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 (H(2)O(2)) and cytochrome c (10 mg/L). CL intensity was decreased by the presence of radical scavengers and the reduction was linearly proportional to the concentration and ability of scavengers; butylated hydroxytoluene (BHT), caffeic acid and gallic acid. The order 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 flavonoids plays a key role in a good radical scavenging activity. Of eight catechins obtained from green tea extracts, (-)-catechin was the least effective and (-)-epigallocatechin gallate (EGCg) showed the strongest activity. This result indicates that the stereoscopic structure between the C-3 group 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% of the radical scavenging activity. Copyright 2000 John Wiley & Sons, Ltd.