Inactivation of food microorganisms by high-pressure carbon dioxide treatment with or without explosive decompression

In order to elucidate the sterilization mechanism underlying the explosive decompression system, baker's yeast was pressurized with CO2, N2O, N2, or Ar gas at 40 atm and 40 degrees C for 4h, and then explosively discharged. The survival ratio was markedly decreased only by the treatments with CO2 and N2O, which are relatively soluble gases in water, suggesting that the microorganisms' death may be highly correlated with gas absorption by the cells. Lower decompression rates to atmospheric pressure, however, led to neither any lower reduction of remaining cells nor any smaller release of total cellular proteins. Furthermore, operating with a longer treatment time and smaller number of repetitions was usually more lethal than with a shorter time and more frequent repetition. From these results, most of the yeast cells appear to have been sterilized during the pressurization process. The spore cells of B. megaterium are considered to have been killed in a somewhat different manner, because of their distinct sensitivity to the applied gases.