1

Postharvest Biology OverviewOverview

of Horticultural Crops

Marita Cantwell, UC Davis

micantwell@ucdavis.edu

http://postharvest.ucdavis.edu

POSTHARVEST SPECIALISTSPOSTHARVEST SPECIALISTS

M L A i Di B tt

http://postharvest.ucdavis.edu

Ch i ti B h M it C t ll

Carlos Crisosto Associate DirectorFruits,

Stone Fruit

Elizabeth Mitcham

Faculty DirectorFruits, MA &

IPM Research

Mary Lu ArpaiaSubtropical

Fruits

Diane BarrettProcessing &

Quality

Michael ReidCut Flowers & Potted Plants

Linda HarrisFood Safety

Christine BruhnConsumer

Issues

Adel KaderFruit & Nut

Quality

Marita CantwellVegetables &

Fresh-Cut

Jim Thompson Cooling, Transport,

Fumigation

Roberta CookMarketing & Economics

Trevor SuslowVegetables &

Microbial Safety

Postharvest Losses are costlyRepresent loss of inputs and profitsReduce postharvest losses and increase sustainability

--reduce land, chemical, energy other inputs--conserve land, water, energy

From Adel Kader, Nov 2009, BMG project

Profitable Horticulture Dependson Good Postharvest Handling

• Reduce losses!• Increase sales and

consumption• Improve quality• Improve quality

– Taste– Nutritional

• New products• Niche markets• Lightly processed• Food safety

Causes of Quality & postharvest LossesCauses of Quality & postharvest Losses

Leafy VegetablesLeafy Vegetables

LettucesLettuces

SpinachSpinach

CabbageCabbage

Water lossWater loss

Mechanical damageMechanical damage

L f hl h llL f hl h llChardChard

BroccoliBroccoli

CeleryCelery

HerbsHerbs

EndivesEndives

AsparagusAsparagus

Loss of chlorophyll Loss of chlorophyll and other nutrientsand other nutrients

Respiration ratesRespiration rates

Microbial growthMicrobial growth

Sensitivity to Sensitivity to ethyleneethylene

Causes of Quality & Postharvest LossesCauses of Quality & Postharvest Losses

FruitsFruits

BananaBanana

AppleApple

AvocadoAvocado

Mechanical damageMechanical damage

Maturity, Maturity, immature, overmatureimmature, overmature

Poor ripening, conditioningPoor ripening, conditioningMelonsMelons

CitrusCitrus

MangoMango

TomatoTomato

ChilesChiles

BerriesBerries

Softening, texture lossSoftening, texture loss

Changes in composition Changes in composition

Water loss Water loss

Chilling injury Chilling injury

Microbial growthMicrobial growth

2

From Gordon Mitchell, UC Davis

Fresh Produce Fresh Produce DeteriorationDeterioration

•• Metabolic changes: Metabolic changes: –– respiration, ethylene, respiration, ethylene,

–– texture, aroma, etc.texture, aroma, etc.

T tT t•• Growth and developmentGrowth and development

•• TranspirationTranspiration

•• Mechanical injuryMechanical injury

•• Physiological disordersPhysiological disorders

•• Decay; microbial growthDecay; microbial growth

Temperature Temperature Affects All Affects All Causes of Causes of DeteriorationDeterioration

Temperature ‐ why is it important?

• Rate of deterioration  rate of respiration

• Respiration: 

Sugar + O2 CO2 + H20 + Energy (Heat)

• Respiration increases exponentially with T

CO2O2

µL

CO

2/g

-h)

80

100

120

140 0°C (32°F)5°C (41°F)10°C (50°F)

15°C (59°F) 20°C (68°F)

A. Heads B. Florets

Cauliflower heads and florets have very similar respiration rates & quality changes during storage

Days

1 2 3 4 5 6

Re

spira

tion

(µ

0

20

40

60

Days

1 2 3 4 5 6

Hevajulige & Cantwell, 2004

Relative Perishability

AppleApple

BananaBananaTomatoTomato

ArtichokeArtichokeBroccoliBroccoliStrawberryStrawberry

AsparagusAsparagusPeasPeasSweet CornSweet Corn

10

Relative Respiration Rate

NutsNutsDatesDates

CitrusCitrusGarlicGarlicPotatoPotato

AppleAppleCarrot Carrot OnionOnion

PeachPeach

ays

(to

in

itia

te y

ello

win

g)

