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(formaldehyde gas and glutaraldehyde) are noxious to humans and chicks, and may pose a serious health risk (Russell, 2003). Furthermore, the use of formaldehyde gas and glutaraldehyde are gradually being limited because of the adverse effects this chemical has on the environment. Sakurai et al. (2003) also stated that EO water provides a useful means of cleaning and disinfecting digestive endo- scopes between patients. It is safe for the human body and for the environment. In addition, the cost of using EO water is much less expensive (5.3 yen/L) compared with glutaraldehyde (1200 yen/L) (Sakurai et al., 2003). When EO water comes into contact with organic matter, or is diluted by tap water or reverse osmosis (RO) water, it becomes ordinary water again. Thus, it’s less adverse impact on the environment as well as users’ health. More- over, compared with other conventional disinfecting tech- niques, EO water reduces cleaning times, is easy to handle, has very few side effects, and is relative cheap (Tanaka et al., 1999). Chemicals used for cleaning and dis- infection are expensive and represent an operating expense for the dairy producer. Once the initial capital investment is made to purchase an EO water generator, the only oper- ating expenses are water, salts and electricity to run the unit (Walker et al., 2005b). The main disadvantage of EO water is that the solution rapidly loses its antimicrobial activity if EO water is not continuously supplied with H+, HOCl and Cl2 by electrol- ysis (Kiura et al., 2002). EO water is gaining a reputation in various fields as a more capable disinfectant than conven- tional chemical disinfectants. However, problems, such as chlorine gas emission, metal corrosion, and synthetic resin degradation, due to its strong acidity and free chlorine con- tent have been a matter of concern. Although metal corro- sion and synthetic resin degradation occurred, they were not serious on hemodialysis equipment (Tanaka et al., 1999). Ayebah and Hung (2005) also indicated that EO water did not have any adverse effect on stainless steel, it can still be safely used as a sanitizer to inactivate bacteria on food contact surfaces made from stainless steel in food processing. After disinfection, washing food equipment with sterile water can completely avoid metal corrosion. During the EO water generation process, chlorine ions are generated, and thus chlorine gas is emit- ted. This necessitates the use of standard-type extractor fan. 5. Inactivation of microbes using EO water As shown in Table 1, many studies have been conducted in evaluating the bactericidal activity of EO water. EO water possess antimicrobial activity on a variety of micro- organisms including Pseudomonas aeruginosa (Kiura et al., 2002; Vorobjeva et al., 2003), Staphylococcus aureus (Park et al., 2002b; Vorobjeva et al., 2003), S. epidermidis, E. coli O157:H7 (Kim et al., 2000a, 2000b; Park, Hung, & Chung, 2004; Venkitanarayanan et al., 1999b), Salmonella Enteriti- dis (Venkitanarayanan et al., 1999b), Salmonella Typhimu- rium (Fabrizio & Cutter, 2003), Bacillus cereus (Len, Hung, Erickson, & Kim, 2000; Sakashita, Iwasawa, & Nakamura, 2002; Vorobjeva et al., 2003), Listeria monocytogenes (Fab- rizio & Cutter, 2003; Park et al., 2004; Vorobjeva et al., 2003), Mycobacterium tuberculosis (Iwasawa & Nakamura, 1993), Campylobacter jejuni (Park et al., 2002a), Enterobac- ter aerogenes (Park et al., 2002b) and Vibrio parahaemolyt- icus (Huang et al., 2006a; Kimura et al., 2006). EO water can also reduce germination of many fungal species, such as Alternaria spp., Bortrytis spp., Cladosporium spp., Col- letotrichum spp., Curvularia lunata, Didymella bryonaie, Epicoccum nigrum, Fusarium spp., Helminthosporium spp., Pestalotia spp., Phomopsis longicolla, Rhodosporidium toru- loides, Stagonospora nodorum, Thielaviopsis basicola, Trich- oderma spirale, Acidovorax avenae subsp., Erwinia chrysanthemi, Pantoea ananatis, Pseudomonas syringae (Buck, Iersel, Oetting, & Hung, 2002), Aspergillus spp. (Buck et al., 2002; Suzuki et al., 2002b), Botryosphaeria berengeriana (Al-Haq et al., 2002), Monilinia fructicola (Al-Haq et al., 2001; Buck et al., 2002), Penicillium expan- sum (Okull & Laborde, 2004) and Tilletia indica (Bonde et al., 1999). In general, bacteria generally grow in a pH range of 4–9. Aerobic bacteria grow mostly at ORP range +200 to 800 mV, while anaerobic bacteria grow well at 700 to +200 mV. The high ORP in the EO water could cause the modification of metabolic fluxes and ATP production, probably due to the change in the electron flow in cells. Low pH may sensitize the outer membrane of bacterial cells to the entry of HOCl into bacterial cells (McPherson, 1993). HOCl, the most active of the chlorine compounds, appears to kill the microbial cell through inhibiting glucose oxidation by chlorine-oxidizing sulfhydryl groups of cer- tain enzymes important in carbohydrate metabolism. Other modes of chlorine action that have been proposed are: (1) disruption of protein synthesis; (2) oxidative decarboxyl- ation of amino acids to nitrites and aldehydes; (3) reactions with nucleic acids, purines, and pyrimidines; (4) unbal- anced metabolism after the destruction of key enzymes; (5) induction of deoxyribonucleic acid (DNA) lesions with the accompanying loss of DNA-transforming ability; (6) inhibition of oxygen uptake and oxidative phosphoryla- tion, coupled with leakage of some macromolecules; (7) formation of toxic N-chlorine derivatives of cytosine; and (8) creation of chromosomal aberrations (Marriott & Gra- vani, 2006). A theory for inactivation of bacteria based on the high oxidation potential of EO water causing damage of cell membranes was reported by Liao, Chen, and Xiao (2007). The chemical process of oxidation occurs when oxygen contacts with other compounds causing them to lose electrons and further causing the compounds to break down and change functions. In the case of microbes, oxida- tion could damage cell membranes, create disruption in cell metabolic processes and essentially kill the cell. The bacte- ricidal effects of EO water on Staphylococcus saprophyticus, Micrococcus luteus and Bacillus sphaericus can be seen byPDF Image | electrolyzed water in the food industry ROC
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