Irradiation D-Values for Escherichia coli O157:H7 and Salmonella sp. on Inoculated Broccoli Seeds and Effects of Irradiation on Broccoli Sprout Keeping Quality and Seed Viability†

Abstract

Like alfalfa sprouts, broccoli sprouts can be a vehicle for bacterial pathogens, which can cause illness when they are consumed. The gamma irradiation process was used to reduce numbers of bacterial pathogens on broccoli sprouts and seeds, and the effect of this process on the seeds was studied. The irradiation destruct values for Salmonella sp. and for strains of Escherichia coli O157:H7 inoculated on broccoli seeds were determined. Results obtained in this study indicate that a dose of 2 kGy reduced total background counts for broccoli sprouts from 106 to 107 CFU/g to 104 to 105 CFU/g and increased the shelf life of the sprouts by 10 days. Yield ratio (wt/wt), germination percentage, sprout length, and thickness were measured to determine the effects of various irradiation doses on the broccoli seeds. Results show a decreased germination percentage at a dose level of 4 kGy, whereas the yield ratio (wt/wt), sprout length, and thickness decreased at the 2-kGy dose level. The radiation doses required to inactivate Salmonella sp. and strains of E. coli O157:H7 were higher than previously reported values. D-values, dose required for a 1-log reduction, for the nonvegetable and vegetable Salmonella sp. isolates were 0.74 and 1.10 kGy, respectively. The values for the nonvegetable and vegetable isolated strains of Escherichia coli O157:H7 were 1.43 and 1.11 kGy, respectively. With the irradiation process, a dose of up to 2 kGy can extend the shelf life of broccoli sprouts. A dose of >2 kGy would have an adverse effect on the broccoli seed and decrease the yield of broccoli sprouts.