Indirect identification of antioxidants in Polygalae Radix through their reaction with 2,2-diphenyl-1-picrylhydrazyl and subsequent HPLC-ESI-Q-TOF-MS/MS

A rapid and efficient method for the identification of antioxidants in the traditional Chinese medicine Polygalae Radix (PR) by HPLC-ESI-Q-TOF-MS/MS is described. The method is based on the hypothesis that upon reaction of antioxidants with 1,1-diphenyl-2-picrylhydrazyl (DPPH), the peak areas of compounds with potential antioxidant activities in the HPLC chromatogram will be significantly reduced in comparison to the untreated sample. The identity confirmation was achieved by Q-TOF-MS/MS technique. With this method, eight components were proposed possessing potent antioxidant activity. They were identified as sibiricose A5, sibiricose A6, sucrose monoester, polygalaxanthone III, tenuifoliside B, 3',6-disinapoylsucrose (DISS), sucrose diester, tenuifoliside C, respectively. DISS was proposed to be the most potent one. The antioxidant activity of DISS was evaluated by DPPH, ABTS radical scavenging assay and ferric-reducing antioxidant power (FRAP) assay in vitro. Vitamin C (Vc) was used as positive control substance. DISS showed moderate DPPH (DISS's IC50 value was 1024.17 μg/mL, Vc's was 294.68 μg/mL) and ABTS (IC50 324.13 μg/mL, Vc's was 117.50 μg/mL) free radical scavenging capacity and ferric-reducing antioxidant power. DISS can be used as a new source of natural antioxidant in foods and cosmetics.