# Postharvest Reduction of _Salmonella enterica_ on Tomatoes Using a Flagmonic Acid Emulsion
## 4 Discussion
Because the 30 mM formulation performed similarly to 50 mM, lower PEL concentrations should be examined to determine the minimum range required for equivalent biocidal activity. [PERSON] and [PERSON] [22] used a modified resazurin assay to determine that the minimal inhibitory concentration (MIC) of the PEL emulsion against _Salmonella_ in a 96-well plate was 31.25 mM. However, the MIC could differ when PEL is added to a food matrix, so concentrations below 30 mM may still be viable options. [PERSON] and [PERSON] also found that PEL caused a decrease in culturable _Salmonella_ cells within one hour, however live-dead staining revealed a mixture of viable and dead cells [22]. Survival of such stress could lead to resistance to PEL and cross-tolerances to other environmental stressors such as heat, starvation and other sanitizers. Once genetic encoding for resistance occurs, it is mobile within a population and has the potential to be horizontally transferred to other populations [43]. A 2012 study found that _S. enterica_ ser. Typhimurium can form biofilms on the surface of cherry tomatoes after 48 h of exposure at 25 \({}^{\circ}\)C, which has been visualized using scanning electron microscopy [44]. Biofilms increase bacterial resistance to oxidative stress [45], which may impact the efficacy of oxidative sanitizers like chlorine and PAA. However, PEL treatments form an oily coating on the tomato and other surfaces, potentially prolonging PEL contact time with the fruit surface and reducing the ability of _Salmonella_ to effectively attach to the tomato surface and subsequently form biofilms. This biocidal activity could also reduce the likelihood of subsequent tomato contamination during further handling or while in transit. However, as PEL is phytotoxic, this increased contact time may contribute a deleterious impact on tomato firmness and skin strength over time when compared to chlorine and PAA-treated tomatoes. Undissociated organic acids penetrate the phospholipid membrane of bacterial cells, then dissociate once inside of the cell. The dissociation into anion and proton acidifies the internal cellular pH, requiring the cell to expend energy to maintain a roughly neutral pH [43; 46]. Below its pKa of 4.95, PEL is predominantly present in undissociated form and is biocidal; however, if the pH of postharvest wash water increases above 4.95, PEL dissociates and loses antimicrobial efficacy [12; 47]. In this study, the average pH of the PEL treatments ranged from 3.89 \(\pm\) 0.04 (50 mM PEL) to 4.06 \(\pm\) 0.04 (30 mM + OL and 50 mM + OL PEL; Table 1). Because the pH values were well below the pKa of PEL, the acid was present mainly in the efficacious, undissociated form. While water pH will still need monitoring in postharvest wash systems using PEL-based sanitizers, especially in areas with high water pH, pH management will likely be less rigorous than is needed in chlorine-based systems. Organic loading with grape tomato puree did not significantly affect the efficacy of any of the four sanitizers. This is contrary to previous studies which found that chlorine efficacy is greatly decreased in the presence of organic material. [PERSON] et al. [14] found that a 1% (\(w/v\)) sweet pepper puree significantly decreased chlorine efficacy against _Salmonella_ on inoculated peppers and in postharvest wash. The pepper study also found that _Salmonella_ levels recovered from a used chlorine wash solution supplemented with 1% organic load were not significantly different from levels recovered from used water. In another study, organic loading using <2.5% blended iceberg lettuce reduced chlorine efficacy against _E. coli_ O157:H7 [48]. [PERSON] et al. found that the addition of <0.3% tomato extract rapidly depleted free chlorine, while significantly increasing chemical oxygen demand and turbidity [49]. PAA was also not significantly impacted by organic loading, in agreement with a study that found that the efficacy of 50 ppm PAA against _E.