Recherches sur les macromolécules du bois de chêne de tonnellerie - interactions avec les Flavans-3-Ols des vins et les aldéhydes du bois de chêne

Le bois est le matériau qui fut utilisé en remplacement des différents récipients de conservation et de transport antique des vins. Les chênes européens et particulièrement Quercus robur et Q. petraea sont largement utilisés en tonnellerie grâce à leurs propriétés mécaniques, physiques et chimiques exceptionnelles, apportant des caractéristiques sensorielles extrêmement appréciées. La connaissance de la diversité de la composition du matériel végétal et de sa composition en polymères tels que les polysaccharides, les lignines et les ellagitanins permet de mieux appréhender les différents phénomènes se produisant lors de l’élevage des vins en barriques. C’est pourquoi, nous avons mis au point une méthode de fractionnement par précipitations sélectives et de caractérisation des polymères extractibles du bois : lignines, polysaccharides et ellagitanins. Grâce à la technique de pyrolyse/GC-MS, les fractions lignines et polysaccharides sont étudiées in situ. Un profil aromatique des produits formés durant la chauffe peut être établi, les bois de chênes de différentes espèces peuvent être différenciés (chimiotaxinomie). Nous présentons également une caractérisation partielle des ellagitanins polymériques dans le bois de chêne Quercus petraea Liebl. et Q. robur L., ainsi qu’une caractérisation structurale des lignines extraites du bois de coeur. Nous terminons par une étude sur les interactions entre les flavan-3-ols des vins et les aldéhydes du bois et la formation de polymères par additions nucléophiles.Wood is the material which was used to replace the various containers of conservation and ancient transport of the wines. The European oaks and particularly Quercus robur and Q. petraea are largely used in cooperage thanks to their exceptional mechanical, physical and chemical properties, bringing extremely appreciated sensory characteristics. The knowledge of the composition diversity of the plant material and its composition out of polymers such as polysaccharides, lignins and ellagitannins makes it possible to better apprehend the various phenomena occuring during wine ageing in barrels. That is why, we developed a global method of fractionation by selective precipitations and a characterization of extractable polymers of wood : lignins, polysaccharides and ellagitannins. Thanks to the pyrolysis/GC-MS technique, the lignin and polysaccharide fractions are studied in situ. An aromatic profile of the products formed during toasting can be established, oak wood of various species can be differentiated (chimiotaxinomy). We also present a partial characterization of the polymeric ellagitannins in Quercus petraea Liebl. and Q. robur L. wood, as well as a structural characterization of the lignins extracted from heartwood. We finish by a study on the interactions between the wine flavan-3-ols and oak wood aldehydes, and the formation of polymers by nucleophilic additions. Keywords : oak wood, macromolecules, structure, composition, caracterization, flavan-3-ols, aldehydes, barrels, polymerization, colour, white wines, lignans, polymerized ellagitannins

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

This paper describes the formation and diversity of new compounds resulting from the polymerisation of furanic andphenolic flavanol-aldehydes with HPLC‑DAD and LC‑ES/MS analysis. Polymerisation, resulting from nucleophilicreactions, formed dimers, trimers, soluble and insoluble polymers. Reactions in hydroalcoholic solution with purealdehydes (phenolic and furanic) and flavanols (catechin) were studied. The study was repeated with differentaldehydes in white wine. This research focused particularly on the colour properties of the released products and theirpotential 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, andcatechin-syringaldehyde dimers. The most powerful coloured products resulted from furanic aldehydes. Over thecourse of the experiment, the reaction produced dimers, trimers and oligomers. After 50 to 60 days, the colour of thesolution was mainly due to soluble polymeric forms. In addition, the role of SO2, generally used during vinificationand ageing, was studied. The influence of SO2 on the kinetics of the reaction was limited

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.

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