Hydrostatic pressure-induced germination and inactivation of Bacillus spores in the presence or absence of nutrients

The influence of pressure and temperature, in the presence (in glucose broth, GB) or absence (in phosphate buffer, PB) of nutrients, on hydrostatic pressure (HP) induced-germination and inactivation of Bacillus subtilis, B. cereus, and B. polymyxa spores was investigated for a relatively low range of 20-100 MPa (low HP). Low HP-induced germination was more potent in GB than in PB at 20-60MPa, and the difference in germination ratio between the growth media (GB and PB) tended to decrease with increasing pressure. For B. subtilis and B. cereus, the optimal temperature for the low HP-induced germination in PB tended to be higher than in GB, whereas temperature dependence on low HP-induced germination of B. polymyxa was different considerably from those of B. subtilis and B. cereus. After 30-60 min incubation at 40 degrees C and 60 MPa, the three types of bacterial spores germinated 5 log-cycles in the presence of nutrients and 2-3 log-cycles in the absence of nutrients. These results indicate that the low HP-induced germination of Bacillus spores has potential as a method of reducing bacterial spores in foods and foodstuffs, especially those containing large amounts of nutrients.