Effect of 222-nm krypton-chloride excilamp treatment on inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium on alfalfa seeds and seed germination

Abstract

We examined the control effect of a 222-nm KrCl excilamp on foodborne pathogens on alfalfa seeds and compared it with a conventional 254-nm low-pressure (LP) Hg lamp. When the 222-nm KrCl excilamp treated seeds at 87, 174 and 261 mJ/cm², the log reductions of Escherichia coli O157:H7 (E. coli O157:H7) were 0.85, 1.77, and 2.77, respectively, and Salmonella Typhimurium (S. Typhimurium) experienced log reductions of 1.22, 2.27, and 3.04, respectively. When the 254-nm LP Hg lamp was applied at 87, 174, and 261 mJ/cm², the log reductions of E. coli O157: H7 were 0.7, 1.16, and 1.43, respectively, and those of S. Typhimurium were 0.75, 1.15, and 1.85, respectively. Therefore, it was shown that the 222-nm KrCl excilamp was more effective than the 254-nm LP Hg lamp in reducing foodborne pathogens. The germination rate decreased to less than 80% after 261 mJ/cm² treatment with the 254-nm LP Hg lamp, while more than 90% was maintained with 261 mJ/cm² 222-nm KrCl excilamp treatment. DNA damage assay showed that the difference in germination rate was due to DNA damage resulting from 254-nm LP Hg lamp treatment. However, 222 nm KrCl excilamp treatment did not cause DNA damage, resulting in no difference in germination rate compared to that of non-treated alfalfa seeds. Overall, these results demonstrate the utility of the 222-nm KrCl excilamp as a foodborne pathogen control intervention for the alfalfa seed industry.

Keywords: Alfalfa seed; Bacteria; Seed germination; Ultraviolet irradiation; excilamp.