10

15

20

25

30

35BroccoliBroccoliShelfShelf--lifelife

&&TemperatureTemperature

cv. Legacy

Storage temperature

Da

0

5

032

2.536

541

7.545

1050

12.5 55

1559

20°C68°F

3

0C32F

5C41F 10C

50F

7 days

50F

15C59F

20C68F

mg

/100

g F

W

0

5

10

15

20

25

mg

/100

g F

W

0

1

2

3

4Chlorophyll Carotenoids

0°C (32°F)10°C (50°F)20°C (68°F)

Limit of Salability

Broccoli Compositional Quality and Storage Temperature

Days

0 5 10 15 20 25

mg

/100

g F

W

05

10152025303540

Days

0 5 10 15 20 25

mg

/100

gF

W

0

5

10

15

20

25Ascorbic Acid Sugars

Cantwell, UC Davis

7 days

Importance of Temperature to Maintain Quality

0°C 5°C 10°C32°F 41°F 50°F

A B C

Commercial Cooling Methods

• Room Cooling• Forced Air Cooling• Vacuum Cooling • Hydrocooling• Icing

C li i f i d

Product requirementsScale appropriate technologyConventional, Organic productsMicrobial food safety issues

• Cooling in refrigerated transport

Cold ChainMonitoring

Maintaining temperature is a major challenge during distribution

Effect of Temperature on Deterioration

Temp. °F

Temp. °C Q10

Relative Velocity of Deterioration

Relative Shelf-life

Daily Loss (%)

32 0 -- 1.0 100 1

50 10 3.0 3.0 33 3

68 20 2.5 7.5 13 8

86 30 2.0 15.0 7 14

104 40 1.5 22.5 4 25

Q10 = rate of deterioration at T+10°rate of deterioration at T

4

No fresh product freezes at 0°C (32°F)

Lettuce freezes at -0.2°C (31.7ºF)

• Non-chilling sensitive products

• Chilling sensitive products

• Chilling sensitivity occurs at temperatures above the freezing point

Eggplants are Chilling Sensitive

Cantwell, UC Davis

Symptoms of chilling injury

• Surface pitting

• Water soaking

• Browning

• Necrosis• Necrosis

• Rots

• Poor flavor

• Poor ripening10C vs 7.5C, 4 wk Galia melon

Commonly chilling symptoms do not appear until product is transferred from the cold room to a warmer temperature

Temperature and other Postharvest Recommendations

• http://postharvest.ucdavis.edu

Produce Facts

• http://www.ba.ars.usda.gov/hb66/USDA Agriculture Handbook Number 66

The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks

Modified or Controlled Atmospheres•• Reducing oxygenReducing oxygen

•• Increasing carbon dioxideIncreasing carbon dioxide

•• Removing carbon dioxideRemoving carbon dioxide

•• Removing ethylene and other volatilesRemoving ethylene and other volatiles

•• Degree of precision differentiates MA and CADegree of precision differentiates MA and CA

Composition of Normal Air

78.08% Nitrogen (N2)

20.95% Oxygen (O2)

0.93% Argon (Ar)

0.03% Carbon dioxide (CO2)

0.0001% Ethylene (C2H4) (1 ppm)

5

MAP Salad Products

Some uses of MA for fruits and vegetables

MA for strawberry pallets to control Botrytis

Bag‐in‐box MA for melons

Factors contributing to postharvest losses

• Temperature• Water loss

• Damage

• Diseases

• Ethylene

• Continued growth

• Physiological disorders

Transpiration (water loss)

<3% no visual effect, texture3-5% visual quality affected>5% shrivel, lose salability

Loss of Salable WeightLoss Fresh AppearanceLoss of Texture

Water loss is Cumulative

Wt loss (%/day) = product K x VPD

Water lossWater loss• Products are covered

with holes - needed for gas exchange

• Loss of water depends on the vapor pressure deficitvapor pressure deficit (VPD)

• VPD increases exponentially with rising temperature

• Increases linearly with falling humidity

Stomates in leaves; lenticels in fruits

Water loss and temperature

Wt loss (%/day) = product K x VPD

Psychrometric ChartThermodynamic properties of airTemperature and Water Content

oss,

% p

er d

ay

12

15

18

21

24

Strawberry y = 0.506x + 0.35 R2 = 0.91

Broccoli y = 1.01x + 0.34 R2 = 0.97

Romaine y = 0.64x + 0.43 R2 = 0.94

Mushroom y = 1.48x + 0.21, R2 = 0.98

Weight loss in relation to VPD in 4 products

Vapor pressure deficit, mm Hg

0 2 4 6 8 10 12 14 16

Wei

ght

lo

0

3

6

9

Strawberry

Broccoli

Romaine lettuce

Mushroom

Cantwell, UC Davis

6

Preventing water loss - reduce VPD

• Harvest when cool

• Reduce temperature

• Increase external VP

– polyethylene bags– polyethylene bags

– increase humidity

• Beware of condensation

– disease!

