High-pressure inactivation of Saccharomyces cerevisiae and Lactobacillus plantarum at subzero temperatures

The yeast, Saccharomyces cerevisiae and the bacterium, Lactobacillus plantarum were pressurized for 10 min at temperatures between −20 and 25 °C and pressure between 100 and 350 MPa. Pressurization at subzero temperatures without freezing significantly enhanced the effect of pressure. For example, at a pressure of 150 MPa, the decrease in temperature from ambient to −20 °C allowed an increase in the pressure-induced inactivation from less than 1 log up to 7-8 log for each microorganism studied. However, for comparable inactivation levels, the kinetics of microorganism inactivation did not differ, which suggests identical inactivation mechanisms. Implications of water thermodynamical properties like compression, protein denaturation, as well as membrane phase transitions, are discussed.