Optimization and Validation of a Method to Determine Enolones and Vanillin Derivatives in Wines-Occurrence in Spanish Red Wines and Mistelles.

Understanding the chemical nature of wine aroma demands accurate quantitative determinations of different odor-active compounds. Quantitative determinations of enolones (maltol, furaneol, homofuraneol, and sotolon) and vanillin derivatives (vanillin, methyl vanillate, ethyl vanillate, and acetovanillone) at low concentrations are complicated due to their high polarity. For this reason, this paper presents an improved and automated version for the accurate measure of these common trace wine polar compounds (enolones and vanillin derivatives). As a result, a faster and more user-friendly method with a reduction of organic solvents and resins was developed and validated. The optimization of some stages of the solid phase extraction (SPE) process, such as washing with an aqueous solution containing 1% NaHCO3 at pH 8, led to cleaner extracts and solved interference problems. Due to the polarity of these type of compounds, an optimization of the large volume injection was also carried out. Finally, a programmable temperature vaporization (PTV) quartz glass inlet liner without wool was used. The injector temperature was raised to 300 °C in addition to applying a pressure pulse of 180 kPa for 4 min. Matrix effects were solved by the use of adequate internal standards, such as ethyl maltol and 3',4'-(methylenedioxy)acetophenone. Method figures of merit were highly satisfactory: good linearity (r2 > 0.98), precision (relative standard deviation, RSD < 10%), high recovery (RSD > 89%), and low detection limits (<0.7 µg/L). Enolones and vanillin derivatives are associated with wine aging. For this reason, the methodology was successfully applied to the quantification of these compounds in 16 Spanish red wines and 12 mistelles. Odor activity values (OAV) indicate that furaneol should be considered an aroma impact odorant in red wines and mistelles (OAV > 1) while homofuraneol and sotolon could also produce changes in their aroma perceptions (0.1 < OAV < 1).

Study of the influence of varietal amino acid profiles on the polyfunctional mercaptans released from their precursors.

Polyfunctional mercaptans such as 4-mercapto-4-methyl-2-pentanone, 3-mercaptohexanol and 3-mercaptohexyl acetate contribute strongly to the varietal aroma of wines. These compounds are released during alcoholic fermentation from their precursors and their concentration is strongly linked to the grape variety. The aim of this work was to determine the effect of nine different amino acid profiles of grape varieties on the release of these polyfunctional mercaptans and on the consumption of their precursors as well as to determine which are the preferred precursors. A set-up of fermentations of synthetic must was prepared, which simulated the amino acid profiles of nine different grape varieties, containing known amounts of polyfunctional mercaptan precursors as well as the elements necessary for the yeast metabolism. The yeast assimilable nitrogen was adjusted in percentage to reach 150mgN/L in all the fermentations. Polyfunctional mercaptans and their precursors were analyzed in the final wine by gas chromatography coupled to mass spectrometry with negative chemical ionization and ultrahigh liquid performance chromatography coupled to mass spectrometry, respectively. The results showed significant differences in the release of these polyfunctional mercaptans as well as in the consumption of their precursors according to the amino acid profile. Moreover, it was observed that the preferred precursor of 4-mercapto-4-methyl-2-pentanone was its cysteinylated precursor. These results suggest that the amount of the amino acids as well as the ratio between them could modify the amount of polyfunctional mercaptans released. This could be a tool for the wine industry to vary the aromatic profile of wines by increasing or decreasing these volatile thiols.

Straightforward strategy for quantifying rotundone in wine at ngL(-1) level using solid-phase extraction and gas chromatography-quadrupole mass spectrometry. Occurrence in different varieties of spicy wines.

