Article pubs.acs.org/JAFC
UHPLC Quantification of Sotolon in White Wine Mario Gabrielli, Daniela Fracassetti, and Antonio Tirelli* DeFENSDepartment of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via Giovanni Celoria 2, 20133 Milano, Italy ABSTRACT: Sotolon (4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one) is a volatile compound involved in the atypical aging of dry white wine, causing an irreversible defect when it exceeds 7−8 μg L−1, and it might be adopted as a chemical marker of oxidative aging. An easier and sensitive ultrahighpressure liquid chromatography method for its determination in white wine is reported. The sample preparation is based on the liquid/liquid extraction by dichloromethane and the purification by solid phase extraction of the redissolved dry sample. This method showed good linearity and intermediate repeatability (89.5%), and low detection limit (0.029 μg L−1). This method was usefully applied to 30 Italian sparkling and still white wine samples, where sotolon was not detected in most of them and exceeded the perception threshold only in one sparkling wine (13 μg L−1). The proposed method could be used to further investigate the aging/storage conditions and the chemical−physical parameters affecting its formation in wine. KEYWORDS: sotolon, white wine, ultrahigh-pressure liquid chromatography, liquid/liquid extraction
1. INTRODUCTION Sotolon (4,5-dimethyl-3-hydroxy-2,5-dihydrofuran-2-one) is an odorous compound related to the oxidized character of wine.1 Its flavor is usually described as curry, fenugreek, and old honey, and it is sought in oxidatively aged wines such as Madeira and Porto.2,3 Sotolon’s odor is considered a defect in young, dry, white wine, as it can decrease the intensity of the fruity and flowery flavor notes as well as the expected freshness character.4 This defect is termed atypical aging.1 Sotolon is a thermolabile chiral lactone and it is stable in hydroalcoholic solution (14% ethanol v/v) at acid pH value. The chiral properties of carbon 5 in the furanic ring originate two optical isomers of sotolon with very different olfactory perception threshold: 5 and 89 μg L−1 in white wine for the S and R form, respectively. Since their quantitative ratio S/R can range from 1:3 to 3:1 in white wines,5 perception threshold values up to 8 were proposed. Detrimental amounts of sotolon in wine can rise through a number of chemical pathways mainly involving ethanal and 2ketobutyric acid,7 though other molecules can be involved through different chemical paths. Both hexoses and pentoses can give rise to sotolon formation via the Maillard reaction involving amino acids such as cysteine and 4-hydroxyisoleucine.8 Sotolon formation can increase in wine containing threonine9 and ascorbic acid,7,10 as well as following exposure to high temperature11 or oxygen1 during aging or storage with oxidative aging in oak casks.2 The negative effect of sotolon on wine flavor and the wide number of chemical and physical factors affecting sotolon formation in wine have two important consequences on the role of this compound in wine evaluation. First, the role of wine compounds in sotolon formation should be better investigated. © 2014 American Chemical Society
Second, the suitability of this off-flavor as a chemical marker of appropriate white wine aging and storage should be evaluated. Several analytical methods were reported for sotolon quantification in water solution and wine. Nevertheless, the sensitivity of the analytical methods based on head space sampling technique (DHS and SPME) is negatively affected by both the low concentration in wine and the high boiling temperature (184 °C) of sotolon.12,13 As a consequence, the chromatographic separation needs to be preceded by liquid/ liquid extraction or solid-phase extraction (SPE) and concentration.7,11 The analytical methods reported in the literature require long lasting sample extraction14 and a substantial volume of sample and solvents,7,15,16 leading to both long time and costly analysis. This research aimed to develop an analytical method to assess sotolon by using ultrahigh-pressure liquid chromatography (UHPLC) coupled with UV detection. The availability of a fast, sensitive, and reliable analytical method could allow a better monitoring of the oxidative fate of white wine aging as well as a deeper knowledge of wine-making practices and wine compounds affecting sotolon formation.
