## 3 Results
### Effect of 455 nm LED Treatments on Low-\(\mathrm{a_{w}}\) S. Typhimurium
Typhimurium in this study could also contribute to the oxidative stress. This was supported by previous studies by [PERSON] et al. (2022) [24] and [PERSON] et al. (2021) [25], where drying induced oxidative stress in _E. coli_ and _Salmonella enterica_, respectively. Sanitizing solutions such as peracetic acid were found to be active in dry cells as they have produced promising antimicrobial activity against _Salmonella_ in low-moisture foods such as seeds, dried fruit, nuts, chocolate crumbs and cornflakes [48; 49]. The drying and the oxidative stress conditions trigger the bacteria to enter the viable but nonculturable (VBNC) state and increase their resistance to the subsequent intervention methods. The addition of catalase or pyruvate in the recovery media after the drying step would resuscitate the VBNC cells [24; 25; 36; 50] and would aid in evaluating the effect of the LED treatments in bacteria. [PERSON] et al. [51] reported improvement in the inactivation of UV-C-treated _E. coli_ ATCC 11229 by 365 nm (UV-A) LED pre-treatment. Their inactivation mechanism experiments showed that hydroxyl radicals had a major role on the _E. coli_ inactivation during the UVA pre-treatment. Our study showed significant generation of intracellular ROS and membrane lipid oxidation of \(S\). Typhimurium after 365, 395 and 455 nm LED treatments. During the 365 nm LED treatment of \(S\). Typhimurium, the major contributor to oxidative stress and membrane lipid peroxidation could be hydroxyl radicals. Studies focusing on the contribution of individual ROS (e.g., hydroxyl, singlet oxygen, superoxide, and hydrogen peroxide) on bacterial inactivation during 395 and 455 nm LED treatments are limited or not available in the literature. Future research can provide more information on the contribution of the main ROS on the microbial inactivation potential of 395 and 455 nm LED treatments. Since high doses of light pulses emitted from the LEDs were required to produce antibacterial effects in low-a\({}_{\mathrm{w}}\) conditions in this study, combining this technology with other non-thermal technologies such as high-pressure CO\({}_{2}\) treatment or mild heat treatment could result in better inactivation effectiveness in low-a\({}_{\mathrm{w}}\) conditions. The high doses of light pulses from LEDs can also result in photochemical reactions such as oxidation of food ingredients. For instance, previous studies reported significant lipid oxidation in pet foods by 395 and 455 nm LED treatments [29; 47]. However, an improvement in functional properties of UV-LED-treated wheat flour was reported in another study [31]. For instance, the wheat flour treated by 365, 395 and 455 nm LEDs showed a reduction in yellowness and water-holding capacity [31]. The changes in food qualities and functional properties by UV-LED treatment will depend on the type of product and the treatment conditions. Futureresearch is needed to optimize the LED treatment conditions, considering food safety and food quality aspects, based on the product of interest. In conclusion, the LEDs emitting light pulses of wavelengths 365, 395 and 455 nm showed antibacterial efficacy against \(S\). Typhimurium in low-\(\mathrm{a}_{\mathrm{w}}\) conditions. The 365 nm LED treatments showed a better inactivation effect against low-\(\mathrm{a}_{\mathrm{w}}\)\(S\). Typhimurium than the 395 nm LED treatment. Cell membrane damage due to the high-intensity light pulses could not be evaluated due to the drying and equilibration periods involved in the preparation of dried \(S\). Typhimurium equilibrated to 0.75 \(\mathrm{a}_{\mathrm{w}}\). Significant generation of intracellular ROS was observed with the LED treatments. In addition, the membrane lipid oxidation of the \(S\). Typhimurium cells was observed in the cases of all three LED treatments. Significant weight loss and increase in the surface temperature of the low-\(\mathrm{a}_{\mathrm{w}}\)\(S\). _typhimuriumum_ was observed with the 365, 395 and 455 nm LED treatments.