Effect of surface characteristics on the bactericidal efficacy of UVC LEDs

Abstract

UVC LED lamps have gained interest as a possible technology to replace the use of low- pressure mercury UV lamps due to the Minamata convention which is an international treaty enacted to eliminate the use of mercury. In this study, we investigated the influence of surface properties on inactivation efficacy of foodborne pathogens (E. coli O157:H7, S. Typhimurium, and L. monocytogenes) on various food contact surfaces, including glass, PVC, Stainless steel (SUS), Teflon, and silicon by using UVC light-emitting-diode (LED) irradiation. An optimized treatment chamber was constructed and UVC LED irradiation was applied to spot-inoculated surfaces. Also, in order to achieve enhanced pathogen inactivation, combined intervention of 60 degrees C mild heat and UVC LED irradiation was applied. Different levels of inactivation of foodborne pathogens were observed among surfaces; bactericidal effect decreased in this order: glass, PVC, SUS, Teflon, and silicon (0.5-1 log reduction differences), and this order was closely associated with surface hydrophobicity and roughness. Because of varying hydrophobicity among different surfaces, different bacterial stacking arrangements were developed, and causing undesirable shading effects negating collimated UVC LED irradiation of pathogens located beneath the top layer. Combination treatment of 60 degrees C mild heat and UVC LED achieved an additive or synergistic inactivation effect (up to 1 log reduction) on E. coli O157:H7, S. Typhimurium, and L. monocytogenes. The combined treatment can compensate for lower penetration and other limitations of UV irradiation, so that effective control of bacteria on food processing surfaces can occur.