Separation and preparation of 6-gingerol from molecular distillation residue of Yunnan ginger rhizomes by high-speed counter-current chromatography and the antioxidant activity of ginger oils in vitro

Molecular distillation residue (MD-R) from ginger had the most total phenol content of 247.6 mg gallic acid equivalents per gram (GAE/g) among the ginger oils. High-speed counter-current chromatography (HSCCC) technique in semi-preparative scale was successfully performed in separation and purification of 6-gingerol from MD-R by using a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (10:2:5:7, v/v/v/v). The target compound was isolated, collected, purified by HSCCC in the head-tail mode, and then analyzed by HPLC. A total of 90.38 +/- 0.53 mg 6-gingerol was obtained from 600 mg MD-R, with purity of 99.6%. In addition, the structural identification of 6-gingerol was performed by EI/MS, H-1 NMR and C-13 NMR. Moreover, the orders of antioxidant activity were vitamin E (VE) > supercritical fluid extraction oleoresin (SFE-O) = MD-R = 6-gingerol > molecular distillation essential oil (MD-EO) and butylated hydroxytoluene (BHT) = VE > 6-gingerol > MD-R = SFE-O > MD-EO, respectively in 2,2-diphenyl-1-picrylhydrazyl radical (DPPH center dot) scavenging and beta-Carotene bleaching. (C) 2016 Elsevier B.V. All rights reserved.