Reduction ofEscherichia coliO157:H7 on radish seeds by sequential application of aqueous chlorine dioxide and dry-heat treatment

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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 μg ml−1 ClO2 for 5 min and subsequently heated at 60°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.

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