Effect of the degree of toasting on the extraction pattern and profile of antioxidant polyphenols leached from oak chips in model wine systems

The effect of the degree of toasting of oak chips used in wine ageing on the extraction pattern of polyphenols was investigated using model wine systems. Pattern identification was carried out employing a Box-Behnken experimental design and response surface methodology, using resident time (t) and amount of chips (A (Chip)) as the independent variables. The responses selected to assess the process were the total polyphenol concentration, the antiradical activity and the reducing power of the model wines. Further, a deeper insight into the effects exerted by chip toasting was provided by the examination of the analytical polyphenolic composition of model wines, using liquid chromatography-mass spectrometry. The results obtained demonstrated that even moderate toasting provoked drastic decrease in the native oak wood polyphenols (ellagitannins), as indicated by the Folin-Ciocalteu assay, with a concomitant reduction in both the antiradical activity and reducing power. The evolution pattern for all three independent variables during model wine treatment with chips having different degree of toasting was also substantially affected. Light toasting was shown to generate a series of small molecular weight phenolics, but some of them did not survive more intense (heavy) toasting.