Inactivation of Escherichia coli by CO2 Microbubbles at a Lower Pressure and Near Room Temperature

The ability of CO2 microbubbles (MB-CO2) to inactivate Escherichia coli suspended in a saline solution at a pressure lower than 2.0 MPa was investigated. A 6-log reduction in E. coli population occurred with MB-CO2 at 40 degrees C and 2.0 MPa after 60 min treatment, and a slight reduction occurred with low-pressurized CO2 under the same conditions. The dissolved CO2 concentration in the solution with MB-CO2 was much higher than that with low-pressurized CO2. On the other hand, E. coli could not be inactivated with N-2 microbubbles instead of CO2 under the same conditions. The ability of MB-CO2 to inactivate E. coli increased concomitant with increasing the CO2 feeding rate, pressure, and temperature. These results demonstrate that, with the experimental conditions and apparatus used in this study, MB-CO2 could very effectively inactivate E. coli at a temperature of 30 degrees C to 40 degrees C and at a pressure of 0.5 to 2.0 MPa.