Assessing Effective Quality Controls of Chlorination in Postharvest Wash Water Sanitation of Fresh Produce

Introduction: Postharvest produce sanitation is a key food safety step to control and reduce microbial loads and its importance is addressed in newly proposed rules for produce safety under FDA’s Food Safety Modernization Act. There are common farm sanitization practices which require further examination for effectiveness due to variables like sanitizer concentration, efficacy lost due to turbidity, chemical dissipation, temperature, and pH. The intention is to compare and evaluate monitoring practices such as oxidation reduction potential for effective water sanitation in postharvest practices in order to aid and ease transition of industrial safety methods onto small commercial farms.

Purpose: To evaluate methods of postharvest produce sanitation management and the factors that affect the efficacy of chlorine sanitation in control of microbial loads.

Methods: Autoclaved water was inoculated with 10⁶ CFU/ml Escherichia coli BL21. Water samples at pH of 6.0-7.0 and were exposed to different chlorine concentrations (50-75ppm), turbidity levels (1-50 NTU through the addition of autoclaved soil), and different exposure times (1, 3, 5 minutes).  ORP was measured and then samples de-chlorinated with sodium thiosulfate prior to performing standard plate counts.

Results: Data shows that chlorine concentration 50 ppm measured ORP 850 RmV in low turbidity (below 10 NTU) with a 3 log reduction in microbial load. Water with increased turbidity exposed to 50 ppm resulted with decreased ORP (650 RmV to 300 RmV) and produced a 1-2 log reduction.

Significance:  Data suggests ORP values 600-800 RmV with low turbidity can be used as a monitoring range for indication of chlorine efficacy required in postharvest wash water for reduction of microbial loads.