Fruit

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Fruit Vegetable ProcessingPostharvest
Physiology

• I. INTRODUCTION
• Fruits and vegetables when harvested from vines
  or plants are living structures, continuing
  metabolic reactions and sustaining physiological
  processes for a considerable time during their
  postharvest period.
• Fruits and vegetables respire by taking up
  oxygen, and giving off carbon dioxide and
  generating heat
• they also transpire, i.e., lose water in vapor
  form.

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• The respiration and transpiration losses are made
  up by replenishing water, photosynthates (sucrose
  and amino acids), and minerals from the time-flow
  of cell sap while fruits and vegetables are
  attached to the plants or vines.
• Subsequent to harvest, the source of water,
  photosynthates and minerals are cut off, and they
  enter into a deterioration or perishable phase.

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• Several changes take place in cell-wall
  composition and structure that result in the
  softening of the fruits and vegetables.
• In general, visual color gradually changes as
  chlorophyll is degraded and yellow pigment of the
  skin and flesh increases in content.
• In fruits and vegetables respiration involves the
  enzymatic oxidation of sugars to carbon dioxide
  (C02) and water, accompanied by release of
  energy.
• However, other substances such as organic acids
  and proteins also enter the respiratory chain.

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• Consequently, the loss of these reserves in
  fruits and vegetables results in the production
  of energy and the accompanying need for oxygen
  (0,) and removal of CO,.
• Cellular water is lost because of respiration and
  transpiration, resulting in fruits and vegetables
  becoming soft, shriveled, and limp.
• Anthocyanins that give the typical red, orange,
  blue, and other pigments of some fruits and
  vegetables may increase after harvest.

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• Apples, plums, pumpkins, and others enhance color
  development in a packaging shed or in a
  refrigerator.
• The skins of some fruits and vegetables develop
  bloom or waxes after harvest that gives them an
  attractive appearance which may aid in reducing
  transpirational losses.
• Starchy fruits and vegetables undergo a decrease
  in starch and increase in sugar and acids after
  harvest.
• However, there may be changes in the kinds of
  acids present.

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• In certain cases as maturity advances,
  astringency decreases caused by tannins or
  polyphenols.
• Volatiles and aroma components of many kinds of
  fruits and vegetables are produced after harvest
  if they are mature or ripe.
• However, when they are harvested rather immature
  or at the green stage for distant shipment,
  they do not yield typical aroma.
• For example, if Jordanian peaches are harvested
  for shipment to Kuwait market they do not develop
  as good aroma as when allowed to mature and ripen
  on the tree.

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• Ethylene is one of the volatiles synthesized in
  certain fruits and vegetables at certain stages
  of maturity and development when it reaches a
  high enough concentration, it triggers the
  ripening process and more ethylene is produced
  and the process of ripening is accelerated.
• Growth, development. prematuration, maturation,
  ripening, and senescence (Figure 1) are the most
  important phases in fruit and vegetable ontology.
• The growth of fruits and vegetables begins with
  cell division and cell enlargement, which
  accounts for the final size.

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• Growth and maturation is referred to as fruit
  development.
• Senescence is the period when anabolic and
  biochemical processes give way to catabolic
  processesleading to aging and final death of the
  tissue.
• Ripening generally begins during the later stages
  of maturation and is considered the beginning of
  senescence.
• The relative changes in weight, sugars,
  chlorophyll, and acidity are common to most
  fruits and vegetables (Figure 2) but other
  parameters such as respiration, flavor, aroma,
  and carotenoids can vary from commodity to
  commodity.

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• II. RESPIRATION
• Respiration of fruits and vegetables is an index
  of physiological activity and potent storage
  life.
• It is one of the basic processes of life and
  directly related to maturation, handling,
  transportation, and subsequently, storage life.
• Respiration of fruits and vegetables involves the
  enzymatic oxidation of sugars to carbon dioxide,
  water, and release of energy (Figure 3).

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• Other substrates such as organic acids, fats, and
  proteins also play an important role during the
  process of respirarion.
• The energy produced by the oxidation of sugars is
  convened into the energy of adenosine
  triphosphate (ATP), as an energy carrier.
• The oxidation of sugars takes place in several
  steps under control of specific enzymes. A simple
  formula for respiration may be as follows Sugar
  602 gt 6C02 6H20 Energy

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• As indicated above this respiration of fruits and
  vegetables involves the following aspects
• 1. Substrate the quantity of substrate
  (predominantly sugars) in fruits and vegetables
  available for respiration is a deciding factor
  for their longevity at that temperate.
• The weight loss due to increased temperature and
  respiration usually is more than to five percent
  depending upon the structure of the fruits and
  vegetables.

