fruit ripening & ethylene why use cold storage? management...

Mikal E. SaltveitMann Laboratory, Department of Plant Sciences

University of California, Davis

Fruit Ripening & Ethylene Management Workshop

Cold Storage Disordersof Fruits and Vegetables

2017 Fruit ripening workshop Cold storage disorders

Why use cold storage?• Shelf-life is inversely proportional to respiration

(colder temp ® slower respiration ® longer shelf-life).

• Respiration is halved for every 10 °C (18 °F) drop in temperature (i.e., a Q10 of 2).

• Low temperatures reduce microbial growth.

• Low temperatures reduce water loss(air at 10 °C can hold twice as much water as at 0 °C)


Effect of temperatures on strawberries

Holding for 48 h at different temperatures (5 or 20°C)

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 12 h periods at 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


Chronological vs PhysiologicalChronological time is time measured on your watch – uniform intervals independent of external conditions.

Physiological time is time measured on tissue changes – intervals depend on rate of physiological changes (e.g., rate of respiration).

For example: An hour in the dentist chair is not the same perceived length of time as one hour engaged in an enjoyable activity like listening to this lecture.

Plants are poikilothermic (i.e., ectothermic) and are unable to maintain a tissue temperature above ambient, while we are homoeothermic and are able to maintain a relatively constant internal body temperature irrespective of the external temperature.

Our biological clock ‘ticks’ as a relative uniform rate, while the plant’s biological clock ‘ticks’ at rates dependent on its temperature.


Respiration and Temperature

Brussels sprouts

Shasta strawberry

Wickson plum

0 5 10 15 20 25 30

20

40

10

50

30

0He

at p

rodu

ctio

n (1

,000

BTU

/Ton

day

)

Temperature (°C)

100

300

200

00 5 10 15 20 25

Temperature (°C)

Resp

iratio

n (m

g CO

2/kg

h)

Asparagus spears

Globe artichokes

Head lettuce

4

Q10 = 10/4 = 2.5

Respiration can be expressed as the rate of CO2 or heat produced


Organisms can survive and even thrive as long as there is liquid water (even < 0°C).

Life can exists at extreme temperatures (-273 to > 100°C), but production agriculture tries to maintain crops within a narrow range of temperatures for optimal growth.

Temperature sensitivity is predicted by the concept of the Temperature Quotient or Q10, which compares the rate of a process at one temperature to its rate at a higher

or lower temperature (usually a difference of 10°C). Q10 = (rate at temperature T + 10) / (rate at temperature T)

For example, the Q10 = Rate at 15°C / Rate at 5°CPhotochemical and physical processes (e.g., heat loss) have a Q10 of about 1. That

means that temperature changes (within the biological range) do not effect the rate of the reaction.

On the other hand, biological processes (enzymatic reactions, biochemical reactions, metabolism, etc.) have a Q10 values between 2-3, while some complicated processes

(e.g., respiration of cut flowers, broccoli) have much higher values (4-6).

Life, Temperature, and the Q10


Chronological vs. Physiological TimeMany developmental processes,

such as germination, flowering, and ripeningare controlled through internal or external signals.

Internal signals include the passage of a given amount of chronological time (e.g., calendar days, absolute time) or

physiological time (e.g., degree days, perceived time).

How many days of shelf-life would be lost if strawberries

(Q10 = 2.5) were held for 24 h at 15 °C instead of at 5 °C?

One day of chronological time would have passed, but for the

fruit, 2.5 days of physiological time would have passed;

so 1.5 day would have been lost.

2017 Fruit ripening workshop Cold storage disordersSocrative poll– roomnumber:FRUITRIPENING

The Temperature window

-5 0 5 10 15 20 25 35Freezing Chilling Heat stress


Outside the Optimum• High temperature - scald, sunburn• Non-freezing Temperatures - chilling sensitivity• Sub-zero temperatures - frost injury, freezing

0 5 10 15 20 25 35 40


Problems with cold storage• Excessive water loss can occur even at low temperatures

because of low relative humidity produce by mechanical refrigeration.

• Temperatures below 32 °F (0 °C) can cause freezing(depends on the tissue’s sugar content).

• Non-freezing temperatures below about 50 °F (10 °C) can cause chilling injury.

