Electrochemistry of White Wine Polyphenols Using PEDOT Modified Electrodes

Qiang Zhang,Alexander Türke,Paul Kilmartin

doi:10.3390/beverages3030028

Qiang Zhang, Alexander Türke + Show 1 more

Open Access

https://doi.org/10.3390/beverages3030028

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Abstract

The conducting polymer PEDOT (poly-3,4-ethylenedioxythiophene) has been polymerized onto 3 mm and 10 µm electrodes from a propylene carbonate solution. The electrodes have then been tested in a Chardonnay wine, including dilutions in a model wine solution, with comparisons made to scans with a glassy carbon electrode. A well-defined oxidation peak was obtained for the white wine at PEDOT in the 400 to 450 mV (Ag/AgCl) range, where peaks were also obtained for the representative phenolics caffeic acid and catechin. The voltammetry at PEDOT was typical of a surface-confined process. Significant preconcentration, leading to an increased current response, was noted over a period of 20 min of holding time. Extensive PEDOT growth was observed in the microelectrode case, leading to current densities for the oxidation of caffeic acid over 1000 times greater than those observed at the macroelectrode, matching the high surface area and fractal-type growth observed in SEM images.

Highlights

Electrochemical methods to characterize the phenolic content of wines have been applied widely over the past 15 years, mainly based upon cyclic voltammetric analyses at carbon-based electrodes [1,2,3,4,5,6,7].Many polyphenols contain ortho-diphenol or triphenol groups, which are important in beverage oxidation processes, given that they are they are recognized as the main initial substrate of wine oxidation [7], and they are oxidized at a relatively low electrode potential
The anodic current response can be related to levels of monomeric phenolics determined by HPLC, at least with white wines, where the phenolic composition is dominated by hydroxycinnamic acids and small flavonoids [1,7]
PEDOT electrodes electrodes show show considerable considerable promise promise for for applications applications in in electroanalytical electroanalytical chemistry, chemistry, based upon their responsiveness to oxidizable substrates, such as wine polyphenols, and the the based upon their responsiveness to oxidizable substrates, such as wine polyphenols, and separation of of signals signals obtained obtained when when other other reducing reducing agents, agents, such separation such as as ascorbic ascorbic acid, acid, are are present

Summary

Introduction

Electrochemical methods to characterize the phenolic content of wines have been applied widely over the past 15 years, mainly based upon cyclic voltammetric analyses at carbon-based electrodes [1,2,3,4,5,6,7].Many polyphenols contain ortho-diphenol (catechol) or triphenol (galloyl) groups, which are important in beverage oxidation processes, given that they are they are recognized as the main initial substrate of wine oxidation [7], and they are oxidized at a relatively low electrode potential. Dilution of wines is generally required to improve peak resolution and to obtain a linear relationship between dilution factor and peak current. The removal of free sulfites, through addition of acetaldehyde, has been used to obtain a more reliable measure of the phenolic compounds present [7]. Under these conditions, the anodic current response can be related to levels of monomeric phenolics determined by HPLC, at least with white wines, where the phenolic composition is dominated by hydroxycinnamic acids and small flavonoids [1,7]. The advantages of the use of differential pulse voltammetry have been reported, including improved peak resolution and a good correlation with spectrophotometric measures of red wine phenolics [8,9,10]

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