2009_Book_FoodChemistry

354 5 Aroma Compounds
Fig. 5.11. Instrumental analysis of 5-methyl-(E)-2-hepten-4-one (according to Emberger, 1985) (a) mass spectrum,
(b) 1 H-NMR spectrum (for discussion, see text)
tetrahydro-3,6-dimethyl-2(3H)-benzofuranone
(wine lactone) represents an impressive example
which shows how much the odor activity of
enantiomers can vary. The four enantiomeric
pairs of this compound have been separated by
gas chromatography on a chiral phase (Fig. 5.12).
The 3S,3aS,7aR-enantiomer (No. 6 in Table 5.12)
has the lowest odor threshold of the eight diastereomers.
The identification of this substance
in wine (cf. 20.2.6.9) led to the name wine
lactone. Two diastereomers (No. 3 and 8) are
odorless.
The determination of the ee value can be used to
detect aromatization with a synthetic chiral aroma
substance because in many cases one enantiomer
is preferentially formed in the biosynthesis of chiral
aroma substances (examples in Table 5.13). In
contrast to biosynthesis, chemical synthesis gives
the racemate which is usually not separated for
economic reasons. The addition of an aroma sub-