Distribution and Organoleptic Impact of Sotolon Enantiomers in Dry White Wines ALEXANDRE PONS,* ,†,§ VALÉRIE LAVIGNE, †,§ YANNICK LANDAIS, # PHILIPPE DARRIET, § AND DENIS DUBOURDIEU § Seguin Moreau France, Z.I. Merpins, B.P. 94, 16103 Cognac, France; Université Bordeaux 1, Institut des Sciences Moléculaires, CNRS UMR 5255, 351 cours de la Libération, 33405 Talence Cedex, France; and UMR 1219 Oenologie-Ampelologie, Institut des Sciences de la Vigne et du Vin, Université Victor Segalen Bordeaux 2, 351 cours de la Libération, 33405 Talence Cedex, France The enantiomers of sotolon, a flavor compound typical of oxidized white wines, were separated by preparative HPLC to determine their perception thresholds and distribution in wines. The enantiomeric ratios of chiral sotolon were evaluated in several dry white wines using gas chromatography and a chiral column (-cyclodextrin) connected to a 2 m precolumn (BP20). The perception threshold of (S)-sotolon (0.8 µg/L) in model wine solution was 100 times lower than that of the (R) form (89 µg/L), indicating that (S)-sotolon contributes to the characteristic aroma of prematurely aged dry white wines. Both enantiomers are detected in white wines. Analysis of commercial dry white wines from various vintages and origins revealed three types of distribution patterns: the racemic form, an excess of R, and an excess of S. The proportions found in these wines may be partially explained by the slow racemization kinetics (20 months) of optically active sotolon. KEYWORDS: Sotolon; enantiomers; wine; racemization; chiral GC INTRODUCTION Sotolon [3-hydroxy-4,5-dimethyl-2(5H)-furanone] is a chiral lactone with an intense curry odor. This volatile compound is known to impact flavor in many foodstuffs and wines. It contributes significantly to the burnt note of cane sugar (1) and aged sake (2), as well as the curry odor of fenugreek seeds (3). Sotolon contributes to the aromas of “vins jaunes” from the Jura and sherries (4, 5), as well the “dried fig” and “rancio” nuances in French fortified wines [Vins doux Naturels (VDN)] and port (6, 7). Concentrations of sotolon found in these types of wines are generally >10 µg/L. Sotolon has also been detected in white wines made from botrytized grapes (8, 9). The contribution of this powerful flavor compound to the aroma of prematurely aged dry white wines has now also been clearly established (10–12). Concentrations in prematurely aged dry white wines are generally <10 µg/L (10, 13). The perception threshold is 2 µg/L in model solution and 8 µg/L in dry white wine. All of these analyses were obtained using a synthetic racemate molecule. The perception threshold and descriptors of an odoriferous compound may differ according to the stereoisomer considered (14, 15). It was, therefore, important to separate the two enantiomers of sotolon and determine the perception thresholds and distribution of the R and S forms in wine to obtain an accurate assessment of their organoleptic impact. These data may also contribute to our understanding of the origins of the chemical formation of this compound during the oxidative aging of white wines. The stereoisomer distribution of sotolon in sherry and Vin jaune has already been analyzed by two-dimensional gas-phase chromatography coupled with an FID detector (16). However, to our knowledge, their distribution in dry white wines aged under reducing conditions has not previously been reported. MATERIALS AND METHODS Reagents. 4,5-Dimethyl-3-hydroxy-2(5)H-furanone (>99%), dichlo- romethane (Chromasolv grade), ethyl acetate (HPLC grade), isopropanol (HPLC grade), and heptane (HPLC grade) were obtained from Sigma- Aldrich (St Quentin Fallavier, France). Anhydrous sodium sulfate (99%) was supplied by Prolabo (France). L(+)-Tartaric acid (99.5%) was supplied by Fluka (France) and sodium hydroxide (99%) by Riedel de Haen. Ethanol (Lichrosolv grade) was supplied by Merck (France). Wine Samples. White wines from several vintages and origins were all analyzed in 2005. The composition of the model wine solution was as follows: L(+)-tartaric acid (5 g/L), ethanol (12% vol.), adjusted with NaOH (M) to pH 3.5. Sotolon Extraction from Wine. The extraction procedure was based on the method described by Cutzach (7). Wine samples (100 mL) were spiked with 100 µL of 3-octanol (100 mg/L solution in ethanol), as an internal standard, and 15 g of anhydrous sodium sulfate (to increase ionic strength and extractability). Wines were extracted three times with 10, 5, and 5 mL of CH 2 Cl 2 (magnetic stirring for 10, 5, and 5 min at * Author to whom correspondence should be addressed (e-mail alexandre.pons@oenologie.u-bordeaux2.fr; telephone 33 5 40 00 64 90; fax 33 5 40 00 64 68). † Seguin Moreau France. § Université Victor Segalen Bordeaux 2. # Université Bordeaux 1. 1606 J. Agric. Food Chem. 2008, 56, 1606–1610 10.1021/jf072337r CCC: $40.75  2008 American Chemical Society Published on Web 02/14/2008