Modeling lipase and protease production by psychrotrophic bacteria in refrigerated pasteurized milk

This study evaluated the lipase and protease production by psychrotrophic bacteria in refrigerated pasteurized milk. Samples were stored at 4, 6, 8, and 10 °C during 10 days to simulate refrigerated storage including abuse temperatures. The results demonstrated that although the pasteurization reduced significantly the bacterial counts, part of the psychrotrophs population is able to survive and grow during refrigeration. Moreover, enzymatic activity occurred mainly at the higher temperatures (8 and 10 °C) during the lag and exponential growth phases throughout the 10-day analysis period, contributing to the samples spoilage. Thus, the study reinforces the importance of a strict control of refrigeration temperature during storage of pasteurized milk. A mathematical model comprised of three differential equations was able to describe successfully the bacterial growth and lipase and protease production. This approach can provide helpful insights regarding spoilage of refrigerated pasteurized milk.