Ability of scavenging free radicals and preventing lipid peroxidation of some phenols and ascorbic acid

The capacity for scavenging free radicals and preventing lipid peroxidation of gallic, caffeic, and p-coumaric acids, thymol, eugenol and ascorbic acid were evaluated. The capacity for scavenging DPPH• free radicals were performed in ethanol 96% and ethanol 70%. In the same assay, the activity estimation was followed at 10, 20 and 30 minutes. In this assay, eugenol presented the best activity (IC50 ranging from 2.10 mg/mL to 9.74 mg/mL. In the opposite site, p-coumaric had the lowest activity, in which the IC50 values were not possible to determine. Generally, 10 minutes of reaction provided lower scavenging activities than 30 minutes. The sole exception was ascorbic acid in which the activities were independent on the time of reaction. Ascorbic acid, eugenol and thymol possessed higher ability for scavenging DPPH free radicals in ethanol 70% than in ethanol 96%. Gallic and p-coumaric acids as well as thymol revealed to be the best scavengers of ABTS•+ free radicals in contrast to ascorbic acid. The capacity for preventing lipid peroxidation was dependent on the concentration of samples. The assay showed that higher concentrations of gallic acid, thymol and p-coumaric acid added to sunflower oil (from 0.3 to 0.6%) induced higher lipid peroxidation with higher peroxide values. In contrast, increasing the percentages of caffeic acid and eugenol induced lower peroxidation of the sunflower oil. The percentage of samples added to this fat did not influence the index of p-anisidine. In this test, gallic acid had the best capacity for preventing the formation of 2,4-dienals and 2-alkenals decadienals able to react with p-anisidine.