1. Abdul MoizAbdul Moiz Dept of Food EngineeringDept of Food Engineering U.A.FU.A.F OnOn Fruit & Vegetable ProcessingFruit & Vegetable Processing PostharvestPostharvest 11

2. 22 Fruit & Vegetable ProcessingFruit & Vegetable Processing Postharvest PhysiologyPostharvest Physiology I. INTRODUCTIONI. INTRODUCTION Fruits and vegetables when harvested fromFruits and vegetables when harvested from vines or plants are living structures,vines or plants are living structures, continuing metabolic reactions and sustainingcontinuing metabolic reactions and sustaining physiological processes for a considerable timephysiological processes for a considerable time during their postharvest period.during their postharvest period. Fruits and vegetables respire by taking upFruits and vegetables respire by taking up oxygen, and giving off carbon dioxide andoxygen, and giving off carbon dioxide and generating heat;generating heat; they also transpire, i.e., lose water in vaporthey also transpire, i.e., lose water in vapor form.form. 3. 33 The respiration and transpiration lossesThe respiration and transpiration losses are made up by replenishing water,are made up by replenishing water, photosynthates (sucrose and aminophotosynthates (sucrose and amino acids), and minerals from the time-flowacids), and minerals from the time-flow of cell sap while fruits and vegetables areof cell sap while fruits and vegetables are attached to the plants or vines.attached to the plants or vines. Subsequent to harvest, the source ofSubsequent to harvest, the source of water, photosynthates and minerals arewater, photosynthates and minerals are cut off, and they enter into a deteriorationcut off, and they enter into a deterioration or perishable phase.or perishable phase. 4. 44 Several changes take place in cell-wallSeveral changes take place in cell-wall composition and structure that result in thecomposition and structure that result in the softening of the fruits and vegetables.softening of the fruits and vegetables. In general, visual color gradually changes asIn general, visual color gradually changes as chlorophyll is degraded and yellow pigment ofchlorophyll is degraded and yellow pigment of the skin and flesh increases in content.the skin and flesh increases in content. In fruits and vegetables respiration involves theIn fruits and vegetables respiration involves the enzymatic oxidation of sugars to carbon dioxideenzymatic oxidation of sugars to carbon dioxide (C0(C022) and water, accompanied by release of) and water, accompanied by release of energy.energy. However, other substances such as organic acidsHowever, other substances such as organic acids and proteins also enter the respiratory chain.and proteins also enter the respiratory chain. 5. 55 Consequently, the loss of these reserves in fruitsConsequently, the loss of these reserves in fruits and vegetables results in the production ofand vegetables results in the production of energy and the accompanying need for oxygenenergy and the accompanying need for oxygen (0,) and removal of CO,.(0,) and removal of CO,. Cellular water is lost because of respiration andCellular water is lost because of respiration and transpiration, resulting in fruits and vegetablestranspiration, resulting in fruits and vegetables becoming soft, shriveled, and limp.becoming soft, shriveled, and limp. Anthocyanins that give the typical red, orange,Anthocyanins that give the typical red, orange, blue, and other pigments of some fruits andblue, and other pigments of some fruits and vegetables may increase after harvest.vegetables may increase after harvest. 6. 66 Apples, plums, pumpkins, and others enhanceApples, plums, pumpkins, and others enhance color development in a packaging shed or in acolor development in a packaging shed or in a refrigerator.refrigerator. The skins of some fruits and vegetables developThe skins of some fruits and vegetables develop bloom or waxes after harvest that gives them anbloom or waxes after harvest that gives them an attractive appearance which may aid in reducingattractive appearance which may aid in reducing transpirational losses.transpirational losses. Starchy fruits and vegetables undergo aStarchy fruits and vegetables undergo a decrease in starch and increase in sugar anddecrease in starch and increase in sugar and acids after harvest.acids after harvest. However, there may be changes in the kinds ofHowever, there may be changes in the kinds of acids present.acids present. 7. 77 In certain cases as maturity advances, astringencyIn certain cases as maturity advances, astringency decreases caused by tannins or polyphenols.decreases caused by tannins or polyphenols. Volatiles and aroma components of many kinds ofVolatiles and aroma components of many kinds of fruits and vegetables are produced after harvest iffruits and vegetables are produced after harvest if they are mature or ripe.they are mature or ripe. However, when they are harvested rather immatureHowever, when they are harvested rather immature or at the green stage for distant shipment, theyor at the green stage for distant shipment, they do not yield typical aroma.do not yield typical aroma. For example, if Jordanian peaches are harvestedFor example, if Jordanian peaches are harvested for shipment to Kuwait market they do not developfor shipment to Kuwait market they do not develop as good aroma as when allowed to mature andas good aroma as when allowed to mature and ripen on the tree.ripen on the tree. 8. 