techniques that delay senescence and maintain the...

PostharvestBiology and

Technology: AnOverview

Adel A. Kader

POSTHARVEST BIOLOGY AND TECHNOLOGY 39

Losses in quantity and quality affect horticultural crops between har-vest and consumption. The magnitude of postharvest losses in freshfruits and vegetables is an estimated 5 to 25% in developed countriesand 20 to 50% in developing countries, depending upon the com-modity, cultivar, and handling conditions. To reduce these losses, pro-ducers and handlers must first understand the biological and environ-mental factors involved in deterioration, and second, use postharvesttechniques that delay senescence and maintain the best possible qual-ity. This chapter briefly discusses the first item and introduces thesecond, which is covered in detail in subsequent chapters.

Fresh fruits, vegetables, and ornamentals are living tissues that aresubject to continuous change after harvest. While some changes aredesirable, most-from the consumer's standpoint-are not. Posthar-vest changes in fresh produce cannot be stopped, but they can beslowed within certain limits. Senescence is the final stage in the devel-opment of plant organs, during which a series of irreversible eventsleads to breakdown and death of the plant cells.

Fresh horticultural crops are diverse in morphological structure'(roots, stems, leaves, flowers, fruits, and so on), in composition, aridin general physiology. Thus, commodity requirements and recommen-dations for maximum postharvest life vary among the commodities.All fresh horticultural crops are high in water content and are subjectto desiccation (wilting, shriveling) and to mechanical injury. They arealso susceptible to attack by bacteria and fungi, with pathologicalbreakdown the result.

BIOLOGICAL FACTORS INVOLVED INDETERIORATION

RESPIRATION

Respiration is the process by which stored organic materials (carbohy-drates, proteins, fats) are broken down into simple end products witha release of energy. Oxygen (02) is used in this process, and carbondioxide (CO2) is produced. The loss of stored food reserves in thecommodity during respiration means the hastening of senescence asthe reserves that provide energy to maintain the commodity's livingstatus are exhausted; reduced food value (energy value) for the con-sumer; loss of flavor quality, especially sweetness; and loss of salabledry weight, which is especially important for commodities destinedfor dehydration. The energy released as heat, known as vital heat,affects postharvest technology considerations, such as estimations ofrefrigeration and ventilation requirements.

The rate of deterioration (perishability) of harvested commoditiesis generally proportional to the respiration rate. Horticultural com-modities are classified according to their respiration rates in table 4.l.Based on their respiration and ethylene (C2H4) production patternsduring maturation and ripening, fruits are either climacteric or non-climacteric (table 4.2). Climacteric fruits show a large increase in CO2and C2H4 production rates coincident with ripening, while nonclimac-teric fruits show no change in their generally low CO2 and C2H4 pro-duction rates during ripening.

ETHYLENE PRODUCTION

Ethylene (C2H4), the simplest of the organic compounds affectingthe physiological processes of plants, is a natural product of plant

40 CHAPTER 4

Table 4.1. Horticulturalcommoditiesclassifiedaccordingto respirationrates

ClassRangeat soC(41°F)

(mg COz/kg-hr)* Commodities-

<5 Dates,driedfruits andvegetables,nuts

Apple,beet,celery,citrusfruits,cranberry,garlic,grape,honeydewmelon,kiwifruit,onion,papaya,persimmon,pineapple,pomegranate,potato(mature),pumpkin,sweetpotato,watermelon,winter squash

Apricot,banana,blueberry,cabbage,can-taloupe,carrot(topped),celeriac,cherry,cucumber,fig, gooseberry,lettuce(head),mango,nectarine,olive,peach,pear,plum,potato (immature),radish(topped),sum-mersquash,tomato

Avocado,blackberry,carrot(with tops),cauliflower,leek,lettuce(leaf),limabean,

radish(with tops),raspberry,strawberry

Artichoke,beansprouts,broccoli,Brus-selssprouts,cherimoya,cut flowers,endive,greenonions,kale,okra,passionfruit, snapbean,watercress

Verylow

Low

Moderate

High

Veryhigh

Extremely high

nn --- -

5-10

10-20

20-40

40-60

>60 Asparagus, mushroom, parsley, peas,spinach, sweet corn

- ---------------------------

Note: *Vital heat (Btu/ton/24 hrs) = mg COz/kg-hrx 220.Vital heat (kcal/1,000 kg/24 hrs) = mg COz/kg-hrx 61.2.

metabolism and is produced by all tissues ofhigher plants and by some microorganisms-As a plant hormone, C2H4regulates manyaspects of growth, development, and senes-cence and is physiologically active in traceamounts (less than 0.1 ppm). It also plays amajor role in the abscission of plant organs.

