Application of flow injection - Chemiluminescence to the study of radical scavenging activity in plants

Chemiluminescence (CL) was observed during the oxidation of Luminol (2 mg/L ), mediated by 0.06% hydrogen peroxide (H2O2) and cytochrome c (10 mg/L), C L intensity was decreased by the presence of radical scavengers and the red uction was linearly proportional to the concentration and ability of scaven gers; butylated hydroxytoluene (BHT), caffeic acid and gallic acid, The ord er of effectiveness as radical scavengers was gallic acid > caffeic acid > BHT, which shows that the number of hydroxyl groups (OH) in the B-ring of f lavonoids plays a key role in a good radical scavenging activity, Of eight catechins obtained from green tea extracts, (-)-catechin was the least effe ctive and (-)-epigallocatechin gallate (EGCg) showed the strongest activity . This result indicates that the stereoscopic structure between the C-3 gro up and the B ring of flavonoids as well as substituents at the C-3 position make a contribution to radical scavenging activity. Of the tested Chinese herbal ingredients, five species of ingredients represented more than 90% o f the radical scavenging activity. Copyright (C) 2000 John Wiley & Sons, Lt d.