Factors Affecting the Efficacy of Depuration for Decreasing Vibrio parahaemolyticus Contamination in Pacific Oysters (Crassostrea gigas)

• Main Author: Hou, Yishu
• Other Authors: Su, Yi-Cheng, Wang, Yan, Morrissey, Michael T., Torres, Antonio J., Food Science and Technology, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Vibrio parahaemolyticus; Shellfish as carriers of disease > Prevention; Oysters > Contamination; Pacific oyster > Microbiology; Oyster fisheries > Sanitation; Crassostrea gigas; Pacific oyster
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sx61dr664

Vibrio parahaemolyticus is a foodborne pathogen recognized as the leading cause of acute gastroenteritis associated with consumption of raw and undercooked seafood, particularly raw oysters, with major symptoms of nausea, vomiting, abdominal cramps and diarrhea. It is estimated that 45,000 cases of V. parahaemolyticus infection occur each year in the United States. In order to reduce the high risks of V. parahaemolyticus infection associated with raw oyster consumption, post-harvest processes capable of decreasing V. parahaemolyticus levels by >3.52 log MPN/g are recommended by the U.S. Food and Drug Administration for oyster processing upon harvest. Depuration is a process of holding shellfish in clean seawater allowing shellfish to purge contaminants and may be applied by the shellfish industry as a post-harvest process to reduce contamination of V. parahaemolyticus in oysters. Currently, depuration at controlled temperatures between 7 and 15°C for 5 days has been developed to achieve >3.0 but <3.52 log MPN/g reductions of V. parahaemolyticus in oysters. The aim of this study was to investigate the factors, including water pH value, water temperature and oyster to water ratio, affecting the efficacy of depuration in decreasing V. parahaemolyticus in oysters and to improve the efficacy of depuration process to achieve >3.52 log MPN/g reductions of V. parahaemolyticus in oysters for application as a post-harvest treatment of oysters by the shellfish industry to produce safe oysters for raw consumption. Studies of growth of V. parahaemolyticus in trypticase soy broth with 2% salt (TSB-Salt) medium of various pH values (5.5, 7.3 and 9.0) found that growth of five clinical V. parahaemolyticus strains were retarded in TSB-Salt at pH 5.5 compared with at pH 7.3 or 9.0. Investigation of oyster gaping in artificial seawater (ASW) of different pH values ranging from 4.0 to 10.5 unveiled that oysters survived well in ASW of pH between 5.0 and 9.5 at room temperature. Based on these findings, oyster depuration ...