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High intensity pulsed light emitting diode (LED) treatment is a novel approach to inactivate foodborne pathogens. The objective of this study was to evaluate the antibacterial potential of high intensity 365 (UV-A) and 395 nm (NUV-Vis) LED treatments against Escherichia coli and Salmonella enterica at high and low water activity (a w ) conditions, and to understand the influence of different process parameters on their antibacterial efficacy. Bacteria at high (in phosphate buffer saline, PBS) and low a w (a w = 0.75) conditions were treated with both the LEDs with specific doses at a fixed distance from the LEDs. The 365 nm LED showed more effectiveness in reducing the dried bacteria compared to 395 nm LED. The dry E. coli showed more resistance to LED treatments compared to Salmonella. The 365 and 395 nm LED treatments with~658 J/cm 2 dose resulted in reductions of 0.79 and 1.76 log CFU/g of Salmonella, respectively, on 0.75 a w pet foods. The LED treatments increased the surface temperature, resulting in water loss in the treated samples. This study showed that the dose, duration of light exposure, bacterial strain, and a w played a major role in the antibacterial efficacy of the 365 and 395 nm LEDs.

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Salmonella is a foodborne pathogen responsible for several outbreaks in low-water activity (aw) foods. Treatment using light pulses emitted from light-emitting diodes (LED) is an emerging decontamination method to inactivate foodborne pathogens. The objective of this study was to understand the antibacterial mechanisms of light pulses with 365, 395 and 455 nm wavelengths against Salmonella Typhimurium in low-aw conditions. The 365 nm light pulses showed better inactivation efficacy against low-aw S. Typhimurium than the 395 nm light pulses. For instance, the 365 nm LED treatment with an ~217 J/cm2 dose produced a reduction of 2.94 log (CFU/g) in S. Typhimurium cell counts, as compared with a reduction of 1.08 log (CFU/g) produced by the 395 nm LED treatment with the same dose. We observed a significant generation of intracellular reactive oxygen species (ROS) in S. Typhimurium cells after treatments with the 365, 395 and 455 nm light pulses at low-aw conditions. The LED treatments also showed a significant membrane lipid oxidation of S. Typhimurium cells after treatments with 365, 395 and 455 nm light pulses. Overall, a major role of ROS generation was observed in the inactivation efficacy of the 365, 395 and 455 nm light pulses against S. typhimurium at low-aw conditions.

Eradication of biofilms from the food contact surfaces is a challenging task, owing to their increased resistance to sanitizers and regular cleaning practices. The treatment with the light pulses emitted from the light emitting diode (LED) is an emerging surface decontamination technology, that can produce the antibiofilm effect by photodynamic inactivation. The objective of this study was to understand the antibiofilm efficacy of the 275 (Ultraviolet‐C [UV‐C]) and 455 nm (Blue) light pulses emitted from the LEDs against single and dual‐species biofilms of Salmonella Typhimurium ATCC13311 and Aeromonas australiensis 03‐09 on stainless steel (SS) coupons formed at different time. The biofilm formation by S. Typhimurium was improved when grown with A. australiensis in dual‐species culture. Both 275 and 455 nm light pulses showed significant antibiofilm activity against S. Typhimurium and A. australiensis in single and dual‐species biofilms. For instance, the 275 nm LED treatment of surfaces of SS coupons with 1.8 J/cm2 dose on each surface, produced reductions of 4.24 and 3.9 log (CFU/cm2) in single (cell attachment) and dual‐species biofilms of S. Typhimurium, and reductions of 4.45 and 4.99 log (CFU/cm2) in single and dual‐species biofilms of A. australiensis. However, the susceptibility of A. australiensis toward 455 nm LED treatments was influenced by the presence of S. Typhimurium in the dual‐species biofilm. The confocal laser scanning microscopy images revealed significant cell membrane damage in the dual‐species biofilms by the LED treatments with 275 and 455 nm light pulses. Overall, several factors like surface temperature increase, strains used, treatment dose, treatment time, and incubation period of biofilms influenced the inactivation efficacy of the 275 and 455 nm LED treatments against the biofilms formed on SS coupons. This study provides an insight into the inactivation efficacy of LED light pulses against bacterial biofilms on food grade SS surfaces.