2. MATERIALS AND METHODS 2.1. Chemicals and Reagents. Sotolon (purity exceeding 97%), methanol, ethanol, dichloromethane (DCM), heptane, chloroform, sodium chloride (NaCl), anhydrous sodium sulfate were purchased from Sigma-Aldrich (St. Louis, MO). Polyvinylpolypirrolidone (PVPP) Received: Revised: Accepted: Published: 4878
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was purchased from Dal Cin (Sesto San Giovanni, Milan, Italy). All the chemicals were of analytical grade, at least. HPLC grade water was obtained with a Milli-Q system (Millipore Filter Corp., Bedford, MA). The synthetic wine contained 5 g L−1 tartaric acid in 12% ethanol/ water solution (v/v), adjusted to pH 3.5 with 12 M sodium hydroxide (Sigma-Aldrich). 2.2. Commercial Wine Samples. Sotolon content was assessed in 18 Chardonnay sparkling wine samples (Brut-nature Champenoise method, 7 months in-bottle aging) produced in one single winery (Franciacorta area, Lombardy, Italy) according to the rational wine making conditions usually adopted to produce quality wine (PDO). Moreover, 12 commercial dry white wine samples purchased at the market and produced in Italy from three different grape cultivars (Chardonnay, Catarratto, and Trebbiano) in the vintages 2011−2012 were analyzed. 2.3. Sample Preparation Development. 2.3.1. Liquid/Liquid Extraction Trials. A water solution containing sotolon (25 μg L−1) was extracted by using different solvents: heptane, chloroform, and DCM. The solution (300 mL) was liquid/liquid extracted once with 100 mL of each solvent by stirring for 30 min. The organic phase was separated from the aqueous phase by a separatory funnel, to which about 2 g of anhydrous sodium sulfate was added before vacuum-drying. The dry material was dissolved in 2 mL of water and submitted to UHPLC separation. Partition coefficient and extraction yield were calculated as follows K=
gsn =
gsVa Cs = Ca (g0 − gs)Vs n−1 KVs g0 ⎛ KVs ⎞ ⎜1 − ⎟ Va + KVs ⎝ Va + KVs ⎠
solvent extraction procedure was carried out three times, and the three organic solvent fractions were jointly collected and to them were added about 2 g of anhydrous sodium sulfate in order to remove the dispersed water. The DCM was evaporated under vacuum and the dry material was dissolved with 2 mL of 5% methanol. The solution was loaded in a conditioned SPE column containing 50 mg of PVPP, and 2 mL of the purified sample was recovered. 2.5. Calibration Curves and Method Performances. Spiked white wine (young Chardonnay/Trebbiano) samples containing 2.36, 4.67, 11.7, and 23.4 μg L−1 of sotolon were prepared to assess the response linearity of the analytical method as well as its intermediate precision parameters. Each sample was submitted to three replicated determinations for three different days (nine determinations per sample). Standard water solutions containing sotolon (117, 219, and 438 μg L−1) were submitted to triplicated UHPLC separations on three different days to assess the response linearity of water solutions. In order to assess the recovery parameters of the method, the response factors obtained were compared to the analytical response obtained by submitting spiked wine samples containing sotolon (7.8, 14.6, and 29.2 μg L−1, equivalent to a 15× dilution factor compared to the water standard solutions) to triplicated determinations performed on three different days. 2.6. Limit of Detection and of Quantification. The LOD was calculated as indicated as follows LOD = a + 3sx / y
where a is the intercept point of the regression line and sx/y is the standard deviation of the linear regression. 2.7. Ultrahigh-pressure liquid chromatography. The UHPLC separation was performed by an Acquity HClass UPLC (Waters, Milford, MA) system equipped with a photo diode array detector (2996 Waters). The column used was a Kinetex C18 (100 × 3 mm, 2.6 μm particle size, 100 Å pore size; Phenomenex, Torrence, CA). The chromatographic separation was carried out with an isocratic elution running 5% methanol for 4 min followed by column washing (100% methanol for 1 min) and column conditioning (4 min). The flow rate was 1 mL min−1 and the system pressure was 6700 psi. Sotolon was detected at 235 nm wavelength (detector sampling rate fixed as five points per second). The injection volume was 20 μL and the column was thermostated at 30 °C. All the samples were filtered through a 0.22 μm pore size PVDF membrane (Millipore, Billerica, MA) before injection. 2.8. Quantification of Sotolon. Sotolon was quantified in synthetic wine solutions and white wine samples by the external standard method. Chromatographic data acquisition and processing were performed by Empower 2 software (Waters). 2.9. Statistical Analysis. The equations of the calibration curves were assessed by the linear regression analysis. Differences between the calibration curve slopes obtained in aqueous solution and white wine were evaluated by the F-test (P < 0.05).
