Elevated Inactivating Efficacy of a Pulsed UVC Light-Emitting Diode System on Foodborne Pathogens on Selective Media and Food Surfaces

ABSTRACT

UVC light, a strong surface disinfection technology, is used world-wide to ensure not only environmental safety, but also food safety. Several drawbacks associated with usage of mercury-containing UV lamps, especially, human and environmental health risks, led to the Minamata convention which prohibits manufacturing and import/export of products containing mercury. Therefore, LED-based UVC irradiation, a new technology which is eco-friendly and an effective UV emitting source, has been researched recently. However, to date, there has been no report describing pulsed UVC-LED for improving inactivation of foodborne pathogens, although much research regarding conventional pulsed xenon lamps has been published. In this investigation, we evaluated the enhanced bactericidal effect of a pulsed UVC-LED system compared to continuous irradiation and optimum conditions for maximizing the effect were determined. Also, elucidating the difference in inactivation between pulsed and continuous UVC-LED irradiation was determined by inactivation mechanism analysis. The combination of 20 Hz frequency and 50% duty ratio pulsed UVC-LED irradiation achieved 4 to 5 log reductions of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium and Listeria monocytogenes; this combination showed the highest bactericidal effect among various treatment conditions at 2 or 5 mJ/cm². From mechanism assessment, membrane integrity (propidium iodide; PI uptake) was not affected by UVC-LED treatment but membrane potential (bis-(1,3-Dibutylbarbituric Acid) Trimethine Oxonol; DiBAC₄ (3) accumulation) showed significantly different values when comparing pulsed and continuous treatments. Also, changes in membrane lipid peroxidation and respiratory enzyme activity was attributed to more reactive oxygen species generated by pulsed UVC-LED irradiation .

IMPORTANCE The United Nations Environment Program (UNEP) convened the Minamata convention on mercury in 2013, which prohibits trade in mercury-containing products in order to ensure human health. It will be effectuated in 2020 so that use of low pressure mercury lamps will be discontinued and a new UV emitting source selected to replace the conventional technology. In this regard, UVC-LEDs have been developed and the fundamental inactivating effect has been researched. However, a pulsed UVC-LED system has not been studied because of the difficulty of generating a UVC-LED pulse wave. An optical chopper system which physically divides the light with an adjustable blade into personalized frequency and duty ratio was introduced for generating pulsed UVC-LED irradiation. This study elucidated the efficacy of a pulsed UVC-LED system and explicated its enhanced bactericidal effect by mechanism analysis.