color



10


for maintenance of cell integrity. Organic acids are metabolized into many constituents, includingamino acids, which are the building blocks of proteins.

Most fresh fruits are acidic with a pH range of 3 to 5. Some fruits, such as lemons and limes,contain as much as 2 to 3% of their total fresh weight as acid. Total titratable acidity, specificorganic acids present and their relative quantities, and other factors influence the buffering systemand affect pH. Acid content usually decreases during ripening due to the utilization of organic acidsduring respiration or their conversion to sugars. Malic and citric acids are the most abundant infruits (Table 1.2), except grapes (tartaric acid is the most important in most cultivars) and kiwifruits(quinic acid is the most abundant).

1.5.5 P

IGMENTS

Pigments, which are the chemicals responsible for skin and flesh colors, undergo many changesduring the maturation and ripening of fruits. These include the following:

1. Loss of chlorophyll (green color), which is influenced by pH changes, oxidative condi-tions, and chlorophyllase activity

2. Synthesis and revelation of carotenoids (yellow and orange colors)3. Development of anthocyanins (red, blue, and purple colors), which are fruit specific

(Table 1.3)

Beta-carotene is a precursor to vitamin A and thus is important in terms of nutritional quality.Carotenoids are very stable and remain intact in fruit tissues even when extensive senescence hasoccurred. Anthocyanins occur as glycosides in the cell sap. They are water soluble, unstable, andare readily hydrolyzed by enzymes to free anthocyanins, which may be oxidized by phenoloxidasesto give brown oxidation products.

1.5.6 P

HENOLIC

C

OMPOUNDS

Total phenolic content is higher in immature than in mature fruits and typically ranges between0.1 and 2 g/100 g fresh weight. Fruit phenolics include chlorogenic acid, catechin, epicatechin,

TABLE 1.2Organic Acids of Selected Fruits

Fruit

Organic Acid (mg/100 ml of Juice)

Citric Ascorbic Malic Quinic Tartaric

Apple ND tr 518 ± 32 ND NDCherry ND tr 727 ± 20 ND NDGrape tr tr 285 ± 58 ND 162 ± 24Kiwifruit 730 ± 92 114 ± 6 501 ± 42 774 ± 57 trNectarine 140 ± 39 tr 383 ± 67 136 ± 28 NDPeach 109 ± 16 tr 358 ± 72 121 ± 11 trPear ND tr 371 ± 16 220 ± 2 NDPlum ND tr 294 ± 24 214 ± 68 NDStrawberry 207 ± 35 56 ± 4 199 ± 26 ND ND

Note:

ND = not detected, tr = trace (<10 mg/100 ml).

Source:



40:784–789.




11

leucoanthocyanidins, flavonols, cinnamic acid derivatives, and simple phenols. Chlorogenic acid(ester of caffeic acid) occurs widely in fruits (Figure 1.1) and is the main substrate involved inenzymatic browning of cut or otherwise damaged fruit tissues when exposed to air.

Enzymatic browning occurs due to the oxidation of phenolic compounds and is mediated, inthe presence of O

2

, by the enzyme polyphenoloxidase (PPO). The initial product of oxidation isusually O-quinone, which is highly unstable and undergoes polymerization to yield brown pigmentsof higher molecular weight. Polyphenoloxidase catalyzes the following two reactions:

Normally phenolic compounds are separated from the PPO enzyme in the intact cells of planttissue. Once the tissue is damaged, PPO and the phenolic compounds that it acts on are decompart-mentalized and the above-mentioned reactions occur, leading to tissue browning. The extent of browndiscoloration depends upon the total amount of phenolic compounds in the tissue and the level of PPOactivity. Differences among cultivars of a given species in terms of browning potential in response tomechanical injury are related to the variation in the total phenolic content and PPO activity of thecultivar. Differences in phenylalanine ammonia lyase (PAL) enzyme activity influence phenolic content.

Astringency is directly related to phenolic content, and it usually decreases with fruit ripeningbecause of conversion of astringent phenolic compounds from the soluble to the insoluble nonas-tringent form. Loss of astringency occurs via (1) binding or polymerization of phenolics, (2) changein molecular size of phenolics, and (3) change in the hydroxylation pattern of phenolic compounds.

