Effect of Chlorine Dioxide Treatment on Human Pathogens on Iceberg Lettuce

In the vegetable processing industry, the application of chlorine dioxide (ClO₂) as a disinfectant solved in washing water to eliminate undesirable microorganisms harmful to consumers' health and the shelf life of produce has been discussed for years. The disinfection efficacy depends on various factors, e.g., the location of microorganisms and the organic load of the washing water. The present study analyzed the sanitation efficacy of various concentrations of water-solved ClO₂ (cClO₂: 20 and 30 mg L^-1) on Escherichia coli (1.1 × 10⁴ cfu mL^-1), Salmonella enterica (2.0 × 10⁴ cfu mL^-1) and Listeria monocytogenes (1.7 × 10⁵ cfu mL^-1) loads, located on the leaf surface of iceberg lettuce assigned for fresh-cut salads. In addition, it examined the potential of ClO₂ to prevent the cross-contamination of these microbes in lettuce washing water containing a chemical oxygen demand (COD) content of 350 mg L^-1 after practice-relevant washing times of 1 and 2 min. On iceberg leaves, washing with 30 mg L^-1 ClO₂ pronouncedly (1 log) reduced loads of E. coli and S. enterica, while it only insignificantly (<0.5 × log) diminished the loads of L. monocytogenes, irrespective of the ClO₂ concentration used. Although the sanitation efficacy of ClO₂ washing was only limited, the addition of ClO₂ to the washing water avoided cross-contamination even at high organic loads. Thus, the application of ClO₂ to the lettuce washing water can improve product quality and consumer safety.