88 Ethylene is one of the volatiles synthesized in certainEthylene is one of the volatiles synthesized in certain fruits and vegetables at certain stages of maturity andfruits and vegetables at certain stages of maturity and development; when it reaches a high enoughdevelopment; when it reaches a high enough concentration, it triggers the ripening process and moreconcentration, it triggers the ripening process and more ethylene is produced and the process of ripening isethylene is produced and the process of ripening is accelerated.accelerated. Growth, development. prematuration, maturation,Growth, development. prematuration, maturation, ripening, and senescence (Figure 1) are the mostripening, and senescence (Figure 1) are the most important phases in fruit and vegetable ontology.important phases in fruit and vegetable ontology. The growth of fruits and vegetables begins with cellThe growth of fruits and vegetables begins with cell division and cell enlargement, which accounts for thedivision and cell enlargement, which accounts for the final size.final size. 9. 99 10. 1010 Growth and maturation is referred to as fruitGrowth and maturation is referred to as fruit development.development. Senescence is the period when anabolic andSenescence is the period when anabolic and biochemical processes give way to catabolicbiochemical processes give way to catabolic processesleading to aging and final death of theprocessesleading to aging and final death of the tissue.tissue. Ripening generally begins during the later stagesRipening generally begins during the later stages of maturation and is considered the beginning ofof maturation and is considered the beginning of senescence.senescence. The relative changes in weight, sugars,The relative changes in weight, sugars, chlorophyll, and acidity are common to most fruitschlorophyll, and acidity are common to most fruits and vegetables (Figure 2) but other parametersand vegetables (Figure 2) but other parameters such as respiration, flavor, aroma, and carotenoidssuch as respiration, flavor, aroma, and carotenoids can vary from commodity to commodity.can vary from commodity to commodity. 11. 1111 12. 1212 II. RESPIRATIONII. RESPIRATION Respiration of fruits and vegetables is an indexRespiration of fruits and vegetables is an index of physiological activity and potent storage life.of physiological activity and potent storage life. It is one of the basic processes of life andIt is one of the basic processes of life and directly related to maturation, handling,directly related to maturation, handling, transportation, and subsequently, storage life.transportation, and subsequently, storage life. Respiration of fruits and vegetables involves theRespiration of fruits and vegetables involves the enzymatic oxidation of sugars to carbon dioxide,enzymatic oxidation of sugars to carbon dioxide, water, and release of energy (Figure 3).water, and release of energy (Figure 3). 13. 1313 Other substrates such as organic acids, fats, andOther substrates such as organic acids, fats, and proteins also play an important roleproteins also play an important role duringduring thethe process of respirarion.process of respirarion. The energy produced by the oxidation of sugarsThe energy produced by the oxidation of sugars is convened into the energy of adenosineis convened into the energy of adenosine triphosphate (ATP), as an energy carrier.triphosphate (ATP), as an energy carrier. The oxidation of sugars takes place in severalThe oxidation of sugars takes place in several steps under control of specific enzymes. A simplesteps under control of specific enzymes. A simple formula for respiration may be as follows:formula for respiration may be as follows: Sugar + 60Sugar + 6022 > 6C0> 6C022 ++ 6H6H2200 ++ EnergyEnergy 14. 1414 As indicated above this respiration of fruits andAs indicated above this respiration of fruits and vegetables involves the following aspects:vegetables involves the following aspects: 1.1. Substrate:Substrate: the quantity of substratethe quantity of substrate (predominantly sugars) in fruits and vegetables(predominantly sugars) in fruits and vegetables available for respiration is a deciding factor foravailable for respiration is a deciding factor for their longevity at that temperate.their longevity at that temperate. The weight loss due to increased temperature andThe weight loss due to increased temperature and respiration usually is more than to five percentrespiration usually is more than to five percent depending upon the structure of the fruits anddepending upon the structure of the fruits and vegetables.vegetables. 15. 1515 2.2. OxygenOxygen: the supply of 0: the supply of 022, for normal, for normal respiration is generally adequate unlessrespiration is generally adequate unless intentionally restricted as in the case ofintentionally restricted as in the case of CA (Controlled Atmosphere) StorageCA (Controlled Atmosphere) Storage.. 3.3. Carbon DioxideCarbon Dioxide: removal of: removal of respiratory COrespiratory CO22 requires more attentionrequires more attention than supply of 0than supply of 022 because CObecause CO22 may be inmay be in excess even when supply ofexcess even when supply of 0022 isis adequate.adequate. 16. 1616 A three to five percent reductions of 0A three to five percent reductions of 022 concentration would not have an adverse effectconcentration would not have an adverse effect on a product, but a comparable increase in COon a product, but a comparable increase in CO22 could suffocate and ruin certain fruits andcould suffocate and ruin certain fruits and vegetables.vegetables. 4.4. EnergyEnergy: removal of heat from respiration is: removal of heat from respiration is vitally important; otherwise the life of fruitsvitally important; otherwise the life of fruits and vegetables will be reduced to an increasedand vegetables will be reduced to an increased temperature around the commodity.temperature around the commodity. Increase in rate of respiration causesIncrease in rate of respiration causes acceleration of substrate utilization.acceleration of substrate utilization. 17. 1717 5.Rate of Respiration5.Rate of Respiration: The rate of respiration: The rate of respiration determines the quantity of 0determines the quantity of 022 that must he availablethat must he available per unit of time.per unit of time. The quantities ofThe quantities of COCO22 removed at he same time.removed at he same time. Increased rate of respiration will reduce theIncreased rate of respiration will reduce the storage life of product.storage life of product. Rate of respiration is a function ofRate of respiration is a function of temperaturetemperature and available concentration of 0and available concentration of 022 around the fruitsaround the fruits and vegetables.and vegetables. 