Introduction to Postharvest Biology and Practices

Postharvest losses

Postharvest Biology

• A practical science.

• Primarily deals with Perishable Commodities.

• Postharvest = After Harvest

• Concerned with the harvest of the crop

(when & how to harvest; maturity standards).

• Also in pre-harvest factors (seed source, rootstock, etc.) because they strongly influence postharvest quality.

The fruit quality is set during growth.

• Ultimately, the maximal

product quality is determined at harvest.

The Postharvest Goals

• Harvest the product at its optimum maturity.

• Maintain the product’s internal and external quality throughout packing, storage and distribution.

It is Alive during this process!

• Deliver the fruit to consumers at the time and in a form (e.g. ripe, cut up, etc.) that they will purchase it.

Historical background

Early postharvest practices:

• Dried fruits, vegetables, meats, pickles, etc.

• Fermentation of juices.

• Salting or smoking.

All these methods KILL the product!

It is easier to transport and store the products.

Historical Background

Early Storage Practices:

• Basket making developed by 7,000 B.C.

• Underground pits and silos by 9,000 B.C.

Silos were the major means of long term storage by Roman times.

• Roman era – modified atmosphere storage of grains.

• 1803- Ice refrigeration developed.

• 1855- mechanical refrigeration was invented.

• 1872 - ice refrigerated rail cars were common.

• 1889 - ammonia refrigeration was widely used to make ice.

• 1928 - mechanical refrigerated displays used in retail stores.

• 1927 - Controlled atmosphere studies begun.

• 1929 - Commercial CA storage built in England.

Historical Background

Postharvest issues became important when cities developed:

• The Industrial Revolution (18th century).

• The Problem:

How to deliver fresh fruits and vegetables from areas of

production to areas of consumption and keeping their quality?

Historical Background

All fresh produce is alive

↓

The Challenge is to Keep Healthy Until Consumed!

World-Wide Perspective

• World population has reached almost 7 billion.

• Technological advances have helped to feed much of the world (e.g. China, India & Brazil).

• Many parts of the world still in need.

Western style, capitol intensive methods often not suitable for an area.

Food distribution is a major worldwide problem:

• Urbanization expected to continue at a greater rate in developing countries.

• Produce grown in these areas are the least studied.

Worldwide production (2001):

• Cereals (durable food goods) = ~2.1 billion MT.

• Fruits, Vegetables, Roots & Tubers =~1.8 billion MT.

World-Wide Perspective

Overlap of world hunger and world poverty

% of population

earn less than 1.25 $ per day

% of population

undernourished

World overall production of vegetables and fruits (1000 tones)

0 500,000 1,000,000 1,500,000

1994- 1996

1999- 2001

2005 2006 2007

vegetables fruits

FAO Statistical Yearbook 2009

The importance of postharvest

The increase of vegetables and fruit production:

• Population growth.

• Higher standard of living.

• Awareness for nutritional value of food.

0 200 400 600 800 1000 1200 1400 1600

1970 1980 1990 1994

Africa Asia

South/Central America USA/Canada

Europe Oceania

Million tons fruits and vegetables

Fruit and vegetable production increased

by 44%

between 1970 to 1994

India: No 3 of the world fruit and vegetables producer. About 50% of the products deteriorates until

reaching the consumer.

Therefore, consumption is low and prices are high.

0 200 400 600 800 1000

1970 1980 1990 1994

Africa Asia

South/Central America USA/Canada

Europe Oceania

Million tons fruits and vegetables without root crops

Fruit and vegetable production

increased by 75%

between 1970 to 1994 ) not including roots

and tubers (

China and India produce 30% of the world fruits

and vegetables.

The importance of postharvest

Characteristics of Perishable Commodities

Compared to grains:

• More subject to deterioration after harvest (shelf life days to months vs. > 1yr).

• Relatively larger in size (up to 5 kg vs. < 1g).

• Soft textured.

• Higher water content (70 to 90% vs. 10 to 20%).