There is a strong positive relationship between phenolic content and antioxidant capacity offruits and their products.

TABLE 1.3Anthocyanins of Selected Fruits

Fruit

Anthocyanin

Identification Peak Area

Apple Cyanidin 3-arabinoside 22 ± 6Cyanidin 7-arabinoside or cyanidin 3-glucoside 27 ± 15Cyanidin 3-galactoside 260 ± 69

Cherry Cyanidin 3-glucoside 189 ± 40Cyanidin 3-rutinoside 1320 ± 109Peonidin 3-rutinoside 47 ± 36

Grape Cyanidin 3-glucoside 121 ± 33Delphinidin 3-glucoside 586 ± 110Malvidin 3-glucoside 2157 ± 375Peonidin 3-glucoside 478 ± 92

Nectarine Cyanidin 3-glucoside 322 ± 51Peach Cyanidin 3-glucoside 180 ± 43Plum Cyanidin 3-glucoside 42 ± 5Strawberry Cyanidin 3-glucoside 70 ± 18

Pelargonidin 3-glucoside 1302 ± 29Pelargonidin 3-glycoside 78 ± 9

Source:



40:784–789.

Monophenol -

2 0-diphenol -quinone

+ æ Æææ +

+ æ Æææ +

O quinone H O

O H O

ppO

ppO

2 2

2 2

2 0

2 0



12


1.5.7 V

OLATILES

Volatiles are responsible for the characteristic aroma of fruits. They are present in extremely smallquantities (<100

m

g/g fresh wt.). The total amount of carbon involved in the synthesis of volatilesis <1% of that expelled as CO

2

. The major volatile formed in climacteric fruits is ethylene (50 to75% of the total carbon content of all volatiles). Ethylene does not have a strong aroma and doesnot contribute to typical fruit aromas.

Volatile compounds are largely esters, alcohols, acids, aldehydes and ketones (low-molecular-weight compounds). Very large numbers of volatile compounds have been identified in fruits andmore are identified as advances in separation and detection techniques and gas chromatographicmethods are made. However, only a few key volatiles are important for the particular aroma of agiven fruit. Their relative importance depends upon threshold concentration (which can be as lowas 1 ppb), potency, and interaction with other compounds.

1.5.8 V

ITAMINS

The water-soluble vitamins include vitamins C, thiamin, riboflavin, niacin, vitamin B6, folacin,vitamin B12, biotin, and pantothenic acid. Fat-soluble vitamins include vitamins A, D, E, and K.Fat soluble vitamins are less susceptible to postharvest losses.

Ascorbic acid is most sensitive to destruction when the commodity is subjected to adversehandling and storage conditions. Losses are enhanced by extended storage, higher temperatures,low relative humidity (which may cause wilting), physical damage, and chilling injury. Postharvestlosses in vitamins A and B are usually much smaller than losses in vitamin C. They are, however,susceptible to degradation at high temperatures in the presence of oxygen.

1.5.9 M

INERALS

Important fruit minerals include base-forming elements (Ca, Mg, Na, and K) and acid-formingelements (P, Cl, S). Minerals present in microquantities include Fe, Cu, Co, Mn, Zn, I, and Mo.High nitrogen content is often associated with reduced soluble solids content, lower acidity, andincreased susceptibility to physiological disorders in fruits.

FIGURE 1.1

Phenolic compounds of selected fruits.

Phe

nol c

once

ntra

tion

(mg

per

100

ml j

uice

)

appl

e

cher

ry

kiw

i

nect

arin

e

peac

h

pear

plum

prun

e

stra

wbe

rry

stra

wbe

rry

prun

e

plum

pear

peac

h

nect

arin

e

kiw

i

cher

ry

appl

e

stra

wbe

rry

prun

e

plum

pear

peac

h

nect

arin

e

kiw

i

cher

ry

appl

e

24

22

20

18

16

14

12

10

8

6

4

2

0

4

2

0

24

22

20

18

16

14

12

10

8

6

4

2

0

4

2

0

(+)-catechin chlorogenic acid (−)-epicatechin

caffeic acid ferulic acid phloridzin




13

Potassium is the most abundant mineral found in fruits. It most often occurs in combinationwith organic acids. High potassium content is often associated with increased acidity and improvedcolor of fruits.

