HOW OXYGEN CONSUMPTION INFLUENCES RED WINES VOLTAMMETRIC PROFILE

Abstract

Phenolic compounds play a central role in sensory characteristics of wine, such as colour, mouthfeel, flavour and determine its shelf life. Furthermore, the major non-enzymatic wine oxidation process is due to the catalytic oxidation of phenols in quinones. Due their importance, during the years have been developed different analytical methods to monitor the concentration of phenols in wine, such as Folin-Ciocalteu method, spectrophotometric techniques and HPLC. These methods can also be used to follow some oxidation-related chemical transformations. However, these methods are complex, expensive and time consuming, thus not affordable for most small winery. Consequently, the development of several techniques that are faster, cheaper and user-friendly are currently of great interest. Among these, voltammetry has shown to be able to discriminate well wines according to their chemical composition, in particular in relationship to phenolic compounds. Aims: Our work aimed to understand the effect of oxygenation on voltammetric signals of wines. Material and Methods: DIfferent commercial red wines purchased from a local stores have been used in this study. The experimental protocol involved oxygenation of the wines in a 1 L bottle by hand shaking until the desired oxygen level was reached. Three level of oxygenation were chosen: 1.5 (TA), 5 (TB) and 7 mg/L O₂ (TC). Measures of oxygen have been carried out with a portable oximeter. The oxygenated wine was placed in 125 ml glass vials fitted with an oxygen sensor, filled without leaving any headspace and closed with sealing wax in order to not have oxygen exchanges with the outside. Electrochimical measurements were performed with a with a potentiostat using disposable screen- printed sensors in a three-electrode arrangement. Total polyphenols, anthocyanins, free and total SO₂ measurements were carried out using a multiparametric analyser and the dedicated kit. For colour de- termination were measured the absorbances at wavelengths 420, 520 and 620. The measures to determine the oxygen kinetic consumption were performed every 24 for hours. At the same time were carried out analysis with the multiparametric analyser and for colour determination. Results: Red wine voltammograms were impacted by oxygenation, with several voltametric features showing variation in profile and peak intensity according to the level of oxygen consumption. Different signal treatments strategies were applied to highlight the regions of the voltammograms mostly affected by oxidation, in particular through the use of derivative voltammetry.