The amino acid methionine is converted

to S-adenosylmethionine (SAM), which is theprecursor of l-aminocyclopropane-l-car-boxylic acid (ACC), the immediate precursorof C2H+ ACC synthase, which converts SAMto ACe, is the main site of control of ethylenebiosynthesis. The conversion of ACC intoethylene is mediated by ACC oxidase. The

synthesis and activities of ACC synthase andACC oxidase are influenced by genetic factorsand environmental conditions, includingtemperature and concentrations of oxygenand carbon dioxide.

Horticultural commodities are classified

according to their C2H4 production rates intable 4.3. There is no consistent relationshipbetween the C2H4 production capacity of agiven commodity and its perishability; how-ever, exposure of most commodities to C2H4accelerates their senescence.

Generally, C2H4 production rates increasewith maturity at harvest and with physicalinjuries, disease incidence, increased temper-atures up to 30°C (86°F), and water stress.On the other hand, C2H4 production rates byfresh horticultural crops are reduced by stor-age at low temperature, by reduced O2 levels(less than 8%), and elevated CO2 levels(more than 2%) around the commodity.

COMPOSITIONAL CHANGES

Many changes in pigments take place duringdevelopment and maturation of the commod-ity on the plant; some may continue afterharvest and can be desirable or undesirable:

. Loss of chlorophyll (green color) is desir-able in fruits but not in vegetables.

. Development of carotenoids (yellow andorange colors) is desirable in fruits such asapricots, peaches, and citrus. Red colordevelopment in tomatoes and pink grape-fruit is due to a specific carotenoid(lycopene); beta-carotene is provitamin Aand thus is important in nutritional quality.

. Development of anthocyanins (red andblue colors) is desirable in fruits such as

apples (red cultivars), cherries, strawber-

ries, cane berries, and red-flesh oranges.These water-soluble pigments are muchless stable than carotenoids.

. Changes in anthocyanins and other phe-nolic compounds may result in tissuebrowning, which is undesirable forappearance quality. On the other hand,these constituents contribute to the total

antioxidant capacity of the commodity,which is beneficial to human health.

Changes in carbohydrates include starch-to-sugar conversion (undesirable in pota-toes, desirable in apple, banana, and otherfruits); sugar-to-starch conversion (undesir-able in peas and sweet corn; desirable in

potatoes); and conversion of starch and sug-ars to CO2 and water through respiration.Breakdown of pectins and other polysaccha-rides results in softening of fruits and a con-sequent increase in susceptibility to mechan-ical injuries. Increased lignin content isresponsible for toughening of asparagusspears and root vegetables.

Changes in organic acids, proteins, amitlOacids, and lipids can influence flavor qualityof the commodity. Loss in vitamin content,

especially ascorbic acid (vitamin C) is detri-mental to nutritional quality. Production offlavor volatiles associated with ripening offruits is very important to their eating quality.

GROWTH AND DEVELOPMENT

Sprouting of potatoes, onions, garlic, androot crops greatly reduces their food valueand accelerates deterioration. Rooting of

Table4.3. Classificationof horticultural commodities accordingto eth-ylene (CZH4)production rates

------------------

Rangeat 20°C(68°F)(IJLCzH4/kg-hr)Class Commodities

- --- --- __OM -------------------------

Verylow Lessthan 0.1 Artichoke,asparagus,cauliflower,cherry,citrusfruits,grape,jujube,strawberry,pomegranate,leafyvegetables,root veg-etables,potato,mostcut flowers

Blackberry,blueberry,casabamelon,cranberry,cucumber,eggplant,okra,olive,pepper(sweetandchili),persim-mon,pineapple,pumpkin,raspberry,tamarillo,watermelon

Banana,fig, guava,honeydewmelon,Iychee,mango,plantain,tomato

Apple,apricot,avocado,cantaloupe,fei-joa, kiwifruit (ripe),nectarine,papaya,peach,pear,plum

Cherimoya,mammeeapple,passionfruit, sapote

Low 0.1-1.0

Moderate 1.0":10.0

High 10.0-100.0

Veryhigh Morethan 100.0

-----------------


onions and root crops is also undesirable.Asparagus spears continue to grow after har-vest; elongation and curvature (if the spearsare held horizontally) are accompanied byincreased toughness and decreased palatabil-ity. Similar geotropic responses occur in cutgladiolus and snapdragon flowers storedhorizontally. Seed germination inside fruitssuch as tomatoes, peppers, and lemons is anundesirable change.

