Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/18/2013
Publication Date: 5/15/2013
Citation: Yu, M., Huang, Y., Gurtler, J., Niemira, B.A., Sites, J.E., Chen, H. 2013. Effects of storage conditions before or after high-hydrostatic pressure on inactivation of Vibrio parahaemolyticus and Vibrio vulnificus in oysters. International Journal of Food Microbiology. 163(2013):146-152. Interpretive Summary: The bacterium Vibrio causes illness in humans from the consumption of raw oysters. We tested the effects of pre-HHP (high-hydrostatic pressure) and post-HHP storage temperatures on inactivation of Vibrio. HHP at 300 megapascals (MPa) for 2 min killed 99.999 percent of Vibrio in oysters. Cold storage at -18, 4 and 10 deg C, prior to HHP, decreased Vibrio populations up to 99.9 percent; however, no pre-treatment storage temperatures affected HHP inactivation. No appreciable differences of Vibrio inactivation occurred between HHP-treated oysters and shucked oyster meat. When HHP was lowered to 250 MPa for 2 min, followed by 10-day ice or 7-day frozen storage, 100 percent of Vibrio was inactivated. The combination of HHP at 250 MPa followed by frozen storage (7 days) could be applied by the shellfish industry to eliminate Vibrio.
Technical Abstract: The effect of storage conditions on subsequent high-hydrostatic pressure (HHP) inactivation of V. parahaemolyticus and V. vulnificus in oyster meat was investigated. Live oysters were inoculated with V. parahaemolyticus or V. vulnificus to ca. 7-8 log MPN/g by feeding and stored at different conditions (i.e., 21 or 35 deg C for 5 hours, 4 or 10 deg C for 1 and 2 days and -18 deg C for 2 weeks). Oyster meats were then treated at 225 - 300 MPa for 2 min at 4, 21 or 35 deg C. HHP at 300 MPa for 2 min achieved a greater than 5-log MPN/g reduction of V. parahaemolyticus, completely inactivating V. vulnificus (negative by enrichment) in oysters. Treatment temperatures of 4, 21 and 35C did not significantly affect pressure inactivation of V. parahaemolyticus or V. vulnificus (P is greater than 0.05). Cold storage at -18, 4 and 10 deg C, prior to HHP, decreased V. parahaemolyticus or V. vulnificus populations by 1.5 – 3.0 log MPN/g, but did not increase their sensitivity to subsequent HHP treatments. The effects of cold storage after HHP on inactivation of V. parahaemolyticus in oyster meat was also determined. Oysters were inoculated with V. parahaemolyticus and stored at 21 deg C for 5 h or 4 deg C for 1 d. Oyster meat was then treated at 250-300 MPa for 2 min at 21 or 35 deg C and stored for 15 days in ice or in a freezer. V. parahaemolyticus populations in HHP-treated oysters gradually decreased during post-HHP ice or frozen storage. A validation study using whole-shell oysters was conducted to determine whether the presence of oyster shells influenced HHP inactivation of V. parahaemolyticus. No appreciable differences of inactivation between shucked oyster meat and whole-shell oysters were observed. Treating with 300 MPa for 2 min at 21 deg C, followed by 5-day ice storage or 7-day frozen storage, and treating with 250 MPa for 2 min at 21 deg C, followed by 10-day ice or 7-day frozen storage, completely inactivated V. parahaemolyticus in whole shell oysters. The combination of HHP at a relatively low pressures (e.g., 250 MPa) followed by short term frozen storage (7 days) could potentially be applied by the shellfish industry as a post-harvest process to eliminate V. parahaemolyticus in oysters.