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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-

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