TRANSPIRATION OR WATER lOSSWater loss is a main cause of deterioration

because it results not only in direct quantita-tive losses (loss of salable weight), but alsoin losses in appearance (wilting and shrivel-ing), textural quality (softening, flaccidity,limpness, loss of crispness and juiciness),and nutritional quality.

The commodity's dermal system (outer --

protective coverings) governs the regulationof water loss. It includes the cuticle, epider-mal cells, stomata, lenticles, and trichomes.(hairs). The cuticle is composed of surfacewaxes, cutin embedded in wax, and a layerof mixtures of cutin, wax, and carbohydratepolymers. The thickness, structure, andchemical composition of the cuticle varygreatly among commodities and among.developmental stages of a given commoditt.

The transpiration rate (evaporation ofwater from the plant tissues) is influenced byinternal, or commodity, factors (morphologi-cal and anatomical characteristics, surface-to-

volume ratio, surface injuries, and maturitystage) and by external, or environmental, fac-tors (temperature, relative humidity [RH], airmovement, and atmospheric pressure). Tran-spiration is a physical process that can be con-trolled by applying treatments to the com-modity (e.g., waxes and other surface coatingsor wrapping with plastic films) or by manipu-lating the environment (e.g., maintaining highRH and controlling air circulation).

PHYSIOLOGICAL BREAKDOWN

Exposure of the commodity to undesirabletemperatures can result in physiological dis-orders:

. Freezing injury results when commoditiesare held below their freezing temperatures.The disruption caused by freezing usually.results in immediate collapse of the tissuesand total loss of the commodity.

Table 4.2. Fruitsclassifiedaccordingto respiratorybehavior duringripening------------------ ----- ---..- ----------- - --------- ---

Climacteric fruits Nonclimacteric fruits------------------------- ---------------..--------

Apple Muskmelon Blackberry Lychee

Apricot Nectarine Cacao Okra

Avocado Papaya Carambola Olive

Banana Passionfruit Cashewapple OrangeBiriba Peach Cherry Pea

Blueberry Pear Cranberry Pepper

Breadfruit Persimmon Cucumber Pineapple

Cherimoya Plantain Date Pomegranate

Durian Plum Eggplant Pricklypear

Feijoa Quince Grape Raspberry

Fig Rambutan Grapefruit Strawberry

Guava Sapodilla Jujube Summersquash

Jackfruit Sapote Lemon Tamarillo

Kiwifruit Soursop Lime Tangerineand

Mango Sweetsop Longanmandarin

Mangosteen Tomato Loquat Watermelon-------------------- -- ----- ------

42 CHAPTER 4

. Chilling injury occurs in some commodi-ties (mainly those of tropical and subtrop-ical origin) held at temperatures abovetheir freezing point and below 5° to 1S0C(41 ° to S9°F), depending on the commod-ity. Chilling injury symptoms becomemore noticeable upon transfer to higher(nonchilling) temperatures. The mostcommon symptoms are surface and inter-nal discoloration (browning), pitting,watersoaked areas, uneven ripening orfailure to ripen, off-flavor development,and accelerated incidence of surface

molds and decay (especially the incidenceof organisms not usually found growingon healthy tissue).

. Heat injury is induced by exposure todirect sunlight or excessively high temper-atures. Its symptoms include bleaching,surface burning or scalding, uneven ripen-ing, excessive softening, and desiccation.

Certain types of physiological disorders orig-inate from pre harvest nutritional imbalances.For example, blossom end rot of tomatoesand bitter pit of apples result from calcium

deficiency. Increasing calcium content bypreharvest or postharvest treatments canreduce the susceptibility to physiological dis-orders. Calcium content also influences the

textural quality and senescence rate of fruitsand vegetables; increased calcium content

has been associated with improved firmnessretention, reduced CO2 and C2H4 productionrates, and decreased decay incidence.

Very low °2( d %) and high CO2 (>20%)atmospheres can cause physiological break-down of most fresh horticultural commodi-

ties, and C2H4 can induce physiologicaldisorders in certain commodities. The inter-

actions among °2, CO2, and C2H4 concentra-tions, temperature, and duration of storageinfluence the incidence and severity of physi-ological disorders related to atmosphericcomposition.

