## 3 Results
### Response Surface Methodology for Extraction Process of S. officinalis
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Input Variables**} & \multicolumn{4}{c}{**Process Functions Examined**} \\ \cline{2-4}  & **AA-DPPH** & **AA-FRAP** & **TPC-F-C** \\ \hline Raw material content [g/100 mL of solvent] & 11 & 4.7 & 2.6 \\ Ethanol concentration [\% \(v/v\)] & 47 & 48 & 47 \\ Extraction time [min] & 11 & 11 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The input variable values for which the functions described take extreme values. For the tested functions describing the extraction process, the antioxidant activity (AA-FRAP) and total polyphenolic content (TPC-FC), the fitted surface has a local minimum for the plant's raw material content of 4.7 and 2.6 g/100 mL of solvent, respectively. In the input conditions area, the function describing the extraction process is monotonically increasing with respect to the raw material content, as shown in Figure 1B,C for a fixed extraction time of 10 min. The fixed extraction time is close to the time for which the function describing the process takes extreme values (Table 4). The choice of the extraction running time was dictated by the maximum recovery of active substances with the antioxidant potential and economic considerations of running the process. The optimum extraction parameters were identified, i.e., those at which the maximum values of the main functions describing the process were obtained (Table 5). The changes in antioxidant activity (AA-DPPH and AA-FRAP) and total polyphenol content (TPC-F-C) are shown in Figure 2A-C. Studies on the effects of the ethanol concentration and extraction time on the extraction process of _S. offcinalis_ were conducted at a plant material content of 7.5 g/100 mL of solvent (considered to be the most favourable and corresponding to the maximum concentration resulting from the technical conditions) and with the other parameters adopted as starting parameters at the beginning of the study. Figure 2A, showing the relationship between the ethanol concentration and extraction time, shows that the function of AA-DPPH reaches its highest value (above 11 mmol Trolox/L) using an ethanol concentration of 47% \(v/v\) and an extraction time in the range of 7-11 min, with a plant material content of 7.5 g/100 mL of solvent. The observed antioxidant activity of the extracts depended on the extraction time: increasing (i.e., above 11 min) or decreasing (i.e., below 7 min) the extraction time results in a decrease in the value of the test function (<11 mmol Trolox/L)--Figure 2A. Figure 2B, showing the relationship between the ethanol concentration and extraction time, shows that for an ethanol concentration of 48% \(v/v\) and an extraction time ranging from about 9 to about 14 min (at a plant material content of 7.5 g/100 mL of solvent), the highest antioxidant activity by the FRAP method is achieved (i.e., above 14 mmol FeSO4/L). Reducing the extraction time (below 9 min) or increasing the extraction time (above 14 min) results in lower AA-FRAP values (below 14 mmol FeSO4/L. Extending the extraction time positively affects the antioxidant activity of the extract only during a certain time interval, i.e., until the equilibrium state of concentrations of extracted components inside and outside the plant material is established. After this time, prolonging the extraction (more than 14 min) does not affect the activity of FRAP, causing secondary changes in the composition of the extract--Figure 2B. Figure 2C, showing the relationship between the ethanol concentration and extraction time (at a constant plant material content of 7.5 g/100 mL of solvent), shows that using an ethanol concentration of 47% \(v/v\) and an extraction time ranging from about 8 to about 10 min, the highest contents of phenolic compounds (above 1.6 g GA/L) are achieved. The choice of an ethanol concentration of 47% \(v/v\) was dictated by the fact that the aqueous