The decontaminative effects of acidic electrolyzed water for Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on green onions and tomatoes with differing organic demands Eun-Jin Park a , Edward Alexander b , Gary A. Taylor b , Roy Costa b , Dong-Hyun Kang a, * a School of Food Science, Washington State University, Pullman, WA 99164-6376, USA b Proton Labs, Inc., 980 Atlantic Avenue, Suite 110, Alameda, CA 94501, USA article info Article history: Received 12 September 2008 Received in revised form 24 October 2008 Accepted 28 October 2008 Available online 11 November 2008 Keywords: Acidic electrolyzed water Organic matter Foodborne pathogen Green onion Tomato abstract Acidic electrolyzed water (AC-EW) has strong bactericidal activity against foodborne pathogens on fresh vegetables. However, the efficacy of AC-EW is influenced by soil or other organic materials present. This study examined the bactericidal activity of AC-EW in the presence of organic matter, in the form of bovine serum against foodborne pathogens on the surfaces of green onions and tomatoes. Green onions and tomatoes were inoculated with a culture cocktail of Escherichia coli O157:H7, Salmonella typhimu- rium, and Listeria monocytogenes. Treatment of these organisms with AC-EW containing bovine serum concentrations of 5, 10, 15, and 20 ml/l was performed for 15 s, 30 s, 1 min, 3 min and 5 min. The total residual chlorine concentrations of AC-EW decreased proportional to the addition of serum. The bactericidal activity of AC-EW also decreased with increasing bovine serum concentration, whereas unamended AC-EW treatment reduced levels of cells to below the detection limit (0.7 logCFU/g) within 3 min. Ó 2008 Published by Elsevier Ltd. 1. Introduction Electrolyzed water (EW) is generated by electrolysis of a 0.1% sodium chloride solution, producing acidic EW (AC-EW) and alkaline EW (AK-EW) in separate anode and cathode compart- ments, respectively (Anonymous, 1997). AC-EW has been reported to have a strong bactericidal activity against foodborne pathogens and has a pH of below 2.5 (Izumi, 1999). However, AK-EW has a pH of above 11.5 and has not been reported to have any sanitizing properties. AC-EW has been shown to effectively inactivate Escherichia coli O157:H7, Salmonella enteritidis, Salmonella typhi- murium, Listeria monocytogenes, Campylobacter jejuni, Enterobacter aerogenes, Staphylococcus aureus, and Bacillus cereus (Bari et al., 2003; Stevenson et al., 2004; Koseki et al., 2004; Park et al., 2002; Kim et al., 2000). Electrochemically produced free chlorine (10–90 mg/l) and a high oxidation-reduction potential (ORP, above 1100 mV) have been strongly associated with the bactericidal effects of AC-EW (Kim et al., 2000; Bari et al., 2003). The effects of reducing or eliminating pathogens by AC-EW on the surfaces of fresh fruits and vegetables have been reported (Koseki et al., 2001; Bari et al., 2003; Koseki et al., 2004; Guentzel et al., 2008). Bari et al. (2003) evaluated the efficacy of AC-EW (30.3 ppm of available chlorine concentrations) and water containing 200 ppm chlorine in killing E. coli O157:H7, S. enteritidis, and L. monocytogenes on the surfaces of spot-inoculated tomatoes. In their study, treatment with 200 ppm chlorine water and AC-EW reduced the number of tested pathogens by 4.69–4.87 logCFU and 7.46–7.85 logCFU per tomato, respectively. Although a variety of sanitizers, such as chlorine, chlorine dioxide, calcinated water, and organic acids, has been examined for their ability to reduce levels of foodborne pathogens on fresh produce, some studies showed microbial reductions of less 2.0 logCFU/g (Kim et al., 2000; Bari et al., 1999; Taormina and Beuchat, 1999; Zhang and Farber, 1996). Besides their minimal bactericidal efficacy, the preparation of working solutions of sanitizers from hazardous concentrates involves some risk for workers in processing environments. Several factors affect the efficacy of AC-EW. In a fresh produce processing plant, sanitizers generally are used in the presence of organic matter, such as produce debris, soils, and microorganisms present on fruit and vegetable surfaces, all of which reduce sani- tizer efficacy. Oomori et al. (2000) reported that organic matter, including amino acids and proteins, potentially react with free available chlorine and change it into the combined form. Ayebah et al. (2006) showed that chicken serum decreased the oxidation- reduction potential and chlorine concentration of AC-EW, as well as * Corresponding author. Tel.: þ1 509 335 3937; fax: þ1 509 335 4815. E-mail address: dhkang@wsu.edu (D.-H. Kang). Contents lists available at ScienceDirect Food Microbiology journal homepage: www.elsevier.com/locate/fm 0740-0020/$ – see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.fm.2008.10.013 Food Microbiology 26 (2009) 386–390