INVESTIGATION OF PROTEASE PRODUCTION BY PSEUDOMONAS FLUORESCENS BJ-10 AND DEGRADATION ON MILK PROTEINS

The production of protease by Pseudomonas fluorescens BJ-10 and degradation on milk proteins were carried out. The results showed that the growth rate and protease activity in nutrient broth were lower than in milk. The maximum viable counts at both 6 and 28C in milk were approximately 10-11 log colony forming units (cfu)/mL. The highest protease activity in milk reached 227.99 U/mL. The protease preferentially degraded caseins in the following order kappa-casein > beta-casein > alpha(s)-casein and had low activity on whey proteins. Correlation analyses showed that protease activity was significantly (P < 0.01) related to viable counts. Regression equation was y = 31416.26-31415.33/(1 + 101.64 x -26.97), R-2 = 0.98. The protease showed a typical heat-stable behavior. After treatment at 130C for 3 min, more than 39.36 % activity remained. Crude protease caused coagulation of ultra high temperature milk after 5 days of storage at room temperature. We concluded that protease plays an important role in milk spoilage.