Sterilization of sudachi juice by compressed oxygen gas

We studied the lethal action of compressed oxygen gas on yeast cells and discussed its application to the sterilization processing of Sudachi juice. When the yeast cells (Saccharomyces cerevisiae IFO 10149) suspended in YPD medium were compressed directly with oxygen gas, the number of viable cells decreased rapidly and their survival rate was depressed in a short time with increasing pressure or temperature. When oxygen partial pressure was same, the sterilization rate of yeast did not alter even if total pressure changed. This shows that dissolved oxygen concentration relates to the lethality of yeast. The increase of oxidation-reduction potential of Sudachi juice with increasing in temperature closely correlates to the survival ratio of yeast. The yeast cells (Candida boidinii SYM-1) suspended in Sudachi juice could be sterilized completely when treated under the following conditions : 5.0 MPa for 15min at 30 deg C, 10.0 MPa for 5 min at 40 deg C, and 5.0 MPa for < 1 min at 50 deg C. Sudachi juice was sterilized by the treatment at 50 deg C without loss of vitamin C content. The method sterilizing directly with oxygen gas is superior to the usual high-pressure sterilization techniques which use pressures higher than 400 MPa, because our processing is performed under lower pressures than 10 MPa and does not require heavy equipments and high costs to operate.