Effects of green tea extract on reducing Vibrio parahaemolyticus and increasing shelf life of oyster meats Dunyu Xi a , Chengchu Liu b, c , Yi-Cheng Su a, * a Seafood Research and Education Center, Oregon State University, Astoria, OR, USA b College of Food Science and Technology, Shanghai Ocean University, Shanghai, PR China c Institute of Marine Science, Shanghai Ocean University, Shanghai, PR China article info Article history: Received 23 May 2011 Received in revised form 26 October 2011 Accepted 1 November 2011 Keywords: Vibrio parahaemolyticus Green tea extract Oysters Shelf life Seafood safety abstract This study investigated effects of tea extract on growth of pathogenic Vibrio parahaemolyticus and potential utilization in post-harvest treatment to extend shelf life of Pacific oysters (Crassostrea gigas). Longjing Tea, which exhibited strong bactericidal activity against V. parahaemolyticus, was selected to use in this study. Tea extract containing equal or higher than 4.6 g/l total phenolic contents (TPC) as gallic acid equivalents (GAE) determined by Folin-Ciocalteau method could reduce a mixture of five clinical V. parahaemolyticus strains in tryptic soy broth plus 1.5% NaCl from 4.5 log CFU/ml to non-detectable level (<1 log CFU/ml) within 8 h. A treatment of shucked oysters with tea extract containing 9.1 g/l TPC as GAE for 2 h at 23  1  C with oyster/tea extract ratio of approximate 0.9 g/ml resulted in greater (p < 0.05) V. parahaemolyticus reductions (0.8 log MPN/g) compared to controls (0.2 log MPN/g). The following shelf life study indicated that green tea treatment at oyster/tea extract ratio of approximate 0.7 g/ml could enhance reducing V. parahaemolyticus while retarding the growth of total bacteria in oysters during 5  1  C storage. Therefore, green tea might be utilized as a natural antimicrobial agent to inactivate V. parahaemolyticus in oysters and extend the shelf life during refrigeration storage. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Tea is rich in polyphenols, which are generally classified into flavonoids, phenolic acids, lignans and stilbenes. Major tea poly- phenols (TP) are flavanols (flavan-3-ols), which are a subgroup of flavonoids, and the monomers of flavanols (also called catechins) are the major TP in green tea. Predominant catechins include epi- catechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC) and epigallocatechin gallate (EGCG) (Peterson et al., 2005; Wang & Ho, 2009). Tea extract has been reported capable of inhibiting growth of a number of spoilage bacteria and foodborne pathogens such as Bacillus, Campylobacter , Clostridium, Escherichia coli, Listeria mono- cytogenes, Pseudomonas, Staphylococcus aureus, Salmonella and Vibrio. EGCG, which generally is the most abundant TP in green tea, has been reported the compound mainly contributing to the anti- bacterial activity (Almajano, Carbó, Jiménez, & Gordon, 2008; Chou, Lin, & Chung,1999; Diker, Akan, Hascelik, & Yurdakök, 1991; Hara, 2001; Mbata, Debiao, & Saikia, 2008; Sakanaka, Juneja, & Taniguchi, 2000; Si et al., 2006; Tagura, Tanaka, & Kouno, 2004). Extensive studies on application of green tea extract for reducing pathogenic and spoilage bacteria in foods including beef, pork, chicken and mutton have been reported (Juneja, Bari, Inatsu, Kawamoto, & Friedman, 2007; Kim, Ruengwilysup, & Fung, 2004; Kumudavally, Phanindrakumar, Tabassum, Radhakrishna, & Bawa, 2008). However, no study has been conducted to evaluate effects of tea extract on reducing pathogenic bacteria and retarding growth of spoilage bacteria in molluscan shellfish. Vibrio parahaemolyticus is a human pathogen occurring naturally in the coastal and estuarine environments and commonly found in oysters. Consumption of raw or undercooked oysters contaminated with V. parahaemolyticus can result in foodborne illness with major symptoms of gastroenteritis (Butt, Aldridge, & Sanders, 2004). Numerous outbreaks of V. parahaemolyticus infections resulted from consumption of raw oysters in the U.S. were documented over the past decade (CDC, 2005, 2006). Since oysters are commonly consumed raw, contamination with V. parahaemolyticus in oysters is a public health concern. Moreover, vibriosis including V. para- haemolyticus infections has become national notifiable diseases since January 2007 (CDC, 2010). In addition, growth of spoilage bacteria during storage is also a concern for the highly perishable * Corresponding author. Seafood Research and Education Center, Oregon State University, 2001 Marine Drive, Suite 253, Astoria, OR 97103, USA. Tel.: þ1 503 325 4531; fax: þ1 503 325 2753. E-mail address: yi-cheng.su@oregonstate.edu (Y.-C. Su). Contents lists available at SciVerse ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont 0956-7135/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2011.11.002 Food Control 25 (2012) 368e373