• 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: CO2, C2H4


Relative humidity (%)20100 80 60 4050 30

30

25

0

10

20

15

-5-10

5

250 10 2015 35-5-10 5 5030 60554540Dry bulb temperature (°C)

45

40

20

10

5

0

15

30

25

35

Wat

er v

apor

pre

ssur

e (m

illib

ars)

0.028

0.024

0.020

0.016

0.012

0.008

0.004

0.000

Spec

ific h

umid

ity (k

g/kg

)

Coil temperature = 0 °C (32 °F)Room temperature = 5 °C (41 °F)

Air at 0°C and 100% RH will become air at 70% RH

when warmed to 5°C

Excessive water loss can occur even at low temperatures because

of low relative humidity.


100% RH at the 5°C surface of the commodity

100% RH at the 0°C surface of the coils Vapor pressure

deficit driving water loss

70% Freezing InjuryWater 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

first form 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 FormationIce 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!A growing ice crystal can’t

puncture a cell. Once water freezes, the volume of the ice actually decreases as it cools2017 Fruit ripening workshop Cold storage disorders

Sugars and Freezing SusceptibilityWhy does fruit tissue close to the pit freeze first,

and not tissue in the flesh near the surface?Core tissues freeze before outer flesh tissues because of

differences in soluble solids content within

the fruit.

Freezing point depression; dependent on the number of molecules or ions and their ability to organize

water.


Examples of Freezing Injury

Why did it freeze on just those edges?

Tissue collapse Water logging


Examples of Freezing Injury

Water logging

White patches


Most Fruits and Vegetables are chilling tolerant

But many are chilling sensitive2017 Fruit ripening workshop Cold storage disorders

Chilling Injury• Chilling injury is a physiological disorder; however, symptom

development can involve increases susceptibility to specific microbes.

• Chilling injury develops after exposure to non-freezing temperatures below a ‘critical’ temperature.

• The severity of the injury depends on the temperature and duration of exposure.

• The ‘critical’ or ‘threshold’ temperature varies with: crop, cultivar, growing conditions, pre-treatments, etc.

• Symptoms usually develop upon return to room temperature.• The post-chilling environment can mitigate or accentuate

symptom development.


Chilling and Shelf-life

0

20

40

60

80

100

0 5 10 15 20 25 30

Temperature (°C)

Perc

ent o

f pos

sible

she

lf-lif

e

Level of chilling injury

Shelf-life of non-chillingsensitive commodity

Threshold for chilling

Shelf-life of chilling sensitive commodity

The shelf-life of non-chilling sensitive commodities

steadily increases as the temperature declines to the freezing point of the tissue.

In contrast, while the shelf-life of chilling sensitive commodities also steadily increases as the temperature declines,

it rapidly decreases as the temperature falls below the

threshold temperature.


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)


Symptoms of Chilling Injury

Internal and external tissue browning2017 Fruit ripening workshop Cold storage disorders

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

Chilling injury

High temperature injury

Just right


Surface pitting & discoloration


GrapefruitBell pepper



Tissue necrosis followed by attack by specific pathogens

CucumberDracaena String beans


Chilling of Bananas

ControlChilled

Skin discoloration, Failure to ripen

Browning of inner side of peel

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


Control (left two) and chilled (right two) bananas

Control Chilled

Chilling of Bananas


Chilling of Pineapples

7.2 °C (45 °F) 5.5 °C (42 °F) 3 °C (38 °F)

Endogenous Brown Spot

1.7 °C (3 °F) 2.5 °C (4 °F)


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.

ü Mealiness (soft but not juicy)ü Flesh Browningü Lack of Flavorü Failure to Ripen

Internal Breakdown is induced

at intermediatestorage temperatures

(2-8°C, 1-6 weeks)

Internal Breakdown of Stone Fruit


Category Cultivar 0°C 5°C

A Betty Anne 5 5

October Sun 5 5

Flavor Rich 5 5

Joanne Red 5 5

B Angeleno 5 3

Fortune 5 3

Hiromi Red 5 3

Black Amber 5 2

Purple Majesty 5 3

C Show Time 4 2

Friar 4 2

Earliqueen 3 2

Plum market life (in weeks) held at 2 storage

temperatures based on chilling injury symptom

developmentCrisosto et al., 2008. Adv. Hort. Sci. (Italy) 22(3): 201-204.

Susceptibility Varies with Cultivar


Variation 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 temperature conditioning.


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.

Conditioning at 20 °C for 2 days

prevents mealiness from developing during

20 days of cold storage at 5 °C


Preventing Chilling Injury• Are we preventing injury or

symptom development?• Don’t chill• Controlled atmospheres• Conditioning

– High temperature pre-treatment – Low temperature treatment

(above threshold)– Intermittent warming


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