Antimicrobial activities of a combination of chlorine dioxide gas and heat against Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds

We developed a short-time treatment to inactivate Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds by a combination of chlorine dioxide (ClO₂) gas and heat. ClO₂ gas was evaporated from a mixed solution which contained hydrochloric acid (1 N) and sodium chlorite (100,000 ppm) (ClO₂ solution). To produce ClO₂ gas (3,000 ppm) in an 1.8 L airtight container, a standard curve indicating the amount of ClO₂ solution and time needed to produce desired concentrations was constructed (y = 5758.3x; R² = 0.9981). The influence of simultaneous treatment with ClO₂ gas (3,000 ppm) and heat (70 °C at 85% relative humidity [RH]) on seed germination rates was determined. It was found that the germination rates of cabbage, chili pepper, and radish seeds were not significantly (P > 0.05) changed after 30, 20, and 60 min of treatment, respectively. The antimicrobial effects of the combined treatment against X. campestris and S. enterica on cabbage, chili pepper, and radish seeds were determined. When 3,000 ppm of ClO₂ gas were applied at 70 °C and 85% RH for 10 min, the populations of X. campestris (initial populations: 6.2–6.4 log CFU/g) on seeds were reduced by > 4.4 log CFU/g regardless of seed type. The initial populations of S. enterica (6.3–6.5 log CFU/g) on cabbage and chili pepper seeds treated for 10 min was reduced by > 5.3 log CFU/g. However, populations on radish seeds decreased only by 2.5 log CFU/g. The lower lethality against S. enterica on radish seeds, revealed by field-emission scanning microscopy to have a rougher surface than do cabbage and chili pepper seeds, is attributed in part to inhibited access of ClO₂ gas to cells in protected areas. Our findings provide useful information when developing more efficacious methods to decontaminate vegetable seeds using a combination of ClO₂ gas and heat.