Anti-oxidant capacity of dietary polyphenols determined by ABTS assay:: a kinetic expression of the results

The 2, 2'-Azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS)/Trolox equivalent anti oxidant capacity (TEAC) assay, which measures the ability of compounds to scavenge the ABTS radical cation (ABTS(center dot+)) in relation to Trolox (TEAQ is one of the most widely used methods to determine anti oxidant capacity. Usually, the measurements are based on a fixed end-point (4-6 min), which may not take into account the different kinetic behaviour of anti-oxidants. The aim of this work was to propose a kinetic procedure for ABTS(center dot+) assay, by using the kinetic parameters ED50, t(EC50) and AE [antiradical efficiency = 1/ED50 X t(EC50)A)], previously applied to the 2, 2-Diphenyl-l-picrylhydrazyl (DPPH center dot) assay. It was found that some polyphenols standards - ferulic acid, resveratrol and others-have not yet completed their reaction at the fixed end-point. The consideration of kinetic parameters in this method may provide a more thorough understanding of the behaviour of the anti-oxidants. A comparison of the activity of anti-oxidants measured by the scavenging of ABTS(center dot+) with that of DPPH center dot was also carried out.