Community diversity of psychrophilic bacteria in dairy farm raw milk and its characteristic enzyme production at different temperature

Psychrophilic bacteria and their heat-resistant enzymes are important risk factors affecting the quality of shelf life of UHT milk, and it is important for the development of the industry to uncover their action pattern. In these study, 40 raw milk samples were taken from dairy farms in Hebei (northern China) and Guangdong (southern China) in four seasons. The structure and composition of psychrophilic bacteria by PCR targeting 16S rRNA, as well as its extracellular protease, lipase activity and heat resistance was analyzed. The results showed that there was a significant temperature dependence but not geographical dependence in the distribution of the psychrophilic bacteria community. Secondly, P. fluorescens, P. azotoformans and P. paralactis were not only the dominant bacterium, but also had higher proteolytic and lipolytic activities. Lastly, Analysis of the enzyme-producing heat resistance of a typical psychrophilic bacteria, P. azotoformans B15-1. At 135 °C, the average residual rate of protease only 3.08%, however, lipase was more heat resistant and the average residual rate was still 19.16%. The present study investigated the psychrophilic bacteria and its hydrolytic enzymes activity in raw milk from different regions and seasons, in order to assess the baseline of psychrophilic bacteria contamination in the dairy farm.