## 3 Results and Discussion
### Total Aerobic Mesophilic Viable Count of Endive Lettuce along the Washing Process Chain
In contrast the microbial reductions on strawberries [13] and button mushrooms [15] were higher after storage than for the endive lettuce after storage observed in this study. However, it has to be taken into account that the strawberries were artificially contaminated with _S. aureus_, which is not comparable with naturally occurring contamination and its reduction. The achieved reduction of the TVC by PTW on endive lettuce at the end of the washing process was within the range of other sanitizers tested for application in the fresh-cut produce industry. Chlorine also reduced the microbial load of fresh-cut produce by only 1-2 log units, and a similar reduction was achieved for ozone, electrolyzed water, and H\({}_{2}\)O\({}_{2}\)[22]. The limited reduction of microorganisms on fresh produce using sanitizers is attributed to the presence of biofilms, internalization of microorganisms, and the attachment of the microorganisms to the surface or near stomata [23]. Other studies showed that, despite the reduction achieved after treatment with sanitizers, the microbial count increased again during storage to a level similar to that observed for the unwashed sample, resulting in minor differences in the microbial count between samples treated with sanitizers and samples treated without sanitizers at the end of storage [2,22]. This was also observed for the PTW-treated lettuce in this study, revealing the importance of the evaluation of the microbial load of the products at the end of storage since the reduction of the microbial load must be maintained during storage [2]. However, the sampling of \begin{table}
\begin{tabular}{|l c c|} \hline  & **After Processing log N/N\({}_{\mathbf{0}}\)** & **After Storage log N/N\({}_{\mathbf{0}}\)** \\ \hline
**[A] Washing with water and pre-bath (180 s)** & \(-1.18\,^{\mathrm{a},c,d}\)\(\pm\) 0.21 & \(-0.80\,^{\mathrm{a},c}\)\(\pm\) 0.20 \\
**[B] Washing with PTW in pre-rinsing (10 s)** & \(-0.64\,^{\mathrm{b}}\)\(\pm\) 0.16 & \(-0.44\,^{\mathrm{a},b,c}\)\(\pm\) 0.54 \\
**[C] Washing with PTW in pre-rinsing (30 s)** & \(-1.04\,^{\mathrm{b},c,d}\)\(\pm\) 0.52 & \(-0.34\,^{\mathrm{b}}\)\(\pm\) 0.27 \\
**[D] Washing with PTW in pre wash bath (180 s)** & \(-1.60\,^{\mathrm{c}}\)\(\pm\) 0.45 & \(-0.29\,^{\mathrm{b}}\)\(\pm\) 0.25 \\
**[E] Washing with PTW in second wash (180 s)** & \(-1.01\,^{\mathrm{d}}\)\(\pm\) 0.09 & \(-0.27\,^{\mathrm{b}}\)\(\pm\) 0.41 \\
**[F] Washing with PTW in pre-bath (180 s) in pre-rinsing (30 s) and in second wash (180 s)** & \(-1.10\,^{\mathrm{a},c,d}\)\(\pm\) 0.46 & \(-0.95\,^{\mathrm{c}}\)\(\pm\) 0.51 \\ \hline \end{tabular} Columns with different letters indicate statistically significant differences (\(p<0.05\)).  
\end{table} 
Table 3: Reduction of total viable count on endive lettuce after washing process with or without addition of plasma-treated water at different processing steps and subsequent storage at 2 \({}^{\circ}\)C for seven days. Letters in square brackets refer to the six trials described in Section 2.2.  
the entire lettuce at the point of PTW addition showed the ability of PTW to reduce the microbial load of the endive lettuce significantly up to 2.4 log units. However, the reduction did not remain stable; as such, at the end of the washing process, the analysis of the final product revealed a lower reduction. This can be attributed to the inhomogeneity of the biological material and corresponding high variability of the microbial load. Another explanation for the lower reduction of the microbial load on the endive lettuce could be re-contamination of the product during the washing process.