Whey protein influences the production and activity of extracellular protease from Pseudomonas fluorescens W3

Abstract The heat-resistant protease secreted by Pseudomonas in raw milk is an important reason for reducing the quality of dairy foods. Protease from Pseudomonas fluorescens W3 (P. fluorescens W3) performed higher activity in milk than that in tryptic soy broth (TSB). In this study, the effects of different milk components on the activity of protease from P. fluorescens W3 were explored. The results showed that whey protein was the main reason that influenced the protease activity secreted by P. fluorescens W3, which exert positive correlation with the concentration of whey protein content (from 0.3% to 1%). The zymogram and mass spectrometry proved that the protease secreted by P. fluorescens W3 was AprX, which had a better ability to hydrolyze casein than whey protein. The AprX hydrolysised casein by the suquence as follows: κ-casein > β-casein > α-casein. The results of RT-qPCR showed that whey protein could increase the expression of gene aprX by P. fluorescens W3. The results could help us better understand how milk promoted the protease activity of Pseudomonas fluorescens. Destroying whey protein may become the key method to inhibit the activity of protease from psychrotrophic bacteria, and reduce the waste of dairy foods.