POST-HARVEST TECHNOLOGY OF AGRICULTURAL PRODUCT (Lecture 01)

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FET 418
POST-HARVEST TECHNOLOGY OF
AGRICULTURAL PRODUCT
What is Post-Harvest Technology?
• Post‐harvest technologies constitute an inter‐disciplinary
science and techniques applied to agricultural commodities
after harvest for the purpose of preservation, conservation,
quality control/enhancement, processing, packaging, storage,
distribution, marketing, and utilization to meet the food and
nutritional requirements of consumers in relation to their
needs.

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Post‐harvest technology stimulates agricultural
production by
• prevents post‐harvest losses;
• improves nutrition ;
• adds value to agricultural products;
• opens new marketing opportunities; and
• generates new jobs
The three main objectives of applying postharvest technology
1. to maintain quality (appearance, texture, flavor and nutritive
value)
2. to protect food safety, and
3. to reduce losses between harvest and consumption.

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Major field crops in Bangladesh
Cereals Pulses Oilseeds Sugar-
cane
Fruits &
Vegetables
1. Rice
2. Wheat
3. Maize
4. Barley
5. Oat
6. Rye
7. Millets
8. Triticale
(cross
variety of
wheat and
rye)
1. Bengal gram
(chick pea)
2. Lentil (Masoor)
3. Black gram
(Maskalai)
4. Green gram
(Moog)
5. Lathyrus pea
(Khesari)
6. Peas (Motor)
7. Red gram
(Arohor)
1. Mustard
2. Indian mustard
(rai)
3. Indian rapel
(Tori)
4. Gingelly
(Seasame)
5. Linseed (Tisi)
6. Soyben
7. Sunflower
Storage of Cereal Grains
• Cereal grains are harvested, threshed, dried, and stored to
prevent deterioration of quality of grain.
Purposes of storage:-
1. Retain the supply of the food grain throughout the year,
2. Retain viability of the seed for planting in the following
season
3. Take advantages of higher prices by the traders, and
4. Serve as a reserve during the times of scarcity.

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Factors influencing deteriorative changes during
storage
1. Physical: Temperature, humidity
2. Chemical: Moisture, oxygen, oxidation
3. Physiological: Respiration, heating
4. Biological: Insects, microorganisms, mites, rodents, birds.
Changes occurring during storage: CHO, Proteins, Fats, Vit., Minerals,
Discoloration, Viability, Flavor.
Nature of loss during storage
1. Weight loss
2. Nutritional loss
3. Quality loss presence of dust, contaminants e.g. insects
fragments, rodent hairs, pesticide residue, damaged grains)
4. Loss in viability
5. Damage physical damage during harvesting, threshing or
milling)

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Principles of grain storage
• The deterioration of grain is done indirectly by controlling
moisture, air movement, and preventing attack of
microorganism, insects and rodents.
• Here the main objective is to reducing the metabolic activity
to such stable level that that grain mass is sufficiently stable
with minimal deterioration.
• Two alternative methods are:
a) Reduction of moisture content to safe level and cooling of
the grain,
b) Modification of atmospheric condition of storage system.
• Deterioration of cereal grains can be retarded by controlling
temperature and moisture, although oxygen free environment
are also useful in this regard.
• Moisture: high moisture content favors biochemical and
chemical changes in the grain as well as the growth of
microorganisms, insects and mites during storage.
• Temperature: critical factor for storage up to certain limits.

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• Moisture
• Moisture content important for Economic value: 1% moisture = 1% value
• Safe storage!
• More correct: importance of water activity (aw= p/p0) as a measure for
water availability
• Differences in relation between moisture content and water activity can
exist
• Mostly: analysis of moisture content

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• Moisture content analysis is difficult:
• Not average is important, but highest concentration at a
particular spot
• Variation in moisture content in a storage facility due to
‐ Harvest time
‐ position in the field
‐Different suppliers
‐ Variation in a single year...
• Given sufficient time (often matter of weeks): equilibrium
• Techniques: NIR, Karl‐Fisher, weight loss,...
Drying of cereal grains
• Often moisture content at harvest: too high
• Low temperature air drying
• Forced convection
• No damage to the grain
• Cheap
• Slow
• Need for low humidity air
• Only possible if moisture content is low enough to begin with to assure
safe storage during drying

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• High temperature drying
• Forced convection with heated air
• More expensive
• Could damage kernels
• Physical damage
• Loss of germination capacity
• Loss of bread making capacity in case of wheat
• Poor gluten starch separation behaviour
Aeration
• During storage, aeration prevents
• Formation of hot spots
• Accumulation of moisture at specific places due to
‐ Increased metabolic activity, coupled to moisture
‐ Seasonal temperature changes

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Assessment of deterioration
• Changes in grain colour
• Sour or musty smell
• Loss of viability
‐ Germination test
‐ Tetrazolium test
• Fat acidity increase
• Glutamic acid decarboxylase activity decrease
• For wheat: “Sick wheat”