This paper presents a straightforward methodology to quantify rotundone in wine at ngL(-1) level. This compound, responsible for the black pepper aromatic note, may have sensorial relevance in some wines due to its low odor threshold, estimated at only 16ngL(-1) in red wines. The proposed strategy is based on solid phase extraction and analysis by GC-MS. The detection limit value was 0.6ngL(-1), which is more than one order of magnitude below its odor threshold in wine. Matrix effects have not been found and a synthetic wine calibration was proposed. The precision of the method was evaluated in reproducibility terms, obtaining a very acceptable value (RSD 4%). The optimized and validated strategy was applied to quantify this molecule in thirty wines belonging to different varieties as Graciano, Maturana tinta, Schioppettino, Shiraz, Duras and Gamay. Two of these wines exhibited levels higher than 100ngL(-1).

Chemosensory characterization of Chardonnay and Pinot Noir base wines of Champagne. Two very different varieties for a common product.

Five different methodologies were applied for the quantitative analysis of 86 volatile molecules in 32 Chardonnay and 30 Pinot Noir Champagne white base wines. Sensory characterization was carried out by descriptive analysis. Pinot Noir wines had more constitutive compounds while Chardonnay wines had more discriminant compounds. Only four compounds predominated in Chardonnay wines: 4-vinylphenol, guaiacol, sotolon and 4-methyl-4-mercapto-2-pentanone. Correlation studies and PLSR models were calculated with sensory and chemical variables. For Pinot Noir wines, they were not as revealing as for Chardonnay base wines. Sulfur-related compounds were suggested to be involved in tropical fruit, dried fruit and citric sensory notes. This family of compounds seemed to be responsible for discriminant sensory terms in Champagne base wines. Fermentative compounds (aromatic buffer) were found at significantly higher levels in Pinot Noir wines, which would explain the fact that these wines were more difficult to describe in comparison with Chardonnay base wines.

Study of Chardonnay and Sauvignon blanc wines from D.O.Ca Rioja (Spain) aged in different French oak wood barrels: Chemical and aroma quality aspects.

This study discusses chemical data corresponding to the analysis of twenty-one wood-extractable aromatic compounds in twenty-four different barrels varying in the toasting level at three sampling times: at the end of the alcoholic fermentation and after 5 and 12months of aging. Twelve barrels contained monovarietal Chardonnay wine while the other twelve barrels contained Sauvignon blanc wine. The levels of nearly all the analyzed compounds increased with the aging time, with the exception of vinylphenols and methyl vanillate, which decreased. These latter compounds had significantly higher levels in the Chardonnay wines than in the Sauvignon blanc. Furfural, guaiacol and vanillin derivatives increased with the toasting level. ANOVA study showed significant interactions between the toasting level and aging time as well as between the variety and aging time, which revealed significant differences in the levels of the compounds studied in the wines dependent on the toasting level, variety and aging time. Quality perception based exclusively on orthonasal aroma stimuli was evaluated by a panel of Spanish wine professionals in 12-month aged wines belonging to both grape varieties. Experts from D.O.Ca Rioja aroma did not share a common aroma quality concept for aged Chardonnay and Sauvignon blanc wines. Considering the cluster formed by the majority of experts (76%) for the Chardonnay and cluster 1 (56%) for Sauvignon blanc, quality scores were negatively correlated with the concentration level of 4-vinylphenol and positively with the concentration level of (E)-isoeugenol. The opposite was observed for cluster 2 (44%) identified for Sauvignon blanc wines.

Key changes in wine aroma active compounds during bottle storage of Spanish red wines under different oxygen levels.

Samples from 16 Spanish red wines have been stored for 6 months at 25 °C under different levels of oxygen (0-56 mg/L). Amino acids, metals, and phenolic compounds were analyzed and related to the production or depletion of key oxidation- and reduction-related aroma compounds. Oxidation brings about sensory-relevant increases in Strecker aldehydes, 1-octen-3-one, and vanillin. Formation of Strecker aldehydes correlates to the wine content on the corresponding amino acid precursor, Zn, and caffeic acid ethyl ester and negatively to some flavonols and anthocyanin derivatives. Formation of most carbonyls correlates to wine-combined SO2, suggesting that part of the increments are the result of the release of aldehydes forming bisulfite combinations once SO2 is oxidized. Methanethiol (MeSH) and dimethylsulfide (DMS), but not H2S levels, increase during storage. MeSH increments correlate to methionine levels and proanthocyanidins and negatively to resveratrol and aluminum. H2S, MeSH, and DMS levels all decreased with oxidation, and for the latter two, there are important effects of Mn and pH, respectively.

