Time to detection experiments (TTD) based on turbidometry using an automatic Bioscreen C is a useful and straightforward method for estimating microbial growth parameters (lag time (), growth rate () and work to be done (h0)) at constant temperature. This study investigated the effects of slightly acidic electrolyzed water (SAEW) and heat treatment on Listeria monocytogenes growth at different recovery temperatures (10 C, 15 C, 25 C, and 30 C). Similar surviving and sublethally injured L. monocytogenes populations were obtained by heat treatment (55 C for 10 min) and SAEW treatment (available chlorine concentration of 30 mg/l and ratio of bacteria against SAEW of 8:2 for 30 s). In these experimental conditions, stresses had greater impact on the and h0 parameter in comparison with recovery temperature while there was no great change in growth rate under isothermal conditions. Larger values and h0 parameters were observed in sublethal-heat injured L. monocytogenes (the maximum and h0 parameters are 30.199 h and 1.6492) as compared to SAEW groups (the maximum and h0 parameters are 22.634 h and 1.4396). The sensitivity analysis of SAEW and heat treatments on h0 parameter indicated that SAEW treatment showed a higher influence. The collinearity diagnostics of independent variables recovery temperature (T), , for dependent variable (h0 parameter) demonstrated that T, and had strong collinearity. In addition, the established secondary models in this study have good performances on predicting the effect of recovery temperature on bacterial growth parameters.
The effects of low-concentration electrolysed water (LcEW) (4 mg/L free available chlorine) combined with mild heat on the safety and quality of fresh organic broccoli (Brassica oleracea) were evaluated. Treatment with LcEW combined with mild heat (50 C) achieved the highest reduction in naturally occurring microorganisms and pathogens, including inoculated Escherichia coli O157:H7 and Listeria monocytogenes (P < 0.05). In terms of the antioxidant content of the treated broccoli, the total phenolic levels and ferric reducing antioxidant power remained unchanged however, the oxygen radical absorbance capacity of the treated broccoli was higher than that of the untreated control. In addition, mild heat treatment resulted in an increase in firmness. The increased firmness was attributed to changes in the pectin structure, including the assembly and dynamics of pectin. The results revealed that mild heat induced an antiparallel orientation and spontaneous aggregation of the pectin chains. This study demonstrated that LcEW combined with mild heat treatment was effective to reduce microbial counts on fresh organic broccoli without compromising the product quality.
Electrolysed oxidising water (E.O. water) is produced by electrolysis of sodium chloride to yield primarily chlorine based oxidising products. At neutral pH this results in hypochlorous acid in the un-protonated form which has the greatest oxidising potential and ability to penetrate microbial cell walls to disrupt the cell membranes. E.O. water has been shown to be an effective method to reduce microbial contamination on food processing surfaces. The efficacy of E.O. water against pathogenic bacteria such as Listeria monocytogenes, Escherichia coli and Vibrio parahaemolyticus has also been extensively confirmed in growth studies of bacteria in culture where the sanitising agent can have direct contact with the bacteria. However it can only lower, but not eliminate, bacteria on processed seafoods. More research is required to understand and optimise the impacts of E.O. pre-treatment sanitation processes on subsequent microbial growth, shelf life, sensory and safety outcomes for packaged seafood products.