P1-168 Chlorine-based Inactivation of Escherichia coli O157:H7:  Impact of Residual-free Chlorine Content, Organic Load, Residence Time, and pH

Monday, July 10, 2017
Exhibit Hall (Tampa Convention Center)
Zi Teng , University of Maryland , College Park , MD
Yaguang Luo , U.S. Department of Agriculture–ARS , Beltsville , MD
Solmaz Alborzi , University of Maryland , College Park , MD
Bin Zhou , U.S. Department of Agriculture–ARS , Beltsville , MD
Boce Zhang , U.S. Department of Agriculture–ARS , Beltsville , MD
Patricia Millner , U.S. Department of Agriculture–ARS , Beltsville , MD
Qin Wang , University of Maryland , College Park , MD
Introduction: During fresh produce washing, the sanitizing efficacy (SE) of chlorine is constantly compromised by organic load (OL), which reportedly contributes to rapid chlorine depletion and unsuccessful maintenance of residual free chlorine (FC). However, it is unclear whether chlorine performs equally well at identical, well-maintained FC residual levels, with and without OL. Knowledge in this regard is important for accurate determination of effective FC levels under high OL.

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.