Chlorine inactivation of Escherichia coli O157:H7 in fresh produce wash process: effectiveness and modeling

This study presents a modified disinfection kinetics model to evaluate the potential effect of organic content on the chlorine inactivation coefficient of Escherichia coli O157:H7 in fresh produce wash processes. Results show a significant decrease in the bactericidal efficacy of free chlorine (FC) in the presence of organic load compared to its absence. While the chlorine inactivation coefficient of Escherichia coli O157:H7 is 70.39 {+/-} 3.19 L.mg-1.min-1 in the absence of organic content, it drops by 73% in chemical oxygen demand (COD) level of 600 - 800 mg.L-1. Results also indicate that the initial chlorine concentration and bacterial load have no effect on the chlorine inactivation coefficient. A second-order chemical reaction model for FC decay, which utilizes a percentage of COD as an indicator of organic content in fresh produce wash was employed, yielding an apparent reaction rate of (9.45 {+/-} 0.22) x 10-4 M-1.min-1. This model was validated by predicting FC concentration (R2 = 0.96) in multi-run continuous wash cycles with periodic replenishment of chlorine.