# Impact of Deep Eutectic Solvents on Extraction of Polyphenols from Grape Seeds and Skin
## 3 Results and Discussion
### Phenolic Composition
\begin{tabular}{c} **Prototacetchic** \\ **Acid** (mg g\({}^{-1}\) DW) \\ \end{tabular}  & \begin{tabular}{c} **(+)-Catechin** \\ **(mg g\({}^{-1}\) DW)** \\ \end{tabular}  & \ \begin{tabular}{c} **(-)-Epicatechin** \\ **(mg g\({}^{-1}\) DW)** \\ \end{tabular}  & \begin{tabular}{c} **Total** \\ **(mg g\({}^{-1}\) DW)** \\ \end{tabular}  \\ \hline \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\) & AcEOH & 0.947 e & & 3.661 d & 1.737 d & 6.345 d \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\) & ChCit & 0.885 e & 0.482 b & 3.347 d & 1.466 d & 6.181 d \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\) & AcEOH & 1.204 d & 0.158 e & 4.355 d & 3.605 c & 9.322 c \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\) & ChCit & 1.142 d & 0.249 d & 3.045 d & 1.626 d & 6.062 d \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\text{}\textbackslash{}^{}\textbackslash{}^{}\) & AcEOH & 1.546 e & 0.569 a & 15.587 e & 4.391 b & 22.093 a \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\text{}\) & ChCit & 1.219 d & 0.605 a & 10.197 b & 2.808 d & 14.829 b \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\text{}^{}\textbackslash{}^{}\textbackslash{}^{}\) & AcEOH & 0.689 f & 0.101 e & 2.911 d & 2.371 d & 6.073 d \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\text{}\textbackslash{}^{}\text{}^{}\text{}\) & ChCit & 1.096 d & 0.291 c & 3.998 d & 1.785 d & 7.7169 d \\ \(\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\textbackslash{}^{}\text{}^{}\textbackslash{}^{}\text{}\textbackslash{}^{}\text{}\textbackslash{}^{ChCit also showed better extraction efficiency for protocatechuric acid irrespective of investigated matrix. Concerning seeds, 'Zupljanka' was characterized with the highest concentration of protocatechuric acid (0.569 and 0.605 mg g\({}^{-1}\) DW, for acidified aqueous ethanol and ChCit, respectively). When it comes to skin, acidified aqueous ethanol demonstrated extremely low extraction efficiency towards protocatechuric acid. Concentrations of protocatechuric acid in ChCit skin extracts varied from 0.065 to 1.663 mg g\({}^{-1}\) DW. The concentration of quercetin 3-\(O\)-glucose, found in skin extracts obtained from red grape varieties, tended to be higher in acidified aqueous ethanol compared to NADES, with some exceptions. The highest concentration of this compound was observed in skin of 'Cabernet Sauvignon' (0.569 and 0.739 mg g\({}^{-1}\) DW, for acidified aqueous ethanol and ChCit, respectively). In general, 'Zupljanka' seeds distinguished with the highest content of total phenolics evaluated applying HPLC, regardless the solvent. Such domination of 'Zupljanka' among the varieties with the highest TPC content determined by _Folin-Ciocalteu_ method, such as 'Gamay', 'Prokupac', and 'Black Tamjanika' is due to remarkably higher (+)-catechin concentrations in 'Zupljanka' seeds. Thus, it is expected that mentioned varieties have higher concentrations of some unquantified polyphenol compounds in seeds. When it comes to grape skin, highly pigmented red varieties, such as 'Cabernet Sauvignon', 'Zacinak', and 'Merlot' could be emphasized as cultivars extremely rich in phenolic compounds. Finally, chromatographic analysis of obtained extracts revealed some interesting observations. Namely, acidified aqueous ethanol was more efficient in extracting phenolics from grape seeds, while ChCit have proved more selective towards target polyphenol compounds in grape skin.