| Budget Amount *help |
¥7,400,000 (Direct Cost: ¥7,400,000)
Fiscal Year 1994: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1993: ¥6,700,000 (Direct Cost: ¥6,700,000)
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| Research Abstract |
This is a research on a novel non-thermal sterilization method using high-pressure carbon dioxide. In the first year, that is, 1993 the lethal effect on yeast cells and bacterial spores were tested under the different condition of temperature, pressure, treatment time, decompression rate and water content. The wet yeast cells (Saccharomyces cerevisiae) with more than 60 % water content were completely destroyed , when the organisms were saturated with CO_2 gas, highly soluble in water, at 40 bar and 40ﾟC for more than 3 hr and then the pressure was suddenly released. The survival ratio of the endospores of Bacillus megaterium QMB 1551 could be reduced to 4*10^<-4> after the CO2treatment at 70 bar and 60ﾟC for 24 hr. It was expected that sorption as well as desorption of CO_2 could be the crucial phenomena to influence the deahth of microbial cells and spores. The death of the organisms was not produced only by mechanical rupture at the time of decompression, and the lethal effects of high-pressure CO_2 itself could work during treatment. In 1994 the bactericidal effects of CO_2, N_2O,N_2 and Ar was examined, and it was found that N_2O was also an effective gas for death of yeast cells. The gases other than CO_2 was, however, not effective for sterilization of the spores. The optimum pressure seemed to appear near the critical pressure of CO_2, when the spores were treated last year. This was confirmed this year by the additional experiments, but the reason for the optimum pressure was not clear. The treatment of the yeast cells by this method produced an increase in extraction of intracellurar proteins by 20 %, but the extraction was not improved in case of the spores.
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