Estimation of growth parameters of Listeria monocytogenes after sublethal heat and slightly acidic electrolyzed water (SAEW) treatment

Abstract

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 (λ), growth rate (μ) 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 λ and h0 parameter in comparison with recovery temperature while there was no great change in growth rate under isothermal conditions. Larger λ values and h0 parameters were observed in sublethal-heat injured L. monocytogenes (the maximum λ and h0 parameters are 30.199 h and 1.6492) as compared to SAEW groups (the maximum λ 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), μ, λ] for dependent variable (h0 parameter) demonstrated that T, μ and λ 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.