(1)
(2)
n
e yn =
∑1 gs g0
(4)
(3)
where K is the partition coefficient, Cs is the concentration of analyte in the extraction solvent, Ca is the concentration of analyte in the water solution, gs is mass of solute in the extraction solvent obtained with a single extraction step, g0 is the overall mass of solute, Vs is the volume of extraction solvent, Va is the volume of water solution, gns is the mass of solute in the extraction solvent following to the nth extraction step, n is the number of extraction steps, and eny is the overall extraction yield after the nth extraction step. The influence of NaCl concentration on the partition coefficient was tested. Thirty milliliters of synthetic wine solution containing 1 mg L−1 sotolon were added with 20, 50, or 100 g L−1 NaCl. The solutions were extracted once with 30 mL of DCM (30 min shaking with a Griffin flask shaker) and prepared as described as above. Moreover, the assessment of the extraction yield after 10, 20, 30, and 40 min of shaking under the above extraction conditions was carried out on synthetic wine solution (1 mg L−1 sotolon) added with 100 mg L−1 NaCl. 2.3.2. Sample Purification Trials. Three SPE resins were tested: C18, 360 mg (Waters, Milford, MA); polymer-based, 200 mg (Phenomenex, Torrence, CA); and in-lab packed PVPP, 50 mg. The SPE columns were conditioned by 5 mL of methanol and 5 mL of water and then loaded with 2 mL of sotolon (5 mg L−1 in water), and the unretained sample was collected. Then one or more aqueous solutions (2 mL each) prepared with increasing amounts of methanol (20, 40, 60, 80, 100% v/ v) were sequentially passed through the column. The eluted fractions were separately collected and submitted to UHPLC separation. Trials were carried out by loading the extracted wine samples recovered with 5% and 10% methanol (v/v) on the PVPP column. 2.4. Sample Preparation. Three grams of NaCl was dissolved in 30 mL of wine in a 100 mL bottle and then 40 mL of DCM was added. The bottle was hermetically closed and shaken for 10 min with a wrist action stirrer (Griffin flask shaker). The mixture was centrifuged 5 min at 5000g and the DCM was separated by a separatory funnel and recovered. The
3. RESULTS AND DISCUSSION 3.1. Analytical Method Development. The general physical−chemical properties of sotolon were first evaluated in order to fulfill the analytical sensitivity required. The UV spectrum of sotolon in water standard solution (5 mg L−1) showed one single peak having a maximum absorbance at 235 nm and a high molar extinction coefficient (ε° = 10 255 L cm−1 mol−1). Preliminary UHPLC runs showed that sotolon concentrations in the range 60−90 μg L−1 (corresponding to 8−12-fold higher values than the perception threshold) were suitable to gain the required detection/quantification levels. Therefore, wine volume as low as 20−30 mL can be used for sotolon quantification. Such values are lower than the condition required in the previous literature.1,10 In order to obtain the required concentration, a liquid/liquid extraction procedure was developed; therefore, sotolon extraction yield was evaluated by using heptane, chloroform, and DCM, which were previously 4879
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employed.15,16 The DCM showed an extraction yield 32% higher than that of chloroform, whereas heptane did not extract detectable amounts of sotolon (Table 1). Comparing the
Table 3. Effect of the Shaking Time on the Sotolon Amount (as peak area ± uncertainty) Extracted from a Synthetic Wine Solution (1 mg L−1 sotolon) with Dichloromethane as Organic Solvent
Table 1. Sotolon Amounts (as peak area) and Corresponding Partition Coefficient Obtained from Water Solution (25 μg L−1 of sotolon) with Different Extraction Solvents solvents heptane chloroform dichloromethane a
sotolon extracted (mV s) nd 32 47
a
shaking time (min)
peak area (mV s)
10 20 30 40
258 ± 6 294 ± 36 207 ± 2 222 ± 74
partition coefficient 0 0.81 2.1
Therefore, the SPE conditions effective in retaining polyphenols and eluting sotolon were evaluated. Polymer and C18 resins showed high retentive properties, and sotolon was eluted with 60% and 40% methanol, respectively. Nevertheless, interfering compounds were still found in the chromatogram. A lower retention property was obtained with PVPP. More than 50% of sotolon was unretained by the resin and a further elution with 20% methanol was needed to complete the recovery (Table 4).
