Antioxidant activity index (AAI) by the 2,2-diphenyl-1-picrylhydrazyl method

The aim of this work was to propose a new antioxidant activity index (AAI) using the DPPH method. Antioxidant activity was expressed as the antioxidant activity index (AAI) calculated as follows: AAI = final DPPH concentration (μg ml−1)/IC50 (μg ml−1). The compounds, BHA, chlorogenic acid, ferulic acid, gallic acid, caffeic acid, quercetin, rutin, protocatechuic acid and trans-cinnamic acid were used, as well as the samples clove essential oil, eugenol and Xanthium strumarium extract. Three concentrations of DPPH were used and no significant difference in the AAI for each compound tested was observed, indicating that the AAI found was appropriate to compare the antioxidant strength of plant extracts, as well as of pure compounds. Gallic acid showed the higher AAI value (AAI = 27) followed by protochatechuic acid (AAI = 20) and quercetin (AAI = 15). Clove essential oil showed very strong antioxidant activity (AAI = 9) while the X. strumarium extract presented strong antioxidant activity (AAI = 1.6).