Isolation of C-Glucosylflavone from Lemon Peel and Antioxidative Activity of Flavonoid Compounds in Lemon Fruit

Two antioxidative two C-glucosylflavones were isolated from the peel of lemon fruit (Citrus limon BURM. f.). They were identified as 6,8-di-C-β-glucosyldiosmin (LE-B) and 6-C-β-glucosyldiosmin (LE-C) by UV, IR, FAB-MS, 1H NMR, and 13C NMR analyses. The antioxidative activities of LE-B, LE-C, and flavonoid compounds (eriocitrin, diosmin, hesperidin, and narirutin) in lemon fruit were examined using linoleic acid autoxidation, the liposome oxidation system, and the low-density lipoprotein (LDL) oxidation system. LE-B and LE-C showed antioxidative activity in these autoxidation systems but exhibited weaker activity than eriocitrin, its eriodictyol of its aglycon. Eriocitrin and its metabolites by intestinal bacteria (eriodictyol, 3,4-dihydroxyhydrocinnamic acid, and phloroglucinol) exhibited stronger antioxidative activity than α-tocopherol in the LDL oxidation system and had approximately the same activity as (−)-epigallocatechin gallate. Eriocitrin and its metabolites are powerful antioxidants using an in vitro oxidation model for heart disease. Keywords: Lemon fruit; Citrus limon; antioxidant; eriocitrin; flavonoid; 6,8-di-C-β-glucosyldiosmin; 6-C-β-glucosyldiosmin