Efficacy of Vibrio parahaemolyticus depuration in oysters (Crassostrea gigas)

This study investigated the influences of seawater to oyster ratio on depuration for decontaminating V. parahaemolyticus in raw oysters with a goal of identifying the proper ratio of oyster to seawater capable of improving the efficacy of the depuration process. The water to oyster ratios tested in this study ranged from 1.0 to 2.5 L of artificial seawater (ASW) per oyster (40 oysters in 40, 60, 80 and 100 L ASW). The depuration efficacy for purging V. parahaemolyticus from oysters was highest when we applied a 2:1, followed by 1.5:1, 2.5:1, and 1:1 L of ASW/oyster. Further studies of depuration with 2:1 L of ASW/oyster found that the concentration of V. parahaemolyticus in oysters decreased in a nonlinear manner. The depuration curve was fitted to a one phase decay model with a coefficient of determination (R-2) of 0.933. The time for a 3 log reduction was 1.75 days with a 95% confidence interval from 1.65 to 1.85 days, which meets the FDA's requirement of larger than a 3.0 log (MPN/g) reduction as a post-harvest process for V. parahaemolyticus control. After 4 days levels in all trials were < 100 MPN/g meeting performance standards established by Japan and Canada. Furthermore, the time for a 3.52 log reduction was 3.17 days with a 95% confidence interval from 2.92 to 3.54 days but it took 5 days to reduce levels to < 30 MPN/g, which satisfies FDA's requirement as a post-harvest control process (> 3.52 log MPN/g reduction) for the purpose of making safety added labeling claims for V. parahaemolyticus.