Abstract
In this study, eight different types of imidazolium-based ionic liquids (ILs) were applied as new solvents in the extraction of flavonoids 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 significantly affected extraction yields. The highest mass fractions of proanthocyanidins and anthocyanins were obtained with 2.5 mol/L of 1-butyl-3-methylimidazolium bromide [C4mim][Br] and 2.5 mol/L of 1-ethyl-3-methylimidazolium bromide [C2mim][Br], respectively. The studied ILs provided an excellent preliminary result in the extraction of anthocyanins. Significantly higher mass fractions of total and all free anthocyanins were extracted with 2.5 mol/L of [C2mim][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 latter. On the other hand, 2.5 mol/L of [C4mim][Br] and 2.5 mol/L of 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate [sC4mim][HSO4] showed significantly higher selectivity towards anthocyanin-3-O-acetylmonoglucosides and anthocyanin-3-(6-O-p-coumaroyl)monoglucosides.
Highlights
IntroductionProanthocyanidins (condensed tannins) and anthocyanins are the main phenolic compounds of grape skin, belonging to the flavonoid family
Proanthocyanidins and anthocyanins are the main phenolic compounds of grape skin, belonging to the flavonoid family
In order to evaluate ionic liquids (ILs) performance in the extraction of main grape skin flavonoids, eight different imidazolium-based ILs varying in concentration (Table 1) were tested
Summary
Proanthocyanidins (condensed tannins) and anthocyanins are the main phenolic compounds of grape skin, belonging to the flavonoid family. In recent years, these compounds have attracted great attention since they are responsible for major grape and wine sensory properties like mouth-feel [1,2,3] and colour [4], and for their protective effect against cardiovascular risk factors due to many biological activities [5]. Methanol, ethanol, acetone, water and their combinations are commonly used in extraction of proanthocyanidins from various plant materials [10]. The two-step procedure using aqueous acetone followed by aqueous methanol represents the most common procedure used in the ex-
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