Enhanced aqueous two-phase extraction of proanthocyanidins from grape seeds by using ionic liquids as adjuvants

Grape seeds are rich in proanthocyanidins, which are well-known natural antioxidants. In this work, an aqueous two-phase system (ATPS) based on ethanol/(NH4)(2)SO4 was proposed to extract and recover proanthocyanidins from grape seeds. Ionic liquids (IL) were used as adjuvants of ATPS to improve the extraction performance. The extraction efficiencies (EE) of proanthocyanidins were dramatically raised from 47.89 to 52.42% to 97.23 - 97.79% by adding 5 wt% [C(6)mirn]BF4 into ATPS. Extraction conditions were optimized as follows: 29 wt% ethanol, 19 wt% (NH4)(2)SO4, 4 wt% [C(6)mim]BF4, solid-liquid ratio = 1:20 g/mL, temperature (T) = 40 degrees C, pH = 5.0, and extraction time (t) = 20 min. Under optimum conditions, the yields of catechin, epicatechin, and procyanidin B2 reached 1.21, 1.22, and 0.14 mg/g dry weight, respectively, with EE of over 99.01%. Compared with conventional organic solvents such as methanol, ethanol, and isopropanol, the ATPS using ILs as adjuvants provided higher extraction yields. Results suggested that ethanol-based ATPS can extract value-added compounds from waste residues in the fruit-processing industry. In addition, low amount of IL addition can significantly enhance the extraction performance of ATPS.