Potential aromatic compounds as markers to differentiate between Tuber melanosporum and Tuber indicum truffles.

The Tuber indicum (Chinese truffle) and Tuber melanosporum (Black truffle) species are morphologically very similar but their aromas are very different. The black truffle aroma is much more intense and complex, and it is consequently appreciated more gastronomically. This work tries to determine whether the differences between the aromatic compounds of both species are sufficiently significant so as to apply them to fraud detection. An olfactometric evaluation (GC-O) of T. indicum was carried out for the first time. Eight important odorants were identified. In order of aromatic significance, these were: 1-octen-3-one and 1-octen-3-ol, followed by two ethyl esters (ethyl isobutyrate and ethyl 2-methylbutyrate), 3-methyl-1-butanol, isopropyl acetate, and finally the two sulfides dimethyldisulfide (DMDS) and dimethylsulfide (DMS). A comparison of this aromatic profile with that of T. melanosporum revealed the following differences: T. indicum stood out for the significant aromatic contribution of 1-octen-3-one and 1-octen-3-ol (with modified frequencies (MF%) of 82% and 69%, respectively), while in the case of T. melanosporum both had modified frequencies of less than 30%. Ethyl isobutyrate, ethyl 2-methylbutyrate and isopropyl acetate were also significantly higher, while DMS and DMDS had low MF (30-40%) compared to T. melanosporum (>70%). The volatile profiles of both species were also studied by means of headspace solid-phase microextraction (HS-SPME-GC-MS). This showed that the family of C8 compounds (3-octanone, octanal, 1-octen-3-one, 3-octanol and 1-octen-3-ol) is present in T. indicum at much higher levels. The presence of 1-octen-3-ol was higher by a factor of about 100, while 1-octen-3-one was detected in T. indicum only (there was no chromatographic signal in T. melanosporum). As well as showing the greatest chromatographic differences, these two compounds were also the most powerful from the aromatic viewpoint in the T. indicum olfactometry. Therefore, either of the two chromatographic methods (GC-O or HS-SPME-GC-MS), together or separately, could be used as a screening technique to distinguish between T. indicum and T. melanosporum and thus avoid possible fraud.

Chemical and sensory effects of the freezing process on the aroma profile of black truffles (Tuber melanosporum).

The aim of this work was to evaluate the effect of freezing black truffles (Tuber melanosporum) on their aroma both in sensory and chemical terms. The truffles were frozen at temperatures of -20 to -80°C. Descriptive and discriminative sensory and chemical analyses, based on headspace solid phase microextraction followed by gas chromatography-mass spectrometry analysis (HS-SPME-GC-MS), were carried out after 1, 20, 40 and 60 days. Fifteen compounds with high aromatic potential in truffles were determined. Their selective ion peak areas were calculated, summed and expressed as percentage of active odour compound, in order to monitor changes in odour profile. The aroma of frozen truffles differed significantly from the aroma of fresh truffles. Volatile composition data revealed that T. melanosporum aromatic profile is deeply modified as a consequence of a freezing process. These aromatic changes could explain the loss of freshness observed in all frozen truffles. Methional and some phenols were suggested as markers of freezing time. Interestingly, 1-octen-3-one appeared as a general marker of freezing process.

Analysis, occurrence and potential sensory significance of aliphatic aldehydes in white wines.

