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

Inactivation rate constant or inactivation coefficient (specific lethality) quantifies the rate at which a chemical sanitizer inactivates a microorganism. 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/min in the absence of organic content, it drops by 73% for a chemical oxygen demand (COD) level of 600-800 mg/L. 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 proportion 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 /mu M/min. This model was validated by predicting FC concentration in multi-run continuous wash cycles with periodic replenishment of chlorine.

Automated summary

This study presented a modified disinfection kinetics model to evaluate the effect of organic content on the chlorine inactivation coefficient, showing a significant decrease in bactericidal efficacy of free chlorine in the presence of organic load. The chlorine inactivation coefficient of Escherichia coli O157:H7 decreased by 73% with higher levels of chemical oxygen demand (COD). Initial chlorine concentration and bacterial load were found to have no effect on the chlorine inactivation coefficient.