Abstract: Adzuki bean (the seed of Vigna angularis) is a medicinal and edible legume. In order to better understand its nutritional value, phenolics from adzuki bean were extracted with 80% methanol and separated into free, glycoside and esterified forms. The phenolics were qualitatively and quantitatively analyzed. The results showed that the 80% methanol extract contained 3.44 mg/g phenolic acid and 2.50 mg/g flavonoid. The contents of the three forms of phenolics and their antioxidant activities varied significantly, among which the glycosidically bound fraction was found to be the richest in phenolic acid, up to 1.44 mg/g, whereas the free fraction was had the highest flavonoid content of 0.85 mg/g. The glycosidically bound fraction showed the strongest ferric reducing antioxidant power (FRAP) (15.76 mmol/g), while the ester bound fraction presented the strongest 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulphonate sulfonic acid) (ABTS) radical cation scavenging abilities. The 80% methanol extract was analyzed by high performance liquid chromatography coupled with triple quadruple mass spectrometry (UPLC-Q TOF-MS), and a total of 25 compounds including 3 organic acids, 6 phenolic acids and 16 flavonoids were identified. Quantitative analysis by HPLC-QQQ-MS showed that adzuki bean was rich in both rutin (327.40 μg/g) and catechin (210.70 μg/g).

Key words: ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry, high performance liquid chromatography coupled with triple quadruple mass spectrometry, adzuki bean, phenolics, antioxidant activity