CO2 sorption by microbial cells and sterilization by high-pressure CO2

The amount of CO2 sorbed by microbial cells in a Saccharomyces cerevisiae-water system was measured by a gravimetric method with a quartz spring, and the correlation between CO2 sorption and the sterilization effect of high-pressure CO2 was investigated. The sterilization rate of Saccharomyces cerevisiae by high-pressure CO2 was measured by varying the water content and CO2 pressure, and analyzed by reaction kinetics, The sterilization rate could be described by a first-order reaction, and the dependence of the sterilization rate constant, k, on the water content and CO2 pressure was evaluated, The amount of CO2 sorbed by the microbial cells reached equilibrium at a constant CO2 pressure within a few minutes and was correlated well with the value of k, In addition, the amount of unfreezable water was measured by DSC as an index of the state of water in the cell-water system, this being considered to be closely related to the amount of CO2 sorbed by the microbial cells, The value of k increased with increasing water content; however, the increase was only slight for a water content by which free water existed.