Relevance of secondary processes in orac values obtained employing pyrogallol red as target molecule

Abstract

Pyrogallol red (PGR) is readily bleached by peroxyl radicals. Addition of cinnamic acid derivatives (coumaric, caffeic, ferulic and sinapic acids), even at relatively high concentrations, barely protects PGR from bleaching, given very low ORAC (oxygen radical absorbance capacity) values. This lack of protection is contrary to that expected from the relative reactivity of cinnamic acid derivatives and PGR. It is concluded that the protection is not determined by competition of the antioxidant and the target molecule for peroxyl radicals, but for secondary processes involving phenoxyl and PGR derived radicals. In particular, the occurrence of processes such as PO{radical dot} + PGR → POH + PGR{radical dot} can explain the lack of PGR protection even in conditions where most of the peroxyl radicals are trapped by the additive. © 2009 Sociedad Chilena de Química.