Postharvest Physiology of Horticultural Crops

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POSTHARVEST PHYSIOLOGY OF

HORTICULTURAL CROPS

Errol W .. Hewett

Professor of Horticultural Science Massey University

Palmerston North

November 1995

Errol W. Hewett _PhD

PROFESSOR Of HORTICl.LTLRAL SCIE,et:

!POSTHARHST PH\SlOLOGISTi

Department of Plant Science Massey University

MASSEY

UNIVERSITY

Palmerston North Telephone: (06) 356-9099 NEW ZEALAND Facsimile: (06) 350-5679 E.Mail Address: E.W. Hewett@massey.ac.nz

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MASSEY

UNIVERSITY

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POSTHARVEST PHYSIOLOGY OF

HORTICULTURAL CROPS

Errol W. Hewett

Professor of Horticultural Science Massey University

Palmerston North

November 1995

Errol W. Hewett ^PhD

PROFESSOR Of HORTICULTt:RAL SCIE:\CE CPOSTHARVEST PHYSIOLOGIST)

Department of Plant Science Massey University

MASSEY

UNIVERSITY

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Palmerston North Telephone: (06) 356-9099 NEW ZEALAND Facsimile: (06) 350-5679 E.Mail Address: E.W. Hewett@ massey.ac.nz

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DETERIORATION Three main types:

Physical * mechanical damage

* cuts, bruises, abrasions

* freezing damage Physiological

*

^disorders

* temperature - chilling - heat

* nutritional imbalance

* atmosphere

* ethylene

Pathological

*

fungi, bacteria

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OUTLINE

• NZ horticultural industry

• Why postharvest physiology?

• Factors affecting quality - preharvest

- temperature - ethylene

- gas atmosphere

• New opportunities

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Horticultural exports from New Zealand 1995

$million

Fresh fruit 869

Processed fruit 131

Fresh vegetables 194

Processed vegetables 151

Flowers/foliage 50

Seeds/plants 41

% 60.5

9.1 13.5 10.5 3.5 2.9 Total $1.436 million 100%

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Value of horticultural exports from New Zealand

1600--- 1400

1200

1000

800

600

400 200

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1970 1975 1980 1985 1990 1995

Year

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VALUE OF MAJOR HORTICULTURAL EXPORTS IN YEAR ENDING 30 JUNE, 1995

Crop type Value($million)

Apples 482

Kiwifruit 321

Onions 93

Squash 58

Grape wines 42

Fruit and vegetable juice 35

Peas, frozen 34

Mixed vegetables, frozen 26

Sweetcorn, frozen 23

Jams 20

Tomatoes, processed 18

Sphagnum 17

Orchids 15

Potatoes, fresh 14

Potatoes, frozen 14

Apples, processed 13

Pears 12

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QUALITY OF HORTICULTURAL PRODUCTS Quality

• freedom from defects

• attractive appearance - colour - shape

• texture - crispness- JU1c1ness

. . .

• consistency/uniformity in taste, flavour

• adequate shelf life

• freedom from chemical residues The Challenge

To satisfy increasingly demanding consumer requirements, keeping ahead of international competitors

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HORTICULTURAL PRODUCTS - LIVING ENTITIES

• harvest - catastrophic disruption

• water loss continues - transpiration

• metabolic activity continues - respiration

• deterioration of living tissue inevitable ripening ➔ senescence ➔ death

• postharvest physiology - understanding physiological and biochemical processes

• postharvest technology - procedures to slow rate of deterioration

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DETERIORATION Three main types:

Physical * mechanical damage

* cuts, bruises, abrasions

* freezing damage Physiological * disorders

* temperature - chilling - heat

* nutritional imbalance

* atmosphere

* ethylene

Pathological * fungi, bacteria

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FACTORS AFFECTING DETERIORATION Respiration

sugar oxygen carbon

dioxide water

• respiration temperature dependent

• deterioration a function of respiration

• shelf life a feature of deterioration rate

Hence rational for low temperature storage

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Temperature effect on respiration rate

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Temperature effects on quality and storage life

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TEMPERATURE EF'FECTS Low temperatures in coolchain

- reduce respiration - reduce water loss

- reduce nutritional loss - reduce decay organisms Freezing * -0.7 to -2.0^°C

* cell breakdown, death, decay Heat - above 35^°C

- metabolic disruption, HSP - delayed/uneven ripening Chilling - 4 to 10^°C

- chilling injury, decay, death

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CIDLLING INJURY

• Serious problem for tropical and subtropical but also temperate crops

• critical temperature above freezing

• time/temperature dependent

• symptons - varied - spotting

- surface pitting

- external and internal browning - mealiness or woolliness

- water soaking - decay

- death

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ETHYLENEINPOSTHARVEST

Simple naturally occurring gaseous hormone

Sources include - ripening fruit

- decaying vegetation

- internal combustion engines - aircraft exhausts

- cigarette smoke

- ballast from fluorescent lights

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ETHYLENE - GOOD AND BAD NEWS Benefits of ethvlene

- essential for normal ripening

- induces abscission, colour changes, softening, flavour development

- promotes uniform ripening

- widespread use for bananas, tomatoes and kiwifruit Problems with ethvlene

- accelerated ripening and senescence even at low temperatures

- loss of green colour - increased softening

- some disorder induction

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ETHYLENE BIOSYNTHESIS Methionine

SAM J (S-adenosylmethionine)

A VG,AOA ACC synthase

low 0₂

ACC (aminocyclopropane carboxylic acid)

low temp. ACC oxidase

cobalt silver

thiosulphate C₂H₄ absorbers

various steps to receptor Ethylene action

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CONTROLLED/MODIFIED ATMOSPHERE STORAGE

• decreased 0₂

increased CO₂ } ➔ reduced respiration and ethylene

• increased use in New Zealand

• supplements temperature management

• reduces ripening rate

• reduces some chilling injury, rots

• tool for insect control

• minimally processed foods

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POSTHARVEST PATHOLOGY

• few pathogens cause large losses

- Botrytis, Altemaria, Colletotrichum

• reduce sources of inoculum - hygiene

- optimise plant health

• minimise handling damage

• cool rapidly to optimum product temperature - avoid chilling injury

• postharvest chemicals?

- generally to be avoided

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NEW OPPORTUNITIES

• transportable CA storage systems

- computer controlled modulated storage regimes manipulated en route

- intermittent shock treatments

• active packaging and/or skin coatings to optimise internal atmospheres

• non-destructive quality assessment

• genetic manipulation

- long life naturally occurring mutants - transgenic plants; Flavr Savr®

- eco-foods; functional foods - antisense technology for

- polygalacturonase

- ACC synthase, ACC oxidase

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CONCLUSIONS

Postharvest physiologists

• elucidated causes of many physiological disorders and recommended treatments e.g. calcium and bitter pit

• unravelled ethylene biosynthetic pathway and cell wall structure

• characterised temperature and ethylene responses

• developed recommendations for optimal postharvest technologies

• working closely with industry to optimise quality of NZ products internationally