Oyster preservation by high-pressure treatment

The purpose of this study was to analyze the effect of 10-min continuous pr essure and pulsed pressure in two 5-min steps (400 MPa at 7 degrees C) on t he microbial flora, total volatile bases, pH, and texture of purified and u npurified oysters. High-pressure treatment reduced the number of all the ta rget microorganisms (total viable count, H2S-producing microorganisms, lact ic acid bacteria, Brochothrix thermosphacta, and coliforms), in some cases by around 5-log units. The difference between the counts in the control and the pressurized oysters remained stable throughout 41 days of storage at 2 degrees C. No Salmonella spp, were detected in either the control batch or the pressurized batches during this storage period. Deterioration of the o yster was accompanied by increased total volatile bases, mainly in the nonp ressurized samples. The pH was practically constant in the pressurized oyst ers and fell slightly in unpressurized samples. As for mechanical propertie s, shear strength values were higher in pressurized than in unpressurized o ysters. Step-pulse pressurizing (400 MPa at 7 degrees C in two 5-min pulses ) produced no apparent advantages over continuous pressurizing based on any of the indices used.