Thermal inactivation of Escherichia coli O157:H7 and Salmonella on catfish and tilapia q Kathleen T. Rajkowski * Food Safety and Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA article info Article history: Received 22 September 2011 Received in revised form 22 November 2011 Accepted 21 December 2011 Available online 17 January 2012 Keywords: Finfish Catfish Tilapia Escherichia coli O157:H7 Salmonella Thermal D-values Z-values abstract Thermal inactivation kinetics of individual cocktails of Escherichia coli O157:H7, or of Salmonella meat isolates or seafood isolates were determined in catfish and tilapia. Determinations were done at 55, 60 and 65  C using a circulating-water bath and calculated using linear regression analysis. Salmonella seafood and meat isolates D-10 values on the finfish were the same and ranged from 425 to450, 27.1 to 51.4, 2.04e3.8 s (z ¼ 4.3  C) at 55, 60 and 65  C, respectively. The E. coli O157:H7 D-10 values ranged from 422 to 564, 45.2 to 55.5 and 3.3e4.2 s (z ¼ 4.3  C) at 55, 60 and 65  C, respectively. The only statistical difference (P  0.05) was found when comparing the D-10 values for E. coli O157:H7 at 55  C on catfish and tilapia. The other D-10 values for the Salmonella at all temperatures and E. coli O157:H7 at 60 and 65  C on the catfish or tilapia showed no statistical difference. D-10 values for the catfish and tilapia were significantly lower than the reported values in other food systems, but the z-values were within the literature reported range. These D-10 values can be used to determine cooking parameters of finfish. Published by Elsevier Ltd. 1. Introduction Globally fish consumption reached 115.1 million tonnes in 2008 (17 kg/person) which can vary from 1 to 100 kg per capita depending on geographical area and can even vary within the individual country (FAO, 2007). Aquaculture contributed an esti- mated 50% of the available fish consumed and for some countries this can mean an increase of imported fish (Greenlees et al., 1998). Since 2001 aquaculture production has increased at an average annual growth rate of 6.2% and in the United States fisheries production averages about 10% for the aquaculture products (FAO, 2007). Consumption of fish products has remained at about 23 kg/capita (1996e2006) in North America. Fish, as defined in Section 21 of the United States’ Code of Federal Register part 123.3 (d), “means fresh or saltwater finfish, crustaceans, other forms of aquatic animal life (including, but not limited to, alligator, frog, aquatic turtle, jellyfish, sea cucumber, and sea urchin and the roe of such animals) other than birds or mammals, and all mollusks, where such animal life is intended for human consumption” (CFR, 2008). Another term used to describe fish is seafood which is divided into three categories: finfish, crustacean (shrimp) and mollusk (shellfish). When the United States General Accounting Office (GAO) issued a report on the seafood safety program in 2004, they stated that 80% of the consumed seafood (finfish, crustaceans and mollusk) was imported and that eating contaminated seafood resulted in about 15% of the reported food borne outbreaks in the U.S. which “is a greater percent than either meat or poultry even through meat and poultry are consumed at 8 and 6 times the rate of seafood, respectively” (GAO, 2004). In 2006 the U.S. Center for Disease Control classified food vehicles implicated in outbreaks into 17 food commodities and determined that fish (47 outbreaks) was associ- ated with most outbreaks (CDC, 2009). Bacterial pathogens were listed as the cause of the seafood- related illnesses (GAO, 2004). In particular Salmonella can contaminate seafood from harvest to consumption and is the major cause of seafood-associated bacterial outbreaks in the EU (EFSA, 2010), in the US (CSPI, 2009) and in other countries worldwide. The United States Food and Drug Adminis- tration tested 11,312 imported and 768 domestic seafood samples from 1990 to 1998 (GAO, 2004). They reported that overall 7.2% for imported and 1.3% for domestic seafood were positive for Salmonella q Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal oppor- tunity provider and employer. * Tel.: þ1 215 233 6440; fax: þ1 215 233 6406. E-mail address: Kathleen.rajkowski@ars.usda.gov. Contents lists available at SciVerse ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm 0740-0020/$ e see front matter Published by Elsevier Ltd. doi:10.1016/j.fm.2011.12.019 Food Microbiology 30 (2012) 427e431