The factors which can cause damage to the stored food materials can be divided into two categories:
1. Abiotic factors
2. Biotic factors.
New let us discuss these factors in detail.
These are the factors, which are not due to any living organism. The various Abiotic factors which damage the stored food materials are:
(b) Moisture content in food grains
(c) Moisture in the air (humidity)
(d) Material of the containers used for storage.
Now let us discuss how these factors agent the stored food materials.
(a) Effect of Temperature:
Temperature is an important factor for the safe storage of foodgrains and other food materials as it affects the growth of insects and microorganisms which attack the stored food materials. The insects which attack the stored foodgrains have maximum growth rate between 30` C and 32`C. Micro-organisms and enzymes which damage the food materials are most active between 30`C and 40`C. Therefore, the damage to the stored food materials can be significantly reduced by storing them at lower temperatures.
(b) Effect of Moisture Content in Foodgrains:
The storage life of the grain is closely related to its moisture content. For safe storage, the moisture content in the foodgrains should be less than 14 per cent. The moisture content in a mature grain is about 16 to 18 per cent. Therefore, the grains should be thoroughly dried to bring down the moisture content below 14 per cent. However, the grain should not be completely dried to bring down the moisture is essential for maintaining the integrity of the grain. High moisture content in food grains adversely affects the storage in the following ways:
1. It increases the rate of physical and chemical changes brought about by the action of microorganisms and enzymes.
2. It increases the population and activity of insects, bacteria and other microorganisms.
3. The respiration of a large population of insects releases large amount of heat, which may raise the temperature of the stored food grain. This is known as DRY HEATING of foodgrains.
4. High moisture content in the foodgrains increases their size. As a result, more space is required for their storage.
(c) Effect of Moisture Content of Air:
High moisture content of air as well as high temperature accelerates the growth of moulds in the stored food grains. This may result in increase in temperature up to 66`C and the moisture content of the foodgrains may increase from 14per cent to 18 per cent. This is known as Wet Heating of Grains or Damp Grain Heating. The damp grain heating not only lowers the quality of stored food grains but also adversely affects the future germination of seeds. For example, in eastern India, the storage of wheat grains without losing viability for the next crop is a big problem due to high humidity prevailing in that region.
(d) Effect of Material of the Containers:
The containers used for storing different types of food materials should be carefully selected. The material of the containers also plays an important role. The material used for making containers for storing food materials should have the following characteristics:
1. The material used for making containers should not be poisonous. For example, lead is a poisonous metal; therefore, it should not be used for making containers.
2. The material of the container should not react with the food material stored. For example, citrus fruits react with copper to from poisonous (toxic) compounds. Therefore, the containers made of copper should not be used for storing citrus fruit products such as orange juice.
3. Microorganisms affect the food materials in the following ways:
i. The action of microorganisms may lead to loss of weight and discoloration of food grains. It may also result in production of some poisonous compounds (toxins) and heating. All these factors reduce the quality of food grains and may make them unfit for human consumption.
ii. Food grains affected by microorganisms may fail to germinate.
iii. The action of microorganisms on the food materials converts’ fat into fatty acids and proteins into amino acids, ammonia and sulphur compounds. Some of these products of decomposition of fats and proteins present in the food material are volatile and have strong smell. Thus, if a strong offensive small is coming from a food material it indicates that the food is spoiled.