In vitro antioxidant activity of Kyoho grape extracts in DPPH and ABTS assays: Estimation methods for EC50 using advanced statistical programs

The antioxidant capacities of Kyoho skin, seed, and flesh extracts were determined using DPPH and ABTS assays and a suitable statistical program was tested for the prediction of EC50 values of Kyoho skin, seed, and flesh extracts obtained by DPPH and ABTS assays. Statistical programs: OriginPro® version 8, GraphPad Prism® version 7, GraphPad Prism® version 7 five-parameter (5P) logistic model, SigmaPlot® version 14.0, Microsoft Excel® version 2016, interpolation log, and direct interpolation methods were employed to estimate the EC50 values. Linear regression and direct interpolation results showed deviations for non-linear models in the prediction of EC50 values of grape extracts. The correlation results of grape flesh extracts demonstrated a positive correlation (r = ≥ 0.95) between EC50 values of antioxidant assays. Therefore, non-linear methods were appropriate for EC50 calculations. These findings have significant implications for selecting an efficient statistical tool to calculate EC50 values for DPPH and ABTS assays.