L8 - Chilling Injury Flashcards
What is Chilling Injury (CI)?
Chilling injury is a disorder caused by exposure to low temperatures.
Not freezing temperatures!
Are all cultivars of a species sensitive?
No, some cultivars are less sensitive than others, even within a species
Typical CI symptoms
- Developmental disorders
-Incomplete or inhibited ripening:
Excessive softening
Deficient aroma and flavour
Unable to colour
- Physiological symptoms
- Pitting
- Skin yellowing
- Tissue decomposition / internal or surface browning
- Fungal or bacterial rot
- Mealy texture
CI may occur in
-(long distance) transit: Often sea transport is cheaper
Tropical fruit
Flower transport
-market distribution
Difficulty with CI is that symptoms are often
- Not visible during cold storage
- Only visible during shelf-life
- Often economic losses due to CI are not recognised!
CI for tomatoes (low temperature storage)
- for green harvested tomatoes -> increased softening (effects on firmness: sunken areas,pitting)
- for red harvested tomatoes -> decrease of lycopene (antioxidant) -> tomato turns orange (effects colour + fungal decay and water soaking)
- volatiles break down
- hexanal (grassy green odour) -> decreases
- mouldy off flavour -> increases
Physiology of Chilling Injury
Chilling injury is caused by membrane ruptures:
Membranes start to leak: electrolyte leakage
Membranes create pockets inside the cell with conditions optimized for:
- Photosynthesis
- Respiration
- Protein synthesis
- Gene transcription, etc
Why do membranes rupture?
-Low temperature makes membranes less fluidic
- Respiration is the source of energy for plant products
- consists of many steps, in different (membrane) compartments
- Less membrane fluidity means that respiration becomes less efficient…as transport is hindered
-ROS
ROS (Reactive Oxygen Species). How do they work? what is the resutl?
ROS oxidize the membrane lipids,
resulting in membrane rupture and cell death
Fruits & vegetables are generally able to cope with short amounts of low temperatures…and will recover
What natural defences do plant products have?
- Presence of unsaturated fatty acids in the bilayer
- Presence of antioxidants in the bilayer
unsaturated fatty acids
Ratio of unsaturated fatty acids higher in chilling resistant cultivars
-ROS will react with the double bonds.
But also makes the bilayer less fluidic.
So this is only a temporary defense
Presence of antioxidants
- Antioxidants have a high affinity to react with ROS
- Are in the membrane and protect the membrane
- 1 molecule of vitamin E (fat soluble) can protect about 200 fatty acids
- Vitamin E is recycled (E and C work together) by vitamin C (water soluble)
- Chilling resistant tomato cultivars have higher vitamin C levels
How to measure Chilling injury?
- Breakdown products of lipid peroxidation: malondialdehyde
- Electrolyte leakage (conductivity measurements)
- Chlorophyll Fluorescence
- Weight loss
How do WE deal with Chilling Injury? (1/4)
A. Pre storage dips (1-3 mM) with:
- Jasmonic acid (tomato)
- Salicylic acid (peach/pomegranate)
- Glycine betaine (green peppers)
- Gibberellins (tomato)