Calcium is the second most important mineral constituent and is associated primarily with thecell wall. High calcium contents reduce CO

2

and C

2

H

4

production rates, delay ripening, reduce theincidence of physiological disorders, and extend the storage life of apples and other fruits. Calciumdeficiency has been associated with several physiological disorders such as bitter pit of apples.

Magnesium is a component of the chlorophyll molecule, which is responsible for the intensityof green color in fresh produce. Phosphorus is a constituent of cytoplasmic and nuclear proteinsand plays a major role in carbohydrate metabolism and energy transfer. High phosphorus contentmay result in decreased acidity in some fruits.

1.6 BIOLOGICAL FACTORS INVOLVED IN POSTHARVEST DETERIORATION OF FRUITS

1.6.1 R

ESPIRATION

Respiration is the process by which stored organic materials (carbohydrates, proteins, and fats) arebroken down into simple end products with a release of energy. Oxygen (O

2

) is used in this process,and carbon dioxide (CO

2

) is produced. The loss of stored food reserves in the commodity duringrespiration hastens senescence as the reserves that provide energy to maintain the commodity’sliving status are exhausted. For the consumer, food value (energy value) is gone, flavor quality isreduced, and sweetness, especially, is lost. Salable dry weight is also lost (especially important forcommodities destined for dehydration). The energy released as heat, which is known as vital heat,affects postharvest technology considerations such as estimations of refrigeration and ventilationrequirements. The rate of deterioration (degree of perishability) of fruits is generally proportionalto their respiration rate (Table 1.4).

1.6.2 E

THYLENE

P

RODUCTION

Ethylene, the simplest of the organic compounds affecting the physiological processes of plants,is a natural product of plant metabolism and is produced by all tissues of higher plants and bysome microorganisms. As a plant hormone, ethylene regulates many aspects of growth, develop-ment, and senescence and is physiologically active in trace amounts (less than 0.1 ppm).

Ethylene biosynthesis starts with the amino acid methionine, which is energized by ATP toproduce

S

-adenosyl methionine (SAM). The key enzyme in the pathway, ACC synthase, convertsSAM to 1-aminocyclopropane-1-carboxylic acid (ACC), which is converted to ethylene by theaction of ACC oxidase.

TABLE 1.4Classification of Fruits According to Their Respiration Rates and Degree of Perishability under Optimum Conditions

Relative Respiration Rateand Perishability Fruits

Very low Nuts, dates, dried fruitsLow Apple, pear, kiwifruit, pomegranate, Chinese date (jujube)Moderate Citrus fruits, banana, cherry, nectarine, peach, plum, avocado (unripe), persimmonHigh Apricot, fig (fresh), avocado (ripe), cherimoya, papayaVery high Strawberry, blackberry, raspberry



14


Ethylene production rates, which depend on the fruit (Table 1.5), generally increase withmaturity at harvest, physical injuries, disease incidence, increased temperatures up to 30

∞

C, andwater stress. On the other hand, ethylene production rates by fresh fruits are reduced by storage atlow temperature and by reduced O

2

(less than 8%) and elevated CO

2

(above 1%) levels in thestorage environment around the commodity.

1.6.3 T

RANSPIRATION

OR

W

ATER

L

OSS

Water loss is the main cause of deterioration because it results not only in indirect quantitativelosses (loss of salable weight) but also in losses in appearance (wilting and shriveling), texturalquality (softening, flaccidity, limpness, and loss of crispness and juiciness), and nutritionalquality.

The dermal system (outer protective coverings) governs the regulation of water loss by thecommodity. This system includes the cuticle, epidermal cells, stomata, lenticels, and trichomes(hairs). The cuticle is composed of surface waxes, cutin embedded in wax, and a layer of mixturesof cutin, wax, and carbohydrate polymers. The thickness, structure, and chemical compositionof the cuticle vary greatly among commodities and among developmental stages of a givencommodity.

