Effects of green tea extract on reducing Vibrio parahaemolyticus and increasing shelf life of oyster meats

This study investigated effects of tea extract on growth of pathogenic Vibrio parahaemolyticus and potential utilization in post-harvest treatment to extend shelf life of Pacific oysters (Crassostrea gigas). Longjing Tea, which exhibited strong bactericidal activity against V. parahaemolyticus, was selected to use in this study. Tea extract containing equal or higher than 4.6 g/l total phenolic contents (TPC) as gallic acid equivalents (GAE) determined by Folin-Ciocalteau method could reduce a mixture of five clinical V. parahaemolyticus strains in tryptic soy broth plus 1.5% NaCl from 4.5 log CFU/ml to non-detectable level (<1 log CFU/ml) within 8 h. A treatment of shucked oysters with tea extract containing 9.1 g/l TPC as GAE for 2 h at 23 ± 1 °C with oyster/tea extract ratio of approximate 0.9 g/ml resulted in greater (p < 0.05) V. parahaemolyticus reductions (0.8 log MPN/g) compared to controls (0.2 log MPN/g). The following shelf life study indicated that green tea treatment at oyster/tea extract ratio of approximate 0.7 g/ml could enhance reducing V. parahaemolyticus while retarding the growth of total bacteria in oysters during 5 ± 1 °C storage. Therefore, green tea might be utilized as a natural antimicrobial agent to inactivate V. parahaemolyticus in oysters and extend the shelf life during refrigeration storage.