INACTIVATION OF SACCHAROMYCES-CEREVISIAE BY SUPERCRITICAL AND SUBCRITICAL CARBON-DIOXIDE

Yeast cells were inactivated by carbon dioxide at subcritical and supercritical temperatures over the pressure range of 1000-3000 psi. A static apparatus was developed for the experiments. The results showed that a maximum of 15 min, depending on the pressure, was sufficient to inactivate yeast cells by 10(7)-fold under supercritical conditions. Subcritical carbon dioxide was found to be much less effective. It took 30-40 min to achieve inactivation of 10(4)-fold and more than 1 h to achieve inactivation of 10(7)-fold. There are two distinct mechanisms in the deactivation of yeast cells. The rate of cell inactivation is slow at first and increases drastically at the later stage, suggesting that the penetration of CO2 into microbial cells was a primary controlling factor of the inactivation process. The inactivation rate was enhanced remarkably by a series of pressure release/recompression of CO2 in the midst of a complete experiment. Other methods to improve the efficiency of inactivation are discussed.