Transpiration rate is influenced by internal or commodity factors (morphological and anatomicalcharacteristics, surface-to-volume ratio, surface injuries, and maturity stage) and external or envi-ronmental factors (temperature, relative humidity, air movement, and atmospheric pressure). Tran-spiration (evaporation of water from the plant tissues) is a physical process that can be controlledby applying treatments to the commodity (e.g., waxes and other surface coatings or wrapping withplastic films) or by manipulation of the environment (e.g., maintenance of high relative humidityand control of air circulation).

1.6.4 P

HYSIOLOGICAL

D

ISORDERS

The following physiological disorders occur in fruits:

1. Freezing injury when fruits are held below their freezing temperatures. The disruptioncaused by freezing usually results in immediate collapse of the tissues and total loss.

2. Chilling injury when fruits (mainly those of tropical and subtropical origin) are held attemperatures above their freezing point and below 5 to 15

∞

C depending on the com-modity. This physiological injury is manifested in a variety of symptoms, which includesurface and internal discoloration, pitting, water-soaked areas, uneven ripening or failureto ripen, off-flavor development, and accelerated incidence of surface molds and decay.A classification of fruits according to their sensitivity to chilling injury is shown inFigure 1.2.

TABLE 1.5Classification of Fruits According to Their Ethylene Production

Ethylene ProductionRate Fruits

Very low Cherry, citrus fruits, grape, jujube, strawberry, pomegranateLow Blueberry, cranberry, olive, persimmon, pineapple, raspberry, tamarilloModerate Banana, fig, guava, mango, plantainHigh Apple, apricot, avocado (ripe), nectarine, papaya, peach, pear, plumVery high Cherimoya, passion fruit




15

3. Heat injury results from exposure to direct sunlight or to excessively high temperatures.Symptoms include surface scalding, uneven ripening, and excessive softening anddesiccation.

4. Certain types of physiological disorders originate from preharvest nutritional imbalancessuch as calcium deficiency, causing bitter pit of apples.

5. Very low (<1%) oxygen and elevated (>20%) carbon dioxide concentrations can resultin physiological breakdown of all fruits.

1.6.5 P

HYSICAL

D

AMAGE

Various types of physical damage (surface injuries, impact bruising, and vibration bruising, etc.)are major contributors to deterioration. Mechanical injuries are not only unsightly but also acceleratewater loss, stimulate higher respiration and ethylene production rates, and favor decay incidence.

1.6.6 P

ATHOLOGICAL

B

REAKDOWN

Decay is one of the most common or apparent causes of deterioration. However, attack by manymicroorganisms usually follows mechanical injury or physiological breakdown of the commodity,which allow entry to the microorganism. In a few cases, pathogens can infect healthy tissues andbecome the primary cause of deterioration.

FIGURE 1.2

Classification of fruits according to their sensitivity to chilling injury.

GROUP I

NON-CHILLING SENSITIVECOMMODITIES

CHILLING SENSITIVECOMMODITIES

HIGH TEMP. INJURY HIGH TEMP. INJURY

OPTIMUM RIPENING TEMP.RANGE FOR FRUITS

OPTIMUM RIPENING TEMP.RANGE FOR FRUITS

IDEAL TEMP. RANGE FORTRANSIT AND STORAGE

IDEAL TEMP. RANGE FORTRANSIT AND STORAGE

CHILLING INJURY

FREEZING INJURYFREEZING INJURY

GROUP II

°F °C122

113

104

9586

77

68

59

50

41

32

23

50

45

40

3530

25

20

15

10

5

0

−5

Apples*ApricotsBush berriesCherriesFigsGrapesKiwifruits

NectarinesPeachesPearsPersimmons*PlumsPrunesStrawberries

AvocadosBananasCherimoyaCitrusFeijoaGuavaJujubes

MangoesOlivesPapayasPassion fruitPineapplesPlantainPomegranatesSapota

*Some varieties are chilling sensitive.



