| L. monocytogenes and S. aureus are zoonotic foodborne pathogens existing in meat, poultry, eggs, seafood, dairy products and vegetables. The risks associated with consuming foods contaminated with L. monocytogenes and S. aureus have caught the attention of public and governmental. In this study, we firstly research slightly acidic electrolyzed water (SAEW) with higher available chlorine concentration----circulating electrolyzed water. Based on the studies on the production and properties of SAEW, the disinfection efficacy and mechanism of SAEW on L. monocytogenes and S. aureus were investigated in comparison with NaClO and HC1. However, we found the existence of sublethal injuried bacteria during disinfection. Then, we investigated the effects of different stressors (SAEW and heat treatment) on lag time and specific growth rate of L. monocytogenes, and compared the effects of recovery temperature on growth parameters (lag time, ?, and specific growth rate, ?) of stressed or sublethal injured L. monocytogenes. The main results are as follows: 1.200 mg/L SAEW was obtained by electrolysis of an aqueous mixture containing 0.03% HC1 and 0.05% NaCl solutions for 4 min. The effective form of chlorine compounds in SAEW (pH 6.44-6.53) is hypochlorous acid (HCIO) and hypochlorite ion (ClO·). The only ClO· in NaClO solutions when the pH of solution is 11.90. Theoretically, the bactericidal activity of HClO is 80 times greater than an equivalent concentration of the hypochlorite ion (CIO-). The disinfection efficacy of SAEW was higher than NaClO which was also approved in this study. Meanwhile, SAEW with higher ACC can be applied through dilution and reduce its reliance on equipment.The results of storage experiment reveled that light or open storage condition had markedly impact on the pH, ORP and ACC of SAEW. CEW1 and CEW2, whereas closed-dark storage condition could prevent the loss of available chlorine and keep essentially stable of electrolyzed waters to a great extent. CEW with higher ACC was more stable than SAEW with lower ACC. No significant difference was found for CEW before and after diluted by distilled water under four different storage conditions.2. This study examined the disinfection efficacy and mechanism of SAEW on L. monocytogenes and S. aureus, compared with that of sodium hypochlorite (NaCIO) and hydrochloric acid (HCl). The TTC-dehydrogenase relative activity and bacterial ultrastructure destruction were studied following disinfection treatment of S. aureus and L. monocytogenes. The results showed that SAEW, NaClO and HCl decreased the relative activity of TTC-dehydrogenase of L. monocytogenes and S. aureus by 78.32%?78.48%?54.61%; 65.8%?54.4%?10.8%. In addition, the ranking of partly agglutinated cellular inclusion formation was HCl> SAEW> NaCIO. It appeared that HCl, along with its low pH value, are responsible for most of the cytoplasmic disruptions. The probably reason is the existence of sublethal injuried bacteria.3. This study investigated the effect of slightly acidic electrolyzed water (SAEW) and heat stress on Listeria monocytogenes growth at different recovery temperatures (10?,15?,25?, and 30?). The sizes of surviving and sublethal injured L. monocytogenes populations heated at 55? for 10 min were 6.4±0.1 and 0.4±0.0 log CFU/ml, respectively. This was similar to results obtained when bacteria were cultured in SAEW at a ratio of 8:2 for 30 s (6.2±0.1 and 0.3±0.2 log CFU/ml, respectively). According to the Bioscreen experiment, recovery temperature had a greater effect on growth parameters than the stress which affected lag time but not specific growth rate of L. monocytogenes. For untreated and SAEW- and heat-treated L. monocytogenes, the square roots of specific growth rate and lag time were linearly and reciprocally related, respectively, to recovery temperature. The reliability of secondary models was validated by RMSE, MRE, and MARE, with the results indicating good performances of the models. |
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