Jean-Louis Puech

Localization of the ellagitannins in the tissues of Quercus robur and Quercus petraea woods

Abstract The heartwoods of a pedunculate oak and a sessile oak were each dissected into four fractions according to tissue type. The ellagitannins roburins A–E, grandinin, castalagin, and vescalagin in each fraction were determined by HPLC. The ellagitannin distributions in the wood of the two species were found to be identical. Both the longitudinal parenchyma enclosing the earlywood and latewood vessels, and the ray parenchyma display high ellagitannin contents, with the ray parenchyma being particularly rich. The fibrous zone displayed the lowest ellagitannin concentration. It comprised the most abundant tissue mass, however, with its diffuse apotracheal and ray parenchyma of the uniseriate rays accounting for half of the total ellagitannins.

Variation in wood volatile compounds in a mixed oak stand: strong species and spatial differentiation in whisky-lactone content

The effect of species and ecological conditions on oak volatile extractive content was investigated in an evenaged (100 years) stand located in western France. The sample included a total of 286 trees (118 sessile, 158 pedunculate and 10 oaks with an intermediate morphology) growing in contrasted environments (plateau, intermediate slope, small valley). The main factor influencing oak extractives level is species. The effect of the local environment appears negligible. No correlation between ring width and volatile extractive content was found. Q. petraea is significantly richer than Q. robur in eugenol and whisky-lactone (10.8 vs. 0.6 μg/g). However, two groups of sessile oaks could be identified, one poor and one rich in whisky-lactone. Among the latter, either the cis or the trans stereoisomer was predominant, suggesting that their production is not independent. A strong spatial structure was detected for whisky-lactone (cis-, trans- and total whisky-lactone, for the two species combined but also for Q. petraea alone in the case of the cis isomer).RésuméLes effets de l’espèce de chêne et des conditions écologiques locales sur les teneurs en composés volatils ont été étudiés dans un peuplement équienne (100 ans) situé dans l’ouest de la France. L’échantillon total inclut 286 arbres (118 chênes sessiles, 158 chênes pédonculés et 10 chênes intermédiaires) répartis en mélange dans trois zones écologiques du peuplement (plateau, pente et fond de vallon). Le facteur principal qui influence la teneur en extractible du bois de chêne est l’espèce botanique. L’effet environnement apparaît négligeable et il n’existe aucune relation entre la largeur de cerne et les substances volatiles. Le bois de chêne sessile (Q. petraea) possède des teneurs plus élevées que le chêne pédonculé (Q. robur) en eugénol et en whisky-lactone (10,8 μg/g contre 0,6 μg/g). Cependant, les chênes sessiles se divisent en deux groupes, l’un pauvre en whisky-lactone et l’autre riche en ce composé. Parmi ce dernier groupe, on observe que l’une des deux formes stéréoisomères (cis ou trans) prédomine, suggérant que leur biosynthèse n’est pas indépendante. On constate enfin une forte structuration spatiale pour les whisky-lactones pour les deux espèces combinées mais également chez Q. petraea seul pour l’isomère cis.

Cork and Alcoholic Beverages

For centuries, cork has been the stopper of choice for various alcoholic beverages. In this review, cork history, sources, production, physical properties, composition, off-flavors, and alternatives to cork stoppers are discussed.

Quality Assessment of Oenological Tannins Utilising Global Selectivity Chemical Sensors Array (“Electronic Tongue”)

Oenological tannin is a common name for food additives containing tannins utilised in winemaking practices. The main taste feature of oenological tannin is the taste sensation of astringency and bitterness. In the present paper, samples of various oenological tannins (oak, chestnut, gall, tara, querbacho, grape seed and grape skin tannins) were analysed by means of a tasting panel, measuring the flavour attributes bitterness, astringency, body, duration of flavour and similarity with wine tannins, and using the array of global selectivity chemical sensors (electronic tongue) “α-ASTREE” Liquid and Taste Analyzer (Alpha M.O.S., Toulouse, France). Principal component analysis of the electronic tongue outputs applied for different tannin solutions provides good discrimination according to their chemical nature. Consequently, three main classes of oenological tannins, namely gallotannins, ellagitannins and condensed tannins, could be identified and separated. The global output of the electronic tongue is quite responsive to changes in the bitterness and astringency of model quinine and alum solutions and, once calibrated (correlation coefficients of 0.976 (p<0.001) and 0.996 (p<0.001) respectively) could quantify their concentrations with good precision. The electronic tongue output was found to be correlated with the flavour attributes of oenological tannins. The best correlation was observed for bitterness. This fact could be explained by more constant calibration and lesser influence of any interfering factors on this attribute.

Comparison of direct and indirect methods of measuring the precursors of β-methyl-γ-octalactone and their application to the analysis of Sessile oak wood [Quercus petraea (Matt.) Liebl.]

Abstract A new indirect method for measuring the level of β-methyl-γ-octalactone precursors in oak wood by GC–MS is described. This level is calculated from the difference between the amount of free β-methyl-γ-octalactone and the amount formed after hydrolysis and lactonization. It is compared to the level of a precursor of cis -β-methyl-γ-octalactone, a 6′- O -gallate derivative of (3 S ,4 S )-4-β- d -glucopyranosyloxy-3-methyloctanoic acid, determined directly by HPLC. These two methods are applied to 12 powdered samples of Sessile oak wood and the results show that the 6′- O -gallate derivative of (3 S ,4 S )-4-β- d -glucopyranosyloxy-3-methyloctanoic acid is by far the most abundant precursor of β-methyl-γ-octalactone in this wood.

Kinetics of ellagitannin extraction from oak wood using white wine

This paper presents the results of an investigation made on the extraction of ellagitannins from oak wood(Quercus robur L.) using Chardonnay white wine in a constant flow‐through reactor. Through high‐pressure liquid chromatography eight ellagitannins were separated and quantitatively determined (roburin A‐E, grandinin, vescalagin, castalagin). An equation has been derived which gives a reliable description of the kinetics of the extraction of individual ellagitannins. It has been established that castalagin and vescalagin are the most abundant ellagitannins extracted from oak wood(Quercus robur L).