Effects of integrated treatment of nonthermal UV-C light and different antimicrobial wash on Salmonella enterica on plum tomatoes

Abstract

The aim of this study was to evaluate inactivation of inoculated Salmonella enterica on whole tomato surface exploiting integration of nonthermal ultraviolet light (UV-C) treatment with antimicrobial wash. The effect of combined treatment on background microflora (aerobic mesophilic, and yeast and mold), during storage at ambient temperature (22 °C) for 21 days was also determined. A bacterial cocktail containing three serotypes of S. enterica (S. Newport H1275, S. Stanley H0558, and S. Montevideo G4639) was used based on their association with produce-related outbreaks. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve cell population of about 107 CFU/tomato. An inoculated tomato was initially treated with a low (0.6 kJ/m2) dose of UV-C light (253.7 nm) followed by immersion in selected sanitizing solution (700 ml) to wash under mild agitation (ca. 250 rpm) for 2 min at room temperature (22 °C). Inactivation efficacy of combined treatments varied widely depending on the sanitizer property. Combined UV-C plus aqueous ozone (1 ppm) provided 3.13 ± 0.47 log CFU/fruit Salmonella reduction which was significantly lower (p < 0.05) compared to the rest of the combination treatments; whereas the treatment of UV-C followed by immersion in a novel antimicrobial preparation ‘HEN’, formulated mixing hydrogen peroxide, EDTA and nisin provided the best log reduction (4.71 ± 0.25 log CFU/fruit). Organic acids (1%) or their binary mixtures, hydrogen peroxide (3%), and HEN provided greater than 4.0 log reductions for UV-C treated tomatoes. Treatments were effective in controlling native microbial loads as the total aerobic mesophilic organisms and the population of yeast and mold remained significantly (p < 0.05) low during storage compared to control. Findings from this study provide safe and effective post harvest intervention strategies for produce industry as an alternative to current chlorine based wash. These results may also help researchers design future decontamination studies.