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

The Fenton reaction results when hydrogen peroxide (HO) 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% HO wash, 1 mM Fe wash, or exposed to UVC during washing, and simultaneously in the following combinations: HO + Fe, HO + UVC, or HO + Fe + 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 HO alone, or in combination, reduced significantly higher populations of the three bacterial pathogens, when compared with water wash alone. The HO + Fe + UVC treatment inactivated 5.24 ± 1.17 log CFU Salmonella/fruit, which was significantly (P < 0.05) greater than those reduced by Fe or UVC alone. However, the reduction was not statistically significant when compared to HO, HO + Fe or HO + UVC. Similarly, the combinations did not inactivate significantly (P > 0.05) more E. coli O157:H7 and L. monocytogenes than individual HO 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 HO + Fe + UVC treatments. Overall, our results demonstrate that UVC-assisted Fenton washing does not consistently exhibit advantages over individual HO 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.