• Higher respiration and heat production.

Estimated Postharvest Losses

very rough estimates are available:

• 5 to 25% in developed countries.

• 20 to 50% in developing countries.

• In the US, a large portion of loss occurs at the consumer.

Loss of product is much more than

just the cost of the commodity

The other losses

• Energy & labor loss (e.g. during packinghouse operations).

• Loss of materials (e.g. packaging).

• Cost of waste disposal.

• Loss of food value (e.g. nutrients).

• Loss of organoleptic quality:

Color changes Water loss

Carbohydrate changes.

Volatile changes

Breakdown of proteins, cell wall components, softening, etc.

Causes of Postharvest Loss

Internal Factors:

• Respiration.

• Compositional changes.

• Morphological changes.

• Physiological disorders.

• General senescence.

Environmental Factors:

• Temperature

• Physical damage

• Pathogens

• Relative humidity

• Atmospheric composition

• Light

• Gravity

• Rodents and other animals

• Contamination

Causes of Postharvest Loss

Perishable Commodities are still alive

!

They consume oxygen and produce carbon dioxide

Sugar+ O

₂

↓

Energy + CO

₂

+ Water + Heat

Respiration and Shelf Life

Respiration rate and shelf life are inversely related.

Higher respiration

↓

Shorter Shelf Life

Temperature & Respiration

• Temperature is the most important factor influencing the postharvest life of the given commodity.

• Temperature dictates the speed of chemical reactions including respiration.

• Typically, for every increase of 10^oC, the respiration increases between 2 and 4 fold.

R1=Respiration at Temperature 1 (T1) R2=Respiration at Temperature 2 (T2)

Q

₁₀

= R2 R1

10 T2-T1

The affect of temperature

The affect of temperature on broccoli after 48 hr of storage at either room temperature or in cold storage

24^oC 4^oC

Postharvest compositional changes

• Water loss

• Nutrients

• Vitamins

• Antioxidants

• Starch to Sugar to Starch

Water Loss

Water Loss resulting a direct loss of salable weight as well as quality loss:

• Appearance quality - wilting, shriveling, and accelerated development of injuries.

• Textural quality – loss of crispness, juiciness, etc.

• Nutritional quality – e.g. vitamins A & C.

Rate of water loss influenced by:

• Environmental factors – e.g. relative humidity.

• Anatomical factors – stomates, hairs, etc.

Postharvest Morphological Changes

• Horticultural commodities are living products and

sometimes are still growing. Therefore, they often continue development in ways that sometimes reduce quality.

Changes include:

• Sprouting (onions, tubers, root crops)

• Rooting (onions, root crops)

• Elongation & Curvature (asparagus, gladiolus)

• Seed Germination (lemon, tomato, pepper)

Postharvest Physiological Disorders

A tissue damage or breakdown which not related to pathogens, insects or mechanical damage.

Temperatures

• chilling injury, freezing injury or High temperature injury.

Altered atmospheric gas concentrations.

• Low O₂ or Elevated CO₂. Nutrition

• As calcium deficiency or boron toxicity.

Chilling Injury

• Physiological injury to some commodities held at temperatures above freezing.

• Susceptible crops include:

Avocado Banana Cherimoya

Citrus Feijoa Guava Jujube Mango

Olive Papaya Passion fruit

Pineapple Plantain Pomegranate Sapote

Cucumber Eggplant Okra

Pepper Sweet Potato

Tomato

Chilling Injury

• Occurs mainly in commodities from subtropical & tropical origins.

• Injury caused by exposing fruit to low temperatures above freezing, between about (5 to 15 ^oC).

• Injury becomes more noticeable after transferring to non- chilling temperatures (shelf life).

