Sawai Y, Moon J H
National Research Institute of Vegetables, Ornamental Plants and Tea, Kanaya, Shizuoka 428-8501, Japan.
J Agric Food Chem. 2000 Dec;48(12):6247-53. doi: 10.1021/jf000500b.
(+)-catechin, ethyl gallate, ascorbic acid, and alpha-tocopherol were reacted with 1,1-diphenyl-2-picrylhydrazyl (DPPH), and the reaction mixtures were subjected to 13C-nuclear magnetic resonance (NMR) analyses to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of each antioxidant. When ascorbic acid was reacted with DPPH, it was oxidized to dehydroascorbic acid by DPPH. When a mixture of ascorbic acid and (+)-catechin was reacted with DPPH, ascorbic acid scavenged DPPH radical faster than (+)-catechin. Ascorbic acid also scavenged DPPH radical faster than ethyl gallate and alpha-tocopherol. When (+)-catechin was reacted with DPPH, the B-ring of (+)-catechin changed to an o-quinone structure. However, it was reduced to (+)-catechin by ethyl gallate or alpha-tocopherol. alpha-Tocopherol and ethyl gallate had almost identical antioxidative activities. Therefore, the order of radical-scavenging ability (speed) suggested by our 13C NMR study was as follows: ascorbic acid > alpha-tocopherol = ethyl gallate > (+)-catechin.
（+）-儿茶素、没食子酸乙酯、抗坏血酸和α-生育酚与1,1-二苯基-2-苦基肼（DPPH）反应，反应混合物进行13C核磁共振（NMR）分析，以阐明每种抗氧化剂的抗氧化和自由基清除活性的分子机制。当抗坏血酸与DPPH反应时，它被DPPH氧化为脱氢抗坏血酸。当抗坏血酸和（+）-儿茶素的混合物与DPPH反应时，抗坏血酸清除DPPH自由基的速度比（+）-儿茶素快。抗坏血酸清除DPPH自由基的速度也比没食子酸乙酯和α-生育酚快。当（+）-儿茶素与DPPH反应时，（+）-儿茶素的B环转变为邻醌结构。然而，它被没食子酸乙酯或α-生育酚还原为（+）-儿茶素。α-生育酚和没食子酸乙酯具有几乎相同的抗氧化活性。因此，我们的13C NMR研究表明的自由基清除能力（速度）顺序如下：抗坏血酸＞α-生育酚=没食子酸乙酯＞（+）-儿茶素。
