Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2008
Publication Date: 7/11/2008
Citation: Kural, A.G., Shearer, A., Kingsley, D.H., Chen, H. 2008. Pressure Inactivation of Vibrio parahaemolyticus in Oysters- Influence of Pressure level and Treatment Temperature. International Journal of Food Microbiology. 127:1-5. Interpretive Summary: Vibrio parahaemolyticus (Vp) is increasingly becoming a significant economic and human health problem for the shellfish industry. Currently, high pressure processing (HPP) is used as an intervention strategy for another type of Vibrio bacterium (V. vulnificus; Vv). HPP is ideally suited for the oyster industry since it is a nonthermal technology that can permit inactivation of bacteria without cooking of oysters. In this publication, we evaluated HPP parameters (pressure, treatment time and sample temperatures) needed for a 99.999% reduction of Vp standard as required by the Interstate Shellfish Sanitation Conference (ISSC). While current pressures used for Vv intervention are not high enough to meet the ISSC standard, results indicate that only slightly higher pressure treatments of approximately 43,500 psi for 2 min at 104 degree F or 50,800 psi for 2 min over a temperature range of 34 degree F-95 degree F will be sufficient to destroy Vp. This finding indicates that current HPP commercial conditions can be easily modified to be an effective intervention against Vp within oysters.
Technical Abstract: The overall objective of this study was to develop processing parameters (pressure level, time, and temperature) needed to achieve a 5-log reduction of V. parahaemolyticus within live oysters (Crassostrea virginica). Ten strains of V. parahaemolyticus were separately tested for their resistances to high pressure. The two most pressure-resistant strains were then used as a cocktail to represent baro-tolerant environmental strains. To evaluate the effect of temperature on pressure inactivation of V. parahaemolyticus, Vibrio-free oyster meats were inoculated with the cocktail of V. parahaemolyticus and incubated at room temperature (approximately 21 degree C) for 24 h. Oyster meats were then blended and treated at 250 MPa for 5 min, 300 MPa for 2 min, and 350 MPa for 1 min. Pressure treatments were carried out at -2, 1, 5, 10, 20, 30, 40, and 45 degree C. Slightly elevated temperatures (greater than but not less than 30 degree C) were found to enhance pressure inactivation of V. parahaemolyticus, while for temperature levels < 30 degree C, inactivation was dependent on the pressure level. Temperatures of 1, 20, 35, and 40 degree C were used to determine the processing parameters needed to achieve a > 5-log reduction in the counts of V. parahaemolyticus accumulated into live oysters through feeding. To achieve a 5-log reduction, pressure treatment needed to be conducted at greater than but not less than 350 MPa for 2 min at 1-35 degree C and greater than but not less than 300 MPa for 2 min at 40 degree C.