Post-harvest respiration

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Post-harvest respiration

• Plant cells live for weeks after harvest!
• Respiration continues in the absence of nutrients
• Cells continue to metabolize/breakdown cellular
  components

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Commodity Respiration Rates
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• Alive and have active metabolism!
• Harvest and post-harvest practices create
• metabolic stresses
• Metabolic stress can cause rapid deterioration of
  plant tissue

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Metabolism is Very Complex!
Simplified Metabolic Chart
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e O2 H ----H20
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High Temperatures

• Increases the rate of all metabolic
  
• reactions!

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Enzymes

• Enzymes control metabolic pathways
• Feed Back!
• Temperature controls enzyme activity

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Enzymes

• High temperatures high enzyme activity
  rapid tissue deterioration
• Temperatures too high (gt 40 C)
• enzyme function ceases cell death

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Temperature Quotient for a 10 C Interval (Q10)

• Q10
• Deterioration rate at temperature (T) 10 C
• Rate of deterioration at T
• Q10 Respiration rate (T) rate at (T10)
• Respiration rate at (T)
• Q10 is about 2 for metabolic processes

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Deterioration Rate Temperature
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Commodity Respiration Rates
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Strawberry Example

• Keeps for five days at 20 C
• 10 days at 10 C
• 20 days at 0 C
• Strawberries can store
• for three weeks at 0 oC (if Botrytis
• cinerea is controlled)

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Temperature Affects Other Factors that Influence
Product Quality

• Growth rate
• Ripening
• Ethylene
• Water uptake
• Nutrient uptake
• Disease(s)

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30 20 10 0
Strawberry
Grape
Respiration (mg CO2/Kg./Hr)
Cherry
Lemon
Time
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Respiración Climatérica
180 160 140 120 100 80 60 40 20 0
Cherimoya
Respiration (mg CO2/Kg./Hr)
Mango
Prickly pear
Tomato
time
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Ethylene and fruit ripening
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Roberts and Hooley  table 8.1 Grierson and Covey
1984 Plant Molecular Biology, Blackie
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Tomato ripening Above is an overview of tomato
ripening after the fruit becomes mature but still
green. The first key element is the peak in
respiration. It classifies tomato as a
climacteric fruit, one that ripens in association
with a respiratory climax. Note that ethylene
formation correlates well with this climax.
Ethylene is the key regulator, its production
triggers ripening. Ripening is associated with
the synthesis and accumulation of b-carotene
(orange) followed by lycopene (red) in the
chloroplast.
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Since the photosynthetic machinery is broken down
at the same time, the chloroplast becomes a
chromoplast. The fruit also become soft,
registered here as the production of a pectinase
dissolves the middle lamella between the cell
walls, Tomatoes also become sweeter as they
ripen since starch is converted to sugars.
Citric acid is also accumulated to give it that
tangy flavour and tomatine, a toxic alkaloid in
green tomatoes, is broken down. In summary, the
plant did not want the fruit to be eaten during
development but when mature it must attract
eaters to disperse the seed. (Crookes and
Grierson 1083 Plant Physiol 72 1088)
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NON-CLIMACTERIC Carambola Egg-Plant Lemon Orange
Watermelon Pineapple
CLIMACTERIC Avocado Mango Guava Plantain Banana P
apaya Apple
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Rep. Rhythm . Mg CO2/Kg./Hr 5 - 10 mg 10 - 20
mg 20 - 40 mg 40 - 60 mg
Respiration rate Low Moderate High Very
High
PRODUCT Sugar beet, garlic, onion,
watermelon, citrus. Cabbage, carrot, cucumber,
mango, tomato. Avocado, cauliflower, lettuce,
strawberry. Artichoke, broccoli, spinach,
parsley, sweet Corn.
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Factors affecting the respiration rates

• mechanical damage and products sanitary
  condition.
• temperature.
• atmosphere composition (lt Oxygen and CO2lt
  respiration gt ethylene gt respiration).
• physical barriers (waxes, plastic films, etc.)

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Mechanical damage during the postharvest chain

• the temperature - affects the degree of
  response/
• severity of mechanical damage.
• Compromise natural barriers -increasing
• water loses and pathogenic infections.

Impact
Respiration
Ethylene
Time
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How Is Temperature Controlled?
1. Removal of field heat after harvest
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How Is Temperature Controlled?
2. Transport cooling
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How Is Temperature Controlled?
3. Storage room cooling
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Prevent spoilage?

• Refrigerate chill decreases cell metabolism
• Freeze cold stops metabolism
• Canning heat stops metabolism
• Preserve canning sugar

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Chilling Injury

• Very sensitive crops are
• Basil
• Cucumber
• Eggplants
• Pumpkins
• Summer squash
• Okra
• Sweet potatoes

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Chilling Injury

• Moderately sensitive
• Snap beans
• Cantaloupe
• Peppers
• Winter squash
• Tomatoes
• Watermelon