A kinetic approach for evaluation of the antioxidant activity of selected phenolic acids

A kinetic approach was used to evaluate the efficiency of eight phenolic acids (chlorogenic, protocatechuic, caffeic, p-coumaric, sinapic, umbellic, rosmarinic and ferulic) in scavenging the alkylperoxyl radical generated in the beta-carotene-linoleic acid emulsion system, the 2,2-dipheny1-1-picrylhydrazyl radical (DPPH center dot) and the superoxide anion radical (O-2(center dot-)). The efficiency of the phenolic acids was estimated at the initial stage (t = 10 s) and expressed as the rate of DPPH center dot radical scavenging (R-S DPPH center dot), the rate of O-2(center dot-) radical scavenging (R-FF) and the rate of beta-carotene bleaching (R-B). The R-S DPPH center dot value for caffeic acid, followed by sinapic acid, showed the highest response in scavenging DPPH center dot radicals. According to its RFF value rosmarinic acid in comparison to the other investigated phenolic acids exhibited the highest response in Cri radical scavenging. Among the investigated phenolic acids, ferulic acid exhibited the lowest RB value indicating the strongest response in alkylperoxyl radical scavenging in the p-carotene-linoleic acid emulsion system, while in the presence of chlorogenic acid beta-carotene bleached most rapidly. The effectiveness of the phenolic acids in scavenging free radicals was also determined at a fixed endpoint. The results for the antioxidant activity coefficient in the beta-carotene-linoleic acid emulsion system showed good agreement with those obtained from the kinetic data: While the results for DPPH center dot and O-2(center dot-) scavenging obtained from the kinetic approach did not necessarily reflect the amounts of these free radicals that were scavenged at the end of the observation period and indicate that the kinetic data are a better discriminator for comprehensive characterisation of an antioxidant. (C) 2009 Elsevier Ltd. All rights reserved.