Packaging to reduce water loss.Contain, Protect, InformRPCs, Paper, Carton, Plastic

Hammock Pack for Ripe FruitThompson & Slaughter, UC Davis

4

5

6

7

Stored at 32°F, 75% RHi t 2 h

Load at 40°F,Transport at 40°F

Table GrapesIdeal vs Poor Postharvest Handling

% Water Loss

0

1

2

3

1 hr32°F, 95% RH

32°F 95% RH, air at 0.5 mph

Load at 32°F,Transport at 40°F

6 hrs 80°F 20% RH

Cooled at40°F, 75% RH

air at 2 mph

Delay Before Cooling

6 hours Cooling

7 dayStorage

7 dayTransit

From G. Mitchell, UC Davis

Factors contributing to postharvest losses

• Temperature• Water loss

• Damage

• Diseases

• Ethylene

• Continued growth

• Physiological disorders

Overcoming damageOvercoming damage

• CARE!• Careful harvesting

• Into lined baskets/bins

• Don’t throw, dump, or drop

• Avoid rough surfaces

• Minimize touch points

• Pack gently but securely

What’s wrong with this picture?

7

‘Ranch Pack’ Peach Handling: Simple, Clean and Careful Handling for High Quality Product

Hairnets; gloves3rd party InspectorsForced Air CoolingNow packers wear hairnets, sometimes gloves

DiseasesDiseases• Major cause of loss

• Relatively few important genera–Most are weak pathogens and need injury

Reduce Physicaldamage

• Many products are not infected

Temperature and Postharvest Decay9=

exc

elle

nt,

1=

un

use

able

1

2

3

4

5

6

7

8

9

5=g

reen

, 1=

yello

w

1

2

3

4

5Visual Quality Color

2.5°C 36°F5°C 41°F

7.5°C 45°F10°C 50°F

Changes in Changes in Spinach quality: Spinach quality:

washed and baggedwashed and bagged

SPINACH: DAMAGE, DECAY, TEMPERATURE

Days

0 3 6 9 12 15 18

9=ex

celle

nt,

1=

un

use

able

1

2

3

4

5

Days

0 3 6 9 12 15 18

9=ex

celle

nt,

1=

un

use

able

1

2

3

4

5Decay Off-odors

ggggproduct stored at 4 product stored at 4 TemperaturesTemperatures

DAMAGE ANDDAMAGE ANDDECAYDECAY

Cantwell, 1999

Microbes present an "invisible challenge”

They don't usually They don't usually h thh th

Raw foods contain microorganismsSome are pathogenic to humans

Raw foods contain microorganismsSome are pathogenic to humans

change the appearance, change the appearance, taste or odor of food.taste or odor of food. Fresh produce with no Fresh produce with no kill stepkill step Prevention of Prevention of Contamination is keyContamination is key

FECES insects

sewage

harvesting, handling,processing

environments

Food Safety IssuesSources of Contamination; PreventionGood Production & Handling Practices

ANIMALS, BIRDS PRODUCE HUMANSWATER

g

soil

meat, milk, eggssilage, feedplants

(cross contamination)

From Trevor Suslow, UC Davis

8

Factors contributing to postharvest losses

• Temperature• Water loss

• Damage

• Diseases

• Ethylene

• Continued growth

• Physiological disorders

Ethylene - an important factorPlant hormone with positive and negative

effects on fresh produce

• Useful:– Accelerates ripening

– Causes abscission

Control Ethylene

– Chlorophyll destruction

• Problematic:– Accelerates ripening

– Causes abscission

– Chlorophyll destruction

– Accelerates senescence

7 d 20°C (68°F)

Respiration rates of Ripening Fruits

pe

r kg

-h

120

140

160

180Breadfruit

Cherimoya

Climacteric Fruits

per

kg-h

20

25

30

GrapeStrawberry

Nonclimacteric Fruits

Days

0 2 4 6 8 10 12 14 16

mL

O2

or C

O2

0

20

40

60

80

100

Mango

Tomato

Apple

Fig

Days

0 2 4 6 8 10

mL

O2 o

r C

O2 p

0

5

10

15

20 p

Pineapple

Cherry

Lemon

Ethylene Production Rates by Fruits at 20°C (68°F)

