This document discusses biochemical changes that occur in food grains during post-harvest storage and preservation. It covers the composition of cereals including carbohydrates, proteins, and lipids. Environmental factors like temperature, moisture, and oxygen content that influence storage are described. The document also discusses microorganisms, insects, rodents and other agents that can cause grain deterioration during storage, and different storage methods using bags or bulk storage.

1. Biochemical changes in food grains
during post harvest storage and
preservation
Jasmine Juliet .R
Teaching Assistant
Biotechnology Dept
AC&RI, Madurai.

2. food grains

3. Food grains - Introduction
• Cereals and legumes generally known as grains constitute the most vital diet
component for the majority of people in the world providing the calories and
proteins.
• Cereals are the edible seeds of plants of the grass family.
• Maize, wheat, and rice contribute about equally to 85% of world cereal
production.
• Properly dried cereals contain less than 14% water, and this limits microbial
growth and chemical changes during storage.
• On a global basis, many fermented cereal products are derived wholly or in
part from grains such as rice, maize, sorghum, millet, barley, and rye.

4. Food grains - Introduction
• Different cereals differ not only in nutrient content, but also in the
composition of the protein and carbohydrate polymers.
• Cereal-based foods, mainly consumed for breakfast, constitute a very
important source of energy, particularly in the case of children.
• For this reason, their processing (baking or extrusion cooking) should be
carefully carried out in order to keep their quality.
• One of the main reactions that takes place during the processing of these
cereal-based foods is non-enzymatic browning including Maillard
reaction and caramelisation, which might contribute to the development of
colour and fluorescence.

5. Cereal Composition - Carbohydrates
• Carbohydrates are the most important constituents of cereal grains, contributing
77–87% of the total dry matter.
• In wheat, the carbohydrate is mainly starch. Almost 100% of the starch granule is
composed of the polysaccharides amylose and amylopectin.
• Nonstarch polysaccharides, the pentosans, which are principally arabinoxylans,
comprise approximately 2–3% of the weight of flour.
• They contribute in baking by increasing the viscosity of the aqueous phase.
• Cereals also contain small amounts (1–3%) of mono-, di- and oligosaccharides,
and these are important as an energy source for yeast at the start of dough
fermentation.

6. Cereal Composition - Protein
• Cereal proteins contribute to the nutritional value of the diet.
• Gluten Proteins: The gliadins and glutenins, collectively called gluten
proteins, make up about 80% of the total protein in the grain. A good bread
flour must contain adequate amounts of gluten proteins.
• Enzyme Proteins: Amylases, Proteases, Lipases are present in cereals.
• The albumin and globulin proteins are concentrated in the bran, germ, and
aleurone.

7. Cereal Composition - Lipids
• Lipids are present in grains as a large number of different compounds, and they
vary from species to species.
• Most lipids are found within the germ.
• Wheat flour contains about 2.5% lipids:
 1% are polar lipids (tri- and diglycerides, free fatty acids, and sterol
esters)
1.5% are nonpolar lipids (phospholipids and galactosyl glycerides).
• During dough mixing, much of the lipid forms hydrophobic bonds to the gluten
protein

9. Storage - Definition
• "Storage" means the phase of the post-harvest system during which the products
are kept in such a way as to guarantee food security. The main objectives of
storage:
• to permit deferred use (on an annual and multi-annual basis) of the agricultural
products;
• To ensure availability of seeds for the crop cycles;
• To guarantee regular and continuous supplies of raw materials;
• To balance the supply and demand of agricultural products.
• In order to attain these general objectives, it is obviously necessary to adopt
measures aimed at preserving the quality and quantity of the stored products.

11. Influences of environmental factors
• To conserve the quality of products over long-term storage, degradation
processes must be slowed down or even stopped.
• Degradation of grains during storage depends principally on a combination
of three factors:
 temperature,
 moisture,
 oxygen content.
• During storage, the combined effects of these three factors can sometimes
cause severe losses.

12. Temperature and moisture
• Temperature and moisture are delaying the biochemical transformation
(especially the "breathing" of the grain) the origin of grain degradation.
• They have a direct influence on development of insects and microorganisms
(moulds, yeasts and bacteria), and on the premature and unseasonal
germination of grain.
• It is easy to observe that the higher the temperature, the lower must be the
moisture of the grain in order to ensure good conservation of the products.
• The temperature and moisture content of the grain condition leads to the
development of the maximal duration of storage.

14. Oxygen content
• Like grain, micro-organisms and insects are living organisms that need
oxygen.
• Storage of grain in places that are low in oxygen causes the death of
insects, cessation of development of micro-organisms, and blockage, or
slowing down, of the biochemical phenomena of grain degradation.
• This favours the conservation of grain.

15. Agents causing deterioration of
stored grain - Micro-organisms
• Micro-organisms (moulds, yeasts, bacteria) are biological agents present
in the soil which, when transported by air or water, can contaminate
products before, during and after the harvest.
• Their presence and growth cause severe changes in the nutritive value
(taste, smell, aspect).
• Micoorganism in the case of moulds, for the potential formation of
dangerous poisons (mycotoxins).
• Impurities, and cracked or broken grains, foster the development of micro-
organisms.

16. Agents causing deterioration of stored
grain - Insects
• Insect infestations can occur in the places where products are stored.
• The damage is provoked by the larvae developing inside the grain.
• The insects to infest stored products belong to the following families:
Coleoptera (damage by larvae and adult insects);
 Lepidoptera (damage only by larvae).
• Insects can be responsible for significant losses of product.
• Insects can live and reproduce at temperatures between +15°C and +35ºC.
• On the contrary, low humidity slows or even stops their development, and a low
supply of oxygen rapidly kills them.

17. Agents causing deterioration of
stored grain - Rodents
• Rodents multiply in storage places, where they can find an abundance of food.
• They cause serious damage not only to stored products but also to packaging and
even to storage buildings.
• The principal rodents, to attack stored products, belong to the following species:
 black rat, also called roof rat (Rattus rattus),
 brown or Norway rat, also called sewer rat (Rattus norvegicus),
 mouse (Mus musculus).
• Prolonged attacks results in serious quantitative losses of stored products. Indeed,
rodents are often the vectors of serious diseases (rabies, leptospirosis).

18. Storage methods
• There are basically two methods of storage:
 in bags and
 in bulk.
• Bags can be stored either in the open air or in warehouses;
• bulk grain is stored in bins or silos of various capacities.
• The choice between these methods and the degree of technological
sophistication of the storage buildings depend on many technical, economic
and socio-cultural considerations.