Non-thermal Inactivation of Bacillus Spores by Pressure-holding

Abstract

Bacillus subtilis spores were pressurized at 60MPa at 40°C for 0∼24 hours in phosphate buffer or GAM broth. After 24 hours, viable counts and spore counts decreased by about 5 log cycles in the broth and by only 1.6 log cycles in the phosphate buffer. Most of the spores in the broth changed from bright to dark after 4 hours, after which some of them began to bud, as observed by phase contrast microscopy. These results show that the spores germinated due to pressure and the presence of germination-inducing components in the broth, and that the germinated spores were then inactivated before changing into vegetative cells. We conclude that it is possible to inactivate B. subtilis spores by pressure-holding in non-thermal conditions. The same phenomenon was observed for B. licheniformis, B. cereus and B. coagulans, but the viable counts for these bacilli did not decrease as much as that of B. subtilis.