High-pressure CO 2 treatment has been studied as a promising method for inactivating bacterial spores. In the present study, we compared this method with other sterilization techniques, including heat and pressure treatment. Spores of Bacillus coagulans, Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, and Geobacillus stearothermophilus were subjected to CO 2 treatment at 30 MPa and 35°C, to high-hydrostatic-pressure treatment at 200 MPa and 65°C, or to heat treatment at 0.1 MPa and 85°C. All of the bacterial spores except the G. stearothermophilus spores were easily inactivated by the heat treatment. The highly heat-and pressureresistant spores of G. stearothermophilus were not the most resistant to CO 2 treatment. We also investigated the influence of temperature on CO 2 inactivation of G. stearothermophilus. Treatment with CO 2 and 30 MPa of pressure at 95°C for 120 min resulted in 5-log-order spore inactivation, whereas heat treatment at 95°C for 120 min and high-hydrostatic-pressure treatment at 30 MPa and 95°C for 120 min had little effect. The activation energy required for CO 2 treatment of G. stearothermophilus spores was lower than the activation energy for heat or pressure treatment. Although heat was not necessary for inactivation by CO 2 treatment of G. stearothermophilus spores, CO 2 treatment at 95°C was more effective than treatment at 95°C alone.

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