Implementation of response surface methodology to assess the antiradical behaviour in mixtures of ascorbic acid and α-tocopherol with grape (Vitis vinifera) stem extracts

► Stem extracts tested for their antiradical efficiency in combination with natural food antioxidants. ► Linear regression approach inadequate in estimating potential synergistic/antagonistic effects. ► Response surface methodology proven valuable in assessing antioxidant interactions. ► Extract polyphenols function in antagonism with natural antioxidants. ► Most potent antioxidants regenerate the less efficient ones resulting in antagonism.