Validation of Washing Treatments to Reduce Escherichia coli O157:H7 and Salmonella spp. on the Surface of Green Leaf Lettuce and Tomatoes

Outbreaks associated with consumption of fresh produce have been linked to Escherichia coli O157:H7 and Salmonella contamination. The objective was to determine the efficacy of a chemical wash treatment (citric acid, sodium lauryl sulfate, sodium carbonate, magnesium carbonate, and grapefruit oil extract) in reducing pathogens on the surface of leaf lettuce and tomatoes. Lettuce (25 ± 0.3 g) and whole tomatoes were inoculated with E. coli O157:H7 (~7.8 log10 CFU/ml) and Salmonella spp. (9.39 log10 CFU/ml) cocktails, respectively. Samples were treated with cold tap water (negative control) or the chemical wash treatment for various exposure times (30, 60, and 120 s), and then rinsed with tap water. Samples then were plated on selective media. The chemical wash treatment was capable of reducing by ca. 3.0 log10 units of E. coli O157:H7 and Salmonella spp. populations on the surface of leaf lettuce and tomatoes, respectively. Even though there were no significant differences among results with different exposure times (P > 0.05), application of the chemical wash treatment for 120 s lowered the mean populations of recovered pathogens by 0.1 to 0.66 log10 CFU. Therefore, it is recommended that the chemical wash treatment be applied for 120 s to obtain optimal log reductions on the surface of leaf lettuce and tomatoes.