Inactivation of Saccharomyces cerevisiae by Supercritical and Subcritical Carbon Dioxide

Abstract

Yeast cells were inactivated by carbon dioxide a t subcritical and supercritical temperatures over the pressure range of 1OOO-3OOO 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 107-fold under supercritical conditions. Subcritical carbon dioxide was found to be much less effective. It took 30-40 min t o achieve inactivation of 104-fold and more than 1 h to achieve inactivation of 107-fold. There are two distinct mechanisms in the deactivation of yeast cells. The rate of cell inactivation is slow at first and increases drastically a t 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 C02 in the midst of a complete experiment. Other methods to improve the efficiency of inactivation are discussed.

Inactivation of Food Microorganisms by High-pressure Carbon Dioxide Treatment with or without Explosive Decompression

“…Although Lin et at. have observed an improvement in the disruption and inactivation rates of baker's yeast with a series of pressure release/recompression treatments with CO 2 gas in the range between 1000psi (about 68.0atm) and 3000psi (204 atm) , 5,6) these results suggest that the explosive decompression of CO 2 would influence the survival ratio of the yeast cells to a lesser extent, at least with our system. Our previous observations with a scanning electron microscope have shown that the yeast cells, at the least some of them, may be mechanically ruptured by the CO 2 treatment with explosive decompression.…”

Antimicrobial effect of pressurised carbon dioxide onEnterococcus faecalis in physiological saline and foods

“…Nevertheless, environmental acidi®cation by pressurised CO 2 alone is unlikely to provide a lethal effect. 11,13,17 Particularly, CO 2 can diffuse into the cellular membrane and accumulate within the cells, since a microbial cell has the plasmic membrane consisting of a lipid bilayer structure. Under pressure it is possible that a large number of CO 2 molecules pass through the membrane and lower the internal pH enough to exceed the buffering capacity of the cytoplasmic pool.…”

“…The in¯uence of temperature on the thermal inactivation of E faecalis under CO 2 pressure appears to be stronger at high temperatures. The synergistic antimicrobial effect of CO 2 with temperature described by Haas et al 13,17 could be explained in part by an increased diffusibility of CO 2 and¯uidity of cell membrane at higher temperatures making cell membrane penetration easier.…”

“…18 For a better understanding of the lethal effects of CO 2 under pressure, further studies on representative microbial species are needed. 10,13,19 In this study, inactivation of E faecalis by high-pressure CO 2 was investigated. It was aimed to study the microbial inactivation by highpressure CO 2 in terms of treatment time, pressure, temperature, suspending medium, the initial number of cells and cell injury.…”

Reactions at supercritical conditions: Applications and fundamentals

“…In closing this section on applications of SCFs in biochemical reactions, we note that processing in SC CO, has been found to be a potentially attractive means of inactivating microorganisms in food and related materials (Lin et al, 1992;Kamihira et al, 1987a;Balaban et al, 1991;Castor and Hong, 1991). The SCF is thought to work by extracting essential intracellular components from within the cell and thereby rendering it inactive.…”