There are mainly three types of causes of food spoilage viz. biological, chemical and physical causes. Biological causes comprise of growth and activity of microorganisms such as bacteria, yeast and moulds; activity of food enzymes and damage due to pests, insects and rodents etc. Chemical causes include reaction with oxygen and light and chemical reactions within food constituents. Physical causes consist of temperature and physical abuse.
All of these factors can act together. For example, bacteria, insects, and light, all can be operating concurrently to spoil food in a field or in a warehouse. Similarly, heat, moisture, and air at the same time affect the multiplication and activities of bacteria and chemical activities of food enzymes.
The major types of spoilage that occur in foods are due to microbiological, biochemical, physical and chemical changes. These include:
- Growth and activity of microorganisms such as bacteria, yeast and moulds
- Activities of food enzymes, present in all raw foods, promote chemical reactions within the food affecting especially the food colour, texture and flavour
- Inappropriate holding temperatures (heat and cold) for a given food
- Gain or loss of moisture
- Reaction with oxygen and light causing rancidity and colour changes due to oxidative reactions
- Physical stress or abuse
- Damage due to pests, insects and rodents etc.
- Non-enzymatic reactions in food such as oxidation and mechanical damage
Spoilage due to growth and activity of microorganisms:
Most significant deteriorative changes occur in foods due to microorganisms present in air, soil, water and on foods. They use our food supply as a source of nutrients for their own growth, which results in deterioration of food and render our food supply unfit for consumption. Microbes spoil any food in many ways viz. by increasing their number; by utilizing nutrients; by producing enzymatic changes; by contributing off-flavours; by breakdown of a product; and by synthesis of new compounds. The three major types of microorganisms which cause food spoilage are bacteria, yeasts and moulds.