A green strategy for obtaining anthraquinones from Rheum tanguticum by subcritical water

Abstract

Rheum tanguticum is a traditional Chinese herbal medicine, which contains abundant anthraquinones. In this study, anthraquinones were efficiently extracted from Rheum tanguticum by subcritical water extraction (SWE). The parameters of extraction time (33-67 min), temperature (100-200°C), and SW flow rate (1.4-4.6 mL/min) were optimized so as to achieve a high yield of the target product. A high yield of the total anthraquinones was achieved under the optimized SWE conditions of extraction time 54 min, extraction temperature 170°C, and the flow rate 2.0 mL/min. The comparison between the SWE and traditional extraction techniques implied that the SWE is an efficient and green alternative method for the extraction of anthraquinones. Four anthraquinone glycosides were purified from the SWE extract by high-speed counter-current chromatography and identified as emodin-1-O-β-D-glucoside, physcion-8-O-β-D-glucopyranoside, chrysophanol-1-O-β-D-glucoside, and chrysophanol-8-O-β-D-glucoside.