The efficacy of UVC LEDs and low pressure mercury lamps for the reduction of Escherichia coli O157:H7 and Listeria monocytogenes on produce

Abstract

The inactivation efficacies of low pressure mercury (LPM) lamps (253.7 nm) and UVC LEDs (277 nm) were compared for Escherichia coli O157:H7 on lettuce leaves and Listeria monocytogenes on apple skin. Reductions ranging from 1.19 ± 0.59 to 1.58 ± 0.27 log CFU per sample at 4 and 25 °C were achieved. At 4 °C, UVC LEDs increased in fluence rate, while achieving log reductions similar to those at 25 °C. The effect of wavelength on lettuce quality was also evaluated. Treatment (500 mJ·cm−2) from either light source increased browning of romaine lettuce, while mesophilic counts, chlorophyll content and spoilage enzyme activity were not affected significantly over a storage period of up to 21 days. Finally, the adjusted germicidal power (AGP) as a means of comparing inactivation performance between UV wavelengths was evaluated. It was found that AGPs generated in a water-based model system did not adequately predict efficacy on solid food matrices. Industrial relevanceThe use of ultraviolet-C (UVC) light for disinfection represents a possible dry means to augment or replace existing batch-wash disinfection systems for fresh produce. In this study we have shown that UVC LEDs at 277 nm have comparable germicidal efficacy to LPM lamps against the foodborne pathogens E. coli O157:H7 and Listeria monocytogenes on lettuce leaves and apple skin, respectively, while both light sources achieve log reductions similar to an aqueous sodium hypochlorite wash. Overall these results indicate that UVC LEDs (and UVC light in general) is an alternative effective and sustainable method of disinfecting apples and lettuce in an industrial setting, reducing or eliminating the dependence on aqueous sanitizers.