16


1.7 ENVIRONMENTAL FACTORS INFLUENCING DETERIORATION OF FRUITS

1.7.1 T

EMPERATURE

Temperature is the most important environmental factor that influences the deterioration rate ofharvested fruits. For each increase of 10

∞

C (18

∞

F) above the optimum temperature, the rate ofdeterioration increases by two- or threefold. Exposure to undesirable temperatures results in manyphysiological disorders as mentioned above. Temperature also influences how ethylene, reducedoxygen, and elevated carbon dioxide levels affect the commodity. The growth rate of pathogens isgreatly influenced by temperature and some pathogens, such as Rhizopus rot, are sensitive to lowtemperatures. Thus, cooling of commodities below 5

∞

C immediately after harvest can greatly reduceRhizopus rot incidence.

1.7.2 R

ELATIVE

H

UMIDITY

The rate of water loss from fruits depends upon the vapor pressure deficit between the commodityand the surrounding ambient air, which is influenced by temperature and relative humidity.

1.7.3 A

IR

M

OVEMENT

Air circulation rate and velocity can influence the uniformity of temperature and relative humidityin a given environment and consequently rate of the water loss from the commodity.

1.7.4 A

TMOSPHERIC

C

OMPOSITION

Reduction of oxygen and elevation of carbon dioxide, whether intentional (modified or controlledatmosphere storage) or unintentional, can have a beneficial or harmful effect on deterioration. Themagnitude of these effects depends upon commodity, cultivar, physiological age, O

2

and CO

2

level,temperature, and duration of storage. A summary of current and potential use of controlled atmo-spheres to maintain the quality of fruits during transport and storage is given in Table 1.6.

1.7.5 E

THYLENE

Ethylene is a natural plant hormone and its effect on harvested fruits can be desirable (degreeningand ripening) or undesirable (abbreviated storage and softening). Ethylene effects are cumulativethroughout the postharvest life of the fruit, and the magnitude of ethylene effects depends upontemperature, exposure time, and ethylene concentration. A concentration as low as 50 ppb ethylene

TABLE 1.6Current and Potential Use of Controlled Atmospheres to Maintain Quality during Transport and Storage of Fruits

Range of Postharvest Life(Months) Fruits

Up to 1 Banana, mango, papaya, cherry, grape, fig, blackberry, blueberry, raspberry, strawberry1 to 3 Avocado, olive, persimmon, pomegranate, some peach, nectarine, and plum cultivars,3 to 6 Kiwifruit, some cultivars of Asian pears6 to 12 Some cultivars of apples and European pears>12 Almond, filbert, macadamia, pecan, pistachio, walnut, dried fruits




17

enhances kiwifruit softening at 0

∞

C. Avocados and “Fuyu” persimmons are also very sensitive toethylene action; exposure to 1 ppm (or higher) ethylene increases chilling injury symptoms. Useof ethylene to degreen citrus fruits can accelerate their senescence and increase their susceptibilityto decay-causing pathogens.

1.8 HARVESTING PROCEDURES

Harvesting methods, especially those involving a once-over procedure, may determine uniformityof maturity at harvest, which in turn influences quality of the fruit. Maturity also influencessusceptibility of the fruit to water loss and mechanical injury. The harvesting system used and itsmanagement have a direct effect on incidence and severity of mechanical injuries. Such injuriescan result in tissue browning, accelerated water loss, higher respiration and ethylene productionrates, and increased decay incidence. Physical injuries may also induce some undesirable compo-sitional changes, such as loss of ascorbic acid content and development of off-flavors.

Management of the harvesting operation, whether manual or mechanical, can have a majorimpact on quality of the harvested fruits. Proper management procedures include selection ofoptimum time to harvest in relation to fruit maturity and climatic conditions, training and super-vision of workers, and effective quality control.

1.9 POSTHARVEST HANDLING PROCEDURES

1.9.1 D

UMPING

Fresh fruits should be handled with care throughout the postharvest handling system in order tominimize mechanical injuries. Dumping in water or in floatation tanks should be used for fruitsthat withstand wetting. If dry dumping systems are used, they should be well padded to reduceimpact bruising. Also, a bin cover may be used to permit inverting the bin and to regulate the flowof fruits out of the bin.

