Application of a 222-nm krypton-chlorine excilamp to control foodborne pathogens on sliced cheese surfaces and characterization of the bactericidal mechanisms

- Conventional low-pressure UV-C germicidal lamps have potential limitations.
- Prospects of 222-nm KrCl excilamp as an alternative surface disinfection method for sliced cheese were evaluated.
- 222-nm UV-C irradiation showed significantly higher inactivation capacity for some pathogens than 254-nm radiation.
- The mechanisms of the enhanced lethal effect of KrCl excilamp treatment were elucidated.

This study was conducted to investigate the basic spectral properties of a 222-nm krypton-chlorine (KrCl) excilamp and its inactivation efficacy against major foodborne pathogens on solid media, as well as on sliced cheese compared to a conventional 254-nm low-pressure mercury (LP Hg) lamp. Selective media and sliced cheese inoculated with Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes were irradiated with a KrCl excilamp and a LP Hg lamp at the same dose. The KrCl excilamp showed full radiant intensity from the outset at a wide range of working temperatures, especially at low temperatures of around 0 to 10 °C. Irradiation with 222 nm UV-C showed significantly (P < 0.05) higher inactivation capacity against all three pathogens than 254-nm radiation on both media and sliced cheese surfaces without generating many sublethally injured cells which potentially could recover. The underlying inactivation mechanisms of 222-nm KrCl excilamp treatment were evaluated by fluorescent staining methods and damage to cellular membranes and intracellular enzyme inactivation were the primary factors contributing to the enhanced bactericidal effect. The results of this study suggest that a 222-nm UV-C surface disinfecting system can be applied as an alternative to conventional LP Hg lamp treatment by the dairy industry.