Fruits and Vegetables

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Fruits and Vegetables
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Fruits and Vegetables

• living, continue respiration postharvest
• 80-90 water, turgor
• ripening
• starch hydrolysis
• acids and phenolics decrease
• glucose and fructose increase
• aroma develops
• chlorophyll breakdown
• anthocyanins and carotenoids synthesized
• softening due to changes in cell wall composition
  and structure, pectin hydrolysis
• ethylene formation

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Rate
fruit growth
respiration climacteric
respiration nonclimacteric
maturation
ripening
senescence
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Quality loss

• Transpiration water loss
• weight loss, 5
• textural changes
• loss of crispness, softening, shrivelling
• structure of surface
• surface to volume ratio
• storage RH and T
• air circulation
• rate of cooling

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• Structure
• peel or skin
• epidermis outermost layer, multilayer cells, no
  air spaces between
• cuticle extracellular layer surface waxes
• stomata water loss and gas exchange

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wound
stomate
cuticle
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• Physical damage, wound
• weaken the protective layers
• water loss
• repair possible when young
• release of enzymes
• environmental contamination
• increase in respiration
• increase in chemical and enzymatic reactions
• microbial growth

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• Surface to volume ratio, leafy vs. fruit
• low temperature
• RH, avoid condensation
• air circulation, not too fast

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Respiration

• Metabolic activity, need energy
• C6H12O6 6O2 nADP nPi
• 6CO2 6H2O nATP heat
• high respiration rate - short storage life
• respiratory quotient (RQ)
• volume of CO2 evolved / volume of O2 consumed

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Respiration

• Respiration rate depends on
• age of plant
• temperature
• injury
• available substrate
• species
• gas composition inside and outside tissue
  (ethylene, oxygen, carbondioxide)

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Respiration

• characteristic rise in respiratory rate
• coincident with the changes in color, flavor,
  texture
• respiratory climacteric marks the end of ripening
  and the onset of senescence
• period of enhanced metabolic activity during
  transition from the growth phase to senescence
• most fleshy fruits exhibit this rise
• vegetables do not exhibit this rise

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Respiration

• According to respiratory patterns
• nonclimacteric fruits
• ripen on the tree
• slow ripening
• respiration rate depends on the ethylene
  concentration
• respiration declines when ethylene removed
• climacteric fruits
• climacteric rise
• harvested mature and ripen off the tree
• produce high concentrations of ethylene
• need ethylene for initiation of respiration
  (0.1-1.0 ppm)
• after the rise no effect of ethylene concentration

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• Nonclimacteric fruits
• berries, grape, citrus fruits, orange, lemon,
  mandarin, fig, cucumber, melon
• Climacteric fruits
• apple, pear, quince, apricot, peach, banana,
  mango, tomato, plum

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Factors affecting ripening

• temperature of storage
• low T low rate
• storage atmosphere
• low rate
• reduction in O2 (lt21)
• increase in CO2 (gt0.03)
• ventilation, hypobaric storage, reduce ethylene
  and oxygen concentration
• species
• surface area/volume ratio
• physical damage

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Postharvest factors affecting quality

• Humidity
• - water loss
• softening, loss of crispness, wilting
• - condensation
• mold growth
• - weight loss

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• Gas composition
• O2, CO2, ethylene
• Modified atmosphere
• Controlled atmosphere
• Hypobaric storage (10-30 kPa)
• Some are sensitive to ethylene (lettuce)
• Some are sensitive to high CO2 levels
• reduce respiration rate, microbial growth, decay

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• Mechanical injury
• temporary localized rise in respiration
• formation of ethylene
• rapid turnover of cellular constituents
• accumulation of secondary metabolites
• stress metabolites
• isoflavonoids, diterpenes, glycoalkaloids
• polyacetylenes, coumarin
• toxic to tissue

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• Temperature
• increase reaction rates
• influence membrane integrity, O2 solubility,
  diffusivity
• commodities with fast respiration rate will
  respond to low temperature storage above the
  temperature at which chilling injury occur

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Chilling injury

• Physical disorder induced by low nonfreezing
  temperature that occurs in susceptible produce
• Symptoms
• - change in internal color (brown, black)
• - external discoloration
• - pitting of surface
• - uneven ripening
• - off-flavor development
• - accelerated decay, mold growth
• - loss of nutritive value
• - failure to ripen
• - wooly texture

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• Imbalance in metabolic reactions
• underproduction of essential constituents
• overproduction of toxic metabolites (ethanol,
  acetaldehyde, oxaloacetic acid)
• Alteration of integrity and permeability
  properties of cell membranes
• saturated fatty acids in cell membrane
• at low temperature solidify and change membrane
  permeability

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• Temperature and RH
• Duration of exposure
• sensitivity of the produce
• ethylene content

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• Chillig injury can be controlled by
• precooling
• regulating humidity
• controlled atmosphere
• intermittent warming

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• High temperature injury
• failure to ripen normally
• symptoms similar to chilling injury
• apples 55C storage
• similar to chilling injury

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• Compatible loads
• temperature
• RH
• modification of atmosphere
• release of toxic volatiles
• production of odors and flavors
• loading requirements

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Deterioration
1. Textural changes (water loss, mechanical
injury) 2. Microbial spoilage 3. Browning 4.
Sensory degradation
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• T control to prevent chilling injury
• MAP
• active vacuum, CO2-O2, ethylene absorbers
• passive modified by respiration
• Waxing to prevent moisture loss, O2
• Fumigation to prevent mold growth, respiration

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Canned Fruits and Vegetables

• Color degradation
• Chlorophyll - Mg -gt Pheophytin
• heat, acid
• Green -gt Olive brown
• Carotenoid degradation
• Flavor degradation
• Texture degradation
• Nutrient degradation

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Frozen Fruits and Vegetables

• Texture degradation
• cooling rate
• T fluctuations
• surface dehydration
• Color degradation
• Nutrient degradation
• Flavor changes