Contribution of SO2 to antioxidant potential of white wine.

The reactivity of SO2 with the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and in Folin Ciocalteu (FC) assays was analysed under different experimental conditions. There was significantly higher reactivity between SO2 and DPPH in buffered methanol than in methanol alone. When DPPH and FC assays were performed in a mixture of caftaric acid and SO2, there were synergistic effects that were more pronounced with the FC assay. Phenolics are an important parameter of wine quality, and their accurate characterisation in wine is essential. Analysis of white wines with DPPH and FC assays overestimates the contribution of phenolics to the antioxidant potential (AOP). SO2 contributes (from 20% to 45%) to the AOP of the white wines analysed. As SO2 reactivity depends highly on buffer composition, pH, time of incubation and other compounds, e.g. phenolics and aldehydes, different experimental protocols can produce large variations in AOPs, and therefore control of experimental conditions is extremely important.