ASSESSMEN OF THE REDUCING EFFECTS IN MIXTURES OF GRAPE (VITIS VINIFERA) SEED EXTRACTS WITH α-TOCOPHEROL USING RESPONSE SURFACE METHODOLOGY

Abstract

The efficiency of grape seed extracts to express reducing power was assessed using two different approaches and the TPTZ as the chromophore probe. Further to that, the mixture effects when the extracts were combined with α-tocopherol (α-Tcp) were also evaluated. The approaches included a simple linear regression analysis between the response (reducing power) and concentration, but also a response surface methodology, which permitted the monitoring of the response upon simultaneous variation of both the concentration of the total polyphenols (TP) of α-Tcp. The outcome of the study indicated that the deployment of linear regression poses important constrains with regard to concentration ranges, whereas the response surface methodology might be a valuable statistical tool for similar assessments and credible modeling of binary mixtures of antioxidants. In all combinations tested it was found that an antagonism is manifested, presumably as a result of α-Tcp regeneration by the extract polyphenols, at the expense of the latter.