Inactivation of Bacillus subtilis spores by combining high-pressure thermal sterilization and ethanol

High-pressure thermal sterilization (HPTS) is a new and promising sterilization technology of foods. Effects of combining HPTS and ethanol treatment on inactivation of Bacillus subtilis spores were investigated. An interesting phenomenon was observed. The inactivation effect of HPTS treatment on the spores was enhanced significantly with the increase in ethanol concentration from 0 to 15%. However, the inactivation effect was decreased with further increase in ethanol concentration up to 70%. In addition, the release of DPA and leakages of OD260 and OD280 material from the spores increased continuously with the increase in ethanol concentration. Moreover, flow cytometry analysis suggested that although the inner membrane of the spores was damaged, PI could not bind with the spore DNA immediately after HPTS treatment. In conclusion, the mechanism of this special phenomenon could be attributed to the germination of spores under HPTS treatment and effects of ethanol on the protein or water activity. HPTS caused other lethal damages to the spores besides its damage to the inner membrane. Ethanol of low concentrations could significantly enhance the sterilization effects of HPTS, which was good for keeping the qualities of foods.