Extraction of Proanthocyanidins and Anthocyanins from Grape Skin by Using Ionic Liquids

In this study, eight diff erent types of imidazolium-based ionic liquids (ILs) were applied as new solvents in the extraction of fl avonoids from grape skin, and compared to the conventional organic solvent extraction that was not reported earlier. The structure of anions, cations and concentration of ILs signifi cantly aff ected extraction yields. The highest mass fractions of proanthocyanidins and anthocyanins were obtained with 2.5 mol/ L of 1-butyl-3-methylimidazolium bromide [C(4)mim][Br] and 2.5 mol/L of 1-ethyl-3-methylimidazolium bromide [C(2)mim][Br], respectively. The studied ILs provided an excellent preliminary result in the extraction of anthocyanins. Signifi cantly higher mass fractions of total and all free anthocyanins were extracted with 2.5 mol/L of [C(2)mim][Br] and 2.5 mol/L of 1-methylimidazolium hydrogen sulfate [mim][HSO4] than with conventional solvent with the exception of anthocyanin-3-O-acetylmonoglucosides in the latt er. On the other hand, 2.5 mol/L of [C(4)mim][Br] and 2.5 mol/L of 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate [sC(4)mim][HSO4] showed signifi cantly higher selectivity towards anthocyanin-3-O-acetylmonoglucosides and anthocyanin-3-(6-O-p-coumaroyl) monoglucosides.