Pasteurization is defined as the process of heating milk to a particular temperature and holding it at that temperature for a particular time till the pathogenic (disease causing) micro-organisms are destroyed causing minimum change in composition flavour and nutritive value of milk.
High temperature short time (HTST) pasteurization at 71.7 {+0} C for 15 seconds is the most common method of pasteurization. Pasteurization conditions are not sufficient to destroy thermo-resistant spores (reproductive part of microorganisms). Pasteurized milk has to be refrigerated.
Sterilization is a more severe thermal process where milk is subjected to temperature of about 135 {+0} C for few seconds followed by aseptic (free of micro-organisms) packaging. Milk processed in this manner is termed as ‘commercially sterile’, but it is not necessarily free of micro-organisms.
These micro-organisms, which survive heat treatment, are unlikely to proliferate during storage and cause spoilage to the product.
However, spores are destroyed during sterilization. Sterilized milk has longer shelf-life even at room temperature. Nutritional losses in sterilization are more compared to pasteurization.
Pasteurization is one of the methods of preservation of products such as milk, alcohol beverages etc. at higher temperatures. The process of heating of the product (milk or beverage) to a controlled temperature (usually below 100 {+0} C) to enhance the keeping quality and to destroy harmful microorganisms is known as pasteurization.
There are two methods of pasteurization (of milk) in general use. One is low temperature holding (LTH) method in which milk is heated to 62.8 {+0} C (145 F) for 30 minutes in commercial pasteurizers (or) large closed vats which are heated by steam coils, hot water jackets etc.
The other method (i.e.) high temperature short-time (HTST) method in which the milk is heated to 71.7 {+0} C (161 F) for 15 seconds. The heating is accomplished by electricity (or) hot water and requires a heat exchange system, which preheats raw, cold milk and cools the hot pasteurized milk.
Pasteurization does not sterilize the products but kills those organisms that grow most readily at low temperatures. The surviving organisms must be kept from multiplying by constant refrigeration.
Pasteurization is sterilization interpolated with a subtle nuance in the process conditions and hence in the final result as well.
Pasteurization is named after the great French chemist Louis Pasteur, is the process of partial sterilization, confined only with the killing of pathogens.
The subject is heated to temperature below its boiling point (usually less than 100 {+0} C) and held at that temperature for a particular time period, with the aim of killing only the pathogens.
The time-temperature combination is decided based on the heat resisting capability of the target micro-organism and the nature of the subject. For instance milk is heated to 73 {+0} C & held for 15 seconds, to destroy Coxciella burnetti and Mycobacterium tuberculosis, which are the target micro-organism.
Sterilization is extended pasteurization where the subject is heated above the boiling point and held for a particular time period to destroy all the microorganisms. The temperature is usually above 100 {+0} C.