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Mikal E. SaltveitMann Laboratory, Department of Plant Sciences
University of California, Davis
Fruit ripening workshop 2015
Cold storage disorders 1
Fruit Ripening & Retail Handling Workshop
Cold Storage Disordersof Fruits and Vegetables
Why use cold storage?
• Shelf-life is inversely proportional to respiration (colder temp slower respiration longer shelf-life).
• The rate of respiration declines about 50% for every 18 °F (10 °C) fall in temperature (Q10 of 2).
• Low temperatures reduce most microbial growth.
• Low temperatures reduce water loss (air at 10 °C can hold twice as much water as at 0 °C)
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Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Respiration and Temperature
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Brussels sprouts
Shasta strawberry
Wickson plum
0 5 10 15 20 25 30
20
40
10
50
30
0
He
at p
rod
uct
ion
(1,0
00
BT
U/T
on
da
y)
Temperature (°C)
100
300
200
00 5 10 15 20 25
Temperature (°C)
Re
spira
tion
(mg
CO
2/kg
h)
Asparagus spears
Globe artichokes
Head lettuce
4
How can we calculate a Q10?
Respiration increases with increasing temperature
The rate of increase increases faster at warmer temperature
Q10 = 10/4 = 2.5
0°C 5°C 10°C32°F 41°F 50°F
A B C
Ripe Strawberries After 7 days
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Slide from Marita Cantwell
What temperature were they stored at?
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Effect of handling temperatures on strawberry deterioration
Treatment (48 h period) % Sound
% Soft
% Rotted
1. 48 h at 5°C (41°F) 95 4 1
2. 24 h each at 5°C (41°F) and 20°C (68°F)
76 10 14
3. 2 x (2 x 12 h) periodsat 5°C (41°F) and 20°C (68°F)
70 7 23
4. 48 h at 20°C (68°F) 44 1 55
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Mitchell et al., 1996 Handling Strawberries, UC Publ. 2442
Fruit condition
Slide from Marita Cantwell
Outside the Temperature Window
• High temperature - scald, sunburn• Sub-zero temperatures - frost, freezing
• Tropical commodities - chilling sensitivity
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-5 0 5 10 15 20 25 35Freezing Chilling Heat stressUsually too warm to retain quality
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Tomato fruit after 2 weeks at 20 °C. Softening and synthesis of pigmentsand aromas may be abnormal at cold (chilling injury) or high temperatures.
Ripening of Tomato Fruit
Chillinginjury
High temperature injury
Just right
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WARMAIR 41°F
CONDENSERHOTAIRHot gas
Fan outside
WARMAIR
cold room
Warm liquid
High pressure side
Insulation
Fan inside cold room
Gas
Liquid
EVAPORATOR
COLDAIR 32°F
Low pressure side
COMPRESSOR
EXPANSIONVALVE
Mechanical Refrigeration
Most cooling technologies rely on a liquid to gas phase change, or on an adiabatic temperature change as a gas expands and contracts.
The RH of saturated (100% RH) cold 32°F air drops to 70% RH when
warmed to 41°F
HEATRESERVOIRWarm liquid
Refrigerant absorbs heat
as it vaporizes
Refrigerant condenses as it looses heat
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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250 10 2015 35-5-10 5 5030 60554540
Dry bulb temperature (°C)
45
40
20
10
5
0
15
30
25
35
Vap
or p
ress
ure
(kP
a)
Wet bulb temperature (°C)
30
25
0
10
20
15
-5
-10
5
Relative humidity (%)20100 80 60 4050 30
The saturated water content of air (SVP) increases logarithmically with increasing air temperature
The SVP doubles for every 11 °C rise in temperature
R.H. = VP * 100 SVP
1 atmosphere= 98 kPa
= 0.10 mPa= 1.01 bars= 14.7 psi
= 760 mm Hg= 33.9 ft H2O
Wet bulb lines
Saturation Vapor Pressure (SVP)
Dry bulb lines
Relative humidity lines
Constant Vapor Pressure
The Psychrometric Chart
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Cold storage disorders 10
Relative humidity (%)20100 80 60 4050 30
Wet bulb temperature (°C)
30
25
0
10
20
15
-5-10
5
250 10 2015 35-5-10 5 5030 60554540
Dry bulb temperature (°C)
45
40
20
10
5
0
15
30
25
35
Wat
er v
apor
pre
ssur
e (m
illi
bars
)0.028
0.024
0.020
0.016
0.012
0.008
0.004
0.000
Spe
cifi
c hu
mid
ity
(kg/
kg)
Coil temperature = 0 °C (32 °F)
Room temperature = 5 °C (41 °F)
RH = 70%
Excessive water loss can occur at low relative
humidity
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Problems with cold storage• Temperatures below 32 °F (0 °C) can cause
freezing (depends on the tissue’s sugar content).
• Freezing reduces quality and shelf-life
• Non-freezing temperatures below ~50 °F (10 °C) can cause chilling injury in sensitive crops.
• Chilling injury may be hidden and only develop after the product is purchase by the consumer.
