Titrimetric method based on potentiometric titration to evaluate redox couples in wine and polyphenols

Polyphenols are electroactive compounds, each molecule having reductive (Rd) and oxidative forms (Ox) due to the presence of several phenolic hydroxyls. Direct study of Rd/Ox forms was conducted using potentiometric titration in two steps: First, a complete reduction of the polyphenol Rd/Ox couples by titanium III chloride TiCl3 (100 % Rd), and then, oxidative titration by dichlorophenolindophenol DCPIP (100 % Ox). The second curve represents the totality of polyphenol couples titration with, for each couple, a characteristic E0 point representing the equilibrium between the concentration of Rd and Ox forms (Rd/Ox = 1). This value was typical for each polyphenol. We conducted several preliminary experiments with a model polyphenol (catechin) to establish the analysis conditions. The titration solution concentration was N/10 in HCl N and N/20 in water for TiCl3 and DCPIP respectively. The concentration of this solution diminished very rapidly, i.e. within 24 h for TiCl3 and DCPIP (under nitrogen and in darkness) and regularly needed a fresh preparation. To control the consistency and precision of the method we performed a few tests on pure products (e.g. hydroquinone/quihydrone, Fe III, Fe II, Cu II) permitting comparison between theoretical and experimental E0 values. Our result indicated less than 5 % variation and curves with a high reproducibility.

Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine - Possible Contribution of These Products to Colour

[EN] This paper describes the formation and diversity of new compounds resulting from the polymerisation of furanic and phenolic flavanol-aldehydes with HPLC¿DAD and LC¿ES/MS analysis. Polymerisation, resulting from nucleophilic reactions, formed dimers, trimers, soluble and insoluble polymers. Reactions in hydroalcoholic solution with pure aldehydes (phenolic and furanic) and flavanols (catechin) were studied. The study was repeated with different aldehydes in white wine. This research focused particularly on the colour properties of the released products and their potential impact on the colour of white wine. Some products were purified and isolated; these were mainly catechinfurfuraldehyde, catechin-methyl-5-furfuraldehyde, catechin-hydroxymethyl-furfuraldehyde, catechin-vanillin, and catechin-syringaldehyde dimers. The most powerful coloured products resulted from furanic aldehydes. Over the course of the experiment, the reaction produced dimers, trimers and oligomers. After 50 to 60 days, the colour of the solution was mainly due to soluble polymeric forms. In addition, the role of SO2 , generally used during vinification and ageing, was studied. The influence of SO2 on the kinetics of the reaction was limited.Vivas, N.; Nonier, MFB.; Absalon, C.; Lizama Abad, V.; Jamet, F.; De Gaulejac, NV.; Vitry, C.... (2008). Formation of Flavanol-aldehyde Adducts in Barrel-aged White Wine - Possible Contribution of These Products to Colour. South African journal of enology and viticulture. 29(2):98-108. http://hdl.handle.net/10251/105310S9810829

Occurrence and specificity of glucose oxidase (E.C: 1.1.3.4) in botrytized sweet white wine. Comparison with laccase (E.C: 1.10.3.2), considered as the main responsible factor for oxidation in this type of wine

Two types of oxidizing enzymes are present in botrytized white grapes and wines: laccase (PPO) and glucose oxidase (GOX). The evolution of these two enzymes is similar both during the over-ripening of grapes and during wine making. Yet, PPO is severely inhibited by the addition of SO2 following the alcoholic fermentation, and shows a marked instability in both the must and wine environments. GOX, however, remains free and active in solution and helps develop the main characteristics of the wine. In particular, as is to be expected from its activity, GOX oxidizes tartaric acid, ethanol and glycerol, the major components of must and wine, respectively to glyoxylic acid, acetaldehyde and glyceraldehyde. And then, by nucleophilic additions under acidic conditions, these products react with catechins and proanthocyanidins to form several new compounds, some of which appear in a colored form. These reactions can have an impact on the visual quality of the wine.

Validation of a Mass Spectrometry Method To Quantify Oak Ellagitannins in Wine Samples

[EN] Detection and individual quantification of oak wood ellagitannins in oak barrel aged red wine samples are difficult mainly due to their low levels and the similarity between their structures. In this work, a quantification method using mass spectrometry has been developed and validated to quantify wine ellagitannins after sample fractionation with a previously reported method. The use of an internal standard is a requirement to correct mass signal variability. (−)-Gallocatechin, among the different tested compounds, was the only one that proved to be a suitable internal standard making possible the accurate and individual quantification of the main oak wood ellagitannins. The developed methodology has been used to detect and quantify these ellagitannins in different Spanish commercial wines, proving its usefulness