L6 - Respiration Flashcards
Respiration
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
Primary Biochemical Reactions of respiration
- Glycolysis
- Pyruvate Oxidation
- Citric Acid Cycle
- Oxidative
Phosphorylation
- Electron Transport Chain
- Chemiosmosis
Glycolysis
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
Where do these reactions take place
- Glycolysis (cytosol)
- Pyruvate Oxidation (mitochondrial matrix)
- Citric Acid Cycle (mitochondrial matrix)
- Electron Transport Chain (mitochondrial membranes: cristae)
Summary of each reaction (1/4) - Glycolysis
(cytosol)
• Breaks glucose (6C) into 2 pyruvates (3C)
• Generates net 2 ATP
• Independent of O2
Summary of each reaction (2/4) - Pyruvate Oxidation
(mitochondrial matrix)
• Removes CO2 (1C)
• Produces one NADH and Acetyl-CoA (2C)
Summary of each reaction (3/4) - Citric Acid Cycle
(mitochondrial matrix)
• Converts acetyl CoA into CO2
• Generates NADH, FADH2, and ATP/GTP
Summary of each reaction (4/4) - Electron Transport Chain
(mitochondrial membranes: cristae)
• Transfers electrons from NADH and FADH2 to reduce O2 to H2O
• Generates ATP
Respiration: ATP cycle
Total ATP yield is 30-32
• 2 in Glycolysis
• 2 in Citric Acid Cycle
• 26-28 in oxidative phosphorylation
Anaerobic respiration
- 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
Pasteur effect
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!
Pasteur effect
Reduce respiration by reducing O2 • low O2: increased glycolysis • Pasteur effect • more substrate used • quality loss • substrates lost • alcohol produced
Sweet spot for best keeping Quality: CA/MAP
L6 - Slide 22
*the best way to reduce respiration without getting fermentation
Effects of CO2 on aerobic and anaerobic respiration and anaerobic respiration rates
- High CO2has similar effect as low O2, but effect is less strong
- Acetaldehyde and ethanol production
Summary (Slide 24)
- 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
Carbohydrates - Respiration and postharvest quality
Consequence: decrease of substrate
• Loss of flavour, raw material, turgor, weight, etc.
How harvest affect postharvest quality?
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)
Respiration after harvest
- 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)
Stress
mechanical stress (dropping a tomato) stress -> increase ethylene -> increase respiration -> increase ripening -> decreased shelf life
Ripening
(Graph slide 33)
Respiration after harvest the same as if the apple had fallen on its own (?)
Ripening climacteric vs non climacteric
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
Flowers and respiration
- During development: Respiration increases
- After harvest: Respiration declines
Increase of respiration in petals
towards senescence
*chrysanthemum are not sensitive to ethylene
Respiration rate of various fruits e.t.c.
Table at slide 37
the closer to the ground the lower the respiration rate
Summary (1/2) (slide 39)
• 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
Summary (2/2) (slide 39)
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
Temperature
THE MOST IMPORTANT factor for quality control during post-harvest phase
• BECAUSE IT REDUCES RESPIRATION
Temperature effect
- 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!
CHECk slide 47 effect of temperature respiration rate
Field and vital heat
- 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)
Cooling methods
Before storage and/or transport
- Room cooling, Air-cooling
- Forced-air cooling
- Hydro-cooling
- Package-icing
- Vacuum-cooling
During transit:
a. Top-icing
b. Channel-icing
c. Mechanical refrigeration
Room-cooling
- 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
Hydro-cooling
- 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
Vacuum-cooling
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