18. 1818 In addition. some fruits such as potatoes willIn addition. some fruits such as potatoes will have a lower rate of respiration than spinachhave a lower rate of respiration than spinach or lettuce due to inherent substrate availableor lettuce due to inherent substrate available for respiration and the anatomical variationsfor respiration and the anatomical variations of the commodities.of the commodities. The rate of respiration can he defined as theThe rate of respiration can he defined as the weight of COweight of CO22 produced per unit fresh weightproduced per unit fresh weight and time (mg COand time (mg CO22/kg/h) (Table 1)./kg/h) (Table 1). The rate of respiration may be expressed inThe rate of respiration may be expressed in ml COml CO22/kg/h or the quantity of 0/kg/h or the quantity of 022 taken uptaken up rather than COrather than CO22 given out.given out. 19. 1919 20. 2020 21. 2121 22. 2222 The classification of the rate of respiration isThe classification of the rate of respiration is presented in Table 2.presented in Table 2. 6. Initial Rate of Respiration6. Initial Rate of Respiration: the rate of: the rate of prevailing respiration or within a few hoursprevailing respiration or within a few hours varies depending upon crop and temperature)varies depending upon crop and temperature) 7.7. Average Rate of RespirationAverage Rate of Respiration: It is: It is determined by measuring rates at a definitedetermined by measuring rates at a definite time interval, summing the rates thustime interval, summing the rates thus determined, and dividing by the number ofdetermined, and dividing by the number of intervals involved.intervals involved. 23. 2323 24. 2424 8.8. Effects of Temperature and Days in StorageEffects of Temperature and Days in Storage on Rate of Respiration:on Rate of Respiration: the rate of respirationthe rate of respiration generally increases as the temperature and thegenerally increases as the temperature and the storage duration of fruits and vegetables increases.storage duration of fruits and vegetables increases. However, at very high temperatures and at the veryHowever, at very high temperatures and at the very long storage duration, the rate of respirationlong storage duration, the rate of respiration decreases until the death of products. However, onedecreases until the death of products. However, one does not store fresh commodities at such highdoes not store fresh commodities at such high temperatures (Figures 4 and 4A).temperatures (Figures 4 and 4A). 9.9. Effects of Commodity on Rate of RespirationEffects of Commodity on Rate of Respiration:: the rate of respiration varies depending uponthe rate of respiration varies depending upon commodity and variety, also the commodity willcommodity and variety, also the commodity will vary with other varieties of the same commodity.vary with other varieties of the same commodity. 25. 2525 26. 2626 27. 2727 10.10. Maturity of Fruits and Vegetables onMaturity of Fruits and Vegetables on Respiration Rate:Respiration Rate: fruits and vegetables harvested atfruits and vegetables harvested at early maturity for distant market respire faster thanearly maturity for distant market respire faster than those harvested at the firm-ripe maturity.those harvested at the firm-ripe maturity. 11.11. Vant Hoffs LawVant Hoffs Law: this law indicates that the rate: this law indicates that the rate of chemical reaction is controlled by temperature.of chemical reaction is controlled by temperature. He coined the termHe coined the term QQ1010..This indicates at each 10CThis indicates at each 10C rise in temperature, the rate of reaction doubles.rise in temperature, the rate of reaction doubles. However,However, QQ1010 for respiration may not always befor respiration may not always be doubled; sometimes it may be more than doubleddoubled; sometimes it may be more than doubled depending upon the maturity and anatomical structuredepending upon the maturity and anatomical structure of the fruits or vegetables.of the fruits or vegetables. 28. 2828 Postharvest physiology is influenced byPostharvest physiology is influenced by preharvest factors on the farm or in the orchard.preharvest factors on the farm or in the orchard. Physiology of fruits and vegetables begins at thePhysiology of fruits and vegetables begins at the time of blossoming or bud formation and istime of blossoming or bud formation and is affected by agricultural practicesfertilization,affected by agricultural practicesfertilization, variety, and irrigationand by environmentalvariety, and irrigationand by environmental factors such as sunlight duration and quality,factors such as sunlight duration and quality, temperature, humidity, etc.temperature, humidity, etc. The genetics of fruits and vegetables determineThe genetics of fruits and vegetables determine postharvest storage life. Those crops that arepostharvest storage life. Those crops that are most perishable such as lettuce, spinach,most perishable such as lettuce, spinach, strawberries and raspberries have a short growingstrawberries and raspberries have a short growing season life.season life. 29. 2929 In contrast, Winesap apples whichIn contrast, Winesap apples which require 160 to 170 days to developrequire 160 to 170 days to develop have a longer storage life.have a longer storage life. Summer cultivars of apples generallySummer cultivars of apples generally have a shorter storage life becausehave a shorter storage life because they ripen earlier.they ripen earlier. Likewise, early summer apples have aLikewise, early summer apples have a higher respiration rate than fall apples;higher respiration rate than fall apples; they also have a greater number ofthey also have a greater number of cells, more lenticels, and give off morecells, more lenticels, and give off more ethylene.ethylene. 