# Postharvest Reduction of _Salmonella enterica_ on Tomatoes Using a Flagmonic Acid Emulsion
## 4 Discussion

Table 4: Effect of the interactions among sanitizer treatments (including water and NR controls) and storage time on tomato surface compression (N; \(n=8\)). than chlorine at 1 d (3.23 log CFU/g _Salmonella_ recovered) but was a less robust biocide than both PEL treatments. This trend continued to 7 d, at which time 2.92 log CFU/g _Salmonella_ was recovered from PAA-treated tomatoes. The storage results indicate that PEL emulsions may be useful biocidal agents, especially on commodities or surfaces where bacterial regrowth or post-processing contamination is anticipated. Produce may be particularly susceptible to contamination while in transit to retailers or restaurants compared to most ready-to-eat foods because it is typically stored and shipped in vented, unsealed containers to facilitate gas exchange due to continued, postharvest metabolic activity [38]. While many of these containers (e.g., clamshells for blueberries, vented bags for grapes, etc.) are shipped in secondary boxes or crates, these too are vented by design and may allow environmental microbial hazards contact to produce contained within. Sanitizers that exhibit continued microbial control for days after initial washing could be useful to protect against contamination while in transit and could be invaluable to control endemic spoilage microorganisms present on the produce surface. Interestingly, PAA also appeared to exert continued antimicrobial activity throughout storage. While the reduction from 1 d to 7 d was not significantly different, from 0 d to 7 d PAA resulted in a significant, nearly 4 log CFU/g reduction; this was a 2 log CFU/g greater reduction at 7 d compared to chlorine at 7 d. While generally a more expensive sanitizer, PAA does not require stringent pH monitoring and adjustment such as is required in wash systems using chlorine, making it easier to incorporate into a produce wash system. The enhanced antimicrobial efficacy over time, its relative ease of use compared to chlorine and degradation into nontoxic compounds is a key consideration for growers as they select or change postharvest sanitizers [13]. One possible explanation for the lack of significant _Salmonella_ reduction during storage after treatment with PAA or chlorine is that rifampicin and nalidixic acid-adapted _Salmonella_ could have had a cross-tolerance to the oxidizers. Examples of previously described development of antimicrobial cross-tolerances include _Listeria monocytogenes_ grown under acidic conditions exhibiting increased tolerance to sodium dichloroisocyanuric acid and dodecyl dimethyl ammonium bromide (DDAB) and _S. enterica_ ser. Typhimurium grown in the presence of plant-derived terpen exhibiting increased tolerance to PAA and DDAB [39; 40]. Examining wild-type strains and recovering on _Salmonella_-specific media (i.e., Xylose Lysine Deoxycholate agar; XLD) may have reduced any interference due to cross-tolerance but preliminary studies (data not shown) indicated that XLD insufficiently reduced background microflora from the tomato surface. The ability of each sanitizer to prevent cross-contamination was also investigated. Very low populations of _Salmonella_ (<1.0 log CFU/g) were recovered from SUS exposed to sanitizers. This is consistent with the results of the wash solution sampling, as no _Salmonella_ was recovered from sanitizers. Conversely, 4.1 log CFU/g was recovered from SUS exposed to water (0 d) and 5.7 log CFU/mL were recovered from spent water after it was used to wash the inoculated tomatoes and SUS. These results show that the four sanitizers were similarly effective to each other and also superior to water in ability to limit cross-contamination. These findings agree with previous research showing that solutions containing sanitizers including chlorine and PAA are more effective than water alone at maintaining microbial quality of postharvest wash tanks [14; 37; 41; 42].