## 3 Results and Discussion
### Microbial Diversity on Endive Lettuce along the Washing Process Chain  
Even though some research concluded that the microbial load of a product affects its product quality, other studies demonstrated that the TVC or the specific count of spoilage microorganisms cannot predict the quality of the product. An exception is the count of lactic acid bacteria and yeasts where a good correlation was found with the product quality [2]. Furthermore, faster growth during storage was observed for epiphytic microbiota of fresh produce after application of sanitizers [3] and Enterobacteriaceae count on iceberg lettuce was higher during storage on samples treated with sanitizers than on untreated samples [24]. This implies that it is not only important to monitor the TVC after certain decontamination treatments and subsequent storage, but it is also important to get insight into the microbial community structure on the products in relation to the treatments and storage. In this study, the culturable microbial community structure on endive lettuce was evaluated using MALDI-ToF MS. Dependent on the grown microorganisms on the plate count agar, an uneven number of microorganisms was selected for the identification via MALDI-ToF MS, and, due to the high amount of samples, it was not possible to evaluate each sample in triplicate. The number of analyzed samples was divided into identified and not identified microorganisms per sample (Supplementary Materials Table S1). However, since the experiments were performed at a pilot scale, the results of this study can help gain knowledge about the dynamic changes on endive lettuces due to the application of PTW during washing. The culturable microbial community of endive salad before washing with water (trial A) consisted of 37% identified microorganisms, and 63% of the measured microorganisms could not be identified with the applied database. The identified microorganisms were _Flavobacterium_ sp. _Herbspirillum huttiense_, Pseudomonas fluorescens_, _Pseudomonas_ spp., _Rahnella aquutilis_, Rhizobiaceae, Staphylococcus-cocaceae, and _Pseudoxanthomonas spday_. After washing with water, the measurement of the culturable microbial community revealed 77% not identified microorganisms and 23% identified microorganisms and, in comparison to the unwashed sample only _Flavobacterium_ sp., _Herbspirillum huttiense_, and _Pseudomonas_ spp. were not detected (Figure 1A) After storage, the culturable microbial community of the endive raw material consisted of 60% not identified microorganisms and 40% identified microorganisms, which were Pseudomonas fluorescens_, Rhizobiaceae, and Staphylococcus-cocaceae (Figure 1B). The culturable microbial community structure of the washed and stored endive lettuce showed higher diversity in comparison to the unwashed and stored samples. Specifically, 56% of the measured colonies could not be identified and 44% could be identified, revealing the additional occurrence of _Pseudomonas_ spp. and _Pseudomonas viridiflawa_ in comparison to the unwashed and stored endive lettuce. After washing with water followed by storage for seven days at 2 \({}^{\circ}\)C, the predominant identified bacteria on endive lettuce was _Pseudomonas fluorescens_. Bacteria belonging to the family Pseudomonas are as food spoilage microorganisms, and their presence can lead to textural changes and changes in the sensory quality [25]. A closer look at the not identified microorganisms showed that this cluster can be split into 30 different clusters for endive raw material before storage and into 18 different clusters after storage. The not identified cluster of the washed endive lettuce consisted of 25 sub-clusters before storage and 16 sub-clusters after storage (data not shown). Regarding the TVC, washing with PTW in the pre-bath for 180 s (trial D) showed the best reduction after washing (1.6 log cfu/g reduction).