Identification of anthocyanin compositions in black seed coated Korean adzuki bean (Vigna angularis) by NMR and UPLC-Q-Orbitrap-MS/MS and screening for their antioxidant properties using different solvent systems

•The acidic 60% methanol extract of black adzuki bean exhibited highest antioxidant effects.•Ten anthocyanins were first characterised from the black seed coated adzuki bean.•Delphinidin-3-O-glucoside (3) showed the predominant in black adzuki bean.•Delphinidin profiles were the most abundant anthocyanin type.•Antioxidant effects of this crop were correlated with total phenolics and flavonoids. The aim of the present research was to investigate the antioxidant properties and anthocyanin profiles in the black seed coated adzuki bean (Vigna angularis, Geomguseul cultivar). The acidic 60% methanol extract (40 μg/mL) contains the highest total phenolic and flavonoid contents (486 ± 3 mg GAE/100 g; 314 ± 10 mg CE/100 g) with potent antioxidant properties (trolox equivalent 1272 ± 26 and 662 ± 24 mg TE/100 g) against ABTS and DPPH radicals compared to other methanol–water ratios (20, 40, 80, and 100%). Ten anthocyanin components were identified in this extract including delphinidin-3,5-O-digalactoside (1), delphinidin-3,5-O-diglucoside (2), delphinidin-3-O-galactoside (3), delphinidin-3-O-glucoside (4), delphinidin-3-O-rutinoside (5), delphinidin-3-O-(p-coumaroyl)glucoside (6), cyanidin-3-O-glucoside (7), petunidin-3-O-galactoside (8), petunidin-3-O-glucoside (9) and petunidin-3-O-(p-coumaroyl)glucoside (10) via NMR spectroscopy and UPLC-Q-Orbitrap-MS/MS analysis. The key anthocyanins 3 and 4 of delphinidin type were isolated by reversed phase C-18 MPLC. Our results indicate that the anthocyanin profiles as well as the high phenolic and flavonoid contents are important factors determining the antioxidant effects of black adzuki bean.