An analytical method was developed for C8-C11 aliphatic aldehydes in wine consisting of solid phase extraction (SPE) followed by multidimensional gas chromatography/mass spectrometry (MDGC/MS). The method achieves low detection limits (<30ngL(-1)), minimises problems of blank contamination and shows high repeatability (RSD%<5%), but strong matrix effects were noticed during validation. These matrix effects were attributed to strong interactions between aliphatic aldehydes and other matrix elements. Three fractions were differentiated: free extractable aldehydes, aldehydes bound in hydrophilic complexes (extractable in the presence of acetaldehyde) and aldehydes bound in hydrophobic complexes (extractable in the presence of heptanal). The distribution of the three aldehyde species in wine samples was estimated using a surrogate (3,5,5-trimethylhexanal) and an internal standard (methyl phenylacetate) in double determinations (directly and after incubation with 1000mgL(-1) acetaldehyde). These components had a clear additive sensory effect in mixtures and odour thresholds in wine were very low. This caused that although they were present at very low levels, in 2 out of 24 white wine samples were clearly above threshold, and in six more were at levels close to threshold. These results suggest that these components are active contributors to the citrus fruit notes of some white wines.

Effects of the nonvolatile matrix on the aroma perception of wine.

Eighteen reconstituted wine samples were prepared by mixing nonvolatile and volatile fractions obtained from six different wines, two whites and four reds, with different characteristics, in an approach that makes it possible to have the same aroma composition in different nonvolatile matrices and vice versa. The aroma elicited by those reconstituted samples was described by a specifically trained sensory panel. Additional gas chromatography-olfactometric and gas chromatography-mass spectrometric studies were carried out to measure differences in aroma release. Results have shown that the nonvolatile matrix of wine exerts a powerful effect on the perception of aroma, strong enough even to make a white wine aroma to smell as a red wine (increasing red, black, and dry fruit notes in detriment of white, yellow, citrus, and tropical) and vice versa and also to create differences in the aroma of reds. It has also been confirmed that the wine nonvolatile matrix exerts a powerful influence on the release of odorants. In particular, headspaces above a white wine matrix are richer in fruity esters and volatile fatty acids. Red wine nonvolatile matrices seem also to retain strongly 3-mercaptohexyl acetate, hence reducing its sensory impact. Comparison of red wine nonvolatile matrices reveals that differences in the retention power of the matrix can affect differentially the pattern of release of linear and branched esters and also of acids.

Selectivity and efficiency of different reversed-phase and mixed-mode sorbents to preconcentrate and isolate aroma molecules.

A comparison of the ability of different sorbent systems, including mixed-mode resins and reversed-phase sorbents, to extract and isolate volatile molecules from hydroalcoholic medium has been carried out by means of the determination of liquid-solid distribution coefficients. Eighteen volatile compounds covering a wide range of physicochemical properties (acids, bases and neutrals) and chemical functionalities, and thirteen different sorbents have been tested. LiChrolut EN and Isolute ENV (both polymeric with high surface area) showed the highest retention capability for nearly all analytes at all pHs tested. Exceptions were 2,3,5-trimethylpyrazine, most efficiently extracted with Strata XC at acidic pH, and indole best retained with Oasis MCX and Strata XC at any pH. Although nearly all basic compounds were most selectively extracted with cationic mixed-mode resins at acid pHs and 3-mercaptohexyl acetate and m-cresol show maxima alpha at pH 10 with Oasis MAX, the alpha values obtained have been relatively low, which suggests that retention is not particularly driven by ionic forces. The study has also shown that selectivity depends on the pH, the exact kind of mixed-mode sorbent and on the polarity of the analyte. High selectivity towards ionogenic compounds can be obtained by combining retention in mixed mode, a rinsing with a non-polar solvent and further elution with a solvent containing a neutralizing agent. However, not all the ionogenic molecules seem to be retained in ionic mode in the conditions tested and the complete elution of some analytes can be difficult, which suggests that analyte-specific isolation procedures should be analyzed case by case.

Off-odor compounds produced in cork by isolated bacteria and fungi: a gas chromatography-mass spectrometry and gas chromatography-olfactometry study.