1.9.2 W

ASHING

To clean fruit, water alone or with added cleaning agents and/or chlorine (typically 100 to 150ppm) may be used. The final rinse should be made with fresh, clean water. Following washing,removal of excess surface water may be necessary and this can be done by blotting rollers or byair flow over the fruits.

1.9.3 S

ORTING

Manual sorting is usually carried out to eliminate fruit exhibiting defects or decay. For some fruits,it may also be necessary to sort the fruit into two or more classes of maturity or ripeness (accordingto their color and firmness) before ripening or processing. Mechanical sorters, which operate onthe basis of color, soluble solids, moisture, or fat content, are being implemented and may greatlyreduce time and labor requirements.

1.9.4 S

IZING

In some cases, sizing the fruits into two or more size categories may be required before processing.Sizing can be done mechanically on the basis of fruit dimension or by weight. Mechanical sizingcan be a major source of physical damage to the fruit if the machines were not adequately paddedand adjusted to the minimum possible fruit drop heights.



18


1.9.5 R

IPENING

Ripening before processing may be required for certain fruits (e.g., avocado, banana, kiwifruit,mango, nectarine, papaya, peach, pear, persimmon, plum, and melons) that are picked immature.Ethylene treatment can be used to obtain faster and more uniform ripening. The optimum temper-ature range for ripening is 15 to 25

∞

C and within this range, the higher the temperature the fasterthe ripening. Relative humidity should be maintained between 90 and 95% during ripening.Although 10 ppm ethylene is sufficient to initiate ripening, a concentration of 20 to 100 ppm forat least 2 d is recommended for commercial application.

Adequate air circulation within the room is important to ensure uniform distribution of ethylene.One method to achieve this is by forcing the ethylene-containing air through the fruit containers(forced-air ripening or pressure ripening). It is also important to avoid accumulation of carbondioxide (produced by the commodity through respiration) above 1% in the ripening room sincecarbon dioxide counteracts ethylene effects. This can be accomplished by periodic air exchange(introduction of fresh air into the ripening room) or by using hydrated lime to absorb carbon dioxide.

1.9.6 I

NHIBITING

E

THYLENE

A

CTION

Since July 2002, the ethylene-action inhibitor, 1-methylcyclopropene gas (1-MCP) under the tradename “SmartFresh” at concentrations up to 1 ppm was approved by the U.S. EnvironmentalProtection Agency for use on apples, apricots, avocados, kiwifruit, mangoes, nectarines, papayas,peaches, pears, persimmons, plums, and tomatoes. The first commercial application has been onapples to retard their softening and scald development and extend their postharvest life. As moreresearch is completed, the use of 1-MCP will no doubt be extended to several other commoditiesin the future.

1.9.7 C

OOLING

Cooling is utilized to remove field heat and lower the fresh fruit’s temperature to near its optimumstorage temperature. Cooling can be done using cold water (hydrocooling) or cold air (forced-aircooling or pressure cooling). Highly perishable fruits, such as strawberries, bush berries, andapricots should be cooled to near 0

∞

C (32

∞

F) within 6 h of harvest. Other fruits should be cooledto their optimum temperature within 12 h of harvest.

1.9.8 S

TORAGE

Short-term or long-term storage of fresh fruits may be needed before processing to regulate theproduct flow and extend the processing season. A classification of fresh fruits according to theiroptimum storage temperature and potential storage life is shown in Table 1.7. In all cases, therelative humidity in the storage facility should be kept between 90 and 95%. To reduce decay,elevated CO

2

(15 to 20%) may be added to the atmosphere within pallet covers for strawberries,bush berries, and cherries; sulfur dioxide (200 ppm) fumigation may be used on table grapes.

There is a continuing trend toward increased precision in temperature and relative humiditymanagement to provide the optimum environment for fresh produce during cooling, storage, andtransport. Precision temperature management tools, including time–temperature monitors, arebecoming more common in cooling and storage facilities. Several manufacturers have developedself-contained temperature and RH monitors and recorders, which are small and can be packed ina box with the product. Data are read by connecting these units to a personal computer with theappropriate software made by the manufacturer. Infrared thermometers are used to measure surfacetemperature of products from a distance in various locations within storage facilities. Electronicthermometers (with very thin, strong probes for fast response) are used for measuring producttemperature during cooling, storage, and transport operations.