PHYSICAL DAMAGE

Various types of physical damage (surfaceinjuries, impact bruising, vibration bruising,and so on) are major contributors to deteri-oration. Browning of damaged tissuesresults from membrane disruption, whichexposes phenolic compounds to thepolyphenol oxidase enzyme. Mechanicalinjuries not only are unsightly but also

accelerate water loss, provide sites for fun-gal infection, and stimulate CO2 and C2H4production by the commodity.

PATHOLOGICAL BREAKDOWNOne of the most common and obvious

symptoms of deterioration results from theactivity of bacteria and fungi. Attack by mostorganisms follows physical injury or physio-logical breakdown of the commodity. In afew cases, pathogens can infect apparentlyhealthy tissues and become the primarycause of deterioration. In general, fruits andvegetables exhibit considerable resistance topotential pathogens during most of theirpostharvest life. The onset of ripening infruits, and senescence in all commodities,

renders them susceptible to infection bypathogens. Stresses such as mechanicalinjuries, chilling, and sunscald lower the'resistance to pathogens.

ENVIRONMENTAL FACTORSINFLUENCINGDETERIORATION

Temperature. Temperature is the environ-mental factor that most influences the deteri-oration rate of harvested commodities. Fer

each increase of lOOC (lSOF) above optirrlum,the rate of deterioration increases by two- tothreefold (table 4.4). Exposure to undesirabletemperatures results in many physiologicaldisorders, as mentioned above. Temperaturealso influences the effect of C2H4, reduced°2, and elevated CO2, The spore germinationand growth rate of pathogens are greatlyinfluenced by temperature; for instance, cool-ing commodities below SOC (41°F) immedi-ately after harvest can greatly reduce the inci-dence of Rhizopus rot. Temperature effectson postharvest responses of chilling-sensitiveand nonchilling-sensitive horticultural cropsare compared in table 4.5.

Relative humidity. The rate of water lossfrom fruits and vegetables depends on thevapor pressure deficit between the commodi-ty and the surrounding ambient air, whichis influenced by temperature and RH. At agiven temperature and rate of air movement,

the rate of water loss from the commoditydepends on the RH. At a given RH, water lossincreases with the increase in temperature..

Atmospheric composition. Reduction ofO2 and elevation of CO2, whether intentional

Table 4.4. Effectof temperature on deteriorationrate of a non-chilling-sensitivecommodity ----------------

Note: 'Q1O =--- --- --------------------------------------------------------------

Rate of deterioration at temperature (T) + 10°CRate of deterioration at T

Table 4.5.Fruits and vegetables classified according to sensitivity tochillinginjury

GROUPI GROUPII

Non-chilling-sensitive of 'C Chilling-sensitivecommodities

1

122 50

1

commodities113 45

High-temperature injury - 104 40 - High-temperature injury, 95 35,

.;.. 86 30 .;..Optimumripening 77 25 Optimumripeningtemperature ran~e--{ 68 20}- temperature rangeforfruits for fruits

59 15} Ideal temperature range

50 10 l~ for transit and storageIdealtemperature range 41 5 r Chillinginjuryfor transit and storage ---{

r

32 0

1Freezinginjury--- 23 -5 - Freezinginjury

GROUPI------------

Fruits Vegetables,-----

Apple' ArtichokeApricot AsparagusBlackberry Beans,limaBlueberry BeetCherry BroccoliCurrant BrusselssproutsDate CabbageFig CarrotGrape CauliflowerKiwifruit CeleryLoquat Corn,sweetNectarine' EndivePeach' GarlicPear LettucePersimmon' MushroomsPlum' OnionPrune ParsleyRaspberry ParsnipStrawberry Peas

RadishSpinachTurnip

Note: 'Some cultivars are chillingsensitive.

GROUPII- ,- --- --- - --- -

Fruits

AvocadoBananaBreadfruitCarambola

CherimoyaCitrus

CranberryDurian

FeijoaGuavaJackfruitJujubeLonganLycheeMangoMangosteenOlivePapayaPassion fruitPepinoPineapplePlantainPomegranatePricklypearRambutanSapodillaSapoteTamarillo

Vegetables- --- -

Beans, snapCassavaCucumber

EggplantGingerMuskmelonOkraPeppersPotato

PumpkinSquashSweet potatoTaroTomatoWatermelon

Yam


(modified or controlled atmosphere storage)or unintentional (restricted ventilation within

a shipping container or transport vehicle), caneither delay or accelerate the deterioration offresh horticultural crops. The magnitude ofthese effects depends on the commodity, culti-var, physiological age, O2 and CO2 levels,temperature, and duration of holding.