The risk of development of specific olfactory profiles in cork was evaluated after inoculation of cork granules and agglomerated and natural cork stoppers with isolated bacteria and fungi. The highest incidence of off-odor development was found in assays when fungi were inoculated. Cork granules with musty-earthy, musty-earthy-TCA, and vegetative deviations were inspected by gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS). Sixteen odor zones were clearly recognized in the GC-O analyses. Among these, octanal, 2-methoxy-3,5-dimethylpyrazine (MDMP), Z-2-nonenal, 2-methylisoborneol, 2,4,6-trichloroanisole (TCA), geosmin, and guaiacol were the most significant odorants and helped in the discrimination of sensory deviations. Only TCA and guaiacol were detected above their respective detection limits by HS-SPME-GC-MS. The fungi Cryptococcus sp. isolate F020, Rhodotorula sp. isolate F025, Penicillium glabrum isolate F001, and Pennicillium variabile F003A and the bacterium Pseudomonas jessenii isolate A1 were found to produce TCA to a greater extent. Additionally, 13 of 38 isolated microorganisms (2 bacteria and 11 fungi) proved able to produce unpleasant musty-earthy or vegetative odors that were not related to a significant TCA accumulation.

Modeling quality of premium spanish red wines from gas chromatography-olfactometry data.

The aroma compositions of 25 premium Spanish red wines have been screened by quantitative gas chromatography-olfactometry and have been related to the quality scores of the wines. The study has shown that up to 65 odorants can be present in the aroma profiles of those wines, 32 of which have been detected in less than half of the samples. One new odorant is reported for the first time in wine [(Z)-2-nonenal], and only 11 odorants, most of them weak and infrequent, remain unknown. Quality was not positively correlated with any single compound or with any olfactometric vector built by the summation of odorants with similar odors. However, an olfactometric vector built by the summation of the olfactometric scores of defective odorants, such as 2-methoxy-3,5-dimethylpyrazine, 4-ethylphenol, 3-ethylphenol, 2,4,6-trichloroanisole, and o-cresol was significant and negatively related to quality. Quality could be satisfactorily explained by a simple partial least-squares model (79% explained variance in cross-validation) with just three X-variables: the aforementioned defective vector, a second vector grouping 9 other compounds with negative aroma nuances, and the fruity vector, grouping 15 compounds with fruit-sweet descriptors. This result shows that the quality of these red wines is primarily related to the presence of defective or negative odorants, and secondarily to the presence of a relatively large number of fruit-sweet odorants. Remarkably, only in a few low-quality samples could defective aroma nuances be detected, which suggests that defective and negative odorants exert a strong aroma suppression effect on fruity aroma.

Multidimensional gas chromatography-mass spectrometry determination of 3-alkyl-2-methoxypyrazines in wine and must. A comparison of solid-phase extraction and headspace solid-phase extraction methods.

Two different strategies for the quantitative determination of 3-alkyl-2-methoxypyrazines in wine and must have been developed and validated. Comparison between both the techniques has been presented and the most adequate has been applied to the determination of these compounds in different samples of wine, made from several varieties of grapes, and also in different samples of must made from Cabernet Sauvignon grapes. Both the methods consisted of a dynamic headspace coupled with a solid-phase extraction (HS-SPE) and solid-phase extraction (SPE) directly from the sample, coupled with multidimensional gas chromatography-mass spectrometry system (MDGC-MS). Both of them require resins LiChrolut EN, and analyte elution has been carried out with dichloromethane. The repeatability of both methodologies was evaluated at two concentration levels. The relative standard deviations (RSD%) were acceptable in every case, but smaller when working with HS-SPE. The recoveries obtained for the three analytes with the two methodologies were almost 100%, with the exception of IBMP, which had a recovery of only 70% with HS-SPE. The linearity was satisfactory with both methods for the range of occurrence of methoxypyrazines in wine and must. The limits of detection of the direct SPE technique were much lower than those of HS-SPE in every case. Direct SPE method detection limits ranged from 0.09 to 0.15 ng L(-1). The method based on direct SPE was chosen finally because it had better detection limits and was easier and quicker than the HS-SPE-based method. It has been applied to the determination of these components in 36 wine and 17 musts samples. The quantitative results suggest that the Spanish wines show meaningless amounts of these compounds. IBMP has been found just in between 1.9 and 15 ng L(-1).

An assessment of the role played by some oxidation-related aldehydes in wine aroma.