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• 2. Oxygen the supply of 02, for normal
  respiration is generally adequate unless
  intentionally restricted as in the case of CA
  (Controlled Atmosphere) Storage.
• 3. Carbon Dioxide removal of respiratory CO2
  requires more attention than supply of 02 because
  CO2 may be in excess even when supply of 02 is
  adequate.

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• A three to five percent reductions of 02
  concentration would not have an adverse effect on
  a product, but a comparable increase in CO2 could
  suffocate and ruin certain fruits and vegetables.
• 4. Energy removal of heat from respiration is
  vitally important otherwise the life of fruits
  and vegetables will be reduced to an increased
  temperature around the commodity.
• Increase in rate of respiration causes
  acceleration of substrate utilization.

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• 5.Rate of Respiration The rate of respiration
  determines the quantity of 02 that must he
  available per unit of time.
• The quantities of CO2 removed at he same time.
• Increased rate of respiration will reduce the
  storage life of product.
• Rate of respiration is a function of temperature
  and available concentration of 02 around the
  fruits and vegetables.

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• In addition. some fruits such as potatoes will
  have a lower rate of respiration than spinach or
  lettuce due to inherent substrate available for
  respiration and the anatomical variations of the
  commodities.
• The rate of respiration can he defined as the
  weight of CO2 produced per unit fresh weight and
  time (mg CO2/kg/h) (Table 1).
• The rate of respiration may be expressed in ml
  CO2/kg/h or the quantity of 02 taken up rather
  than CO2 given out.

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• The classification of the rate of respiration is
  presented in Table 2.
• 6. Initial Rate of Respiration the rate of
  prevailing respiration or within a few hours
  varies depending upon crop and temperature)
• 7. Average Rate of Respiration It is determined
  by measuring rates at a definite time interval,
  summing the rates thus determined, and dividing
  by the number of intervals involved.

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• 8. Effects of Temperature and Days in Storage on
  Rate of Respiration the rate of respiration
  generally increases as the temperature and the
  storage duration of fruits and vegetables
  increases.
• However, at very high temperatures and at the
  very long storage duration, the rate of
  respiration decreases until the death of
  products. However, one does not store fresh
  commodities at such high temperatures (Figures 4
  and 4A).
• 9. Effects of Commodity on Rate of Respiration
  the rate of respiration varies depending upon
  commodity and variety, also the commodity will
  vary with other varieties of the same commodity.
  

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• 10. Maturity of Fruits and Vegetables on
  Respiration Rate fruits and vegetables harvested
  at early maturity for distant market respire
  faster than those harvested at the firm-ripe
  maturity.
• 11. Vant Hoffs Law this law indicates that the
  rate of chemical reaction is controlled by
  temperature.
• He coined the term Q10.This indicates at each
  10C rise in temperature, the rate of reaction
  doubles.
• However, Q10 for respiration may not always be
  doubled sometimes it may be more than doubled
  depending upon the maturity and anatomical
  structure of the fruits or vegetables.

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• Postharvest physiology is influenced by
  preharvest factors on the farm or in the orchard.
  
• Physiology of fruits and vegetables begins at the
  time of blossoming or bud formation and is
  affected by agricultural practicesfertilization,
  variety, and irrigationand by environmental
  factors such as sunlight duration and quality,
  temperature, humidity, etc.
• The genetics of fruits and vegetables determine
  postharvest storage life. Those crops that are
  most perishable such as lettuce, spinach,
  strawberries and raspberries have a short growing
  season life.

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• In contrast, Winesap apples which require 160 to
  170 days to develop have a longer storage life.
• Summer cultivars of apples generally have a
  shorter storage life because they ripen earlier.
• Likewise, early summer apples have a higher
  respiration rate than fall apples they also have
  a greater number of cells, more lenticels, and
  give off more ethylene.

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• However, one should not conclude that the
  differences in storage life of fruits and
  vegetables can be explained simply by length of
  growing season, respiration rate, or amount of
  ethylene released.
• It involves genetic factors which control growth,
  development. postharvest behavior, and
  physiological and morphological variations.

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• Ill. TEMPERATURE QUOTIENT OF RESPIRATION The
  temperature quotient (Q10) is not the same for
  all fruits and vegetables, nor will it be the
  same for another variety of the same fruit.
• The example is presented in Table 3.
• As a general rule, it can be said that an apple
  or pear will ripen as much in a day at 21 C as
  it will in a week at 0 C.

