Free radical scavenging capacity of hydroxycinnamic acids and related compounds

The capacity of hydroxycinnamic acid derivatives to trap peroxyl radicals was evaluated by competitive kinetics and oxygen radical absorbance capacity (ORAC) indexes, using c‐phycocyanin and pyranine as target molecules. The pattern of results is similar in all the systems, with the reactivity of the compound determined by the bond dissociation energy (BDE) of the hydrogen atom of the phenolic moiety. However, differences in the relative reactivity are observed depending upon the employed methodology (initial rate of consumption or ORAC‐type methodology) and target molecule employed. These differences are explained in terms of the role played by secondary reactions of the initially formed phenoxyl radicals. This emphasizes the need for performing a complete kinetic analysis of the results in order to obtain meaningful evaluations of the relative reactivity of the tested compounds.