The effect of psychrotrophic bacteria on the quality of raw milk and pasteurized and sterilized dairy products

In the past, microorganisms that could grow at refrigerater temperatures were located in the group of Psychrophils, and this term was used for organisms that grow from minus temperatures to 20 ° Celsius, and the optimum growth temperature was considered 15 ° Celsius. By accepting this definition, a large number of microorganisms that were able to grow at a temperature higher than 20 ° C but actually caused food spoilage at a refrigerator temperature (0 ° C to 7 ° C) were effectively abandoned. Therefore, the word psychrotroph was suggested for microorganisms that could grow at 0 to 7° Celsius and create visible colonies within 7 to 10 days. In our country, pscycrotrophic bacteria have become an important challenge in the dairy industries, and by producing heatresistant lipolytic and proteolytic enzymes, they play an important role in reducing the quality and degradation of pasteurized and sterilized products. Also pathogenic bacteria such as Listeria and Bacillus cereus are also included in this category. There are several reasons for increasing the number of pscycrotrophic colonies in raw milk, most notably, the rinsing lack of equipment, completely, after each use or neglecting the disinfection of equipment before use in livestock farms. Also Long-term storage at temperatures above 4 ° C due to the absence of a tank cooling system or it s inadequacy, the low speed of reducing the raw milk temperature in the bulk tank of the livestock or keeping the raw milk in inappropriate conditions in the storage tanks of the plants, can increase the number of psychrotrophic bacteria. In a study conducted in Kerman province (May 2018), on the rate of bacterial growth in industrial livestock, it was determined that the average number of psychrotrophic bacteria in the livestocks which deliver the raw milk to the plant immediately after milking and cooling was less than 100 cfu/ml while in the livestocks which keep the raw milk cold and then transfer to the plant the average number of psychrotrophic bacteria was more than 15000 cfu/ml. The aim of this study was to determine the importance of the number of psychrotrophic bacteria in raw milk and its effect on the quality of pasteurized and sterilized products.

کلیدواژه ها:

Psychrotrophic bacteria ، raw milk ، pasteurized and sterilized products