30. 3030 However, one should not conclude thatHowever, one should not conclude that the differences in storage life of fruits andthe differences in storage life of fruits and vegetables can be explained simply byvegetables can be explained simply by length of growing season, respiration rate,length of growing season, respiration rate, or amount of ethylene released.or amount of ethylene released. It involves genetic factors which controlIt involves genetic factors which control growth, development. postharvestgrowth, development. postharvest behavior, and physiological andbehavior, and physiological and morphological variations.morphological variations. 31. 3131 Ill. TEMPERATURE QUOTIENT OF RESPIRATIONIll. TEMPERATURE QUOTIENT OF RESPIRATION The temperature quotientThe temperature quotient (Q(Q1010)) is notis not the same for all fruits andthe same for all fruits and vegetables, nor will it bvegetables, nor will it be the same fore the same for another variety of the same fruit.another variety of the same fruit. The example is presented in Table 3.The example is presented in Table 3. As a general rule, it can be said that anAs a general rule, it can be said that an apple or pear will ripen as much in a day atapple or pear will ripen as much in a day at 21 C as it will in a week at 0 C.21 C as it will in a week at 0 C. 32. 3232 33. 3333 Thus it is apparent that refrigeration is anThus it is apparent that refrigeration is an effective means of extending the commercial life ofeffective means of extending the commercial life of fresh produce.fresh produce. Fruit growers and shippers have learned by practicalFruit growers and shippers have learned by practical experience that the growing season has a powerfulexperience that the growing season has a powerful influence on the storage age of fruits.influence on the storage age of fruits. For example, it has been recognized that t isFor example, it has been recognized that t is hazardous to store or to ship Bartlett pears grown inhazardous to store or to ship Bartlett pears grown in cool coastal areas to distant places, because they oftencool coastal areas to distant places, because they often develop core breakdowna physiological disorderdevelop core breakdowna physiological disorder that makes pears too soft and mushy.that makes pears too soft and mushy. 34. 3434 Some cultivars of apples grown in coolSome cultivars of apples grown in cool climates cannot tolerate storage temperature ofclimates cannot tolerate storage temperature of 0 C and must be stored at higher temperatures0 C and must be stored at higher temperatures such as (2.24.4 C) Insuch as (2.24.4 C) In order to avoid loworder to avoid low temperature breakdown.temperature breakdown. Sweet as well as sour cherries develop scaldSweet as well as sour cherries develop scald when weather in is unusually warm and drywhen weather in is unusually warm and dry during the several weeks before harvestduring the several weeks before harvest Chemical reactions of respiration areChemical reactions of respiration are controlled by temperature and ideally, onecontrolled by temperature and ideally, one could expect acould expect a QQ1010 of about 2.5of about 2.5 for respiration.for respiration. 35. 3535 This means that for a 10C rise in temperature,This means that for a 10C rise in temperature, the respiration would double.the respiration would double. Rapidly growing young tissue respires fasterRapidly growing young tissue respires faster than that which develops slowly.than that which develops slowly. The rate of respiration of asparagus is one ofThe rate of respiration of asparagus is one of the highest rates of all fruits and vegetablesthe highest rates of all fruits and vegetables because of the rapidly growing shoots of thebecause of the rapidly growing shoots of the plant.plant. 36. 3636 Fruits and vegetables vary in respiration rates andFruits and vegetables vary in respiration rates and there are differences between cultivars and theirthere are differences between cultivars and their maturitiesso it is not to be expected that thematuritiesso it is not to be expected that the respiration rate will be a fixed value at any givenrespiration rate will be a fixed value at any given temperature.temperature. It tends to be more constant at temperatures of (0 toIt tends to be more constant at temperatures of (0 to 4.4C) than at higher temperatures of (21.1 to4.4C) than at higher temperatures of (21.1 to 26.7C).26.7C). At the temperature range (0 4.4C), where fruitsAt the temperature range (0 4.4C), where fruits and vegetables are held the longest-time, their heat ofand vegetables are held the longest-time, their heat of respiration is a factor to be included in calculating therespiration is a factor to be included in calculating the refrigeration requirements for refrigeration storagerefrigeration requirements for refrigeration storage and transportation.and transportation. 37. 3737 In the case of fruits and vegetables, after harvest, fastIn the case of fruits and vegetables, after harvest, fast cooling is generally desirable especially forcooling is generally desirable especially for perishable soft fruits such as berries and leafyperishable soft fruits such as berries and leafy vegetables.vegetables. This not only reduces metabolic activity of fruits andThis not only reduces metabolic activity of fruits and vegetables, but also controls fruit decay.vegetables, but also controls fruit decay. Fungi and other microorganisms increase rates ofFungi and other microorganisms increase rates of respiration as do bruises and mechanical injuries;respiration as do bruises and mechanical injuries; the most serious consequences of holding fruits andthe most serious consequences of holding fruits and vegetables at high temperature is the hastening ofvegetables at high temperature is the hastening of ripening, and shortening of storage and marketingripening, and shortening of storage and marketing life.life. 38. 