Data in Table 3 represent the physicochemical properties of treatment solutions applied in the challenge study. EO water had the lowest pH, but the highest in ORP and DO. The free and total chlorine
concentration of DWwas negligible whereas these 2 values of NaOCl
solution were almost 4 times higher than those of EO water. Even
though extensive work has been done to examine the mode of action
of EO water against microorganisms, so far it has not been clarified
which of the characteristics of EO water (low pH, high ORP, or presence of free available chlorine) are the most important bactericidal
factors (Kim and others 2000a, 2000b; Len and others 2000; Park and
others 2004; Liao and others 2007). The outer membrane of microorganisms may be sensitized by low pH or it may become unstable by
exposure to extremely high ORP of EO water, thereby facilitating sanitizer penetration (Venkitanarayanan and others 1999a, 1999b;
Fabrizio and Cutter 2003). At a pH value of 9.55 for NaOCl solution,
OCl−
was predominant as free residual chlorine present. However,
OCl−
was 80 times less effective than HOCl at the same concentration (Eifert and Sanglay 2002). In addition, at the acidic pH of EO
water, most of the free chlorine present was in the form of HOCl,
reported to be the primary component for antimicrobial activity of
EO water (Len and others 2000). This observation supports the results of this study that aqueous NaOCl exhibits an equal bactericidal
activity with EO water that contains significantly less free available
chlorine