2009_Book_FoodChemistry

386 5 Aroma Compounds
Table 5.34. Sensory properties of some terpenes
Compound a
Aroma quality Odor threshold
(µg/kg, water)
Myrcene (I) Herbaceous, 14
metallic
Linalool (IV) Flowery 6
cis-Furanlinalool Sweet-woody 6000
oxide (IVb)
Geraniol (V) Rose-like 7.5
Geranial (Va) Citrus-like 32
Nerol (VI) 300
Citronellol (VII) Rose-like 10
cis-Rose oxide (VIIa) Geranium-like 0.1
R(+)-Limonene (IX) Citrus-like 200
R(–)-α-Phellandrene Terpene-like, 500
(XI)
medicinal
S(–)-α-Phellandrene Dill-like, 200
(XI)
herbaceous
α-Terpineol (XVII) Lilac-like, 330
peach-like
(R)-Carvone (XXI) 50
1,8-Cineol (XXIII) Spicy, 12
camphor-like
(all-E)-α-Sinensal Orange-like 0.05
(XXXIX)
(–)-β-Caryophyllene Spicy, dry 64
(XLIX)
(–)-Rotundone (L) Peppery 0.008
a The numbering of the compounds refers to Table 5.33.
(5.28)
Fig. 5.31. Formation of R-δ-decalactone from linoleic
acid (according to Tressl et al., 1996)
(5.29)
Most terpenes contain one or more chiral centers.
Of several terpenes, the optically inactive form
and the l- and d-form occur in different plants.
The enantiomers and diastereoisomers differ
regularly in their odor characteristics. For example,
menthol (XIV in Table 5.33) in the l-form
(1R, 3R, 4S) which occurs in peppermint oil, has
a clean sweet, cooling and refreshing peppermint
aroma, while in the d-form (1S, 3S, 4R) it has
remarkable, disagreeable notes such as phenolic,
medicated, camphor and musty. Carvone (XXI
in Table 5.33) in the R(−)-form has a peppermint
odor. In the S(+)-form it has an aroma
similar to caraway. Other examples that show
the influence of stereochemistry on the odor
threshold of terpenes are 3a,4,5,7a-tetrahydro-
3,6-dimethyl-2(3H)-benzofuranone (cf. 5.2.5)
and 1-p-menthene-8-thiol (cf. 5.3.2.5).