3838 Climacteric and nonclimacteric fruits and vegetablesClimacteric and nonclimacteric fruits and vegetables A large number of fruits and vegetablesA large number of fruits and vegetables show a sudden and sharp rise inshow a sudden and sharp rise in respiratory activity called the climactericrespiratory activity called the climacteric rise during the life cycle;rise during the life cycle; whereas others which do not showwhereas others which do not show climacteric rise are called nonclimactericclimacteric rise are called nonclimacteric fruits and vegetables.fruits and vegetables. 39. 3939 The time of harvest for climacteric fruits andThe time of harvest for climacteric fruits and vegetables is critical for their maximumvegetables is critical for their maximum storage life and quality.storage life and quality. Non-clirnacteric fruits and vegetables areNon-clirnacteric fruits and vegetables are allowed to ripen on plants or vines and theallowed to ripen on plants or vines and the resulting maturity is regulated by storage.resulting maturity is regulated by storage. Maturity tests such as color, brix, acidity, andMaturity tests such as color, brix, acidity, and others are employed to determine whether theyothers are employed to determine whether they can meet standard grades and can be legallycan meet standard grades and can be legally sold.sold. 40. 4040 The classification of edible fruits and vegetablesThe classification of edible fruits and vegetables according to their respiration patternaccording to their respiration pattern 41. 4141 Respiratory patterns vary from growth andRespiratory patterns vary from growth and development and also from fruit to fruit and vegetabledevelopment and also from fruit to fruit and vegetable to vegetable;to vegetable; most leafy vegetables are of non-climacteric naturemost leafy vegetables are of non-climacteric nature (Figure 5).(Figure 5). Respiration is not merely a catabolic process, but itRespiration is not merely a catabolic process, but it provides energy to synthesize enzymes, cellprovides energy to synthesize enzymes, cell membrane constituents, and other material necessarymembrane constituents, and other material necessary for life of the cell.for life of the cell. It takes place within the cell at the site of the variousIt takes place within the cell at the site of the various enzymes that participate in the process of respiration.enzymes that participate in the process of respiration. 42. 4242 43. 4343 Respiration and ripening can be retarded by reducingRespiration and ripening can be retarded by reducing the amount of Othe amount of O2.2. Ethylene, if OEthylene, if O22 is present, will increase the respirationis present, will increase the respiration rates and other metabolic processes as well.rates and other metabolic processes as well. The ethylene may come from the fruit or theThe ethylene may come from the fruit or the vegetable itself or be added to the atmosphere.vegetable itself or be added to the atmosphere. In a fruit or a vegetable that has climacteric rise inIn a fruit or a vegetable that has climacteric rise in respiration, ethylene treatment initiates the riserespiration, ethylene treatment initiates the rise earlier, but the rates reach no higher levels.earlier, but the rates reach no higher levels. The climacteric in respiration of certain fruitsThe climacteric in respiration of certain fruits generally occur at the onset of processes involved ingenerally occur at the onset of processes involved in ripening.ripening. The peak of respiration does not always coincide withThe peak of respiration does not always coincide with peak of ripening.peak of ripening. 44. 4444 IV. ETHYLENE PRODUCTION AND EFFECTSIV. ETHYLENE PRODUCTION AND EFFECTS The Chinese knew in ancient times that pearsThe Chinese knew in ancient times that pears could be ripened by exposing them to the smokecould be ripened by exposing them to the smoke of incense burned in closed rooms.of incense burned in closed rooms. Many years ago in Florida and California, orangesMany years ago in Florida and California, oranges were colored or more correctly degreened bywere colored or more correctly degreened by exposure to fumes from kerosene stoves orexposure to fumes from kerosene stoves or exhaust from a gasoline engine in a specialexhaust from a gasoline engine in a special coloring room.coloring room. Ethylene is the active degreening agent in stoveEthylene is the active degreening agent in stove gas and a concentration of 4 ppm would degreengas and a concentration of 4 ppm would degreen lemons in 6 to 8 d.lemons in 6 to 8 d. 45. 4545 After this discovery, ethylene becameAfter this discovery, ethylene became generally used for degreening citrus fruits,generally used for degreening citrus fruits, bananas, honey dew melons and tomatoes.bananas, honey dew melons and tomatoes. Ripe bananas give off ethylene that ripensRipe bananas give off ethylene that ripens green bananas during shipping.green bananas during shipping. Similarly emanations of ripe pears or applesSimilarly emanations of ripe pears or apples ripen other fruits because of ripe pears andripen other fruits because of ripe pears and apples giving off ethylene which acceleratesapples giving off ethylene which accelerates the ripening of other unripened fruits.the ripening of other unripened fruits. Production of ethylene depends upon fruitsProduction of ethylene depends upon fruits and vegetables (Table 4).and vegetables (Table 4). 46. 4646 47. 4747 A classification of fruits and vegetables according toA classification of fruits and vegetables according to their ethylene production rates is presented in Tabletheir ethylene production rates is presented in Table 5.5. However, thereHowever, there isis no consistent relationship betweenno consistent relationship between ethylene production capacity of the produce and itsethylene production capacity of the produce and its perishability.perishability. Ethylene gas inhibited the sprouting of potatoes.Ethylene gas inhibited the sprouting of potatoes. Small quantities of ethylene is produced bySmall quantities of ethylene is produced by practically all plant parts and tissues, fruits,practically all plant parts and tissues, fruits, vegetables, flowers, leaves, roots, tubers, seeds, andvegetables, flowers, leaves, roots, tubers, seeds, and fungi.fungi. 48. 4848 49. 4949 Very low concentrations of ethylene areVery low concentrations of ethylene are required to produce biochemical andrequired to produce biochemical and physiological responses in climactericphysiological responses in climacteric fruits and vegetables, such as accelerationfruits and vegetables, such as acceleration of the ripening process, and in contrast,of the ripening process, and in contrast, applied ethylene increases the respirationapplied ethylene increases the respiration of non-climacteric fruits and vegetables,of non-climacteric fruits and vegetables, the magnitude of the increase beingthe magnitude of the increase being dependent on the concentration ofdependent on the concentration of ethylene (Figure 6).ethylene (Figure 6). 50. 5050 51. 5151 There is a relationship between theThere is a relationship between the physiological age and the response ofphysiological age and the response of cantaloupes and tomatoes to continuouscantaloupes and tomatoes to continuous treatment with ethylene.treatment with ethylene. Because of ethylenes marked accelerativeBecause of ethylenes marked accelerative effects on ripening of both climacteric and non-effects on ripening of both climacteric and non- climacteric fruits, it is considered to be a plantclimacteric fruits, it is considered to be a plant growth hormone.growth hormone. The effect of ethylene as a ripening stimulantThe effect of ethylene as a ripening stimulant can be inhibited by COcan be inhibited by CO22 concentrations in orconcentrations in or around the fruits and decreased Oaround the fruits and decreased O22.. 52. 5252 These conditions prevail in controlled atmosphereThese conditions prevail in controlled atmosphere storage.storage. Effects of ethylene on fruits and vegetables held at 0Effects of ethylene on fruits and vegetables held at 0 to 4.4C is not possible to detect;to 4.4C is not possible to detect; nor is it detectable at higher temperatures of aboutnor is it detectable at higher temperatures of about 35C.35C. Wholesalers and retailers should know that fleshyWholesalers and retailers should know that fleshy fruits and vegetables give off large quantities offruits and vegetables give off large quantities of ethylene at increased storage temperature.ethylene at increased storage temperature. fleshy fruits and vegetables should not be store andfleshy fruits and vegetables should not be store and shipped with susceptible commodities such as greenshipped with susceptible commodities such as green and leafy vegetables, carrots, and lettuce.and leafy vegetables, carrots, and lettuce. 53. 5353 Also, fruits and vegetables should be stored at lowAlso, fruits and vegetables should be stored at low temperatures to increase their shelf life;temperatures to increase their shelf life; otherwise their quality and storage life reduces.otherwise their quality and storage life reduces. Apples, pears, carrots, etc. should not be stored inApples, pears, carrots, etc. should not be stored in the same room or in a transportation container.the same room or in a transportation container. Ethylene is synthesized within the cellEthylene is synthesized within the cell enzymetically from methionine.enzymetically from methionine. The sites of reaction within the cell areThe sites of reaction within the cell are mitochondria.mitochondria. The avocado will not ripen on the tree but willThe avocado will not ripen on the tree but will ripen and show a climacteric rise in respirationripen and show a climacteric rise in respiration after picking.after picking. 54. 5454 It is believed that an inhibitor ofIt is believed that an inhibitor of ripening is present in the leaves of theripening is present in the leaves of the trees.trees. Pears are another fruit that must bePears are another fruit that must be picked before they are tree ripe in orderpicked before they are tree ripe in order to develop a good eating quality.to develop a good eating quality. Some cultivars of pears must beSome cultivars of pears must be exposed to colds storage temperaturesexposed to colds storage temperatures before they ripen normally.before they ripen normally. Recent research has shown that lowRecent research has shown that low temperatures bring about synthesis oftemperatures bring about synthesis of ethylene in pears.ethylene in pears. 55. 5555 It is now believed that accumulation of ethyleneIt is now believed that accumulation of ethylene in fruits and vegetables precedes the rise inin fruits and vegetables precedes the rise in respiration, triggering the climacteric rise ofrespiration, triggering the climacteric rise of unripe fruits earlier.unripe fruits earlier. Climacteric rise in respiration is an indication ofClimacteric rise in respiration is an indication of the onset of senescence, indicating that thethe onset of senescence, indicating that the fruits should be harvested before it starts thisfruits should be harvested before it starts this rise in respiration.rise in respiration. Picking fruit at the peak of respiration offers thePicking fruit at the peak of respiration offers the best storage quality.best storage quality. 56. 