Ethylene. Because the effects of C2H4 onharvested horticultural commodities can be

desirable or undesirable, C2H4 is of majorconcern to all produce handlers. Ethylenecan be used to promote faster and more uni-form ripening of fruits picked at the mature-green stage. On the other hand, exposure toC2H4 can be detrimental to the quality ofmost nonfruit vegetables and ornamentals.

Light. Exposure of potatoes to light shouldbe avoided because it results in greening dueto formation of chlorophyll and solanine(toxic to humans). Light-induced greening ofBelgian endive is also undesirable.

Other factors. Various kinds of chemicals

(e.g., fungicides, growth regulators) may beapplied to the commodity to affect one ormore of the biological deterioration factors.

POSTHARVESTTECHNOLOGY PROCEDURES

t

TEMPERATURE MANAGEMENT

PROCEDURES

Temperature management is the most effec-tive tool for extending the shelf life of freshhorticultural commodities. It begins with therapid removal of field heat by using one ofthe following cooling methods: hydrocool-ing, in-package icing, top-icing, evaporativecooling, room cooling, forced-air cooling,serpentine forced-air cooling, vacuum cool-ing, or hydro-vacuum cooling.

Cold storage facilities should be well-engi-neered and adequately equipped. Theyshould have good construction and insula-tion, including a complete vapor barrier onthe warm side of the insulation; strongfloors; adequate and well-positioned doorsfor loading and unloading; effective distribu-tion of refrigerated air; sensitive and properlylocated controls; enough refrigerated coilsurface to minimize the difference between

the coil and air temperatures; and adequatecapacity for expected needs. Commoditiesshould be stacked in the cold room with air

spaces between pallets and room walls to

Relative

Temperature velocity of Relative loss per day(OF) (°C) Assumed Q1O' deterioration shelf life (%)----------- --- -------------------- ------------------ ---------- - --------------

32 0 1.0 100 150 10 3.0 3.0 33 368 20 2.5 7.5 13 886 30 2.0 15.0 7 14

104 40 1.5 22.5 4 25

44 CHAPTER 4

ensure good air circulation. Storage roomsshould not be loaded beyond their limit forproper cooling. In monitoring temperatures,commodity temperature rather than air tem-perature should be measured.

Transit vehicles must be cooled before

loading the commodity. Delays between cool-ing after harvest and loading into transitvehicles should be avoided. Proper tempera-ture maintenance should be ensured

throughout the handling system.

CONTROL OF RELATIVE HUMIDITY

Relative humidity can influence water loss,decay development, incidence of some phys-iological disorders, and uniformity of fruitripening. Condensation of moisture on thecommodity (sweating) over long periods oftime is probably more important in enhanc-ing decay than is the RH of ambient air.Proper relative humidity is 85 to 95% forfruits and 90 to 98% for vegetables exceptdry onions and pumpkins (70 to 75%).Some root vegetables can best be held at 95to 100% RH.

Relative humidity can be controlled byone or more of the following procedures:. adding moisture (water mist or spray,

steam) to air by humidifiers. regulating air movement and ventilationin relation to the produce load in the coldstorage room. maintaining the refrigeration coils withinabout 1DC (2DF) of the air temperature. providing moisture barriers that insulatestorage room and transit vehicle walls;adding polyethylene liners in containersand plastic films for packaging. wetting floors in storage rooms. adding crushed ice in shipping containersor in retail displays for commodities thatare not injured by the practice. sprinkling produce with water duringretail marketing (use on leafy vegetables,cool-season root vegetables, and immaturefruit vegetables such as snap beans, peas,sweet corn, summer squash

SUPPLEMENT TEMPERATUREMANAGEMENT

Many technological procedures are usedcommercially as supplements to temperaturemanagement. None of these procedures,alone or in their various combinations, cansubstitute for maintenance of optimal tem-

perature and RH, but they can help extendthe shelf life of harvested produce beyondwhat is possible using refrigeration alone(table 4.6).

