## 3 Results and Discussion
### Partial Least Squares (PLS) Analysis  
A partial least squares (PLS) model was applied in order to determine and propose an optimal extraction mode for the maximum recovery of the total polyphenols and antioxidant activity, as illustrated in the correlation loading plot depicted in Figure 3A and the variable importance plot (VIP) option graphs, where values for each predictor variable are shown in Figure 3B. Considering the concentration of ethanol as a solvent and the extraction technique as the main extraction factors (Figure 3B), the optimum enhanced values were obtained by applying all extraction techniques, (PEF, US, and ST), with 50% ethanolic solvent for the shortest extraction time, 30 min, at the maximum temperature of 80 \({}^{\circ}\)C, as also exhibited in Table 6.  
The high determination coefficient (R\({}^{2}\)) of 0.9659 and the strong correlation coefficient of 0.9828 show that the experimental data and the predictions from the PLS model are in high agreement. Additionally, a \(p\)-value of less than 0.0001 indicates that there was no statistically significant difference in the variations between the experimental and PLS model (predicted) values. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variables** & **PLS Model Values** & **Experimental Values** \\ \hline TPC (mg GAE/g dw) & 29.59 & \(28.82\pm 1.59\) \\ FRAP (\(\mu\)mol AAE/g dw) & 58.27 & \(57.15\pm 3.31\) \\ DPPH (\(\mu\)mol AAE/g dw) & 48.25 & \(47.55\pm 2.90\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The maximum desirability under the optimal extraction conditions (\(X_{1}\): 4, \(X_{2}\): 3, \(X_{3}\): 1, and \(X_{4}\): 5) for all variables using the partial least squares (PLS) prediction profiler. Figure 3: Plot (**A**) illustrates the desirability function with extrapolation control and the partial least squares (PLS) prediction profiler for optimizing watercress plant. The variable importance plot (VIP) option in Plot (**B**) displays the VIP values for each predictor variable. The blue dashed line at the 0.8 mark on the VIT indicates the significance level for each variable. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Resposes** & **TPC** & **FRAP** & **DPPH** \\ \hline TPC & - & 0.0810 & 0.4385 \\ FRAP & - & 0.6179 \\ DPPH & & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Multivariate correlation analysis among the measured variables. Adopting the optimal extraction conditions, individual polyphenic compounds contained in the optimum watercress leaf extracts were analyzed by HPLC-DAD. In accordance with previous research, some of the polyphenic compounds contained in watercress are chlorogenic acid, caffeic acid, rutin, ferulic acid, apigenin, \(p\)-coumaric acid, quercetin, and kaempfer [36; 47]. Substantial quantities of these compounds were also detected in the present investigation, as shown in Table 7. Figure 4 graphically illustrates an exemplary chromatogram. Despite the challenges in separation, the quantification of polyphenols in the chromatogram was reliably determined by the peak area and resolution. The methodology employed was robust, ensuring accurate analysis of the polyphenic content, even in cases of suboptimal chromatographic separation. The most abundant polyphenic compounds present in the optimized extract of watercress were rosmarinic acid and chlorogenic acid, with rutin and apigenin following. Rosmarinic acid is primarily detected in plants of the Lamiaceae family; however, in the present study, it was revealed that it may also be found in plants of the Brassicaceae family [48]. Rosmarinic acid is well known for its anticancer and antioxidant properties, as it is utilized to mitigate the risk of various cancers by preventing cellular damage caused by free radicals [49]. Although the extracts of watercress leaves revealed high antioxidant activity through the DPPH method, no strong correlation between the variables TPC and DPPH was detected. Chlorogenic acid is a natural polyphenic acid compound displaying remarkable properties according to experiments carried out in mice.