• A closed cold storage room allows accumulation of gasses: unusual aromas, CO2, C2H4
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Sugars and Freezing SusceptibilityWhy does fruit tissue close to the pit freeze first,
and not tissue in the flesh?
Core tissues freeze before outer flesh tissues because of
differences in soluble solids (sugar) content
within the fruit.
Freezing point depression; dependent on the number of molecules or ions and their ability to organize
water.
Frozen
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Examples of Freezing Injury
Water logging
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Examples of Freezing Injury
Why did the melons on only two edges
freeze and not all of them?
Tissue collapse Water logging
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Freezing Injury
Water in the cell walls surrounding each plant cell contains less soluble solids (e.g., sugars) than does the cytoplasm in the cell, so ice crystals
form first in the cell wall.
The solution in the cell wall gets more concentrated as ice crystals form. Water moves from the cell into the cell wall to
re-establish osmotic equilibrium, and the cell dehydrates.
Cellular dehydration, not ice crystal formation, causes cellular injury associated with freezing.
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Ice Crystal Formation
Ice crystals form by the accretion of water molecules on the surfaces of an
existing surface.
No motive force can be exerted by a growing crystal.
The volume of an ice crystal actually
decreases as it cools
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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D = 100
Ice at 0 °C (32 °F) = 0.9167 g/cm3
1 g ice = 1.0909 cm3
Water at 0 °C (32 °F) = 0.9998 g/cm3
1 g water = 1.0002 cm3
Water is most dense at 4 °C (32 °F)1 g ice = 1.000 cm3
D = 102.94, same weight, but now larger volume
Volume change upon Freezing
WATER
V = 4/3 r3
This small increase in volume in an elastic cell (unlike an iron pipe) does
not cause mechanical tissue damage.
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Cold storage disorders
Most Fruits and Vegetables are chilling tolerant
But many are chilling sensitive
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Flowering plants originated in the tropics
Flowering plants evolved in the tropics and most tropical and semi-tropical plants are chilling sensitive.
Tropical, sub-tropical, and even some temperature fruit are chilling sensitive and damaged by non-freezing temperatures below 10 °C (50 °F)
Chilling Injury• Chilling injury is a physiological disorder; however, symptom
development can involve increases susceptibility to specific diseases.
• Chilling injury develops after exposure to non-freezing temperatures below a ‘critical’ temperature (e.g., 50 °F, 10 °C).
• The severity of the injury depends on the temperature of exposure (below threshold), and the duration of exposure.
• The ‘critical’ of ‘threshold’ temperature varies with: crop, cultivar, growing conditions, pre-treatments, etc.
• Symptoms often develop after rewarming.
• The post-chilling environment can mitigate or accentuate symptom development.
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Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Symptoms of Chilling Injury
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Internal and external tissue browning
Surface pitting & discolorationFruit ripening workshop 2015
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Symptoms of Chilling Injury
Grapefruit
Bell pepper
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Tissue necrosis followed by attack by specific pathogens
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Symptoms of Chilling Injury
CucumberDracaena String beans
Chilling of Bananas
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ControlControlChilledChilled
Skin discoloration, Failure to ripen
Browning of inner side of peel
Chilled bananas develop a dull gray ‘smoke’ appearance upon ripening.
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Chilling of Pineapples
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7.2 °C (45 °F)7.2 °C (45 °F) 5.5 °C (42 °F)5.5 °C (42 °F) 3 °C (38 °F)3 °C (38 °F)
Endogenous Brown Spot
Crisosto et al., 1999. Susceptibility to chilling injury of peach, nectarine, and plum cultivars in California. HortScience 34(6): 1116-1118.Crisosto et al. 2004. Increasing ‘Blackamber’ (Prunus salicina Lindell) plum consumer acceptance. Postharvest Biol. Tech 34: 237-234. Lurie, S and C. Crisosto. 2005. Chilling injury in peach and nectarine. Postharvest Biol. Tech. 37: 195-208.
Mealiness (soft but not juicy) Flesh Browning Lack of Flavor Failure to Ripen
Internal Breakdown is induced by intermediate
storage temperatures(2-8°C, 1-6 weeks)
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Internal Breakdown of Stone Fruit
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Conditioning or Delayed Cooling
0ºC 20 Days
(43% Mealy)
20ºC 48 Hours + 5ºC 20 Days
(0% Mealy)
5ºC 20 Days
(100% Mealy)
Crisosto, et al. 2004. Controlled delayed cooling extends peach market life. HortTechnology 14:99-104.
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Diurnal changes in Chilling Sensitivity
• Diurnal changes in chilling sensitivity– Cool mornings, hot afternoons, carbohydrate status
• Tomato seedlings are very chilling sensitive in the early morning and less sensitive later in the day.
• Tomato fruit also exhibit diurnal changes
in chilling sensitivity.
• Changes can be duplicated with
postharvest temp conditioning.
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King and Reid
Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis
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Preventing Chilling Injury
• Are we preventing injury or symptom development?
• Don’t chill!
• Use resistant cultivars
• Conditioning– High temperature pre-treatment
– Low temperature treatment
(above threshold)
– Intermittent warming
• Controlled atmospheres
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Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis