The main objective of this study was to determine survivability of a cocktail of three strains of Salmonella enterica (Montevideo, Javiana, and Baildon) and two strains of Listeria monocytogenes (LCDC 81-861 and F4244) on hydroponic tomatoes after treatment with chlorine dioxide (ClO2) gas. An initial concentration of 8–9 log cfu/mL of Salmonella and Listeria cocktails was inoculated individually, in separate experiments, on tomato skin to obtain a population of 7–8 log cfu/cm2 after drying of the inoculums on the tomato skin. The aim was to achieve a 5 log reduction consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. The tomato skins were treated with 0.1, 0.3, and 0.5 mg/L ClO2 gas for 12 min at 22°C and at the relative humidity of 90%. Untreated skin samples were processed under the same conditions. ClO2-gas-treated and untreated samples were recovered by an overlay method. The bottom layer contains tryptic soy agar, and the top layer consists of xylose-lysine-desoxycholate agar or modified Oxford antimicrobial supplement agar for Salmonella and Listeria, respectively. More than a 5 log reduction in Salmonella and Listeria was observed on the tomato skin surfaces after treatment with 0.5 mg/L ClO2 gas for 12 min. Treatment with 0.5 mg/L ClO2 gas for 12 min also delayed the growth of natural microflora on tomato surfaces and extended the shelf life of tomatoes by 7 days during storage at 22°C, compared with the untreated control. These results revealed that ClO2 gas is a promising antimicrobial technology for fresh tomato skin surfaces.
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