Effects of Chlorine-Based Antimicrobial Treatments on the Microbiological Qualities of Selected Leafy Vegetables and Wash Water

The disinfection efficacy of sodium hypochlorite (NaClO) and chlorine dioxide (ClO2) was evaluated singly or in combination with micro-bubbling, ultra-sonication, or mild heat (50 degrees C) against microorganisms on lettuce, spinach and Chinese cabbage. There were no significant differences in reductions of either intrinsic microflora or inoculated Escherichia coli O157:117 between 5 and 10 min of treatment time, between 50, 100, 200 ppm NaClO, or between 25 and 50 ppm ClO2. However, mild heat (50 degrees C) significantly enhanced efficacy, with maximum log reductions of 2.91 in total plate count, 4.10 in total conform count, and 2.13 - 2.53 in E. coli O157:117. Heat was more effective when applied before or with chlorination than after. The concentration and efficacy of the chlorine wash water gradually decreased with reuse, allowing cross-contamination when the initial concentration was less than 50 ppm. These results can be used to guide the fresh-cut vegetable industry in designing chlorine-based treatments for better control of safety and quality.