NMR analytical approach to clarify the molecular mechanisms of the antioxidative and radical-scavenging activities of antioxidants in tea using 1,1-diphenyl-2-picrylhydrazyl.
(+)-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.
Sawai
Y
Y
National Research Institute of Vegetables, Ornamental Plants and Tea, Kanaya, Shizuoka 428-8501, Japan. ysawai@tea.affrc.go.jp
Moon
J H
JH
D000975:Antioxidants; D015764:Bepridil / Q000031:analogs & derivatives*; D001713:Biphenyl Compounds; D002392:Catechin; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010851:Picrates; D013662:Tea / Q000737:chemistry / Q000378:metabolism
D000975:Antioxidants; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D010851:Picrates; D013662:Tea; D015764:Bepridil; D002392:Catechin; C004931:1,1-diphenyl-2-picrylhydrazyl