Masking of antioxidant capacity by the interaction of flavonoids with protein

The effect of antioxidants is often executed in complex biological mixtures where various interactions may take place. Therefore, the antioxidant capa city of antioxidants in blood plasma is examined. The assay used is the tro lox equivalent antioxidant capacity (TEAC). This method gives the antioxida nt capacity of a compound by measuring spectrophotometrically the disappear ance of the blue/green stable ABTS [2.'2'-azinobis-(3-ethylbenzothiazoline- 6-sulfonic acid)] radical, caused by scavenging. The results show that the antioxidant capacity of quercetin, rutin. catechin or 7-monohydroxyethylrut oside (monoHER) and blood plasma is not additive. This is partly due to int eractions between the antioxidant and plasma proteins. However, the antioxi dant capacity of alpha -tocopherol, which also binds to protein. is not aff ected by the interaction. This means that besides the antioxidant capacity of the compound itself the environment in which the antioxidant has to exec ute his function is important. (C) 2001 Elsevier Science Ltd. All rights re served.