Not detectable.
analytical responses (peak areas) obtained from sotolon in the water solution and the extracted sample, DCM showed the highest extraction yield (41%) corresponding to a partition coefficient exceeding 2.1 (Table 1). Moreover, DCM volumes ranging from 40 to 60 mL were calculated from the partition coefficient (see eqs 1, 2, and 3 reported in Materials and Methods) in order to inject quantifiable amounts of extracted sotolon (1.2−1.8 ng) and taking into account about 1 order of magnitude as the concentration factor for 30−40 mL of wine sample. Since sotolon amounts up to 68−76% were extracted by using solvent/wine volume ratios in the range from 1:1 to 2:1, three consecutive extractions were needed to obtain an overall extraction yield approaching 100%. Higher extraction yield can be obtained by increasing the ionic strength of the aqueous solution;17 therefore, different levels of NaCl (20, 50, and 100 g L−1) were evaluated. As expected, the partition coefficient increased exponentially as the salt concentration increased (Table 2). The partition coefficient for
Table 4. Sotolon Recovery (%) Obtained with Different SPE Resins by Loading 2 mL of Extracted Wine Samples (5 mg L−1 sotolon) and Eluting with 2 mL for Each Solvent Testeda methanol (%) unretained sample 5 10 20 40 60 80 100 cumulative
Table 2. Extraction Parameters of Sotolon Obtained with Different Amounts of Sodium Chloride in Synthetic Wine Solution (1 mg L−1 sotolon) Using Dichloromethane as Organic Solvent sodium chloride (g L−1)
extraction yield (%)
partition coefficient
0 20 50 100
65.8 86.5 88.5 93.0
1.8 1.9 2.3 3.5
a
polymer (200 mg)
C18 (360 mg)
PVPP (50 mg)
nd
0.4
56.0
56.0
56.0
− − 0.1 29.4 69.9 0.4 0.1 99.9
− − 37.7 54.1 0.5 0.5 nd 92.3
− − 43.2 0.6 tr tr tr 99.8
31.2 − − − − − − 87.2
− 34.4 − − − − − 89.4
Legend: tr: trace amount; nd: not detectable.
Sotolon recoveries up to 90% were found for the wine samples recovered in 5% and 10% methanol (v/v). The latter concentration allowed a sotolon recovery 2% higher, but 5% methanol was chosen since it allows an interference-free chromatographic separation (Figure 1). In order to avoid sample dilution due to the purification step, the dried sample was dissolved with 5% methanol before the SPE procedure. So 87% of the sotolon was recovered in the unretained sample without any further elution. Finally, the wine samples were prepared using the following optimized analytical conditions: 30 mL of wine added with 100 g L−1 NaCl, three extraction steps with 40 mL of DCM and 10 min shaking each, vacuum drying, sample recovery with 2 mL of 5% methanol/water solution (v/v), SPE purification on PVPP resin, and UHPLC run. The chromatographic separation occurred with low-methanol content (5%) in very short time (2.9 min) due to the low hydrophobicity and molecular weight of sotolon. Moreover, this method was solvent-saving for both sample preparation7,16 and chromatographic separation. No interfering chromatographic peak was found, and sotolon was obtained as a baseline-separated chromatographic peak (Figure 1). The method performances were evaluated for the sotolon concentrations (up to 25−30 μg L−1) usually reported in the literature for about white wine1,11,19 and in agreement with its perception threshold ( 0.999) in the whole range of concentrations tested with both the matrices (Figure 2), but a 10% lower response factor was calculated (as calibration curve slopes ratio) for the dry white wine compared to the corresponding water standard solution owing to the incomplete recovery of the SPE step. The calibration curves obtained are significantly different (p < 0.01), and a 10% higher sotolon amount in wine must be considered when water solutions are used as external standards. Amounts as low as 2.5 μg L−1 were accurately quantifiable in wine, though with slightly higher precision values (Figure 2 and Table 5). The intermediate repeatability20 were calculated for interday determinations; its values were close to 10% for sotolon levels as low as 2.3 μg L−1 and a mean value 3.1% was obtained for higher concentration values.