19

1.9.9 F

OOD

S

AFETY

G

UIDELINES

Over the past few years, food safety has become and continues to be the number one concern ofthe fresh produce industry. A training manual for trainers titled

Improving the Safety and Qualityof Fresh Fruits and Vegetable

was published by the USFDA in November 2002 to provide uniform,broad-based scientific and practical information on the safe production, handling, storage, andtransport of fresh produce. It is available electronically (in English and Spanish) at the followingInternet site: http://www.jifsan.umd.edu/gaps.html.

1.9.10 F

OOD

S

ECURITY

G

UIDELINES

On March 19, 2003, The U.S. Food and Drug Administration (FDA) released food security guidancedocuments for food producers, processors, and transporters. These documents are available elec-tronically at http://www.cfsan.fda.gov/~dms/secguid6.html and are voluntary recommendationsfrom the FDA and not mandatory regulations. The goal is to help operators of food handlingfacilities identify preventive measures to minimize the security risks to their products.

1.10 SUMMARY: KEYS TO SUCCESSFUL HANDLING OF FRESH FRUITS

1.10.1 M

ATURITY

AND

Q

UALITY

1. Harvest at the proper maturity stage that will result in the best eating quality.2. Eliminate fruits with defects in the orchard or soon after delivery to the processing plant.

1.10.2 T

EMPERATURE

AND

H

UMIDITY

M

ANAGEMENT

P

ROCEDURES

1. Harvest during the cool part of the day.2. Keep in the shade while accumulating fruits in the orchard.3. Transport fruits to the processing plant as soon as possible after harvest and use refrig-

erated transport vehicles for distances that require more than a few hours.4. Avoid delays at the processing plant. If delays cannot be avoided, cool and hold fruits

at or near their optimum storage temperature until processed.5. Maintain proper temperature and relative humidity during ripening of fruits requiring

such treatment (with or without added ethylene).

TABLE 1.7Classification of Fruits According to Their Optimum Storage Temperatures and Potential Storage Life

Potential Storage Life (Weeks)

Optimum Storage Temperatures

0 to 2

∞

C 3 to 5

∞

C 12 to 14

∞

C

< 2 Apricot, bush berries, strawberry, fig

Cantaloupe, ripe avocado Cherimoya, guava, pineapple

2 to 4 Cherry, nectarine, peach,plum

Tangerine and mandarin, carambola

Avocado, banana, mango, papaya, honeydew melon

4 to 6 Grape, tamarillo Orange, pomegranate, kumquat Grapefruit, lime, pummelo> 6 Apple (nonchilling sensitive

cultivars), pear, cranberry, kiwifruit, “Hachiya” persimmon, date

Apple (chilling sensitive cultivars)

Lemon, “Fuyu” persimmon



http://www.jifsan.umd.edu/gaps.html

http://www.cfsan.fda.gov

20


1.10.3 P

HYSICAL

DAMAGE

1. Handle fruits with care during harvesting, hauling to the processing plant, and duringhandling operations within the plant.

2. Avoid drops, impacts, vibrations, and surface injuries of fruits throughout the handlingsystem.

3. Use containers that would provide adequate protection of the commodity from physicalinjuries when stacked during temporary storage.

1.10.4 SANITATION PROCEDURES

1. Sort out and properly discard decayed fruits.2. Clean harvest containers, processing plant machinery, cooling and storage facilities, and

transit vehicles periodically with water, soap, and disinfectants.

1.10.5 EXPEDITED HANDLING

1. Reduce the time between harvest and cooling the fruits.2. Avoid exceeding the fruit’s storage life, based on flavor quality, before processing.

