Odor detection thresholds and enantiomeric distributions of several 4-alkyl substituted gamma-lactones in Australian red wine

The individual enantiomers of γ-octalactone (1), γ-nonalactone (2), γ-decalactone (3) and γ-dodecalactone (4) have been synthesized. The (R) series of enantiomers was prepared from l-glutamic acid by a strategy involving deamination and reduction to (S)-5-oxo-2-tetrahydrofurancarboxaldehyde (S)-7. The different length side chains were introduced by a series of Wittig reactions, varying in the choice of phosphorane used. Hydrogenation then gave the final γ-lactones 1−4. The (S) series of enantiomers was prepared in an analogous fashion beginning with d-glutamic acid. Aroma detection thresholds for all eight enantiomers were determined in a “bag in a box” dry red wine by the application of ASTM method E 679, employing a panel of 25 members. The lowest threshold determined was 8 μg/L for (R)-dodecalactone (4) while the highest threshold was 285 μg/L for (R)-nonalactone (2). With the exception of γ-decalactone (3) there were statistically significant differences (at the 5% level) in aroma detection thresholds between the two enantiomers of the same lactone. A stable isotope method developed for quantification of the lactones 1−4 has been extended for use with chiral phase GC (Rt-βDEXcst capillary column) allowing quantification of the individual enantiomers. The enantiomeric distribution of γ-octalactone (1) and γ-nonalactone (2) in seven botrytized wines and of 2 in a total of 34 red wines were thus determined; with few exceptions, the (R) enantiomer of γ-nonalactone (2) was found to be more prevalent than its (S) counterpart in the dry red and botrytized white wines analyzed. The same was true for γ-octalactone (1) in the botrytized white wines.Rachel C. Cooke, Katryna A. van Leeuwen, Dimitra L. Capone, Richard Gawel, Gordon M. Elsey and Mark A. Sefto

Characterization of the key aroma compounds in Shiraz wine by quantitation, aroma reconstitution, and omission studies

The key aroma compounds of premium Australian Shiraz wines from the warm Barossa Valley and cooler Margaret River regions were characterized. GC-Olfactometry was conducted to determine the most important volatile compounds, which were then quantitated. The wine from the Barossa Valley had higher concentrations of ethyl propanoate, dimethyl sulfide (DMS), and oak-derived compounds, whereas the Margaret River wine contained above threshold concentrations of the 'cheesy' compounds 2- and 3-methylbutanoic acid, as well as rotundone, the 'pepper'-smelling compound. The aromas were reconstituted by combining 44 aroma compounds, and sensory descriptive analysis was used to investigate the importance of the omission of several compounds, including DMS, rotundone, fatty acids, and β-damascenone, and the influence of nonvolatiles was also assessed. The study showed that the aroma of the Shiraz wines could be reconstituted in both cases, with the changes in the nonvolatile fraction having a large influence.Christine M. Mayr, Jason P. Geue, Helen E. Holt, Wes P. Pearson, David W. Jeffery, and I. Leigh Franci