Evaluation of mixture effects in binary solutions of ascorbic acid with grape (Vitis vinifera) seed extracts using Response Surface Methodology

Extracts from seeds from three different varieties of grape were combined with ascorbic acid (AA) to evaluate the effects on the antiradical behaviour, using the DPPH assay. The investigations aimed at illustrating possible mixture effects, manifested either as synergism or as antagonism. By employing a simple linear regression approach, combinations of all extracts exhibited antagonism when combined with AA at concentration ratio of 1:1. Furthermore, to thoroughly investigate the role of the relative concentrations of the antioxidants, a 3×3 factorial design was implemented. This approach enabled the recording of the responses upon simultaneous variation of both the polyphenol concentration of the extracts and AA in the mixtures. In this case too, it was demonstrated that combinations of grape seed extracts with AA resulted in antagonism. This effect was discussed on the basis of grape seed composition and plausible antioxidant interactions.