VOLTAMETRIC PROFILING OF RED WINE COMPOSITION DURING MACERATION: A STUDY ON FOUR GRAPE VARIETIES

Abstract

During red wine vinification, maceration allows the must, and consequently the wine, to be enriched with several compounds that contribute to the creation of the typical organoleptic characteristics of red wines. Among these, extraction of polyphenols (PPs) during maceration is a major process of enological interest.

The purpose of this study was the evaluate the suitability of a rapid analytical approach based in linear sweep voltammetry to monitor PPs extraction during vinification. Four red grape varieties were investigated, and fermentations were carried out with three different yeasts in triplicate. The density was evaluated daily and every 48h samples were taken to monitor changes in voltametric profiles and in the anthocyanins, polyphenols and precipitable tannins content.

The voltametric profiles of the wines were monitored using disposable screen-printed carbon electrodes with the working and counter electrode in carbon paste and an Ag/AgCl reference electrode. A drop of sample was loaded onto the sensor, and linear sweep voltammograms were acquired between 0-1200mV at a scan rate of 100mV/s. Analyzing the voltammograms, it was possible to observe differences between varieties and, within each variety, the temporal evolution of maceration.

In the second-derivative voltammograms, a positive peak was observed at low potentials, it increases initially showing a maximum after 7 days of fermentation. This peak is associated with the more easily oxidized compounds in wine. Another region of the voltammogram that shows a trend associated with the progress of fermentation is that around 440mV; in this region the negative peak reaches a maximum after 24 h after the start of maceration and then slowly decreases. This region has been associated with the concentration of monomeric anthocyanins and flavanols. The negative peak around 780mV results initially influenced by the presence of free SO₂, when SO₂ is bound the peak decreases in intensity and then increases again during maceration. By constructing PLS-R models for the concentration of anthocyanins, polyphenols and precipitable tannins the best pre-processing method resulted the second derivative and good regression models were obtained (R2 from 0.75 to 0.95).

In conclusion, this study provides a first proof of concept of the suitability of a simple analytical approach based on linear sweep voltammetry to monitor the evolution of phenolic composition during red wine maceration.