Purpose: This work was undertaken to develop and use appropriate methodology to evaluate the SE of chlorine under varying OLs, at well-maintained FC levels, relevant to commercial fresh produce washing.
Methods: A sustained chlorine decay approach was employed to evaluate the inactivation of Escherichia coli O157:H7 at stabilized FC, chloramine, and chemical oxygen demand (COD) levels. Prepared chlorine-OL solutions were incubated (n=168) at room temperature for four hours to model the effect of residual FC after reacting with OL in a produce wash system. Bacterial survival after 5 and 20 sec exposures to OL-chlorine mixtures was assessed by MPN (n=240).
Results: As OL increased, SE of chlorine decreased. At a 5 s exposure time and pH 6.5, a minimum of 0.5 and 7.5 mg/L FC were needed to achieve a 5 log reduction at 0 and 900 mg/L COD, respectively. The SE decrease was significantly (P<0.05) more pronounced at lower FC, higher COD, higher pH, and shorter exposure time values. The OL-associated interference with FC measurement and disruption of chlorine-bacteria interaction, together with the chlorine demand of concentrated inoculum, collectively resulted in inadequate FC concentration and SE.
Significance: A feasible method for evaluating chlorine-based sanitization was developed and demonstrated the negative impact of OL on SE under well-controlled conditions. To fully account for these chemical interactions in actual commercial-scale produce washing conditions, scale-appropriate evaluations are needed to confirm and incorporate adjustments specific to actual systems.