Holder method of pasteurization is not effective to kill

All nonsporing pathogens like Mycobacterium, Brucellae and salmonella are destroyed by pasteurisation Coxiella burnetti is relatively heat-resistant and may survive Holder method Ref: Essential of microbiology by Kumar 1st edition Pgno : 27 Pasteurization of milk Pasteurization may be defined as the heating of milk to such temperatures and for such periods of time as are required to destroy any pathogens that may be present while causing minimal changes in the composition, flavour and nutritive value (WHO, 1970). There are several methods of pasteurization. Three are widely used : (1) Holder (Vat) method : In this process, milk is kept at 63-66 deg C for at least 30 minutes, and then quickly cooled to 5 deg C. Vat method is recommended for small and rural communities. In larger cities, it is going out of use. (2) HTST method : Also known as "High Temperature and Sho Time Method". Milk is rapidly heated to a temperature of nearly 72 deg C, is held at that temperature for not less than 15 seconds, and is then rapidly cooled to 4 deg C. This is now the most widely used method. Very large quantities of milk per hour can be pasteurized by this method. (3) UHT Method : Also known as "ultra-high temperature method." Milk is rapidly heated usually in 2 stages (the second stage usually being under pressure) to 125 deg C for a few seconds only. It is then rapidly cooled and bottled as quickly as possible. Pasteurization is a preventive measure of public health impoance and corresponds in all respects to the modern principles of supplying safe milk. Pasteurization kills nearly 90 per cent of the bacteria in milk including the more heat-resistant tubercle bacillus and the Q fever organisms. But it will not kill thermoduric bacteria nor the bacterial spores. Therefore, despite pasteurization, with subsequent rise in temperature, the bacteria are bound to multiply. In order to check the growth of microorganisms, pasteurized milk is rapidly cooled to 4 deg C. It should be kept cold until it reaches the consumer. Hygienically produced pasteurized milk has a keeping quality of not more than 8 to 12 hours at 18 degC. Ref: Park 25th edition Pgno : 692