DPPH Assay Adapted to the FIA System for the Determination of the Antioxidant Capacity of Wines: Optimization of the Conditions Using the Response Surface Methodology

The objective of the present work was to adapt the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay to a system of flow injection analysis (FIA) of merging zones to determine the antioxidant capacity of wine samples. The conditions of the FIA system proposed here were optimized with the response surface methodology using central composite rotatable design. The optimization parameters studied here were the carrier flow rate, the length of the sampling and reagent loops, and the length of the reaction coil. The experimental data were fitted to a polynomial model, and the optimal conditions were: flow rate of 1.12 mL min(-1), loop length of 18.5 cm, and reaction coil length of 234.60 cm. The limits of detection and quantification were 2.65 and 8.82 mu M of Trolox, respectively. The method proposed had an analytical frequency of 41 analyses per hour and a reagent consumption economy of 57.3 % for DPPH in relation to the conventional method. The results of the antioxidant activities of the wine samples obtained with the proposed method were correlated and compared to those of the conventional method.