Pasteurisation is a process that slows down microbial growth in food. The aim of pasteurization is not to completely destroy all pathogenic micro-organisms in foods (typically in milk & milk products); but just to reduce the number of viable pathogens so that they are unable to cause disease if the pasteurized product is stored as indicated and consumed before its expiry date. Now- a – days a new method of pasteurisation known as flash pasteurisation (HTST) is used which exposes foods and liquids to short periods of high temperature.
In the same way pasteurization of milk is used to get rid of disease producing bacteria and reduce the total bacteria count in milk substantially. This helps to maintain quality of milk. For milk pasteurisation the current trend is to use low temperature –long-time (LTLT) method. In this method the temperature is held at 63°C for 30 min to eliminate pathogenic bacteria that may be present such as Mycobacterium tuberculosis and Coxiella burnett. On the other hand milk is heated to 72°C for 15 sec in high temperature short time pasteurisation (HTST).
In ultrahigh temperature (UHT) pasteurisation milk and milk products are heated to at least 138°C for 2 sec and packaged aseptically. Pasteurised milk is not sterile it must be quickly cooled after pasteurisation to prevent multiplication of surviving bacteria. The effectiveness of pasteurisation is evaluated by phosphatase test which is alkaline phosphatase activity in milk.
Food Safety Standards Regulation says that the terms “Pasteurisation”, “Pasteurised” and similar terms shall be taken to refer to the process of heating every particle of milk of different classes to at least to 63°C for 30 min or heating it to at least 71.5°C and holding it at that temperature for 15 seconds or any other approved temperature time combination that will serve to give a negative Phosphatase Test. All pasteurised milk of different classes shall be cooled immediately to a temperature of 10°C or less.
The regulations also say that recombined milk that is a homogenised product prepared from milk fat, non-fat-milk solids and water shall be pasteurised and shall show a negative Phosphatase test. The regulations also say that no person shall either by himself or by any servant or agent sell—dahi or curd not prepared from boiled, pasteurised or sterilized milk.