Effect of sequential presoaking and chlorine dioxide treatment on the inactivation of pathogenic Escherichia coli and Salmonella spp. on sprout seeds

This study was conducted to evaluate the effect of sequential presoaking and chlorine dioxide (ClO2) on the reduction of pathogenic Escherichia coli and Salmonella spp. in alfalfa. When unsoaked and presoaked alfalfa were exposed to 200 ppm ClO2 for 15 min, the population of E. coli and Salmonella spp. on presoaked seeds reduced more than those on unsoaked seeds by 2.07 and 1.43 log CFU g−1 (p < 0.05), respectively. To determine the optimal concentration and treatment time to reduce pathogenic E. coli and Salmonella spp. in alfalfa seeds immersed in water for 5 h, presoaked seeds were exposed to four different concentrations of ClO2 (50, 100, 150, and 200 ppm) for 15, 30, 45, and 60 min. The most effective condition to eliminate E. coli and Salmonella spp. from alfalfa seeds was sequential immersion in water for 5 h and 200 ppm ClO2 treatment for 1 h. After the optimal condition was applied to eight kinds of sprout seeds, the pathogens were completely inactivated in all seeds, except radish seeds. Growth of pathogenic E. coli and Salmonella spp. during sprouting after ClO2 treatment of alfalfa seeds was also completely inactivated. However, the germination rate of seeds did not significantly decrease after ClO2 treatment. In addition, ClO2 residues were not present in any sprout during 3 days of cultivation. These results demonstrated that sequential presoaking and 200 ppm ClO2 treatment is the optimal seed disinfection treatment to prevent foodborne diseases associated with sprout consumption.