Flavonoid profile and biological activity of Korean citrus varieties (II): Pyunkyul (Citrus tangerina Hort. ex Tanaka) and overall contribution of its flavonoids to antioxidant effect

The peel of citrus fruit is a valuable source of flavonoids and is used in folk medicine for the curing various diseases in East Asia. In this study, 11 flavonoids and one coumarin derivative in the peel of Citrus tangerina Hort. ex Tanaka (Pyunkyul), native to Korea, were characterized using high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) and compared to the literature data. Flavanones, flavones, and the coumarin derivative were validated in terms of hesperetin, nobiletin, and coumarin levels, respectively, and quantified using the validated methods. The total concentration of the components was 4212.6 ± 37.0 mg/kg fresh peel. Naringin (1) was the most dominant component, followed by hesperidin (2). Antioxidant abilities in terms of DPPH·, ABTS·+ and reducing power were evaluated between 50 and 1000 mg/L. The antioxidant activities of the flavonoids increased in a dose-dependent manner.