Quality of Milk and Psychrotophic Bacteria

우유의 품질과 저온성균

Since generalization of cold storage of raw and processed milk, psychrotrophic bacteria has become more important. The number present in raw milk is related to sanitary conditions during pro-duction and to length and temperature of storage before pasteurization. Growth of psychrotrophs In raw milk often reduces the quality of pasteurized products. Recently, some pathogenic bacteria like Listeria monocytogenes, Yersinia enterocolitica, Bacillus cereus are reported to grow at low temperature and cause food poisoning. The presence of gram positive psychrotrophic bacteria which can survive pasteurization can limit the shelf life of pasteurized milk during extended storage and the survival of heat stable proteases and lipases produced by gram negative psychrotrophic bacteria often brings about proteolytic damage to milk protein in the products. Therefore, in order to prevent the deteorioration of milk and milk products by the growth of psychrotrophs, it is necessary to cool down the temperature of raw milk as soon as possible after milking and to keep the temperature below 5t during storage at farm. As psychrotrophic bacteria become readily predominant in raw milk under refregeration, it can be considered to change the traditional incubating temperature for SPC from 30${\sim}$32$^{\circ}C$ to 25${\sim}$27$^{\circ}C$ at which the psychrotrophs prefer to grow. The psychrotrophic bacterial count(PBC) is of limited use in dairy industry, because of the 10 days incubation period. Although estimates of psychrotrophic bacteria may provide an acceptable shelf-life prediction, there is no single, generally acceptable rapid method for replacing the PBC at the moment. Consequently, faster method for esmating psychrotrophic bacteria has to be developed.