Purpose: To evaluate the effects of gaseous chlorine dioxide in combination with Pseudomonas chlororaphis and P. fluorescens (biocontrol microbes) for reduction of Salmonella enterica on tomatoes at post-harvest.
Methods: P. chlororaphis was spot-inoculated on stem-scars of tomatoes and was then subsequently exposed to S. enterica serovars Montevideo and Typhimurium. Tomato samples (n = 6 per treatment) were stored for 24 or 48 h prior to evaluation. In a comparative assay, tomato (stem scars) inoculated with Salmonella Montevideo and Salmonella Typhimurium serovars and stored at 13°C, were exposed to gaseous chlorine dioxide at 0.4 mg/l for 2 or 4 h in separate experiments (90 % RH, 13°C). The Pseudomonas strain was assessed on Pseudomonas Agar F while Salmonella serovars were quantified on XLT-4 medium.
Results: The reductions of Salmonella Montevideo and Salmonella Typhimurium populations on tomatoes following 4 h chlorine dioxide gas treatment were 4.6 and 5.3 log CFU/g, respectively. In comparison, the populations of these pathogens (5.42 log CFU/g) on the untreated control tomatoes were significantly (P < 0.05) higher than that of the treated tomatoes. Similar results were obtained with the 2 h chlorine dioxide gas treatment. When tomatoes were inoculated with P. chlororaphis preemptively as antagonistic biocontrol, the reductions of Salmonella serovars averaged 2.6 log CFU/g while the untreated control had 5.8 log CFU/g of Salmonella on produce.
Significance: The application of gaseous chlorine dioxide and sequential application of biocontrol microbes such as P. chlororaphis was effective in reducing populations of Salmonella on tomatoes.