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Post Harvest Physiology > L6 - Respiration > Flashcards

L6 - Respiration Flashcards

1
Q

Respiration

A

Respiration provides:
• CO2and energy to drive metabolism: ATP
• Raw material carbon fragments

Exothermic reaction:
• free energy liberated
• reaction runs spontaneously 
• All fuel could be burned in one go
• Split up in strictly controlled steps
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2
Q

Primary Biochemical Reactions of respiration

A
  1. Glycolysis
  2. Pyruvate Oxidation
  3. Citric Acid Cycle
  4. Oxidative
    Phosphorylation
    - Electron Transport Chain
    - Chemiosmosis
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3
Q

Glycolysis

A

Rate controlling enzymes:
•Phosphofructokinase: PFK
•Pyruvate Kinase

•Inhibited by ATP, activated by ADP

ATP production controls rate of glycolysis

*product of glycolysis : 3-carbon pyruvate

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4
Q

Where do these reactions take place

A
  • Glycolysis (cytosol)
  • Pyruvate Oxidation (mitochondrial matrix)
  • Citric Acid Cycle (mitochondrial matrix)
  • Electron Transport Chain (mitochondrial membranes: cristae)
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5
Q

Summary of each reaction (1/4) - Glycolysis

A

(cytosol)
• Breaks glucose (6C) into 2 pyruvates (3C)
• Generates net 2 ATP
• Independent of O2

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6
Q

Summary of each reaction (2/4) - Pyruvate Oxidation

A

(mitochondrial matrix)
• Removes CO2 (1C)
• Produces one NADH and Acetyl-CoA (2C)

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7
Q

Summary of each reaction (3/4) - Citric Acid Cycle

A

(mitochondrial matrix)
• Converts acetyl CoA into CO2
• Generates NADH, FADH2, and ATP/GTP

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8
Q

Summary of each reaction (4/4) - Electron Transport Chain

A

(mitochondrial membranes: cristae)
• Transfers electrons from NADH and FADH2 to reduce O2 to H2O
• Generates ATP

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9
Q

Respiration: ATP cycle

A

Total ATP yield is 30-32
• 2 in Glycolysis
• 2 in Citric Acid Cycle
• 26-28 in oxidative phosphorylation

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10
Q

Anaerobic respiration

A
  • In absence of O2
  • Alternative glucose breakdown to generate energy
    • Glycolysis with additional reactions at the end
    • Produced NADH cannot be recycled to NAD+

-Fermentation
• Purpose is to regenerate NAD+
• Electrons from NADH are dropped off at pyruvate
• Acidic cells: Alcohol fermentations -> ethanol
• Non-acidic cells: Lactic acid fermentation -> lactate

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11
Q

Pasteur effect

A

Glycolysis ran this way only captures about 20% of energy in glucose molecule, and accumulation of lactic acid and/or ethanol can be toxic for the cell
Rate of Glucose metabolism is faster!

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12
Q

Pasteur effect

A 
Reduce respiration by reducing O2
• low O2: increased glycolysis
• Pasteur effect
• more substrate used
• quality loss
• substrates lost
• alcohol produced
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13
Q

Sweet spot for best keeping Quality: CA/MAP

A

L6 - Slide 22

*the best way to reduce respiration without getting fermentation

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14
Q

Effects of CO2 on aerobic and anaerobic respiration and anaerobic respiration rates

A
  • High CO2has similar effect as low O2, but effect is less strong
  • Acetaldehyde and ethanol production
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15
Q

Summary (Slide 24)

A
  • Plant products respire as long as they are alive
  • Respiration is the major force of deterioration
  • Respiration increases by ripening, harvest, senescence, …
  • Aerobic respiration yields 32 ATP
  • Without oxygen, Pasteur effect causes increase in glycolysis, high use of carbohydrates, and production of ethanol
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16
Q

Carbohydrates - Respiration and postharvest quality

A

Consequence: decrease of substrate

• Loss of flavour, raw material, turgor, weight, etc.

17
Q

How harvest affect postharvest quality?

