USING LIGHT EMITTING DIODES FOR INACTIVATING FOODBORNE PATHOGENIC BACTERIA IN FOOD PROCESSING ENVIRONMENTS

Abstract

Nonthermal treatments are increasingly used in food processing due to their potential of microbial inactivation with minimal physicochemical and sensorial quality damage to the food products. Recent advances in Light Emitting Diodes (LED) technology have shown great potential in food preservation, due the lower energy consumption and higher flexibility in design than traditional mercury or gas discharge lamps. This study investigates the use of LED technology in both Ultraviolet (UV) and visible range for inactivation of foodborne bacteria, under lower temperature conditions. One strategy of inactivating bacteria in foods and food processing environment is by using germicidal short- wave UV-C light (200 to 280 nm), which is typically emitted by mercury or amalgam lamps. UV-C LEDs were recently developed as a chemical-free, energy-efficient alternative to deliver germicidal UV and mitigate microbial contamination on material surfaces, but their effectiveness has not been fully explored. One of the objectives of this work was to gain a better understanding of the antimicrobial effectiveness of UV-C LEDs. Specifically, the inactivation kinetics of Escherichia coli ATCC 25922 and Listeria innocua FSL C2-0008 was studied by exposing them to a custom-made UV-C LED array (λ max =280 nm) under a variety of substrate conditions commonly encountered in food processing and handling environment. UV- C resulted in over 5-log reduction of both bacterial strains after 600 s in thin liquid films (thickness ≤ 0.6mm), and on all stainless steel (SS) surfaces. The fastest initial inactivation was achieved on dry SS i surfaces for both bacteria, but maximum inactivation was similar for the dry and wet conditions. The results of this work can help end users design effective and efficient UV-C LED disinfection strategies for various surface conditions. Another approach for eliminating undesirable bacteria in food processing environments is by using antimicrobial blue light in the wavelength spectrum of 400-470 nm. Previous work suggested that 405 nm light has maximum antimicrobial effects in this range, but the effectiveness of the treatment has not been fully explored. In this work, the efficacy of 405 nm LED against Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, and Staphylococcus aureus, and the effect of substrate on inactivation kinetics were investigated. Additionally, the influence of nanoscale surface topography on the inactivation behavior of pathogenic E. coli, L. monocytogenes, and S. aureus was evaluated. Exposure to 405nm LED resulted in over 5-log reduction for P. aeruginosa and S. aureus in liquid films after 48 h. Maximum inactivation was observed for E. coli on stainless steel (SS) surfaces; the highest rate of inactivation was observed on small nanopore anodic aluminum oxide (AAO) for L. monocytogenes and S. aureus, with over 5-log reduction achieved after 12 h, suggesting potential inactivation enhancing properties of nanoscale topography. The results suggest that 405 nm LEDs have great potential for antimicrobial treatments in the food industry, but disinfection success depends on bacterial species, substrate, and environmental conditions. Additionally, surfaces with nanoscale topography may offer additional inactivation enhancing properties. Overall, these approaches can have positive impacts on food safety and quality. This study demonstrates that LED technology can play an important role in combating foodborne bacteria in food processing and handling environments, clinical environments, as well as other areas relevant to human health.