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• Thus it is apparent that refrigeration is an
  effective means of extending the commercial life
  of fresh produce.
• Fruit growers and shippers have learned by
  practical experience that the growing season has
  a powerful influence on the storage age of
  fruits.
• For example, it has been recognized that t is
  hazardous to store or to ship Bartlett pears
  grown in cool coastal areas to distant places,
  because they often develop core breakdowna
  physiological disorder that makes pears too soft
  and mushy.

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• Some cultivars of apples grown in cool climates
  cannot tolerate storage temperature of 0 C and
  must be stored at higher temperatures such as
  (2.24.4 C) In order to avoid low temperature
  breakdown.
• Sweet as well as sour cherries develop scald when
  weather in is unusually warm and dry during the
  several weeks before harvest
• Chemical reactions of respiration are controlled
  by temperature and ideally, one could expect a
  Q10 of about 2.5 for respiration.

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• This means that for a 10C rise in temperature,
  the respiration would double.
• Rapidly growing young tissue respires faster than
  that which develops slowly.
• The rate of respiration of asparagus is one of
  the highest rates of all fruits and vegetables
  because of the rapidly growing shoots of the
  plant.

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• Fruits and vegetables vary in respiration rates
  and there are differences between cultivars and
  their maturitiesso it is not to be expected that
  the respiration rate will be a fixed value at any
  given temperature.
• It tends to be more constant at temperatures of
  (0 to 4.4C) than at higher temperatures of (21.1
  to 26.7C).
• At the temperature range (0 4.4C), where fruits
  and vegetables are held the longest-time, their
  heat of respiration is a factor to be included in
  calculating the refrigeration requirements for
  refrigeration storage and transportation.

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• In the case of fruits and vegetables, after
  harvest, fast cooling is generally desirable
  especially for perishable soft fruits such as
  berries and leafy vegetables.
• This not only reduces metabolic activity of
  fruits and vegetables, but also controls fruit
  decay.
• Fungi and other microorganisms increase rates of
  respiration as do bruises and mechanical
  injuries
• the most serious consequences of holding fruits
  and vegetables at high temperature is the
  hastening of ripening, and shortening of storage
  and marketing life.

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Climacteric and nonclimacteric fruits and
vegetables

• A large number of fruits and vegetables show a
  sudden and sharp rise in respiratory activity
  called the climacteric rise during the life
  cycle
• whereas others which do not show climacteric rise
  are called nonclimacteric fruits and vegetables.

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• The time of harvest for climacteric fruits and
  vegetables is critical for their maximum storage
  life and quality.
• Non-clirnacteric fruits and vegetables are
  allowed to ripen on plants or vines and the
  resulting maturity is regulated by storage.
• Maturity tests such as color, brix, acidity, and
  others are employed to determine whether they can
  meet standard grades and can be legally sold.

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The classification of edible fruits and
vegetables according to their respiration pattern
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• Respiratory patterns vary from growth and
  development and also from fruit to fruit and
  vegetable to vegetable
• most leafy vegetables are of non-climacteric
  nature (Figure 5).
• Respiration is not merely a catabolic process,
  but it provides energy to synthesize enzymes,
  cell membrane constituents, and other material
  necessary for life of the cell.
• It takes place within the cell at the site of the
  various enzymes that participate in the process
  of respiration.

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• Respiration and ripening can be retarded by
  reducing the amount of O2.
• Ethylene, if O2 is present, will increase the
  respiration rates and other metabolic processes
  as well.
• The ethylene may come from the fruit or the
  vegetable itself or be added to the atmosphere.
• In a fruit or a vegetable that has climacteric
  rise in respiration, ethylene treatment initiates
  the rise earlier, but the rates reach no higher
  levels.
• The climacteric in respiration of certain fruits
  generally occur at the onset of processes
  involved in ripening.
• The peak of respiration does not always coincide
  with peak of ripening.

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IV. ETHYLENE PRODUCTION AND EFFECTS

• The Chinese knew in ancient times that pears
  could be ripened by exposing them to the smoke of
  incense burned in closed rooms.
• Many years ago in Florida and California, oranges
  were colored or more correctly degreened by
  exposure to fumes from kerosene stoves or exhaust
  from a gasoline engine in a special coloring
  room.
• Ethylene is the active degreening agent in stove
  gas and a concentration of 4 ppm would degreen
  lemons in 6 to 8 d.

