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|Title:||Odor detection thresholds and enantiomeric distributions of several 4-alkyl substituted γ-lactones in Australian red wine|
|Other Titles:||Odor detection thresholds and enantiomeric distributions of several 4-alkyl substituted gamma-lactones in Australian red wine|
van Leeuwen, K.
|Citation:||Journal of Agricultural and Food Chemistry, 2009; 57(6):2462-2467|
|Publisher:||Amer Chemical Soc|
|Rachel C. Cooke, Katryna A. van Leeuwen, Dimitra L. Capone, Richard Gawel, Gordon M. Elsey and Mark A. Sefton|
|Abstract:||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.|
|Keywords:||Lactones; Alkylation; Stereoisomerism; Wine; Australia; Odorants|
|Appears in Collections:||Wine Science publications|
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