Efficacy of Low-temperature High Hydrostatic Pressure Processing in Inactivating Vibrio parahaemolyticus in Pure Culture and Oyster Homogenates
Vibrio parahaemolyticus (Vp) is the leading cause of gastroenteritis associated with consumption of raw and undercooked seafood, particularly oysters. High hydrostatic pressure processing (HPP) can be utilized as a post-harvest process to eliminate Vp in raw oysters. This study investigated the susceptibility of five environmental isolates and five clinical strains of Vp in 2% NaCl solution to HPP (200 or 250 MPa for 5 min) at low temperatures (5 and 15°C). Survival of Vp was determined by spread-plate method using trypticase soy agar containing 2% NaCl. Among the strains tested, Vp 10290 (clinical strain) and Vp 100311Y11 (environmental strain) were two most pressure-resistant strains while Vp 10292 (clinical strain) was the least resistant strain. These three strains were further studied for resistance to pressures in sterilized oyster homogenates. A treatment of 200 MPa at 15 °C reduced counts of strains 10290, 100311Y11 and 10292 in oyster homogenates by 0.8, 1.1 and 3.4 log CFU/g, respectively. Reductions of these strains increased significantly (P < 0.05) to 1.6, 2.4 and 4.6 log CFU/g, respectively, in oyster homogenates treated with 200 MPa at 5°C. A HPP treatment of 250 MPa at 5°C also significantly (P < 0.05) increased reductions of strains 10292, 10290 and 100311Y11 in oyster homogenates to >7.3, 6.2 and 6.2 log CFU/g, respectively, from 6.1, 4.2 and 4.3 log CFU/g, respectively, yielded from a treatment of 250 MPa at 15°C. Efficacy of HPP in inactivating Vp in oysters can be enhanced by lowering operation temperature to 5°C. Pressure resistance among strains and processing parameters such as pressure and temperature are factors to be considered for improving the safety of pressure-treated oysters.