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• After this discovery, ethylene became generally
  used for degreening citrus fruits, bananas, honey
  dew melons and tomatoes.
• Ripe bananas give off ethylene that ripens green
  bananas during shipping.
• Similarly emanations of ripe pears or apples
  ripen other fruits because of ripe pears and
  apples giving off ethylene which accelerates the
  ripening of other unripened fruits.
• Production of ethylene depends upon fruits and
  vegetables (Table 4).

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• A classification of fruits and vegetables
  according to their ethylene production rates is
  presented in Table 5.
• However, there is no consistent relationship
  between ethylene production capacity of the
  produce and its perishability.
• Ethylene gas inhibited the sprouting of potatoes.
• Small quantities of ethylene is produced by
  practically all plant parts and tissues, fruits,
  vegetables, flowers, leaves, roots, tubers,
  seeds, and fungi.

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• Very low concentrations of ethylene are required
  to produce biochemical and physiological
  responses in climacteric fruits and vegetables,
  such as acceleration of the ripening process, and
  in contrast,
• applied ethylene increases the respiration of
  non-climacteric fruits and vegetables,
• the magnitude of the increase being dependent on
  the concentration of ethylene (Figure 6).

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• There is a relationship between the physiological
  age and the response of cantaloupes and tomatoes
  to continuous treatment with ethylene.
• Because of ethylenes marked accelerative
  effects on ripening of both climacteric and
  non-climacteric fruits, it is considered to be a
  plant growth hormone.
• The effect of ethylene as a ripening stimulant
  can be inhibited by CO2 concentrations in or
  around the fruits and decreased O2.

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• These conditions prevail in controlled atmosphere
  storage.
• Effects of ethylene on fruits and vegetables held
  at 0 to 4.4C is not possible to detect
• nor is it detectable at higher temperatures of
  about 35C.
• Wholesalers and retailers should know that fleshy
  fruits and vegetables give off large quantities
  of ethylene at increased storage temperature.
• fleshy fruits and vegetables should not be store
  and shipped with susceptible commodities such as
  green and leafy vegetables, carrots, and lettuce.

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• Also, fruits and vegetables should be stored at
  low temperatures to increase their shelf life
• otherwise their quality and storage life reduces.
• Apples, pears, carrots, etc. should not be stored
  in the same room or in a transportation
  container.
• Ethylene is synthesized within the cell
  enzymetically from methionine.
• The sites of reaction within the cell are
  mitochondria.
• The avocado will not ripen on the tree but will
  ripen and show a climacteric rise in respiration
  after picking.

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• It is believed that an inhibitor of ripening is
  present in the leaves of the trees.
• Pears are another fruit that must be picked
  before they are tree ripe in order to develop a
  good eating quality.
• Some cultivars of pears must be exposed to colds
  storage temperatures before they ripen normally.
• Recent research has shown that low temperatures
  bring about synthesis of ethylene in pears.

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• It is now believed that accumulation of ethylene
  in fruits and vegetables precedes the rise in
  respiration, triggering the climacteric rise of
  unripe fruits earlier.
• Climacteric rise in respiration is an indication
  of the onset of senescence, indicating that the
  fruits should be harvested before it starts this
  rise in respiration.
• Picking fruit at the peak of respiration offers
  the best storage quality.

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• The effects of various growth regulators on
  fruits and vegetables ripening are attributed to
  inducing ethylene production.
• e.g., the stimulation of the ripening of figs by
  the application of 2,4,5-T.
• Chemicals that are used to bring about abscission
  of fruits and vegetables important in fruit
  thinning and mechanical harvesting, have been
  shown to cause ethylene production.
• Ethylene-releasing chemicals are in commercial
  use in agriculture to bring about desired changes
  in plants or plant products.

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• The chemical 2-chloroethyl phosphoric acid
  (Etheral, CEPA, Ethephon) is one of these.
• This chemical breaks down, releasing ethylene
  within the plant tissue and modifying plant
  flowering, vegetative growth, dormancy,
  abscission, fruit maturation and ripening,
  disease, and freeze resistance.
• Although ethylene is a useful chemical in the
  control of growth and ripening responses, it has
  some harmful effects.
• It can cause premature ripening in fruits,
  defoliation in plants, lethal damage to nursery
  stock, petal fall, failure in bud opening in
  flowers, russeting lettuce, and bitterness in
  carrots.

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VI. TRANSPIRATIONAL LOSS

• Water is lost from fruits and vegetables as they
  grow on a tree or a vine
• they may decrease in volume during the warm and
  dry part of the day, but regain their moisture at
  night.
• With an increase in the relative humidity of the
  storage atmosphere, there is a decrease in
  transpiration.
• After harvesting, the process of transpiration
  continues but there is no way to replenish it.

