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

• Different ginger oils were obtained by using super critical fluid extraction and molecular distillation.
• 6-gingerol could be isolated and prepared from molecular distillation residue by HSCCC with the purity over 99%.
• Ginger oils and 6-gingerol show the antioxidant activity 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, 1H NMR and 13C 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) scavenging and β-Carotene bleaching.