Heating /thermal treatment is a process of food preservation that uses heat to preserve a food. Heat is applied to a food with the aim of destroying micro-organisms and denaturing enzymes that are responsible for spoilage. The high temperatures utilized are destructive to various micro-organisms from spores, moulds to bacteria and viruses.
Methods of heat treatment
- Blanching– This process involves immersing food mainly vegetables and fruits in hot water for a few minutes then in cold water. This method preserves the sensory attributes of a food.
- Pasteurization – Is a heating method that involves the use of temperatures below 100°C,-at least 72°C for 15 seconds. It can be divided broadly into HTST (high temperature and a short time) and LTLT (low temperature and a long time for pasteurization). HTST involves heating at high temperatures for short durations (around 71.5 Celsius degrees (maximum is at 74 Celsius degrees), while LTLT involves using low temperatures for longer durations (around 62.5 °C for 20-30 minutes).In low acidic foods, pasteurization aims to extend the life and destroy micro-organisms .Low acidic foods such as milk are usually pasteurized to extend their shelf-life while acidic foods (pH < 4.6) such as fruit juices are primarily pasteurized to deactivate microorganisms, denature enzymes and extend shelf-life. This process does not significantly impact the organoleptic properties such as flavour.
- Sterilization– It involves the use of temperatures above 100°C to preserve and destroy microorganisms. This process aims to completely destroy spores and other micro-organisms, to maintain product stability in different environments and to extend the shelf -life of a food product. Commercial sterilization is performed on a larger scale whereby food products such as milk, are sterilized at temperatures of about 138–150 °C for 2-3 seconds. Pathogens are inactivated within this temperature range.
Advantages of the heating method
- Enhances food quality– This process of heating could improve the taste and texture of a food.
- Destroys micro-organisms and enzyme activity– The high temperatures used destroy the enzymes and micro-organisms responsible for food spoilage.
- Eliminates anti-nutritional substances -Anti-nutritional components such as lectins interfere with the utilization of nutrients found in a food. Through heating, these undesirable substances are destroyed.