fruit ripening & retail handling workshop · • a closed cold storage room allows accumulation...

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)



Saltveit, Mikal "Fruuit & Vegetable Cold Storage Disorders" (c) 2015 Postharvest Technology Center, UC Davis

Respiration and Temperature



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



Slide from Marita Cantwell

What temperature were they stored at?


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



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



-5 0 5 10 15 20 25 35Freezing Chilling Heat stressUsually too warm to retain quality


Fruit ripening workshop 2015 Cold storage disorders 7

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



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




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



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


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





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




Examples of Freezing Injury

Water logging



Examples of Freezing Injury

Why did the melons on only two edges

freeze and not all of them?

Tissue collapse Water logging




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.



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




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.

18Fruit ripening workshop 2015

Cold storage disorders

Most Fruits and Vegetables are chilling tolerant

But many are chilling sensitive




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.




Symptoms of Chilling Injury



Internal and external tissue browning

Surface pitting & discolorationFruit ripening workshop 2015



Grapefruit

Bell pepper


Tissue necrosis followed by attack by specific pathogens




CucumberDracaena String beans

Chilling of Bananas



ControlControlChilledChilled

Skin discoloration, Failure to ripen

Browning of inner side of peel

Chilled bananas develop a dull gray ‘smoke’ appearance upon ripening.


Chilling of Pineapples



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)



Internal Breakdown of Stone Fruit


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.



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.



King and Reid


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




fruit ripening & retail handling workshop · • a closed cold storage room allows accumulation...

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