5656 The effects of various growth regulators on fruits andThe effects of various growth regulators on fruits and vegetables ripening are attributed to inducingvegetables ripening are attributed to inducing ethylene production.ethylene production. e.g., the stimulation of the ripening of figs by thee.g., the stimulation of the ripening of figs by the application of 2,4,5-T.application of 2,4,5-T. Chemicals that are used to bring about abscission ofChemicals that are used to bring about abscission of fruits and vegetables important in fruit thinning andfruits and vegetables important in fruit thinning and mechanical harvesting, have been shown to causemechanical harvesting, have been shown to cause ethylene production.ethylene production. Ethylene-releasing chemicals are in commercial useEthylene-releasing chemicals are in commercial use in agriculture to bring about desired changes in plantsin agriculture to bring about desired changes in plants or plant products.or plant products. 57. 5757 The chemical 2-chloroethyl phosphoric acidThe chemical 2-chloroethyl phosphoric acid (Etheral, CEPA, Ethephon) is one of these.(Etheral, CEPA, Ethephon) is one of these. This chemical breaks down, releasing ethylene withinThis chemical breaks down, releasing ethylene within the plant tissue and modifying plant flowering,the plant tissue and modifying plant flowering, vegetative growth, dormancy, abscission, fruitvegetative growth, dormancy, abscission, fruit maturation and ripening, disease, and freezematuration and ripening, disease, and freeze resistance.resistance. Although ethylene is a useful chemical in the controlAlthough ethylene is a useful chemical in the control of growth and ripening responses, it has someof growth and ripening responses, it has some harmful effects.harmful effects. It can cause premature ripening in fruits, defoliationIt can cause premature ripening in fruits, defoliation in plants, lethal damage to nursery stock, petal fall,in plants, lethal damage to nursery stock, petal fall, failure in bud opening in flowers, russeting lettuce,failure in bud opening in flowers, russeting lettuce, and bitterness in carrots.and bitterness in carrots. 58. 5858 VI. TRANSPIRATIONAL LOSSVI. TRANSPIRATIONAL LOSS Water is lost from fruits and vegetablesWater is lost from fruits and vegetables as they grow on a tree or a vine;as they grow on a tree or a vine; they may decrease in volume during thethey may decrease in volume during the warm and dry part of the day, but regainwarm and dry part of the day, but regain their moisture at night.their moisture at night. With an increase in the relative humidityWith an increase in the relative humidity of the storage atmosphere, there is aof the storage atmosphere, there is a decrease in transpiration.decrease in transpiration. After harvesting, the process ofAfter harvesting, the process of transpiration continues but there is notranspiration continues but there is no way to replenish it.way to replenish it. 59. 5959 The moisture content of most fruits and vegetables isThe moisture content of most fruits and vegetables is high and weight loss during transportation andhigh and weight loss during transportation and storage can be a serious economic factor, especially ifstorage can be a serious economic factor, especially if fruits are sold by weight.fruits are sold by weight. In most fruits and vegetables with 5 to 10 % loss inIn most fruits and vegetables with 5 to 10 % loss in moisture content, the product are visibly shriveled asmoisture content, the product are visibly shriveled as a result of cellular plasmolysis.a result of cellular plasmolysis. The pedicels of cherries and calyx of strawberriesThe pedicels of cherries and calyx of strawberries turn brown and dry and the berries become dull andturn brown and dry and the berries become dull and loose luster.loose luster. Hence, quick cooling is necessary to preserve freshHence, quick cooling is necessary to preserve fresh appearance.appearance. 60. 6060 The weight loss of fruits and vegetables inThe weight loss of fruits and vegetables in storage depends upon size, maturity,storage depends upon size, maturity, composition and structure, air surroundingcomposition and structure, air surrounding them, storage temperature, relative humidity,them, storage temperature, relative humidity, velocity of air in the storage, thickness ofvelocity of air in the storage, thickness of cuticles, size and number of stomata andcuticles, size and number of stomata and lenticels, and other factors.lenticels, and other factors. A practical way to minimize this effect is toA practical way to minimize this effect is to cool the fruit quickly using hydrocoolingcool the fruit quickly using hydrocooling containing antifungal chemicals which willcontaining antifungal chemicals which will both cool the fruits and control the adheringboth cool the fruits and control the adhering fungal growth.fungal growth. 61. 6161 Similarly, lettuce and other leafy vegetables are cooledSimilarly, lettuce and other leafy vegetables are cooled by sprinkling cold water on them followed by vacuumby sprinkling cold water on them followed by vacuum treatment.treatment. Preventive loss of water from fruits and vegetables canPreventive loss of water from fruits and vegetables can be attempted both by reducing respiration as well asbe attempted both by reducing respiration as well as transpiration.transpiration. Fruits and vegetables should be precooled before storageFruits and vegetables should be precooled before storage at lower temperatures.at lower temperatures. Sometimes, it is essential to package the produce inSometimes, it is essential to package the produce in semi-permeable polyethylene or mylar bags.semi-permeable polyethylene or mylar bags. When dry fruits and vegetables, such as nuts or driedWhen dry fruits and vegetables, such as nuts or dried fruits, are stored in polyethylene containers, the problemfruits, are stored in polyethylene containers, the problem is to maintain desirable low RH (about 60%) and tois to maintain desirable low RH (about 60%) and to avoid fungal growth.avoid fungal growth. 62. 6262 63. 