title: Odor detection thresholds and enantiomeric distributions of several 4-alkyl substituted gamma-lactones in Australian red wine.
abstract: The individual enantiomers of gamma-octalactone (1), gamma-nonalactone (2), gamma-decalactone (3) and gamma-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 gamma-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 microg/L for (R)-dodecalactone (4) while the highest threshold was 285 microg/L for (R)-nonalactone (2). With the exception of gamma-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-betaDEXcst capillary column) allowing quantification of the individual enantiomers. The enantiomeric distribution of gamma-octalactone (1) and gamma-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 gamma-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 gamma-octalactone (1) in the botrytized white wines.
authors.affiliation: School of Chemistry, Physics and Earth Sciences, Flinders University, Adelaide, Australia.
authors.forename: Rachel C
authors.initials: RC
authors.lastname: Cooke Née Brown
authors.forename: Katryna A
authors.initials: KA
authors.lastname: van Leeuwen
authors.forename: Dimitra L
authors.initials: DL
authors.lastname: Capone
authors.forename: Richard
authors.initials: R
authors.lastname: Gawel
authors.forename: Gordon M
authors.initials: GM
authors.lastname: Elsey
authors.forename: Mark A
authors.initials: MA
authors.lastname: Sefton
mesh_terms: D000478:Alkylation; D001315:Australia; D007783:Lactones / Q000032:analysis* / Q000138:chemical synthesis / Q000737:chemistry*; D009812:Odorants / Q000032:analysis*; D013237:Stereoisomerism; D014920:Wine / Q000032:analysis*
chemical_list: D007783:Lactones