Conditions for high pressure inactivation of Vibrio parahaemolyticus in oysters Ayse G. Kural a , Adrienne E.H. Shearer a , David H. Kingsley b , Haiqiang Chen a, ⁎ a Department of Animal & Food Sciences, University of Delaware, Newark, DE 19716-2150, United States b U.S. Department of Agriculture, Agricultural Research Service, Microbial Food Safety Research Unit, W. W. Baker Center, Delaware State University, Dover, DE 19901, United States ABSTRACT ARTICLE INFO Article history: Received 12 March 2008 Received in revised form 2 May 2008 Accepted 2 May 2008 Keywords: High pressure processing Vibrio parahaemolyticus Oysters Treatment temperature Treatment time The objective of this study was to identify the high pressure processing conditions (pressure level, time, and temperature) needed to achieve a 5-log reduction of Vibrio parahaemolyticus in 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 °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 °C. Temperatures ≥ 30 °C enhanced pressure inactivation of V. parahaemolyticus. To achieve a 5-log reduction of V. parahaemolyticus in live oysters, pressure treatment needed to be ≥ 350 MPa for 2 min at temperatures between 1 and 35 °C and ≥ 300 MPa for 2 min at 40 °C. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Bivalve mollusks are filter-feeders that obtain food from the environment by filtering seawater through their gills. In this process they may concentrate pathogens from polluted water. Among bivalves, the oyster predominates as a disease vector in the USA, UK, and Australia (Cliver, 1995; Lees, 2000). Several recent outbreaks of Vibrio parahaemolyticus associated with oysters have heightened concerns about the safety of raw oyster consumption. In 2006, an outbreak of V. parahaemolyticus infections resulted in 177 cases and was linked to the consumption of contaminated raw shellfish including oysters (Balter et al., 2006). In 1998, the largest V. parahaemolyticus outbreak reported to date in the USA involving 416 cases was linked to consumption of raw oysters (DePaola et al., 2000). To control V. parahaemolyticus infections, the Interstate Shellfish Sanitation Conference (ISSC) proposed post-harvest treatment of shellfish using interventions such as pasteurization. The standard set by the ISSC is a 5-log reduction of V. parahaemolyticus levels with an endpoint of non- detectable at the level of b 10 CFU/g (Cook, 2003). Post-harvest treatments including mild heat and irradiation have been proposed to control pathogens in shellfish. However, these treatments are of limited utility since they adversely affect the sensory qualities of shellfish (DiGirolamo et al., 1972; Cook and Ruple, 1992; Harewood et al., 1994). High pressure processing has been used commercially in the USA to facilitate the shucking of raw oysters for several years. The additional advantage of this technology is that it can inactivate V. parahaemolyticus and Vibrio vulnificus in oysters without compromising their sensory attributes (Lopez-Caballero et al., 2000; He et al., 2002; Cook, 2003). A pressure range of 205–275 MPa at temperatures ranging from 10 to 30 °C, and treatment times of 1 to 3 min are typically used. To our knowledge, studies involving pressure inactivation of V. parahaemolyticus have been conducted only at temperatures between 20 and 25 °C (Styles et al., 1991; Berlin et al., 1999; Calik et al., 2002; Cook, 2003; Koo et al., 2006). It is well documented that the temperature of food during pressurization plays a significant role in inactivation of microorgan- isms. Temperatures below and slightly above room temperature can enhance pressure inactivation of bacteria. To give examples, Chen (2007a) found that Listeria monocytogenes was most resistant to pressure at temperatures between 10 and 30 °C; Carlez et al. (1993) found that the rates of pressure inactivation of Pseudomonas fluorescens and Listeria innocua in minced beef muscle were much lower at room temperatures than at 4 °C; and a recent study in our laboratory demonstrated that temperatures b 20 °C or N 30 °C sub- stantially increased pressure inactivation of V. vulnificus in oysters (Kural and Chen, 2008). Therefore, the effect of temperature on pressure inactivation of V. parahaemolyticus in oysters warranted further study. It is economically beneficial to use lower levels of pressure in combination with optimum treatment temperatures to obtain the desired target levels of pathogen inactivation. From a food International Journal of Food Microbiology 127 (2008) 1–5 ⁎ Corresponding author. Tel.: +1 302 8311045; fax: +1 302 831 2822. E-mail address: haiqiang@udel.edu (H. Chen). 0168-1605/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2008.05.003 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro