EC50 estimation of antioxidant activity in DPPH assay using several statistical programs

DPPH assay is a reliable method to determine the antioxidant capacity of biological substrates. The DPPH radical scavenging activity is generally quantified in terms of inhibition percentage of the pre-formed free radical by antioxidants, and the EC50 (concentration required to obtain a 50% antioxidant effect) is a typically employed parameter to express the antioxidant capacity and to compare the activity of different compounds. In this study, the EC50 estimation was performed using a comparative approach based on various regression models implemented in six specialized computer programs: GraphPad Prism® version 5.01, BLeSq, OriginPro® 8.5.1, SigmaPlot® 12, BioDataFit® 1.02, and IBM SPSS Statistics® Desktop 19.0. For this project, quercetin, catechin, ascorbic acid, caffeic acid, chlorogenic acid and acetylcysteine were screened as antioxidant standards with DPPH assay to define the EC50 parameters. All the statistical programs gave similar EC50 values, but GraphPad Prism® five-parameter analysis pointed out a best performance, also showing a minor variance in relation to the actual EC50.