Reduction of Escherichia coli O157:H7 on radish seeds by sequential application of aqueous chlorine dioxide and dry-heat treatment

Aims: To assess the effectiveness of sequential treatments of radish seeds with aqueous chlorine dioxide (ClO2) and dry heat in reducing the number of Escherichia coli O157:H7. Methods and Results: Radish seeds containing E. coli O157:H7 at 5.5 log CFU g(-1) were treated with 500 mu g ml(-1) ClO2 for 5 min and subsequently heated at 60 degrees C and 23% relative humidity for up to 48 h. Escherichia coli O157:H7 decreased by more than 4.8 log CFU g(-1) after 12 h dry-heat treatment. The pathogen was inactivated after 48 h dry-heat treatment, but the germination rate of treated seeds was substantially reduced from 91.2 +/- 5.0% to 68.7 +/- 12.3%. Conclusions: Escherichia coli O157:H7 on radish seeds can be effectively reduced by sequential treatments with ClO2 and dry heat. To eliminate E. coli O157:H7 on radish seeds without decreasing the germination rate, partial drying of seeds at ambient temperature before dry-heat treatment should be investigated, and conditions for drying and dry-heat treatment should be optimized. Significance and Impact of the study: This study showed that sequential treatment with ClO2 and dry-heat was effective in inactivating large numbers of E. coli O157:H7 on radish seeds. These findings will be useful when developing sanitizing strategies for seeds without compromising germination rates.