Effectiveness of UVC-Assisted Fenton Reaction Wash-Based System to Inactivate Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes on Cherry Tomatoes

Abstract

The Fenton reaction results when hydrogen peroxide (H₂O₂) interacts with the ferrous ion, producing highly antimicrobial hydroxyl free radicals (OH). In this study, a UVC-assisted Fenton reaction was tested against cocktails of Salmonella Typhimurium, E. coli O157:H7, and Listeria monocytogenes, inoculated onto cherry tomatoes. Inoculated cherry tomatoes were subjected to 2% H₂O₂ wash, 1 mM Fe³⁺ wash, or exposed to UVC during washing, and simultaneously in the following combinations: H₂O₂ + Fe³⁺, H₂O₂ + UVC, or H₂O₂ + Fe³⁺ + UVC for 2 min at ambient temperature (∼20 °C). In addition, OH were measured using the methylene blue dye test, after combining Fenton reaction components in water. Results revealed that H₂O₂ alone, or in combination, reduced significantly higher populations of the three bacterial pathogens, when compared with water wash alone. The H₂O₂ + Fe³⁺ + UVC treatment inactivated 5.24 ± 1.17 log CFU Salmonella/fruit, which was significantly (P < 0.05) greater than those reduced by Fe³⁺ or UVC alone. However, the reduction was not statistically significant when compared to H₂O₂, H₂O₂ + Fe^3+, or H₂O₂ + UVC. Similarly, the combinations did not inactivate significantly (P > 0.05) more E. coli O157:H7 and L. monocytogenes than individual H₂O₂ or UVC treatments, with reductions of 2.31–3.20 and 1.96–3.17 log CFU/fruit, respectively, although OH were produced in water during the H₂O₂ + Fe³⁺ + UVC treatments. Overall, our results demonstrate that UVC-assisted Fenton washing does not consistently exhibit advantages over individual H₂O₂ or UVC treatments during cherry tomato washing to inactivate foodborne pathogens, presumably due to the inability of short-lived hydroxyl radicals to reach the bacteria on tomatoes.