Temperature modulates the production and activity of a metalloprotease from Pseudomonas fluorescens 07A in milk

This work evaluated the expression and activity of a metalloprotease released by Pseudomonas fluorescens 07A in milk. Low relative expression of the protease by the strain was observed after incubation for 12 h at 25 degrees C while the strain was in the logarithmic growth phase. After 24 h, protease production significantly increased and remained constant for up to 48 h, a time range during which the strain remained in the stationary phase. Conversely, at refrigeration temperatures, at 12 h the strain was still in the lag phase and expressed the protease at higher levels than when the logarithmic phase was reached. Casein fractions were highly degraded by P. fluorescens 07A, the purified protease, and the bacterial pellet on d 7 of incubation at 25 degrees C and to a lesser extent at 10 degrees C for the sample incubated with the bacterium. Heat treatment at 90 degrees C for 5 min completely inactivated the proteolytic activity of the purified protease and the bacterial pellet. This work contributes to the knowledge about the conditions of milk storage that influence the production and activity of this extracellular metalloprotease. The results demonstrate the need to find alternative strategies to control the synthesis and activity of proteolytic enzymes in the dairy industry to ensure the quality of processed products.