6363 A. MINIMIZING TRANSPIRATIONAL LOSSA. MINIMIZING TRANSPIRATIONAL LOSS There is only one way to reduce shriveling andThere is only one way to reduce shriveling and drying of fruits and vegetables in storage roomsdrying of fruits and vegetables in storage rooms and that is by increasing RH.and that is by increasing RH. Vegetables as well as fruits can be protectedVegetables as well as fruits can be protected from a lower RH by using various types offrom a lower RH by using various types of permeable polyethylene bags or films or bypermeable polyethylene bags or films or by providing moisture in the form of ice orproviding moisture in the form of ice or hydrocooling.hydrocooling. Hydrocooling fluid should contain a fungicide toHydrocooling fluid should contain a fungicide to prevent microbial growth.prevent microbial growth. 64. 6464 B. RELATIVE HUMIDITY AND TEMPERATUREB. RELATIVE HUMIDITY AND TEMPERATURE Water loss is rapid at low relative humidity (RH)Water loss is rapid at low relative humidity (RH) and slower at higher RH because the air in theand slower at higher RH because the air in the room contains less water vapor than it can hold atroom contains less water vapor than it can hold at the temperature of the room;the temperature of the room; thus water vapor is readily transferred from thethus water vapor is readily transferred from the humid interior of the leafy vegetables of fruits tohumid interior of the leafy vegetables of fruits to the relatively dry air.the relatively dry air. In contrast, if the RH in the room is 100% (waterIn contrast, if the RH in the room is 100% (water saturated atmosphere), the air in the room andsaturated atmosphere), the air in the room and fruits or vegetables are balanced in respect tofruits or vegetables are balanced in respect to moisture content, the gradient between the two ismoisture content, the gradient between the two is low, and moisture loss is nil.low, and moisture loss is nil. 65. 6565 The amount of moisture the air can hold beforeThe amount of moisture the air can hold before it becomes saturated rises with temperatureit becomes saturated rises with temperature increase.increase. More water is required to saturate air at 15.6CMore water is required to saturate air at 15.6C than at 4.4C.than at 4.4C. Accordingly, at 15.6C and 90% RHI, the air isAccordingly, at 15.6C and 90% RHI, the air is drier than in a room at 4.4C and 90% RHdrier than in a room at 4.4C and 90% RH resulting in rapid dehydration of the produce.resulting in rapid dehydration of the produce. 66. 6666 Further, water has a greater tendency toFurther, water has a greater tendency to evaporate as its temperature rises. Hence, RH isevaporate as its temperature rises. Hence, RH is always expressed with temperature.always expressed with temperature. As the temperature increases, the quality of theAs the temperature increases, the quality of the produce decreases (Figure 7);produce decreases (Figure 7); likewise the quality also decreases as fruits andlikewise the quality also decreases as fruits and vegetables experience a postharvest field delayvegetables experience a postharvest field delay as seen in Figure.as seen in Figure. 67. 6767 68. 6868 69. 6969 C. AIR MOVEMENTC. AIR MOVEMENT High velocity air causes rapid evaporation byHigh velocity air causes rapid evaporation by continuously removing water that is saturated.continuously removing water that is saturated. Air movement should be sufficient enough toAir movement should be sufficient enough to effectively remove respiratory heat from theeffectively remove respiratory heat from the produce after it has cooled to the temperatureproduce after it has cooled to the temperature of the room, trailer, or rail car.of the room, trailer, or rail car. 70. 7070 D. ATMOSPHERIC PRESSURED. ATMOSPHERIC PRESSURE Water evaporates more rapidly in lower atmospheric pressureWater evaporates more rapidly in lower atmospheric pressure than in higher. For every 10% decrease in pressure water lossthan in higher. For every 10% decrease in pressure water loss will increase 10%.will increase 10%. Thus the rate of water loss in an airplane will be about 20%Thus the rate of water loss in an airplane will be about 20% more than a sea level due to the difference in pressure alone.more than a sea level due to the difference in pressure alone. Should the lower air pressure be coupled with lower RH andShould the lower air pressure be coupled with lower RH and relatively higher temperature, a significant amount of waterrelatively higher temperature, a significant amount of water can be lost from produce during air transit.can be lost from produce during air transit. Therefore, during air transportation of fresh fruits andTherefore, during air transportation of fresh fruits and vegetables, appropriate pressurization should be maintainedvegetables, appropriate pressurization should be maintained especially over 5,000 ft altitude.especially over 5,000 ft altitude. 71. 7171 VII. CHILLING INJURIESVII. CHILLING INJURIES Chilling injury is a disorder inducedChilling injury is a disorder induced by low nonfreezing temperaturesby low nonfreezing temperatures which occurs in certain susceptiblewhich occurs in certain susceptible plants or produce (Table 6).plants or produce (Table 6). Usually this damage can occur inUsually this damage can occur in tropical fruits and vegetables whentropical fruits and vegetables when stored al low refrigeratedstored al low refrigerated temperatures (Table 7).temperatures (Table 7). 72. 7272 73. 7373 74. 7474 Chilling injury affects sweet potatoes,Chilling injury affects sweet potatoes, bananas, and mostbananas, and most tropical andtropical and subtropical fruits.subtropical fruits. Chilling injury induces decay and canChilling injury induces decay and can be avoided by storing at higherbe avoided by storing at higher temperatures.temperatures. Vegetables such as potatoes andVegetables such as potatoes and sweet potatoes shouldsweet potatoes should Susceptibility of various vegetablesSusceptibility of various vegetables to chilling injury are presented into chilling injury are presented in Table 8Table 8 75. 7575 76. 7676 77. 7777 78. 7878