Aims: The aim of this study was to identify and characterize heat stable proteinases of psychrotrophic proteolytic bacteria isolated from raw milk.
Methods and results: A strain of Klebsiella oxytoca producing a high proteolytic activity when cultured on milk was isolated. Maximum proteolytic activity was observed at the stationary phase during growth on milk or casein-peptone broth. The bacterium demonstrated the capability to grow at 7 degrees C, classified as psychrotrophic. The crude enzyme showed optimum activity at 37 degrees C, and pH 5.0 and 7.0. The proteinase was very resistant to heat, maintaining 74% of initial activity after incubation at 142 degrees C.
Conclusions: A heat stable protease of a psychrotrophic strain of K. oxytoca was identified and partially characterized.
Significance and impact of the study: Thermal stable proteases may constitute a serious problem to ultra-high temperature (UHT) processed milk, leading to undesirable physical and sensory alterations.