Evaluation of antioxidant activity, and quantitative estimation of flavonoids, saponins and phenols in crude extract and dry fractions of Medicago lupulina aerial parts

This study was designed to evaluate the flavonoid, saponin (TSC) and phenolic (TPC) contents and in vitro antioxidant activity of the crude (CME) and dry extracts and fractions of Medicago lupulina L. aerial parts. A validated RP-HPLC method led to quantitation of flavonols (kaempferol, quercetin and myricetin) and flavones (apigenin and luteolin) in the hydrolyzed extract. TSC and TPC were assayed spectrophotometrically at 560 and 760 nm, respectively. The antioxidant activity of the CME and the dry fractions were followed in vitro by DPPH free radical and ferric reducing antioxidant power (FRAP) methods. The flavonoid content of CME was 1.27 mg/g dw. The prevailing flavonoids were luteolin and myricetin, at concentrations of 0.37 and 0.36 mg/g dw, respectively. TSC and TPC were detected in CME at the level of 90.4 mg ESE/g dw, and 12.9 mg GAE/g dw, respectively. In the DPPH and FRAP tests, the CME exhibited antioxidant capacity with TEAA and FRAP values of 45.4 μmol Trolox®/g dw and 0.2 mmol Fe2+/g dw, respectively. The diethyl ether dry fraction was the most valuable one, showing the highest antioxidant activity (TEAA = 726.1 μmol Trolox®/g dw, FRAP = 2349.4 μmol Fe2+/g dw) that was in accordance with its high TPC (162.4 mg/g dw).