Treatments applied to commodities include. curing of certain root, bulb, and tubervegetables. cleaning followed by removal of excesssurface moisture. sorting to eliminate defects. waxing and other surface coatings, includ-ing film wrapping. heat treatments (hot water or air, vaporheat). treatment with postharvest fungicides. sprout inhibitors. special chemical treatments (scaldinhibitors, calcium, growth regulators,anti-ethylene chemicals for ornamentals). fumigation for insect control. ethylene treatment (de-greening, ripening)

Treatments to manipulate the enviro~-ment include. packaging. control of air movement and circulation

. control of air exchange or ventilation. exclusion or removal of C2H4. controlled or modified atmospheres .(CAor MA) i

. sanitation

RECENT TRENDS INPERISHABLES HANDLING

SELECTION OF CULTIVARS

For many commodities, producers are usingcultivars with superior quality and/or longpostharvest life, such as "super-sweet" sweetcorn, long-shelf-life tomatoes, and sweetermelons. Plant geneticists in public and pri-vate institutions are using molecular biologymethods along with plant breeding proce-dures to produce new genotypes that tastebetter, maintain firmness better, are moredisease resistant, have less browning poten-tial, and have other desirable characteristics.

PACKING AND PACKAGING

The produce industry is increasingly usingplastic containers that can be reused andrecycled in order to reduce waste disposalproblems. For example, standard-sized (4,8by 40 in., about 120 by 100 cm) stacking(returnable) pallets are becoming more

widely used. There is continued increase inuse of modified atmosphere and controlledatmosphere packaging (MAP and CAP) sys-tems at the pallet, shipping container (fiber-board box liner), and consumer package lev-els. Also, the use of absorbers of CZH4' COz,Oz', and/or water vapor as part of MAP andCAP is increasing.

COOLING AND STORAGE

The current trend is towards increased pre-cision in temperature and relative humidity(RH) management to provide the optimalenvironment for fresh fruits and vegetablesduring cooling and storage. Precision tem-perature management (PTM) tools arebecoming more common in cooling andstorage facilities. Forced-air cooling contin-ues to be the predominant cooling methodfor horticultural perishables. Operators canensure that all produce shipments leave the

Table 4.6. Freshhorticultural cropsclassifiedaccordingto relative per-ishability and potential storage life in air at near-optimal temperatureand RH

Relative

perishability

Potential

storage life(weeks) Commodities

~~---~ ~.-~--- ~~--~-~ ~---~-_. ~--~--- - -

<2 Apricot,blackberry,blueberry,cherry,fig,raspberry,strawberry;asparagus,beansprouts,broccoli,cauliflower,cantaloupe,greenonion,leaf lettuce,mushroom,pea,spinach,sweetcorn,tomato(ripe);mostcut flowersandfoliage;fresh-cut(mini-mallyprocessed)fruits andvegetables

Avocado,banana,grape(without 502treatment),guava,loquat,mandarin,mango,melons(honeydew,crenshaw,Persian),nectarine,papaya,peach,pepino,plum;artichoke,greenbeans,Brusselssprouts,cabbage,celery,egg-plant,headlettuce,okra,pepper,summersquash,tomato(partiallyripe)

Appleandpear(somecultivars),grape(504-treated),orange,grapefruit,lime,kiwifruit, persimmon,pomegranate,pummelo;tablebeet,carrot,radish,pota-to (immature)

Veryhigh

High

Moderate

Low

Verylow

2-4

4-8

8-16 Appleandpear(somecultivars),lemon,

potato (mature),dryonion,garlic,pump-kin,winter squash,sweetpotato,taro,yam;bulbsandotherpropagulesof orna-mentalplants

Treenuts,driedfruits andvegetables>16


cooling facility within O.5°C (about 1°F) ofthe optimal storage temperature. Periodicventilation of storage facilities is effective inmaintaining CZH4 concentrations below 1ppm, which permits mixing of temperature-compatible, ethylene-producing, and ethyl-ene-sensitive commodities.

POSTHARVEST INTEGRATED PEST

MANAGEMENT (I PM)Controlled atmosphere (CA) conditionsdelay senescence, including fruit ripening,and consequently reduce the susceptibility offruits to pathogens. On the other hand, CAconditions unfavorable to a given commodi-ty can induce physiological breakdown andrender it more susceptible to pathogens.Calcium treatments have been shown to

reduce decay incidence and severity; woundhealing following physical injury has been.observed in some fruits and has reduced

their susceptibility to decay Biological con-trol agents are being used alone or in comQi-nation with reduced concentrations of

postharvest fungicides, heat treatments,and/or fungistatic CA for control of posthar-vest diseases.

Chemical fumigants, especially methylbromide, are still the primary method used.for insect control in harvested fruits when.

such treatment is required by quarantineauthorities in importing countries. Manystudies are under way to develop alternativemethods of insect control that are effective,

not phytotoxic to the fruits, and present nohealth hazard to the consumer. These alter-

natives include cold treatments, hot water or

air treatments, ionizing radiation (0.15-0.30kilo gray) and exposure to reduced (less than0.5%) Oz and/or elevated CO2 (40-60%)atmospheres. This is a high-priority researchand development area because of the possi-ble loss of methyl bromide as an option forinsect control.