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• The moisture content of most fruits and
  vegetables is high and weight loss during
  transportation and storage can be a serious
  economic factor, especially if fruits are sold by
  weight.
• In most fruits and vegetables with 5 to 10 loss
  in moisture content, the product are visibly
  shriveled as a result of cellular plasmolysis.
• The pedicels of cherries and calyx of
  strawberries turn brown and dry and the berries
  become dull and loose luster.
• Hence, quick cooling is necessary to preserve
  fresh appearance.

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• The weight loss of fruits and vegetables in
  storage depends upon size, maturity, composition
  and structure, air surrounding them, storage
  temperature, relative humidity, velocity of air
  in the storage, thickness of cuticles, size and
  number of stomata and lenticels, and other
  factors.
• A practical way to minimize this effect is to
  cool the fruit quickly using hydrocooling
  containing antifungal chemicals which will both
  cool the fruits and control the adhering fungal
  growth.

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• Similarly, lettuce and other leafy vegetables are
  cooled by sprinkling cold water on them followed
  by vacuum treatment.
• Preventive loss of water from fruits and
  vegetables can be attempted both by reducing
  respiration as well as transpiration.
• Fruits and vegetables should be precooled before
  storage at lower temperatures.
• Sometimes, it is essential to package the produce
  in semi-permeable polyethylene or mylar bags.
• When dry fruits and vegetables, such as nuts or
  dried fruits, are stored in polyethylene
  containers, the problem is to maintain desirable
  low RH (about 60) and to avoid fungal growth.

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A. MINIMIZING TRANSPIRATIONAL LOSS

• There is only one way to reduce shriveling and
  drying of fruits and vegetables in storage rooms
  and that is by increasing RH.
• Vegetables as well as fruits can be protected
  from a lower RH by using various types of
  permeable polyethylene bags or films or by
  providing moisture in the form of ice or
  hydrocooling.
• Hydrocooling fluid should contain a fungicide to
  prevent microbial growth.

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B. RELATIVE HUMIDITY AND TEMPERATURE

• Water loss is rapid at low relative humidity (RH)
  and slower at higher RH because the air in the
  room contains less water vapor than it can hold
  at the temperature of the room
• thus water vapor is readily transferred from the
  humid interior of the leafy vegetables of fruits
  to the relatively dry air.
• In contrast, if the RH in the room is 100 (water
  saturated atmosphere), the air in the room and
  fruits or vegetables are balanced in respect to
  moisture content, the gradient between the two is
  low, and moisture loss is nil.

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• The amount of moisture the air can hold before it
  becomes saturated rises with temperature
  increase.
• More water is required to saturate air at 15.6C
  than at 4.4C.
• Accordingly, at 15.6C and 90 RHI, the air is
  drier than in a room at 4.4C and 90 RH
  resulting in rapid dehydration of the produce.

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• Further, water has a greater tendency to
  evaporate as its temperature rises. Hence, RH is
  always expressed with temperature.
• As the temperature increases, the quality of the
  produce decreases (Figure 7)
• likewise the quality also decreases as fruits and
  vegetables experience a postharvest field delay
  as seen in Figure.

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C. AIR MOVEMENT

• High velocity air causes rapid evaporation by
  continuously removing water that is saturated.
• Air movement should be sufficient enough to
  effectively remove respiratory heat from the
  produce after it has cooled to the temperature of
  the room, trailer, or rail car.

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D. ATMOSPHERIC PRESSURE

• Water evaporates more rapidly in lower
  atmospheric pressure than in higher. For every
  10 decrease in pressure water loss will increase
  10.
• 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. Should the lower
  air pressure be coupled with lower RH and
  relatively higher temperature, a significant
  amount of water can be lost from produce during
  air transit.
• Therefore, during air transportation of fresh
  fruits and vegetables, appropriate pressurization
  should be maintained especially over 5,000 ft
  altitude.

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VII. CHILLING INJURIES

• Chilling injury is a disorder induced by low
  nonfreezing temperatures which occurs in certain
  susceptible plants or produce (Table 6).
• Usually this damage can occur in tropical fruits
  and vegetables when stored al low refrigerated
  temperatures (Table 7).

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• Chilling injury affects sweet potatoes, bananas,
  and most tropical and subtropical fruits.
• Chilling injury induces decay and can be avoided
  by storing at higher temperatures.
• Vegetables such as potatoes and sweet potatoes
  should
• Susceptibility of various vegetables to chilling
  injury are presented in Table 8

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