Range (µL/kg-h) Product

0.01-0.1 Citrus, grape, cherry strawberry

MOST VEGETABLES

0.1-1.0 Pineapple, blueberry, cucumber

1.0-10.0 Banana, mango, tomato, honeydew melon, fig

10-100 Apple, avocado, cantaloupe, nectarine, papaya, pear

>100 Cherimoya, passion fruit, sapotes

Manipulating Manipulating Ethylene EffectsEthylene Effects

1.1. Avoidance Avoidance Products, combustion engines, smokeProducts, combustion engines, smoke

2.2. RemovalRemovalVentilation, oxidation, absorptionVentilation, oxidation, absorption

3.3. Inhibition of productionInhibition of production

Lettuce Apples

ppLow temperature, chemical inhibitors enzymes, antisense Low temperature, chemical inhibitors enzymes, antisense

technologytechnology

4.4. Inhibition of actionInhibition of actionLow temperature, high CO2, low O2, STS, Low temperature, high CO2, low O2, STS, 11--MCP (MCP (SmartfreshSmartfresh))

5.5. GermplasmGermplasm selection/engineeringselection/engineering

CompatibilityCompatibility

•• TemperatureTemperature

•• Relative HumidityRelative Humidity

•• EthyleneEthylene

•• OdorOdor

Transportation and Loading

OdorOdor

7 day storage compatibility chart

http://postharvest.ucdavis.edu/produce_information/Retail & Food Service outlets

Distribution warehouses and Storage rooms

9

Factors contributing to postharvest losses

• Temperature• Water loss

• Damage

• Diseases

• Ethylene

• Continued growth

• Physiological disorders

TIME

Continued growth--temperatureContinued growth--temperature

• Sprouting (potato, onion, garlic)

• Rooting (onion, potato)G th f• Growth away from gravity (asparagus, flowers)

• Internal seed growth (cucumber, beans)

• Opening of immature buds (broccoli)

• Disorders resulting from abnormal conditions during production and marketing

• Abnormal temperatures

E t d d t

PHYSIOLOGICAL DISORDERS

• Extended storage

• Abnormal gases

• Nutritional imbalance

Factors that influence U.S. Consumers’ Produce Purchases

C i t dSizeIn-season

Bulk (loose) displayCalorie content

Growing region/countryOrganic

PrepackagedBrand name

0 20 40 60 80 100 120

Fresh Trends, 1990. Vance Research Services.

% of Consumers

Taste/FlavorFreshness, ripenessAppearance

Nutritional valuePrice

Storage lifeCertified safe, testing

Convenient, prepared

Postharvest Problem…Quality is maximized when the product is 

harvested more mature or ripe, whereas shelf‐and storage life are extended if the product is 

harvested less mature or unripe….

Toivonen, P. 2007. Fruit maturation and ripening and their relationship to quality. Stewart Postharvest Review 2:7.

ACIDSSUGARS

Low High

LowInsipid,

tastelessSweet

Taste and the Sugar:Acid Ratio

Moderate to High

Sour, tartBest flavor

combination

Soluble solids measured by a refractometer = sugars, but also organic acids, soluble pectins,

anthocyanins, phenolic compounds, ascorbic acid

10

Based on Flavor & Nutritional Quality

Based on Firmness & Texture

Based on Appearance (Visual Quality)

0 20 40 60 80 100%

Postharvest Life Under Optimum ConditionsFrom Adel Kader, UC Davis

Characteristics of horticultural crops

• High water content• Easily damaged

Di• Diverse– genome – tissue type – physiological state

• Alive – a biological system

Factors contributing to postharvest losses

• TIME• Temperature

• Water loss

• DamageDamage

• Diseases

• Ethylene

• Continued growth

• Physiological disorders

• Light

1) Harvest at correct maturity

2) Reduce physical handling

3) Protect product from sun

4) Keep packingline simple and

clean; ensure good worker hygiene

10 Basic Postharvest Principles10 Basic Postharvest Principles

5) Select, classify, and pack carefully

6) Align cartons, strap pallet

7) Cool as soon as possible

8) Know market and product requirements

9) Coordinate efficient & rapid handling

10)Train and compensate workers adequately