Influence of high-pressure-low-temperature treatment on the inactivation of Bacillus subtilis cells.

High pressure inactivation processes, especially at subzero temperatures, were performed on Bacillus subtilis vegetative cells at various pressure, temperature and time combinations. Whilst atmospheric pressure, lowering the temperature for various periods to as low as 45 -C was found to have minor anti-microbial effects. Upon application of high pressure various phase transitions of ice occurred in the microbial suspensions under study. After pressure treatment at 150¿450 MPa, cells were plated under optimal conditions to assess cell viability. Treatments of cells between 250 and 350 MPa at 25 -C were the most effective in inactivation. For these conditions, a double effect of extracellular solid¿solid (Ice I¿III) phase transition and possible intracelluar solid¿liquid phase transition is suggested to be the key in mediating the observed drop in viability.