L8 - Chilling Injury

Question 1

What is Chilling Injury (CI)?

Answer 1

Chilling injury is a disorder caused by exposure to low temperatures.

Not freezing temperatures!

Question 2

Are all cultivars of a species sensitive?

Answer 2

No, some cultivars are less sensitive than others, even within a species

Question 3

Typical CI symptoms

Answer 3

1. Developmental disorders

-Incomplete or inhibited ripening:
Excessive softening
Deficient aroma and flavour
Unable to colour

2. Physiological symptoms

• Pitting
• Skin yellowing
• Tissue decomposition / internal or surface browning
• Fungal or bacterial rot
• Mealy texture

Question 4

CI may occur in

Answer 4

-(long distance) transit: Often sea transport is cheaper
Tropical fruit
Flower transport

-market distribution

Question 5

Difficulty with CI is that symptoms are often

Answer 5

• Not visible during cold storage
• Only visible during shelf-life
• Often economic losses due to CI are not recognised!

Question 6

CI for tomatoes (low temperature storage)

Answer 6

• 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

Question 7

Physiology of Chilling Injury

Answer 7

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

Question 8

Why do membranes rupture?

Answer 8

-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

Question 9

ROS (Reactive Oxygen Species). How do they work? what is the resutl?

Answer 9

ROS oxidize the membrane lipids,

resulting in membrane rupture and cell death

Answer 10

Fruits & vegetables are generally able to cope with short amounts of low temperatures…and will recover

Question 11

What natural defences do plant products have?

Answer 11

• Presence of unsaturated fatty acids in the bilayer

- Presence of antioxidants in the bilayer

Question 12

unsaturated fatty acids

Answer 12

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

Question 13

Presence of antioxidants

Answer 13

• 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

Question 14

How to measure Chilling injury?

Answer 14

1. Breakdown products of lipid peroxidation: malondialdehyde
2. Electrolyte leakage (conductivity measurements)
3. Chlorophyll Fluorescence
4. Weight loss

Question 15

How do WE deal with Chilling Injury? (1/4)

Answer 15

A. Pre storage dips (1-3 mM) with:

1. Jasmonic acid (tomato)
2. Salicylic acid (peach/pomegranate)
3. Glycine betaine (green peppers)
4. Gibberellins (tomato)

Question 16

How do WE deal with Chilling Injury? (2/4)

Answer 16

B. Induces plant defences:

1. Production of ascorbic acid
2. Production of antioxidant enzymes
3. Induces Heat Shock Proteins: help partially unfolded proteins in the bilayer to refold

Question 17

How do WE deal with Chilling Injury? (3/4)

Answer 17

Pre storage hot water dips

Typically a 2-5 minutes at 40-50 °C
Induces also plant defences

Increase chilling tolerance for: 
citrus fruit
Kiwifruit
Tomato
papaya

Question 18

How do we deal with chilling injury ? (4/4)

Answer 18

Intermittent warming : warming every 7 days to 20oC
-two cycles optimal
-cultivar/growing conditions dependent 
(far-red treatment)
-workds for bell peppers

Question 19

Sensitive to CI

Answer 19

• tropical/subtropical fruits
• tomato <15
• banana <10
• culinary herbs (basil) <10
• anthurium, gerbera <15
• peaches,nectarines
• avocado, mango
• chrysanthemum

Question 20

Non-sensitive to Cl

Answer 20

• lettuce (high quality at 0oC)
• brussels sprouts (high quality at 0oC)
• some apples
• broccoli, cauliflower

Question 20

LOOK at summary conclusions