## 3 Results
### Effect of 455 nm LED Treatments on Low-\(\mathrm{a_{w}}\) S. Typhimurium
The generation of intracellular ROS can also lead to the oxidation of cellular components such as lipids and proteins and might inhibit enzyme activity inside the cell, eventually leading to cell death [40; 41; 42; 43]. Since we observed a significant oxidative stress of bacterial cells due to the 365 and 395 nm LED treatments, further evaluation of the membrane lipid oxidation was performed. C11-BODIYP\({}^{\mathrm{581/591}}\) dye was used to detect the membrane lipid oxidation in low-a\({}_{\mathrm{w}}\)_S_. Typhimurium that is oxidized by peroxide radicals [24; 44]. Flow cytometry analysis facilitated in the quantification of oxidized and unoxidized cells [14] showed that the inactivation efficacy of the 365 nm LED treatment against _E. coli_ DH5\(\alpha\) was suppressed by the presence of catalase (a scavenger of hydrogen peroxide), indicating the presence of the peroxide radical in the ROS produced due to the 365 nm LED treatments. Similarly, the 365 nm LED treatment produced a significant membrane lipid oxidation in low-a\({}_{\mathrm{w}}\)_S_. Typhimurium in this study. In addition, we observed that the percentage of the cell population indicating membrane lipid oxidation due to the treatment with 365 and 395 nm light pulses emitted from the LED with the \(\sim\)217 J/cm\({}^{2}\) dose were not significantly different as opposed to the log reductions observed in this study (Figures 1 and 3). This would indicate that there might be some additional mode of action involved in the inactivation efficacy of 365 nm LED treatments against \(S\). Typhimurium in low-a\({}_{\mathrm{w}}\) conditions. This study showed a significant inactivation efficacy of the 455 nm LED treatments with the 250 J/cm\({}^{2}\) dose against low-a\({}_{\mathrm{w}}\)_S_. Typhimurium, which is also supported by our previous studies [29; 31]. Exogenous photosensitizers such as curcumin, when combined with blue (462 \(\pm\) 3 nm) LED, enhance their inactivation efficacy against _E. coli_ and _S. aureus_ suspensions and the generation of intracellular ROS in the cells [21]. In this study, we observed a significant generation of intracellular ROS in low-a\({}_{\mathrm{w}}\)_S_. typhimurium_ with the 455 nm LED treatment alone (Table 3). This could be attributed to the photosensitization of endogenous photosensizers such as porphyrin compounds in \(S\). Typhimurium cells by the 455 nm LED treatment, which leads to the generation of ROS in the presence of oxygen [13; 45]. On the contrary, the 462 nm LED treatment of _E. coli_ and _S. aureus_ suspensions alone did not produce any significant intracellular ROS [21], indicating the generation of intracellular ROS in a bacterial cell by the blue LED treatment was influenced by the wavelength, sample type and strain used. A significant membrane lipid oxidation of low-a\({}_{\mathrm{w}}\)_S_. Typhimurium cells was observed with the 455 nm LED treatment in this study, indicating the presence of the peroxide radical in the ROS generated by the LED light pulses. This was supported by [PERSON], [PERSON] and [PERSON] (2018) [46] in their study, where the overexpression of the catalase A enzyme reduced the sensitivity of _Pseudomonas aeruginosa_ to the 464 nm LED treatments, indicating that the blue LED produced the peroxide radical as a major ROS during the treatments. Previously, 405 \(\pm\) 5 nm LED treatment of \(S\). Typhimurium suspension did not show significant membrane lipid peroxidation with the thiobarbituric acid reaction substance (TBARS) assay [20]. On the contrary, the treatment of low-a\({}_{\mathrm{w}}\) pet food pellets with the 455 nm light pulses emitted from the LED showed significant lipid oxidation in low-a\({}_{\mathrm{w}}\) pet foods with the TBARs assay [29; 47]. Therefore, the generation of membrane lipid oxidation due to the LED treatments would depend upon the sample type, strain used, wavelength of the light used, treatment dose, etc. Additionally, the drying step involved in the preparation of low-a\({}_{\mathrm{w}}\)_S_.