Inactivation of foodborne pathogenic and spoilage bacteria by single and dual wavelength UV-LEDs: Synergistic effect and pulsed operation

Abstract

Abstract As an emerging UV source, UV light-emitting diodes (UV-LEDs) are an attractive alternative to traditional mercury vapor lamps for food decontamination. In this work, we sought to find the strategies for the improvement of UV-LED inactivation efficiencies on common foodborne pathogenic and spoilage bacteria. Inactivation efficiencies of UV-LEDs with peak emissions at 369 nm (UVA), 288 nm (UVB), and 271 nm (UVC) and combined emissions at 369/288, 369/271, and 288/271 nm on three foodborne pathogenic bacteria (Escherichia coli, Staphylococcus epidermidis, Salmonella Typhimurium) and two spoilage bacteria (Serratia marcescens, Pseudomonas alcaligenes), were investigated. The solid agar surface was chosen as a model to mimic the food surface. The UV dose delivered to the samples ranged between 0.75 and 6.75 mJ/cm2. For the application of single-wavelength UV-LEDs, 271 nm UV-LED displayed the highest inactivation efficiency on the tested bacteria. A synergistic effect was observed when E. coli, S. epidermidis, and S. Typhimurium were exposed to irradiation from 288/271 nm UV-LEDs. The synergy ratios ranged from 0.20 to 0.87. No synergy was observed for S. marcescens and P. alcaligenes, or any bacteria tested with 369/288 or 369/271 nm combined modules. Besides, the inactivation efficiencies of continuous and pulsed irradiation against E. coli and S. epidermidis were compared using three modules: 288 nm, 271 nm, and 288/271 nm UV-LEDs. All of the tested UV-LED modules showed comparable inactivation by continuous and pulsed irradiation with various duty cycles under an equivalent UV dose of 6.46 mJ/cm2. Based on the operation-specific microbial inactivation data, this study demonstrated an effective and sustainable method for inactivating foodborne pathogens and offered strategies to enhance disinfection efficiency for system designers and industrial engineers.