## 3 Results and Discussion
### Optimal Extraction Conditions  
#### 3.3.1 Total Polyphenol Content of Watercress Extracts  
As indicated in Tables 1 and 3, the experimentally applied optimal extraction parameters coincide with the predicted ones for maximum TPC recovery from watercress leaves. These parameters include extractions with a combination of green and conventional extraction techniques (PEF + US + ST), with 50% ethanolic solvent for 60 min at 65 \({}^{\circ}\)C. This temperature is reasonable, as TPC enhancement efficiencies start to decrease at temperatures above 80 \({}^{\circ}\)C due to their thermosensitive properties [34; 35]. By following these  
Figure 1: Pareto plots represent transformed estimates for TPC (**A**), FRAP (**B**), and DPPH (**C**) assays. A gold dashed rectangular reference line is included in the plot to denote the significance level (\(p<0.05\)). Blue bars indicate positive values, while red bars represent negative values. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Responses**} & \multirow{2}{*}{**Second-Order Polynomial Equations (Models)**} & **R2** & **R2** & **P-Value** & **Eq.** \\  & & **Predicted** & **Predicted** & **Predicted** & **\(p\)-Value** & **Eq.** \\ \hline \multirow{4}{*}{TPC} & \(Y=23.16-19.37X_{1}+11.34X_{2}-2.88X_{3}-1.29X_{4}+3.8X_{1}{}^{2}-\) & & & & \\  & \(2.28X_{2}{}^{2}-0.76X_{3}{}^{2}+1.08X_{4}{}^{2}+0.4X_{1}X_{2}+0.88X_{1}X_{3}-0.59X_{1}X_{4}\) & 0.9731 & 0.8978 & 0.0053 & (6) \\  & \(+0.88X_{2}X_{3}-0.5X_{2}X_{4}+0.08X_{3}X_{4}\) & & & & \\ \hline \multirow{4}{*}{FRAP} & \(Y=13.88-13.93X_{1}-5.92X_{2}+34.77X_{3}+24.33X_{4}-2.7X_{1}{}^{2}-\) & & & & \\  & \(2.05X_{2}{}^{2}+0.79X_{3}{}^{2}-4.69X_{4}{}^{2}+5X_{1}X_{2}-0.27X_{1}X_{3}+2.69X_{1}X_{4}\) & 0.9901 & 0.9623 & 0.0005 & (7) \\  & \(-6.44X_{2}X_{3}+4.96X_{2}X_{4}-5.32X_{3}X_{4}\) & & & & \\ \hline \multirow{4}{*}{DPPH} & \(Y=-2.98-1.07X_{1}+15.07X_{2}+5.7X_{3}+6.68X_{4}+0.45X_{1}{}^{2}-\) & & & & \\  & \(3.89X_{2}{}^{2}+0.54X_{3}{}^{2}-0.46X_{4}{}^{2}+0.68X_{1}X_{2}-1.42X_{1}X_{3}+\) & 0.9662 & 0.8717 & 0.0090 & (8) \\ \cline{1-1}  & \(0.41X_{1}X_{4}-0.02X_{2}X_{3}+0.74X_{2}X_{4}-1.59X_{3}X_{4}\) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mathematical models utilizing RSM were applied to optimize the extraction process from the watercress plant. parameters, the TPC of watercress leaves can be enhanced from 3.61 to 24.67 mg GAE/g, i.e., 583.38%. The maximum TPC previously recorded in watercress leaves was 9.35 mg/g [2], i.e., 163.85% less than the maximum obtained in our case. In another study evaluating water and methanol separately as extraction solvents for watercress leaves, the results exhibited 2.31 mg GAE/g and 3.21 mg GAE/g, respectively [36]. Thus, the use of a combination of green extraction methods with conventional liquid-solid extraction proved to be the most suitable extraction method for obtaining the greatest amount of polyphenols from watercress. These results are fully consistent with previous studies on plant materials. For example, according to the research of [PERSON] et al. [37], after optimizing the extraction parameters for litchi fruit peel, the total TPC of the sample extracted with the PEF-US combination was 2.30 times higher than that of the sample extracted with traditional extraction. Also, the effect of the PEF-US combination as an extraction technique on almond extract resulted in the highest concentration of total phenolics, total flavonoids, anthocyanins, and antioxidant activity (DPPH and FRAP) [38]. These outcomes demonstrate the importance of using green extraction techniques for unlocking the maximum bioactive value that a plant can yield and provide a highly beneficial extract with a plethora of applications. These techniques are \"green\" due to their lower energy requirements, reduced use of hazardous solvents, and greater yields with a minimal environmental footprint.