Using UVC Light-Emitting Diodes at Wavelengths of 266 to 279 Nanometers To Inactivate Foodborne Pathogens and Pasteurize Sliced Cheese

Abstract

UVC light is a widely used sterilization technology. However, UV lamps have several limitations, including low activity at refrigeration temperatures, a long warm-up time, and risk of mercury exposure. UV-type lamps only emit light at 254 nm, so as an alternative, UV light-emitting diodes (UV-LEDs) which can produce the desired wavelengths have been developed. In this study, we validated the inactivation efficacy of UV-LEDs by wavelength and compared the results to those of conventional UV lamps. Selective media inoculated with Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes were irradiated using UV-LEDs at 266, 270, 275, and 279 nm in the UVC spectrum at 0.1, 0.2, 0.5, and 0.7 mJ/cm(2), respectively. The radiation intensity of the UV-LEDs was about 4 μW/cm(2), and UV lamps were covered with polypropylene films to adjust the light intensity similar to those of UV-LEDs. In addition, we applied UV-LED to sliced cheese at doses of 1, 2, and 3 mJ/cm(2). Our results showed that inactivation rates after UV-LED treatment were significantly different (P < 0.05) from those of UV lamps at a similar intensity. On microbiological media, UV-LED treatments at 266 and 270 nm showed significantly different (P < 0.05) inactivation effects than other wavelength modules. For sliced cheeses, 4- to 5-log reductions occurred after treatment at 3 mJ/cm(2) for all three pathogens, with negligible generation of injured cells.

FIG 1

Emission spectra of four different peak wavelengths (266, 270, 275, and 279 nm) of UV-LED PCBs (a) and absolute intensity of a 254-nm UV lamp covered with various numbers of PP films at a 20-cm distance between UV sources and a spectrometer probe (b).

FIG 2

Reduction of E. coli O157:H7 (a), S. Typhimurium (b), and L. monocytogenes (c) cells on each selective medium (E. coli O157:H7; sorbitol MacConkey agar, S. Typhimurium; xylose lysine desoxycholate, L. monocytogenes; Oxford agar base with antimicrobial supplement) treated with a 254-nm UV-lamp and 266-nm UV-LED PCBs at 0.1, 0.2, 0.5, and 0.7 mJ/cm².