The levels of important oxidation-related aldehydes, such as methional, phenylacetaldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methylpropanal, 2-methylbutanal, and 3-methylbutanal, were determined in 41 different wines belonging to different types (young whites and reds, natural sparkling wines, oxidized young whites and reds, Sherry, aged red wines, Port wines). Except (E)-2-hexenal and (E)-2-heptenal, all of them could be found at levels above threshold. Different compositional patterns were identified: Sherry wines have large amounts of branched aldehydes but not of (E)-2-alkenals, wines exposed to oxygen can have large amounts of (E)-2-alkenals but not of branched aldehydes, while aged wine and Port have relatively large amounts of both classes of compounds. Different sensory tests confirmed the active sensory role of these compounds and revealed the existence of interactions (additive or synergic) between them and with other wine volatiles. (E)-2-Alkenals are related to flavor deterioration, while branched aldehydes enhance dried fruit notes and mask the negative role of (E)-2-alkenals.

Critical aspects of the determination of pentafluorobenzyl derivatives of aldehydes by gas chromatography with electron-capture or mass spectrometric detection: Validation of an optimized strategy for the determination of oxygen-related odor-active aldehydes in wine.

This work presents a thorough study of some aspects critical to the quantitative performance of methods for the determination of volatile aldehydes previously derivatized to pentafluorobenzyl hydroxylamine oximes. The conclusions of the study are further applied to the validation of an optimized procedure for the determination of oxidation-related aldehydes from wine. Aspects studied include the chromatographic injection, the analytical performance of electron-capture detection (ECD) or MS detection, and the way in which the derivatization is carried out. Different injection techniques have been optimized and compared (classical splitless-hot injection; cold splitless; and large volume solvent split injection). All of them were carried out in a programmed temperature vaporization (PTV) injector, with a 350 microL internal volume liner (3.4 mm internal diameter). Classical splitless injection of hexane extracts is troublesome and requires large carrier gas flows (>10 mL min(-1)). Cold splitless injection was clearly superior. Large volume solvent split injection has been also optimized. ECD has been found to lack the necessary selectivity for the determination of unsaturated aldehydes in wine, although the quantitation of several minor aldehydes is possible. MS detection has proven to be superior for the determination of these compounds in wine. The way in which the reagent is applied is also critical and for the case of wine is important to ensure that the reagent is applied after some of the major wine aldehydes have been eliminated. The finally proposed method is extremely sensitive. Method detection limits ranged from 0.002 microg L(-1) (for unsaturated aldehydes) to 0.73 microg L(-1) (for phenylacetaldehyde) and precision (measured as relative standard deviation) is < or =6% in all cases. The method makes it possible to determine quantitatively in a single run the wine aldehydes with sensory significance (isobutyraldehyde, 2-methylbutanal, isovaleraldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methional and phenylacetaldehyde).

Gas chromatography-olfactometry and chemical quantitative study of the aroma of six premium quality spanish aged red wines.

The aroma of six premium quality Spanish red wines has been studied by quantitative gas chromatography-olfactometry (GC-O) and techniques of quantitative chemical analysis. The GC-O study revealed the presence of 85 aromatic notes in which 78 odorants were identified, two of which-1-nonen-3-one (temptatively) and 2-acetylpyrazine-are reported in wine for the first time. Forty out of the 82 quantified odorants may be present at concentrations above their odor threshold. The components with the greatest capacity to introduce differences between these wines are ethyl phenols produced by Brettanomyces yeasts (4-ethylphenol, 4-ethyl-2-methoxyphenol, and 4-propyl-2-methoxyphenol), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (furaneol), (Z)-3-hexenol, thiols derived from cysteinic precursors (4-methyl-4-mercaptopentan-2-one, 3-mercaptohexyl acetate, and 3-mercaptohexanol), some components yielded by the wood [(E)-isoeugenol, 4-allyl-2-methoxyphenol, vanillin, 2-methoxyphenol (guaiacol), and (Z)-whiskylactone], and compounds related to the metabolism (2-phenylethanol, ethyl esters of isoacids, 3-methylbutyl acetate) or oxidative degradation of amino acids [phenylacetaldehyde and 4,5-dimethyl-3-hydroxy-2(5H)-furanone (sotolon)]. The correlation between the olfactometric intensities and the quantitative data is, in general, satisfactory if olfactometric differences between the samples are high. However, GC-O fails in detecting quantitative differences in those cases in which the olfactive intensity is very high or if odors elute in areas in which the odor chromatogram is too complex.

