Microbicidal effectiveness of irradiation from Gamma and X-ray sources at different dose rates against the foodborne illness pathogens Escherichia coli, Salmonella Typhimurium and Listeria monocytogenes in rice

Abstract

The radiation response of three foodborne illness pathogens was examined for irradiation with cobalt-60 Gamma and low-energy (125 keV) X-ray at different dose rates. Escherichia coli, Salmonella Typhimurium and Listeria monocytogenes were inoculated into rice and irradiated at target doses of 0 (control), 250, 500, 750, 1000, and 1500 Gy with either Gamma radiation (dose rates of 9.1, 3.9 or 0.22 kGy/h) or X-ray radiation (dose rate of 0.76 kGy/h). Doses were measured with traceability to national standards. The dose rate did not significantly affect D10 values (microbicidal effectiveness) for any of the Gamma-irradiated pathogens. Low energy X-ray irradiated pathogens had significantly higher D10 values (lower microbicidal effectiveness) for all pathogens compared to Gamma-irradiated pathogens. The combination of Gamma or X-ray irradiation with a mixture of oregano/thyme essential oil (EO) fumigation generally increased the microbicidal effectiveness compared to irradiation alone. Gamma or low energy X-ray irradiation and plant essential oils such as oregano/thyme, applied alone or in combination, are effective antimicrobial treatments.