Redox Chemistry of Red Wine. Quantification by an Oscillating Reaction of the Overall Antioxidant Power as a Function of the Temperature

Abstract

The redox and acid-base reactivity of red wines was studied from both the analytical and kinetic standpoint. Four homemade wines, made from Italian red grape varieties of two different vintages, were tested to study the effect of temperature (25 and 37 degrees C) on the overall antioxidant power, through the Briggs-Rauscher oscillating reaction. The reaction was monitored by potentiometry (platinum electrode) and by direct chronometric detection. A reference scale based on the response of gallic acid was also employed, so as to achieve a quantitative evaluation: the novel Briggs-Rauscher antioxidant index (BRAI) was developed to express the overall antioxidant power quantitatively versus the chosen standard molecule. Overall antioxidant power was found to be related to total polyphenol content measured using the Folin-Ciocalteu method: the older wines had a lower antioxidant ability. Total acidity was also estimated indirectly by means of coupled pH-metric/photometric titrations and visible spectrophotometric measurements; it revealed an overlap between acid-base and redox chemistry of red wine.