Characteristics of Antioxidative Flavonoid Glycosides in Lemon Fruit

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We investigated the antioxidative flavonoid glycosides in the peel extract of lemon fruit (Citrus limon). Six flavanon glycosides: eriocitrin, neoeriocitrin, narirutin, naringin, hesperidin, and neohesperidin, and three flavone glycosides: diosmin, 6,8-di-C-β-glucosyldiosmin (DGD), and 6-C-β-glucosyldiosmin (GD) were identified by high-performance liquid chromatography (HPLC) analysis. Their antioxidative activity was examined using a linoleic acid autoxidation system. The antioxidative activity of eriocitrin, neoeriocitrin and DGD was stronger than that of the others. Flavonoid glycosides were present primarily in the peel of lemon fruit. There was only a small difference in the content of the flavonoid glycosides of the lemon fruit juice from various sources and varieties. Lemon fruit contained abundant amounts of eriocitrin and hesperidin and also contained narirutin, diosmin, and DGD, but GD, neoeriocitrin, naringin, and neohesperidin were present only in trace amounts. The content of DGD, GD, and eriocitrin was especially abundant in lemons and limes; however, they were scarcely found in other citrus fruits. The content of flavonoid compounds in lemon juice obtained by an in-line extractor at a juice factory was more abundant than that obtained by hand-squeezing. These compounds were found to be stable even under heat treatment conditions (121°C, 15 min) in acidic solution.