Food Chemistry

(Sean Pound) #1

354 5 Aroma Compounds


Fig. 5.11.Instrumental analysis of 5-methyl-(E)-2-hepten-4-one (according toEmberger, 1985)(a)mass spec-
trum,(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 dia-
stereomers. 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 chi-
ral 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-
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