HPLC–DAD–MS/MS identification and HPLC–ABTS· + on-line antioxidant activity evaluation of bioactive compounds in liquorice ( Glycyrrhiza uralensis Fisch.) extract

Liquorice has being used as a folk medicine for pharmacological activities in China. The phytochemicals and antioxidant activity of liquorice extract were investigated, total phenolics (TP) and total flavonoids (TF) contents were determined, and the antioxidant activity of different fractions from the extract was evaluated by scavenging free radicals (ABTS· + , DPPH· and ONOO − ). On-line HPLC–ABTS· + and HPLC–ESI–MS/MS analysis were applied to screen and identify free radical scavengers of liquorice extract. The results indicated that ethyl acetate and n -butanol fractions of the extract contained higher contents of TP and TF and exhibited stronger antioxidant activities. Thirteen compounds in the extract were identified as glycyrrhizic acid, liquorice-saponin G2, liquiritin, licuraside, ononin, glycycoumarin, isoglycyrol, liquiritin apioside, liquorice-glycoside A, liquorice-glycoside B, licoric-saponin A3, isoliquiritin apioside and isolicoflavonol, in which ten compounds were free radical scavengers. In addition, glycyrrhizic acid, ononin and liquiritin were quantitatively analyzed. These findings revealed that liquorice extract had potential antioxidant activity and could be utilized as a nutraceutical resource. Graphical Abstract