Determination of important odor-active aldehydes of wine through gas chromatography-mass spectrometry of their O-(2,3,4,5,6-pentafluorobenzyl)oximes formed directly in the solid phase extraction cartridge used for selective isolation.

A method for the quantitative determination of octanal, nonanal, decanal, (E)-2-nonenal and (E, Z)-2,6-nonadienal in wine has been developed. In the proposed method, 200 ml of wine percolate through a solid phase extraction (SPE) cartridge packed with 200 mg of LiChrolut EN resins. The interferences are eluted with 60 ml of an aqueous solution containing 40% of methanol and 1% of NaHCO3. In the same SPE cartridge, the corresponding O-(2,3,4,5,6-pentafluorobenzyl)oximes are formed by letting percolate 2 ml of the reagent solution (5 mg ml(-1)). At room temperature the derivatization goes to completion in 15 min. The derivatives are eluted with 2 ml of dichloromethane, and the extract is concentrated and then analyzed by gas chromatography-mass spectrometry (GC-MS). The percentage of recovery in the isolation process is better than 90% in all cases with the exception of octanal, and is independent of the wine studied. In the cases of octanal, nonanal and decanal, the detection limits of the method are determined by the contamination levels of the reagent itself, and vary between 160 and 380 ng l(-1). For (E)-2-nonenal and (E, Z)-2,6-nonadienal, the detection limits were 12 and 20 and ng l(-1), respectively. The linearity of the method upheld until 10 microg l(-1) and was satisfactory in all cases. The reproducibility of the method is independent of the concentration and ranges from 30 to 190 ng (l(-1). The method has been applied to the analysis of these components in several wine samples. With the exception of (E, Z)-2,6-nonadienal, all the components can reach concentrations above their corresponding odor threshold values.

Fast fractionation of complex organic extracts by normal-phase chromatography on a solid-phase extraction polymeric sorbent. Optimization of a method to fractionate wine flavor extracts.

Some properties of LiChrolut-EN resins as normal-phase sorbent have been studied. Retention factors using pentane as solvent range from less than 2 (ethyl esters) to more than 56 (fatty acids and vanillin). All retention factors were smaller than 2 with dichloromethane. The efficiency of the bed was between 4 and 13 plates per cm. A method for the fast fractionation of wine flavor extracts has been further developed. Wine (75 ml) is extracted on a 0.5 g LiChrolut-EN bed. Volatile compounds are recovered in 5 ml of dichloromethane and the extract is further concentrated to 0.1 ml. Recoveries of the extraction procedure are above 85% for all compounds less polar than isoamyl alcohol. This extract is fractionated on a bed (5.0 cm height, 0.6 cm internal diameter) packed with 0.55 g of LiChrolut-EN resins. A first fraction is collected by the elution with 4 ml of pentane. A second one with 6 ml of a mixture pentane/dichloromethane (9:1) and a final fraction with 4 ml of dichloromethane. The first fraction is enriched in ethyl esters and some other non-polar compounds. The second fraction concentrates the alcohols and some volatile phenols, while the third is enriched in fatty acids, vanillin derivatives and some lactones. The recovery in the fractionation is complete. The profile obtained in the fractionation is very stable, and becomes distorted only when the column is loaded with an extract containing 80 mg of major volatiles (coming from more than 150 ml of wine). The fractionation of extracts from different wines showed that the performance of the process does not depend on the composition of the extract. Twenty-seven out of 32 studied compounds eluted reproducibly mainly in one fraction. The results suggest that the method can be applied as an aid for qualitative or quantitative analysis to any kind of organic extract as an alternative to liquid chromatography on silica-gel.