161 Effectiveness of Stable Ozone Microbubble Containing Water on Reducing Bacteria Load on Selected Leafy Vegetables Y. Inatsu, T. Kitagawa, N. Nakamura, S. Kawasaki, D. Nei, M.L. Bari and S. Kawamoto National Food Research Institute National Agriculture and Food Research Organization Tsukuba, Ibaraki Japan Keywords: surface decontamination, ozone micro bubble, microbiological safety Abstract Effectiveness of stable ozone micro bubble containing water (ozone micro bubble water) on decontaminating inoculated Escherichia coli (E. coli) O157:H7 or naturally attached bacteria on four kinds of leafy vegetables was evaluated. For the purpose of comparison, the effectiveness of gaseous ozone, chlorine water and distilled water was also evaluated. Nearly one and two log CFU.g -1 reduction of E. coli viable cells was observed after washing by ozone micro bubble water and chlorine water, respectively for all of tested leafy vegetables. No significant differences were obtained for the effectiveness among ozone micro bubble water, ozonated water and distilled water. No reduction of viable cells was observed after exposure of leaves to ozone gas. Similar results were obtained for naturally attached bacteria. No marked differences in color and appearance among distilled water and other sanitizer treatments were observed. These results suggest that the effectiveness of surface decontamination of leafy vegetables by using ozone micro bubble water was limited. INTRODUCTION Consumption of fresh produce has been suggested to increase public health condition since fresh vegetables and fruits are thought to be an important part of a healthy diet, supplying the much-needed vitamins, minerals and fiber. Most fruits and vegetables or related ready to eat (RTE) foods sold in the market rarely carry pathogenic bacteria in usual condition. However, these kinds of foods always have the possibility of contamination with food borne pathogens such as Enterohaemorrhagic Escherichia coli (E. coli) O157:H7 during production at farm or all stages of product handling from harvest to the point of sale (Matthews, 2006; Hanning et al., 2009). Naturally contaminated bacteria such as Bacillus sp., Enterobacter sp., Erwinia sp, Flavobacerium sp., Pseudomonas sp. and other ones in the same process are related to spoilage of fresh produce during transport and storage (Heard, 2002; Bari et al., 2005; Barth et al., 2009). For these reasons, effectiveness of many kinds of sanitizer for the surface washing of fresh produces have been evaluated (Gil et al., 2009). Sodium hypochlorite (NaClO) is commonly used for surface decontamination of fresh produce to reduce the risk of food poisoning or spoilage because of their advantages of broad spectrum of antimicrobial activity, ease of application and low cost (Sapers, 2006). This compound is usually used for surface decontamination of the foods at levels of 50-200 mg.L -1 free chlorine and with typical contact times of less than 5 min (Rico et al., 2007). However, chlorine is highly corrosive and may damage stainless steel equipment after prolonged exposure. Furthermore, its rapid depletion in the presence of a high organic load and the concern over the carcinogenicity of compounds resulting from the reaction of the active hypochlorite with the nitrogen-containing compounds had prompted the consideration of alternative disinfectant (Wei et al., 1985; Buschini et al., 2004). Ozone (O 3 ) is a strong antimicrobial compound with high oxidative activity and spontaneous decomposition to a non-toxic product (Rico et al., 2007). In contrast to hypochlorous acid (HClO), ozone does not effectively penetrate into the cell, while Proc. Southeast Asia Symp. on Quality Mgt. Posthar. Sys. in conj. w/ Asia-Pacific Symp. Posthar. Quality Mgt. Root & Tuber Crops Eds.: S. Kanlayanarat et al. Acta Hort. 989, ISHS 2013