Table 5. Precision Parameters (n = 9) of Sotolon Quantification in White Winea concn added (μg L‑1) concn found (μg L‑1; mean value) SD repeatability (μg L−1) SD intermediate repeatability (μg L−1) repeatability limit (μg L−1) RSD (%) av RSD (%)
2.34 2.33 0.11 0.10 0.24 3.36
4.67 4.43 0.063 0.060 0.13 0.85
11.68 10.53 0.18 0.19 0.48 1.36 1.66
23.36 21.14 0.27 0.26 0.68 1.08
Legend: SD, standard deviation (μg L−1); RSD, relative standard deviation (%).
a
The LOD of sotolon in white wine was 0.029 μg L−1, a value much lower than the perception threshold in white wine. It is lower than the LOD values reported by other researchers also 4881
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considering the GC techniques.1,3,6,13 The sotolon recovery was evaluated in spiked white wine and its values were 97.7%, 91.1%, and 89.5%, respectively, for sotolon concentrations of 7.78, 14.60, and 29.20 μg L−1. Such values were higher than those previously reported.6,19,21 3.2. Quantification in Commercial White Wine. The proposed method was applied to the determination of sotolon in some commercial white wine samples (Brut-nature sparkling and still dry wines). In spite of the very low sugar content and the high CO2 pressure occurring during bottle corking and storage, the highest sotolon levels (6 and 13 μg L−1) were detected in two samples of sulfur dioxide-free and ascorbate-free sparkling wines (samples 11 and 12, respectively) stored for 7 months at 25 °C (Table 6). The role of sulfur dioxide in preventing sotolon
previously reported for the routine analyses of sotolon. It can be a suitable easy-to-apply analytical tool to investigate the formation of sotolon in either natural or synthetic wine systems. The sensitivity parameters above-described allow sotolon formation kinetics to be investigated at adequate concentration levels.
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*E-mail:
[email protected]. Phone: +390250316673. Fax: +390250316672. Funding
This study was cofinanced by the postdoctoral fellow “Dote Ricerca”: FSE, Regione Lombardia. Notes
The authors declare no competing financial interest.
■
−1
Table 6. Sotolon Amounts (μg L ) Detected in Commercial Samples of Brut-Nature Sparkling and Dry White Winea code
grape cultivar
vintage
description
sotolon
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Chardonnay Catarratto Catarratto Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano Chardonnay/Trebbiano
2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2011 2010 2010 2011 2011 2011 2012 2012 2012 2012 2012
sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine sparkling wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine dry white wine
nd nd nd nd nd nq nq nq nq nq 6.4 13.4 nd nq nd nq nd n.q 3.6 3.0 nd nd nd nd nd nd nd nd nd nd
a
AUTHOR INFORMATION
Corresponding Author
REFERENCES
(1) Lavigne, V.; Pons, A.; Darriet, P.; Dubourdieu, D. Changes in the sotolon content of dry white wines during barrel and bottle aging. J. Agric. Food Chem. 2008, 56, 2688−2693. (2) Silva Ferreira, A. C.; Barbe, J. C.; Bertrand, A. Heterocyclic acetals from glycerol and acetaldehyde in Port wines: Evolution with aging. J. Agric. Food Chem. 2002, 50, 2560−2564. (3) Camara, J. S.; Marques, J. C.; Alves, M. A.; Silva Ferreira, A. C. 3Hydroxy-4,5-dimethyl-2(5H)-furanone levels in fortified Madeira wines: Relationship to sugar content. J. Agric. Food Chem. 2004, 52, 6765−6769. (4) Silva Ferreira, A. C.; Barbe, J. C.; Bertrand, A. 3-Hydroxy-4,5dimethyl-2(5H)-furanone: A key odorant of the typical aroma of oxidative aged Port wine. J. Agric. Food Chem. 2003, 51, 4356−4363. (5) Pons, A.; Lavigne, V.; Landais, Y.; Darriet, P.; Dubourdieu, D. Distribution and organoleptic impact of sotolon enantiomers in dry white wines. J. Agric. Food Chem. 2008, 56, 1606−1610. (6) Guichard, E.; Pham, T.T.; Etievant, P. Quantitative determination of sotolon in wines by high-performance liquid chromatography. Chromatographia 1993, 37, 539−542. (7) Konig, T.; Gutsche, B.; Hartl, M.; Hubscher, R.; Schreier, P.; Schwab, W. 3-Hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) causing an off-flavor: Elucidation of its formation