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Blankenship, S.M. and J.M. Dole. 2003. 1-Methylcyclopropene: a review. Postharvest Biol. Technol., 28:1–25.Brady, C.J. 1987. Fruit ripening. Annu. Rev. Plant Physiol., 38:155–178.Calderon, M. and R. Barkai-Golan (Eds.). 1990. Food Preservation by Modified Atmospheres. CRC Press,

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Eskin, N.A.M. (Ed.). 1991. Quality and Preservation of Fruits. CRC Press, Boca Raton, FL.Gross, J. 1987. Pigments in Fruits. Academic Press, Orlando, FL.Gross, K., C-Y. Wang, and M.E. Saltveit (Eds.). 2002. The commercial storage of fruits, vegetables, and florist

and nursery stocks. U.S. Department of Agriculture, Agricultural Handbook, 66(http://www.ba.ars.usda.gov/hb66/index.html).

Hardenburg, R.E., A.E. Watada, and C-Y. Wang. 1986. The Commercial Storage of Fruits, Vegetables, andFlorist and Nursery Stocks. U.S. Department of Agriculture, Agricultural Handbook, 66.

Hulme, A.C. (Ed.). 1971. The Biochemistry of Fruits and Their Products, Vol. 1 (620 p.) and Vol. 2. (788 p.)Academic Press, New York.

Kader, A.A. 1986a. Biochemical and physiological basis for effects of controlled and modified atmosphereson fruits and vegetables. Food Technol., 40(5): 99–100, 102–104.

Kader, A.A. 1986b. Potential applications of ionizing radiation in postharvest handling of fresh fruits andvegetables. Food Technol. 40(6): 117–121.

Kader, A.A. 1999. Fruit maturity, ripening, and quality relationships. Acta Hortic., 485: 203–208.Kader, A.A. (Ed.). 2002. Postharvest Technology of Horticultural Crops. 3rd ed. University of California,

Division of Agriculture and Natural Resources, Publication No. 3311.Kader, A.A. 2003. A summary of CA requirements and recommendation for fruits other than pome fruits.

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Kalt, W. 2002. Health functional phytochemicals of fruits. Hortic. Rev., 27: 269–315.Knee, M. (Ed.). 2002. Fruit Quality and Its Biological Basis. Sheffield Academic Press, U.K.Lee, C.Y. and J.R. Whitaker (Eds.). 1995. Enzymatic Browning and Its Prevention. ACS Symposium Series,

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cultural crops. Postharvest Biol. Technol., 20: 207–220.Macheix, J., A. Fleuriet, and J. Billot. 1990. Fruit Phenolics. CRC Press, Boca Raton, FL.Mitra, S. (Ed.). 1997. Postharvest Physiology and Storage of Tropical and Subtropical Fruits. CAB Interna-

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Properties, and Uses. Florida Science Source, Lake Alfred, FL.O’Brien, M., B.F. Cargill, and R.B. Fridley. 1983. Principles and Practices for Harvesting and Handling of

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Plant. Physiol., 35: 155–189.

INTERNET SITES

http://postharvest.ucdavis.edu: University of California Postharvest Research and Information Center.http://www.uckac.edu/postharv: University of California Kearney Agricultural Center.http://postharvest.ifas.ufl.edu: University of Florida Postharvest Group.



http://www.nal.Usda.gov/fnic/foodcomp

http://postharvest.ucdavis.edu

http://www.uckac.edu

http://postharvest.ifas.ufl.edu

22 Processing Fruits: Science and Technology, Second Edition

http://www.fdocitrus.com: Florida Department of Citrus postharvest information.http://www.postharvest.tfrec.wsu.edu: Washington State University postharvest information.http://www.ams.usda.gov: U.S. Department of Agriculture, Agricultural Marketing Service information on

quality standards, transportation, and marketing.http://www.ams.usda.gov/nop/: National Organic Program Standards.http://www.nutrition.gov: Gateway to U.S. government information on human nutrition and nutritive value of

foods.http://www.nal.usda.gov/fnic/foodcomp: Composition of foods.



http://www.fdocitrus.com

http://www.postharvest.tfrec.wsu.edu

http://www.ams.usda.gov

http://www.ams.usda.gov

http://www.nutrition.gov

http://www.nal.usda.gov

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