A

Harvest causes stress

What happens at harvest
• large wound
• stimulation of respiration
• increase loss of carbohydrates
• increase in heat production
• water loss (also direct because of wounding)
18
Q

Respiration after harvest

A
  • Initially increase in respiration
  • Followed by decrease due to exhausting of substrate

(Check graph, slide 30. Also distinguishes behaviour between climacteric and non climacteric fruits)

19
Q

Stress

A 
mechanical stress (dropping a tomato)
stress -> increase ethylene -> increase respiration -> increase ripening -> decreased shelf life
20
Q

Ripening

A

(Graph slide 33)

Respiration after harvest the same as if the apple had fallen on its own (?)

21
Q

Ripening climacteric vs non climacteric

A

scale climacteric from low heat production to high heat production depending on the respiration rates
potato < apple < tomato < cucumber< fig < mango< asparagus < brussels sprouts

non climacteric
lemon < pineapple < cherry < grape < strawberry

22
Q

Flowers and respiration

A
  • During development: Respiration increases
  • After harvest: Respiration declines

Increase of respiration in petals
towards senescence
*chrysanthemum are not sensitive to ethylene

23
Q

Respiration rate of various fruits e.t.c.

A

Table at slide 37

the closer to the ground the lower the respiration rate

24
Q

Summary (1/2) (slide 39)

A

• Respiration rate: High during initial
growth, (climacteric) ripening, wound healing
• After harvest: respiration surges -
wound healing and handling
• In non-climacteric fruit and vegetative tissues, it declines after that

  • Climacteric fruit
    •Ripening causes rapid rise in ethylene production and respiration
    •Possibly to power ripening processes (softening, colour, aroma)
    •Non-climacteric fruit do the same
25
Q

Summary (2/2) (slide 39)

A

Flowers
•During development: respiration increases

  • After harvest, respiration declines
  • Towards senescence, respiration increases again, climacteric or not
  • Botanical structure influences respiration level: Low in storage organs, high in flowers and fruit
  • Increased Temp: Higher Respiration
  • Low respiration = Long shelf life
26
Q

Temperature

A

THE MOST IMPORTANT factor for quality control during post-harvest phase

• BECAUSE IT REDUCES RESPIRATION

27
Q

Temperature effect

A
  • Different products respond differently

Lowering temperature:
• prolongs storage life and preserves the quality
• slows down respiration (and heat production)
• slows down senescence (many enzymes involved)
• slows down pathogens
• slows down ethylene (response and production)

BUT Possibility of Chilling Injury!

28
Q

CHECk slide 47 effect of temperature respiration rate

A
29
Q

Field and vital heat

A
  • Field heat:
    Heat contained by the product at harvest because of the environmental conditions just before harvest (you always try to keep the field heat low)
  • Vital heat: (;metabolic heat)
    Heat produced by the product (Due to respiration)
30
Q

Cooling methods

A

Before storage and/or transport

  1. Room cooling, Air-cooling
  2. Forced-air cooling
  3. Hydro-cooling
  4. Package-icing
  5. Vacuum-cooling

During transit:

a. Top-icing
b. Channel-icing
c. Mechanical refrigeration

31
Q

Room-cooling

A
  • Air circulating through room passes over surfaces and through openings
  • Air takes path of least resistance moving past product
  • Cooling from surface to centre of bins largely by conduction
Advantages:
• Cooling and storage in the same room
• No need for transfer after cooling
Disadvantages:
• Too slow for most commodities
• Requires more space than is needed for cold storage
• Excessive water loss
32
Q

Hydro-cooling

A
  • Heat exchange between product and water is much faster than between product and air
  • Cooling time is mostly limited by rate of heat transport WITHIN the product
33
Q

Vacuum-cooling

A 
Works especially well when there is a good exchange of water from the product:
• Large surface/volume ratio
• Many and large intercellular spaces
• Thin cuticle
Disadvantages:
• Water loss
• Batch operation
• Risk of freezing

Post Harvest Physiology (23 decks)

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