The effectiveness of high-pressure sterilization of Escherichia coli JCM 1649T and Staphylococcus aureus IFO12732T at freezing temperatures was tested. At ambient temperature, the count of viable E. coli cells decreased in culture medium (10⁶ cfu/ml) at pressures exceeding 300 MPa, and sterilization was observed at 500 MPa. It took pressures exceeding 400 MPa to reduce the viable cell number of S. aureus in culture medium (10⁶ cfu/ml) and exceeding 600 MPa to sterilize the culture. Although no sterilization was observed at 200 MPa at ambient temperature, the count of viable cells decreased from 10⁶ cfu/ml to 10⁴ cfu/ml at -20’C.

To test the practical applicability of this high-pressure sterilization method, we applied it to herring sashimi. With high-pressure treatment (200 MPa), the count of viable inoculated E. coli and S. aureus cells decreased at -2011 but was unaffected at ambient temperature. On the sashimi, as was observed in the culture medium. the E. coli were more susceptible to high-pressure sterilization than were the S. aureus. The sterilization was less effective on the sashimi than on the culture medium. With high-pressure sterilization at 200 MPa at-20’C, the viable cell count on the commercial herring sashimi was reduced to l/50 of the presterilization figure. The moderately high pressure of 200 MPa pressure produced less prominent changes in sashimi physical properties than did the high pressures of 500MPa or 600MPa. The effect high pressure sterilization was augmented at -20t, and high-pressure sterilization at freezing temperatures is expected to become a commercially feasible method of extending the shelf life of raw seafoods like sashimi.