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    Inactivation of Salmonella Typhimurium in fresh-cut lettuce during chlorine washing: Assessing the impacts of free chlorine concentrations and exposure times
    (Elsevier, 2023) Possas, Aricia; Posada-Izquierdo, Guiomar Denisse; Tarlak, Fatih; Jimenez-Jimenez, Francisco; Perez-Rodriguez, Fernando
    The aim of this study was to evaluate, quantify and model the inactivation of Salmonella in fresh-cut lettuce during washings with chlorinated water at different free chlorine concentrations (FCC, 0-150 mg/L). Individual fresh-cut lettuce samples (4 cm2) were inoculated with a Salmonella culture (ca. 4 log CFU/cm2) and washed with 100-mL solutions with different FCC for different times (0-150 s). The surviving Salmonella cells recovered from samples were enumerated by plate count methodology. A fast decay on Salmonella counts was marked in the first 20 s of washing, followed by a slowing down on reductions. A maximum of 2.6 log-decrease was observed after 2.5-min washing regardless of FCC. The log-linear with tail primary model coupled with a linear secondary model was fitted to inactivation data obtained at FCC from 50 to 150 mg/L through global regression analysis, yielding a suitable model to describe Salmonella concentrations as a function of FCC and washing times (RMSE = 0.34, R2adj= 0.84). Simulations using the developed model showed inactivation rates varying from 0.17 log CFU/ s at 50 mg/L to 0.86 log CFU/s at 150 mg/L. Disinfection models on lettuce are valuable tools for the validation of control measures in the fresh-cut produce industry and for quantitative risk assessments.
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    Quantifying and modelling the inactivation of Listeria monocytogenes by electrolyzed water on food contact surfaces
    (Elsevier Sci Ltd, 2021) Possas, Aricia; Perez-Rodriguez, Fernando; Tarlak, Fatih; Maria Garcia-Gimeno, Rosa
    The efficacy of electrolyzed water (EW) to inactivate Listeria monocytogenes on stainless steel surfaces was evaluated and modelled in the present study. L. monocytogenes was inoculated on stainless steel coupons and subsequently subjected to Neutral EW (NEW, pH = 7.0) and Slightly Acid EW (SAEW, pH = 5.0) with different Available Chlorine Concentration (ACC, 50-200 mg/L) for different exposure times (0-6 min). The number of viable cells on coupons decreased as the exposure time increased at all ACC concentrations. Treatments with SAEW resulted in higher reductions of L. monocytogenes, i.e., 2.30 +/- 0.16 to 5.64 +/- 0.11 log cfu/cm(2), in comparison with NEW treatments (1.55 +/- 0.11 to 5.22 +/- 0.12 log cfu/cm(2)), probably due to the synergistic bactericidal effect between the acidic pH, higher oxidation-reduction potential and the effective form of chlorine, reported in previous studies. Since SAEW was the most effective against L. monocytogenes, two approaches were tested to model the survival data: the one- and two-step modelling procedures. The Weibull model was suitable to describe the survival data and both approaches produced suitable survival models (adj-R-2>0.92 and MSE<0.2). EW is effective in reducing bacterial contamination on food-contact surfaces and the survival data and models derived from this study are relevant to optimize its use as an environment-friendly sanitizer in the food industry.