Sorption Behavior of Volatile Phenols at the Oak Wood/Wine Interface in a Model System V. DANIELA BARRERA-GARCI ÄA, †,‡ RE Ä GIS D. GOUGEON, †,‡ ANDRE Ä E VOILLEY, ‡ AND DAVID CHASSAGNE* ,†,‡ Institut Universitaire de la Vigne et du Vin “Jules Guyot”, Universite ´ de Bourgogne, Campus Montmuzard, 21078 Dijon France, and Equipe IMSAPS, ENSBANA, Universite ´ de Bourgogne, 1 Esplanade Erasme, 21079 Dijon France The sorption in a model system of aroma compounds of enological interest (mixture of the eight derivatives from guaiacol, 4-ethylphenol, and whiskylactone) onto wood was investigated to assess the influence of wood on the concentration of these volatiles during the aging of wine. To evaluate the influence of the solubility of aroma compounds in sorption phenomena, this parameter was determined for each volatile compound in model wine at 10 and 25 °C. The solubility is significantly higher in the model wine than in water and remains constant in the range of temperatures studied, except for guaiacol and vanillin. Kinetic and equilibrium sorptions were investigated. Sorption kinetics showed that the sorption equilibrium for all aroma compounds was reached after 6-7 days. From the study of the individual sorption isotherms, two distinct kinds of sorption behavior were observed depending on the presence or not of an ethylenic para substituent conjugated to the phenyl ring. K ww partition coefficients between the wood and the model wine were determined, which exhibited an unusual positive variation with temperature. KEYWORDS: Oak wood; model wine; phenolic compounds; sorption; isotherm; solubility INTRODUCTION During aging in oak barrels, wine acquires aromatic complex- ity as a result of aroma transfer at the interface between wood and wine. Throughout this period, aromas issued from the fermentation lessen, whereas new compounds appear from oak wood and from the evolution of the primary and secondary aromas (1). The volatile compounds extracted from the wood have different impacts on the wine aroma. For instance, eugenol and cis- and trans--methyl-γ-octalactone are components of oak wood (2, 3) extracted during wine aging (2, 4), which are associated with desired aroma. Alternatively, unpleasant odors can also be generated, caused by the presence of ethylphenol and ethylguaiacol. Although Chatonnet et al. (5, 6) showed that Brettanomyces yeasts are involved in the formation of these volatile phenols, their origin is not only microbial. They found that the contents of volatile phenols in wines increase throughout the aging period, and this increase is even more pronounced when the barrels are old. The extraction of the volatile compounds from oak barrels depends on the amount that is potentially extractable, and the time during which the wine is in contact with the wood. A study of the transfer mechanisms at the interface between wood and wine was recently initiated. Ramirez-Ramirez et al. (7, 8) and Chassagne et al. (9) highlighted the sorption of wine aroma compounds by oak wood under wine-aging simulation. They showed that the amount sorbed at equilibrium depends on the nature of the aroma compound and on the wine matrix. The capacity of sorption of wood has also been investigated for monoaromatic hydrocarbons (10) and has been related to the hydrophobicity (logP) and the fractional lignin content in the wood. All of these results indicate that after several years of use, oak barrels will have exchanged aroma compounds with the different wines that they have contained. At this point, a used oak barrel may have sorbed more aroma compounds than it would have initially comprised. The main goal of this work is to study the transfer mechanisms of volatile phenols at the interface between wood and wine through a physicochemical approach, to help in the understanding of the process of wine contaminations by volatile compounds. To that purpose, we have studied the sorption onto wood of different aroma compounds of enological interest: a homologous series of guaiacol, 4-vinylguaiacol, 4-ethylphenol, and the four major aroma components of oak wood (eugenol, isoeugenol, vanillin, and whiskylactone). These compounds were chosen due to their common presence in the wine and exhibit a broad range of phenolic chemical structures. MATERIALS AND METHODS Materials. Guaiacol, 4-propylguaiacol, 4-vinylguaiacol, isoeugenol, and a racemic mixture of whiskylactone were supplied from Aldrich- * To whom correspondence should be addressed. Tel: +33-380-396392. Fax: +33-380-396265. E-mail: david.chassagne@u-bourgogne.fr. † Institut Universitaire de la Vigne et du Vin “Jules Guyot”. ‡ ENSBANA. 3982 J. Agric. Food Chem. 2006, 54, 3982-3989 10.1021/jf053043d CCC: $33.50 © 2006 American Chemical Society Published on Web 05/02/2006