pathways during storage of citrus soft drinks. J. Agric. Food Chem. 1999, 47, 3288−3291. (8) Hofmann, T.; Schieberle, P. Identification of potent aroma compounds in thermally treated mixtures of glucose/cysteine and rhamnose/cysteine using aroma extract dilution techniques. J. Agric. Food Chem. 1997, 45, 898−906. (9) Pham, T. T.; Guichard, E.; Schlich, P.; Charpentier, C. Optimal conditions for the formation of sotolon from α-ketobutyric acid in the French “Vin Jaune”. J. Agric. Food Chem. 1995, 43, 2616−2619. (10) Pons, A.; Lavigne, V.; Landais, Y.; Darriet, P.; Dubourdieu, D. Identification of a sotolon pathway in dry white wines. J. Agric. Food Chem. 2010, 58, 7273−7279. (11) Cutzach, I.; Chatonnet, P.; Dubourdieu, D. Study of the formation mechanisms of some volatile compounds during the aging of sweet fortified wines. J. Agric. Food Chem. 1999, 47, 2837−2846. (12) Ferreira, V.; Ortega, L.; Escudero, A.; Cacho, J. A comparative study of the ability of different solvents and adsorbents to extract aroma compounds from alcoholic beverages. J. Chromatogr. Sci. 2000, 38, 469− 476. (13) Ferreira, V.; Jarauta, I.; Lopez, R.; Cacho, J. Quantitative determination of sotolon, maltol and free furaneol in wine by solid-phase extraction and gas chromatography−ion-trap mass spectrometry. J. Chromatogr. A 2003, 1010, 95−103. (14) Escudero, A.; Cacho, J.; Ferreira, V. Isolation and identification of odorants generated in wine during its oxidation: A gas chromatography−olfactometric study. Eur. Food Res. Technol. 2000, 211, 105−110. (15) Takahashi, K.; Tadenuma, M.; Sato, S. 3-Hydroxy-4,5-dimethyl2(5H)-furanone, a brunt flavoring compound from aged sake. Agr. Biol. Chem. 1976, 40, 325−330.
Legend: nd, not detectable; nq, not quantifiable.
formation is well-known,1 even if other SO2-free sparkling wine samples (e.g., samples 1 and 2 in Table 6) did not contain detectable amounts of sotolon. No perceptible concentrations of sotolon were found in two samples of still Catarratto dry wine (samples 19 and 20). No quantifiable or detectable amounts were obtained from the other 26 commercial samples of both sparkling wine and still wine. Such results are in agreement with other data reported in the literature1,19,22,23 and highlight the need for deeper knowledge concerning the chemical, physical, and technological factors affecting sotolon formation in wine. The proposed analytical method provides a sample preparation procedure that is faster and easier-to-apply than those 4882
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(16) Schneider, R.; Baumes, R.; Bayonove, C.; Razungles, A. Volatile compounds involved in the aroma of sweet fortified wines (Vins Doux Naturels) from Grenache Noir. J. Agric. Food Chem. 1998, 46, 3230− 3237. (17) Xie, W.; Shiu, W.; Mackay, D. A review of the effect of salts on the solubility of organic compounds in seawater. Mar. Environ. Res. 1997, 44, 429−444. (18) Martin, B.; Etievant, P.; Henry, R. The chemistry of sotolon: A key parameter for the study of a key component of flor Sherry wines. In Flavor Science and Technology, 6th Weurman Symposium; Bessière, Y., Thomas, A. F., Eds.; Wiley: New York, 1990; pp 53−56. (19) Martin, B.; Etievant, P. Quantitative determination of solerone and sotolon in flor Sherries by two-dimensional-capillary GC. J. High Res. Chromatogr. 1991, 14, 133−135. (20) ISO 5725-1. Accuracy (Trueness and Precision) of Measurement Methods and Results. General Principles and Definitions; ISO: Geneva, 1994. (21) Bailly, S.; Jerkovic, V.; Meurée, A.; Timmermans, A.; Collin, S. Fate of key odorants in Sauternes wines through aging. J. Agric. Food Chem. 2009, 57, 8557−8563. (22) Dagan, L.; Schneider, R.; Lepoutre, J. P.; Baumes, R. Stability of sotolon in acidic and basic aqueous solutions application to the synthesis of a deuterated analogue for its quantitative determination in wine. Anal. Chim. Acta 2006, 563, 365−374. (23) Riberau-Gayon, P.; Glories, Y.; Maujean, A.; Dubourdieu, D. Handbook of Enology, The Chemistry of Wine Stabilization and Treatments, 2nd ed.; John Wiley & Sons Ltd: Chichester, UK, 2006; Vol. 2, pp 233−284.
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