USE OF CONTROLLED AND MODIFIEDATMOSPHERES

The use of CA during transport and/or stor-age of fresh fruits and vegetables (marketedintact or lightly processed) continues toexpand because of improvements in nitro-gen-generation equipment and in instru-ments for monitoring and maintainingdesired concentrations of oxygen and carbondioxide. Controlled atmosphere is a useful

46 CHAPTER 4

supplement to the proper maintenance ofoptimal temperature and RH during trans-port and storage of many fresh fruits andvegetables. It allows use of marine transportinstead of air transport of some commodities.

Several refinements in CA storage havebeen made in recent years to improve qualitymaintenance. These include creating nitro-gen by separation from compressed air usingmolecular sieve beds or membrane systems;low O2 (1.0-1.5%) storage; low ethylene CAstorage; rapid CA (rapid establishment of theoptimal levels of O2 and CO2); and pro-grammed (or sequential) CA storage (e.g.,storage in 1% O2 for 2 to 6 weeks followedby storage in 2 to 3% O2 for the remainder ofthe storage period). Other developments,which may expand use of MA during trans-port and distribution, include using ediblecoatings or polymeric films with appropriategas permeabilities to create a desired MAaround and within the commodity. Modifiedatmosphere packaging is widely used in mar-keting fresh-cut fruits and vegetables.

Successful application of atmosphericmodification depends on the commodity,cultivar, maturity stage at harvest, and a posi-tive return on investment (benefit-cost ratio).

Commercial use of CA storage is greatestworldwide on apples and pears; less onkiwifruits, avocados, persimmons, pomegran-ates, nuts, and dried fruits and vegetables.Atmospheric modification during long-dis-tance transport is used on apples, asparagus,avocados, bananas, broccoli, cane berries,

cherries, figs, kiwifruits, mangoes, melons,nectarines, peaches, pears, plums, and straw-berries. Continued technological develop-ments in the future to provide CA duringtransport and storage at a reasonable cost areessential to greater CA applications on freshfruits and vegetables.

TRANSPORTATION

Improvements are continually being made inattaining and maintaining the optimal envi-ronmental conditions (temperature, RH, andconcentrations of O2, CO2, and C2H4) intransport vehicles. Produce is commonlycooled before loading and is loaded with anair space between the palletized produce andthe walls of the transport vehicles to improvetemperature maintenance. In some cases,vehicle and produce temperature data aretransmitted by satellite to a control center,

allowing all shipments to be continuouslymonitored. Some new trucks have air ride

suspension, which can eliminate transportvibration damage. As the industry realizes thevalue of air ride, its popularity will increase.

HANDLING AT WHOLESALE AND RETAILWholesale and retail markets have been

increasingly using automated ripening, inwhich the gas composition of the ripeningatmosphere, the room temperature, and fruitcolor are continuously monitored and modu-lated to meet desired ripening characteristics.Improved ripening systems will lead togreater use of ripening technology to deliverproducts that are ripened to the ideal eatingstage. Better-refrigerated display units, withimproved temperature and RH monitoringand control systems, are being used in retailmarkets, especially for fresh-cut fruit and veg-etable products. Many retail and food serviceoperators are using Hazard Analysis CriticalControl Points (HACCP) Programs to a~sureconsumers that food products are safe.

FOOD SAFETY ASSURANCE

During the past few years, food safety becameand continues to be the number-one concern

of the fresh produce industry. U.S. tradeorganizations such as the International Presh-Cut Produce Association (IFPA), Produce

Marketing Association (PMA), United FreshFruit and Vegetable Association (UFFVA),and Western Growers Association (WGA)

have taken an active role in developing vol-untary food safety guidelines for producersand handlers of fresh fruits and vegetables.The U.S. Food and Drug Administration(FDA) published in October 1998 the Guideto Minimize Microbial Food Safety Hazards for

Fresh Fruits and Vegetables. This guide shouldbe used by all handlers of fresh produce todevelop the most appropriate agricultural andmanagement practices for their operations.

The FDA guide is based on the followingbasic principles and practices associated withminimizing microbial food safety hazardsfrom the field through distribution of freshfruits and vegetables.

Principle 1. Prevention of microbial conta-mination of fresh produce is favored overreliance on corrective actions once contami-

nation has occurred. ,

Principle 2. To minimize microbial foodsafety hazards in fresh produce, growers,

packers, or shippers should use good agricul-tural and management practices in thoseareas over which they have control.