Chilling Injury

Symptoms:

• Surface pitting

• Discoloration (external/internal)

• Water-soaked areas

• Necrotic areas

• uneven ripening or failure to ripen

• Greater susceptibility to decay

• More…

Causes of Postharvest Loss

Environmental Factors

Temperature Light

Physical damage

Gravity

Pathogens Rodents and

other animals

Relative humidity Contamination

Atmospheric

Composition

Temperature

• Mentioned above with respiration and physiological disorders.

• Temperature greatly effects water loss.

• Lower temperature also slows pathogen development.

Physical Damage

• Causes the greatest amount of loss to fresh horticultural products.

Physical Damage Affects:

• Respiration, ethylene production, ripening, and other metabolic processes.

• Pathogen growth and ability to invade tissue.

• Tissue discoloration.

Pathology (decay)

• Fungi (major), bacteria and viruses.

• Preharvest (latent) and postharvest infections.

• Most postharvest infections are a result of rupturing the epidermis of the commodity.

Relative Humidity

• Higher relative humidity slows water loss from the commodity.

• High relative humidities (95 to 100%) might weaken the cartons.

• Free moisture stimulates pathogen development.

5%

10%

15%

Atmospheric Composition

Modified or Controlled Atmospheres:

Modified Atmospheres (MA):

• Altering the normal gas composition surrounding a commodity (e.g. raising or lowering O₂ or CO₂ concentrations).

• Passive. The commodity is placed in a gas impermeable

container and the crop’s respiration consumes (lowers) O₂ and gives off (increases) CO₂.

Controlled Atmospheres (CA):

• Same as MA, except gas concentrations are actively regulated using special equipment.

Modified Atmospheres - Advantages

• Slows down respiration and other metabolic processes

(ripening & senescence).

• Reduces sensitivity to ethylene (at < 8% O₂ or >1% CO₂.

• Reduces development of some physiological disorders

(chilling injury).

• May inhibit pathogen development.

• Can be used to kill insects.

Modified Atmospheres - Disadvantages

• Can cause or exacerbate some physiological disorders (black heart in potatoes).

• Can cause irregular ripening.

• Can result in off-flavors or odors if anaerobic respiration occurs.

• Any MA or CA related injuries stimulate pathogen development.

• May delay periderm development and stimulate sprouting in root or tuber crops.

Causes of Postharvest Loss

Environmental Factors:

• Light- Color and morphological changes (potato greening).

• Gravity- Morphological changes (bending).

• Rodents and other animals.

• Contamination (food safety).

Postharvest

Commercial Considerations

Preharvest factors:

• Cultivars.

• Nutrition and Water effects.

• Weather conditions (e.g. temperature, humidity)

• Field sanitation (both for decay & human pathogens).

Harvesting:

• Best time to harvest for fresh, processing, storage?

Preliminary grading in the field:

• Remove unmarketable produce ASAP.

Postharvest

Commercial Considerations

Packing operations:

• Washing, sorting, sizing, grading, waxing, and more.

• Each step costs, therefore use only if increases value of the crop.

Packaging:

• Protects the product, reduces water loss, organize the product, excludes light & communicates information.

• Must be economic, able to support stacking, allow ventilation (cooling), facilitate recycling or disposal at destination markets.

Postharvest Maturation:

• Ethylene degreening or ripening.

• Curing.

Rapid cooling:

• Air cooling

• Room

• Forced-air

• Hydrocooling

• Ice Cooling

(Top icing, Liquid ice injection)

• Vacuum Cooling

Postharvest

Commercial Considerations

Storage:

• increases the cost of the product.

• Critical accuracy of temperature and RH%.

• CA or MA storage.

Transportation:

• By water – inexpensive but slow.

• Trains – more expensive but faster.

• Truck – predominant method. Fast & reliable.

• Air – Fastest, expensive, & inconsistent scheduling and temperature control.

Postharvest

Commercial Considerations

Marketing:

• Identify markets and qualities desired.

• Entire process to deliver what the consumer will buy.

Retailing:

• Educate the retailer how to handle your commodity.

• Continuation of temperature, RH and sanitation chain.

Postharvest

Commercial Considerations