## 3 Results and Discussion  
### TPC  
Figure 1 shows the influence of input variables on the TPC content for two extraction vessels with diameters of 35 and 25 mm. The shape of the curves shown in Figure 1a indicates that the inflection points have been reached for the variables of ultrasound amplitude and solvent concentration, which means that further increases in the values of these variables will result in a decrease in the polyphenol extraction efficiency. There is a positive linear relationship between the extraction time and polyphenol content, which means that the extraction efficiency increases with increasing time. For the vessel with a diameter of 25 mm (Figure 1b), an inflection point was reached only in the case of solvent concentration. For the variables of ultrasound amplitude and time, we observed a non-linear growth in the TPC value with increasing time and a linear growth with increasing ultrasound amplitude. In order to confirm the significance of the impact of the tested input variables on the TPC content, a statistical analysis was performed. The findings of this examination are displayed in Tables 2 and 3. The results of the analysis of variance showed that for both models, the linear effects of all variables (time, ultrasound amplitude, and solvent concentration) and the square effects of the ultrasound amplitude and solvent concentration turned out to be statistically significant. Despite these similarities, it is easy to see that the impact of the input variables on the TPC content for individual models was different. For the vessel with a diameter of 35 mm, the linear effect of the ultrasound amplitude was the most important, and the  
Figure 1: Dependence of TPC on time, ultrasound amplitude, and solvent concentration for extracts obtained in vessels with diameters of (**a**) 35 mm, (**b**) 25 mm. linear effect of time was the least significant. For the vessel with a diameter of 25 mm, the linear effect of the solvent concentration was the most important, and the linear effect of the ultrasound amplitude was the least significant. The Tukey test (\(p<0.05\)) showed that in all cases of extraction with 60% solvent, the dimensions of the extraction vessels had no effect on the average TPC value. In the case of extraction of polyphenols using a 90% solvent, there were always differences in the average values depending on the extraction vessels used. A regression analysis was employed to develop two models (Equations (1) and (2)) that describe the effect of input variables on TPC:  
\[TPC_{1}=-8.762+0.186X_{1}+0.805X_{2}+0.245X_{3}-0.013X_{2}^{2}-0.002X_{3}^{2} \tag{1}\]  
\[TPC_{2}=6.065-0.493X_{1}+0.048X_{2}+0.139X_{3}+0.041X_{1}^{2}-0.002X_{3}^{2} \tag{2}\]  
Both models exhibit statistical significance (\(p=0.0002\); \(p<0.0001\)), indicating their validity. The lack of fit for the model is statistically insignificant (\(p=0.0612\) and \(p=0.1797\)), which further validates the accuracy of the model. The high values of the determinant coefficient (0.9084 and 0.9436) and the adjusted \(R^{2}\) coefficient (0.8576 and 0.9123) demonstrate a strong correlation between the input variables and polyphenol content. The low values of the coefficient of variation (10.49% and 9.03%) indicate minimal differences between  
\begin{table}
\begin{tabular}{l l l l l l} \hline
**Source** & **Sum of Squares** & **DF** & **Mean Square** & **F-Value** & \(p\)**-Value** & \\ \hline Model & 85.93 & 5 & 17.19 & 17.86 & 0.0002 & significant \\ \(X_{1}\) & 6.95 & 1 & 6.95 & 7.22 & 0.0249 & \\ \(X_{2}\) & 44.05 & 1 & 44.05 & 45.78 &  
the predicted and experimental values, highlighting the precision and reliability of the conducted experiment. The content of polyphenols in the obtained extracts ranged from 3.72 to 11.71 mg GAE/g for the vessel with a diameter of 35 mm and from 3.44 to 11.68 mg GAE/g for the vessel with the smaller diameter, depending on the other conditions of the experiment. The gained results are consistent with those of [PERSON] et al. [25], who showed that the average value of TPC in _S.