Principle 3. Fresh produce can becomemicrobiologically contaminated at any pointalong the farm-to-table food chain. Themajor source of microbial contamination offresh produce i5 associated with human oranimal feces.

Principle 4. Whenever water comes in

contact with produce, the quality of thewater dictates the potential for contamina-tion. Minimize the potential of microbialcontamination from water used with fresh

fruits and vegetables.Principle 5. Practices using animal

manure or municipal biosolid wastes should

be managed closely to minimize the potentialfor microbial contamination of fresh produce.

Principle 6. Worker hygiene and sanita-tion practices during production, harvesting,sorting, packing, and transport playa criticalrole in minimizing the potential for micro-bial contamination of fresh produce.

Principle 7. Follow all applicable local,state, and federal laws and regulations orcorresponding or similar laws, regulations, orstandards for operators outside the UnitedStates, for agricultural practices.

REFERENCES

Brady, C. j. 1987. Fruit ripening. Annu. Rev. Plant

Physiol. 38:155-178.

Cappellini, R. A., and M.j. Ceponis. 1984. Posthar-

vest losses in fresh fruits and vegetables. In H. E.

Moline, ed., Postharvest pathology of fruits and

vegetables: Postharvest losses in perishable

crops. Oakland: Univ. Calif. Bull. 1914.24-30.

Giovannoni, j. 2001. Molecular biology of fruit matu-

ration and ripening. Annu. Rev. Plant Physiol.Plant Mol. BioI. 52:725-749.

Grierson, D. 1987. Senescence in fruits. HortScience22:859-862.

Harvey, j. M. 1978. Reduction oflosses in fresh mar-

ket fruits and vegetables. Annu. Rev. Phy-

topathol. 16:321-341.

International Institute of Refrigeration. 2000. Recom-

mendations for chilled storage of perishable pro-


duce. Paris: International Institute of Refrigera-

tion. 219 pp

Kader, A. A. 1983. Postharvest quality maintenance

of fruits and vegetables in developing countries.

In M. Lieberman, ed., Postharvest physiologyand crop preservation. New York: Plenum.520-536.

Kantor, L S., K. Lipton, A. Manchester. and V

Oliveira. 1997. Estimating and addressing Amer-ica's food losses. Food Review 20:3-11.

Kitinoja, L, and A. A. Kader 1995. Small-scale

postharvest handling practices: A manual for

horticultural crops. 3rd ed. Davis: Univ. Calif.

Postharv. Hort. SeT 8. 231 pp.

Kitinoja, L, andj. R. Gorny. 1999. Postharvest tech-

nology for small-scale produce marketers: Eco-

nomic opportunities, quality and food safety.Davis: Univ. Calif. Postharv. Hort. SeT 21.

Lidster, PD., P D. Hilderbrand, L S. Berard, and S.

W Porritt. 1988. Commercial storage of fruits

and vegetables. Can. Dept. Agric. Pub I. 1532.88 pp.

Lipton, W j. 1987. Senescence in leafy vegetables.HortScience 22:854-859.

Mayak, S. 1987. Senescence in cut flowers.HortScience 22:863-865.

National Academy of Sciences. 1978. Postharvest

food losses in developing countries (Science and

Technology for International Development).

Washington, D.c.: Natl. Acad. Sci. 202 pp.

Rhodes, M. j. C. 1980a. The maturation and ripeningof fruits. In K. V Thimann, ed., Senescence in

plants. Boca Raton, FL: CRC Press. 157-205.

-. 1980b. The physiological basis for the con-

servation of food crops. Prog. Food NUlr Sci.4(3-4): 11-20.

Romani, R. j. 1987. Senescence and homeostasis in

postharvest research. HortScience 22:865-868.Shewfelt, R. L 1986. Postharvest treatment for

extending the shelf-life of fruits and vegetables.Food Technol. 40(5): 70-89.

Tindall, H. D., and F j. Proctor 1980. Loss preven-

tion of horticultural crops in the tropics. Prog.Food Nutr Sci. 4(3-4): 25-40.

United Nations Food and Agriculture Organization

(FAO) 1981. Food loss prevention in perishable

crops. FAO Agric. Serv. Bull. 43. 72 pp.

Wang, C. Y, ed. 1990. Chilling injury of horticultural

crops. Boca Raton, FL: CRC Press. 313 pp.

techniques that delay senescence and maintain the...

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