Effect of high pressure on the viability and enzymatic activity of mesophilic lactic acid bacteria isolated from caprine cheese

The effects of high pressure on the viability and acidifying and peptidolytic activities of lactococci and mesophilic lactobacilli strains were studied. We inoculated 10% reconstituted bovine skim milk with cells in the stationary phase of growth (similar to 8 log(10) cfu/ml) without incubation. Cells were treated at high pressure (100 to 400 MPa) for 20 min at 20 degrees C. The lactococci were more sensitive than the lactobacilli to pressures of 100 to 350 MPa. The pressure-treated cells exhibited lower acidification rates, even with treatments that did not affect cell viability. High pressures increased the hydrolytic activity of lactococci and lactobacilli on the carboxyl-terminal fragment from p-casein (C-peptide), which contributes to bitterness in cheese. Activity levels were highest after treatment of lactococci and lactobacilli at 300 and greater than or equal to 350 MPa, respectively. At these pressures, there was no reduction of aminopeptidase or dipeptidase activity of Lactococcus lactis ssp. lactis IFPL 359, but these activities were partially inhibited in Lactobacillus casei ssp. casei IFPL 731 after pressure treatment at 400 MPa. This paper also discusses the possibility of lactic bacteria being subjected to high pressure to create an extra supply of enzymes with debittering properties.