## 3 Results  
### Response Surface Methodology for Extraction Process of S. officinalis  
Table 2 shows the extraction process's most relevant response surface methodology (RSM) optimisation statistical parameters. On the basis of the statistical coefficients that were determined (Table 2), it can be concluded that, for each output parameter (i.e., response functions AA-DPPH, AA-FRAP,and TPC-F-C), the response surface described by the second-order equation correlates very well with the experimental data, which made it possible to determine the optimal areas of the _S. offcinalis_ extraction process (Table 2). In Table 3, the observed and expected (calculated) values and the corresponding residual values for the respective experiment number are presented. Figures S1-S3 present scatter plots of the observed and expected values (Table 3) during the interaction of the studied extraction process parameters for _S. offcinalis_. The scatter plots indicate a good correlation between the response surface methodology and the experimental values (Figures S1-S3). Table 4 shows the values of the input variables for which the tested functions describing the extraction process (AA-DPPH, AA-FRAP, and TPC-F-C) take extreme values. Figure 1A-C shows the changes in the antioxidant activity (AA-DPPH and AA-FRAP) and total polyphenol content (TPC-F-C) during the interaction of the studied process parameters. Studies on the influence of ethanol concentration and plant material content on the extraction of _S. offcinalis_ were carried out at an extraction time of 10 min, considered to be the most favourable, and with the other parameters used as starting points at the beginning of the study. Figure 1A, which illustrates the relationship between the plant material content and ethanol concentration, demonstrates that the highest plant material content (\(\geq\)7.5 g/100 mL of solvent) and ethanol concentration (47% \(v/v\)) yield the highest values of antioxidant activity (AA-DPPH) by the DPPH method (>12 mmol Trolox/L). A reduction in the plant material content (below 7.5 g/100 mL of solvent) at an ethanol concentration of 47% \(v/v\) results in a decrease in the value of the function tested: below 12 mmol Trolox/L (Figure 1A). Figure 1B, showing the relationship between the plant material content and ethanol concentration and antioxidant activity (AA-FRAP) using the FRAP method, shows that during a 10 min extraction run using 4.7 g/100 mL of solvent of plant material and an ethanol concentration of 48% \(v/v\), the extremum of the function under study is reached as a minimum. In the area of input conditions, the FRAP antioxidant activity function describing the extraction process increases monotonically with respect to the raw material content (from <8 to >20 mmol FeSO4/L) for a constant extraction time of 10 min. During a 10 min extraction run, the highest value of the function under study (i.e., >20 mmol FeSO4/L) is achieved using the maximum amount of plant material (i.e., >7.5 g/100 mL of solvent), while the use of lower amounts of plant material (i.e., less than 7.5 g/100 mL of solvent) results in a decrease in AA-FRAP (Figure 1B). Figure 1C illustrates the relationship between the plant material content and ethanol concentration, showing that the TPC-F-C function reaches a local minimum during a 10 min extraction with 2.6 g/100 mL of solvent of plant material and a 47% \(v/v\) ethanol concentration. In the area of input conditions, the total polyphenol content (TPC-FC) function describing the extraction process increases monotonically with respect to the raw material content (from <0.9 to >2.2 g GA/L) for a constant extraction time of 10 min. During a 10 min extraction, the highest total phenolic compound content in the extract (i.e., >2.2 g GA/L) is obtained using the highest content of plant material (i.e., >7.5 g/100 mL of solvent) --Figure 1C.