382 5 Aroma Compounds
The whisky or oak lactone is formed when
alcoholic beverages are stored in oak barrels.
3-Methyl-4-(3,4-dihydroxy-5-methoxybenzo)oc-
tanoic acid is extracted from the wood. After
elimination of the benzoic acid residue, this
compound cyclizes to give the lactone. The odor
thresholds of the two cis-oak lactones (3R, 4R
and 3S, 4S) are about ten times lower than
those of the trans diastereomers (3S, 4R and
3R, 4S).
5.3.2.4 Terpenes...............................................
The mono- and sesquiterpenes in fruits
(cf. 18.1.2.6) and vegetables (cf. 17.1.2.6),
herbs and spices (cf. 22.1.1.1) and wine
(cf. 20.2.6.9) are presented in Table 5.33. These
compounds stimulate a wide spectrum of aromas,
mostly perceived as very pleasant (examples
in Table 5.34). The odor thresholds of terpenes
vary greatly (Table 5.34). Certain terpenes occur
in flavoring plants in such large amounts that
in spite of relatively high odor thresholds, they
can act as character impact compounds, e. g.,
S(+)-α-phellandrene in dill.
Monoterpenes with hydroxy groups, such as
linalool, geraniol and nerol, are present in
Table 5.33.Terpenes in food
fruit juice at least in part as glycosides.
Linalool-β-rutinoside (I) and linalool-6-0-α-L-
arabinofuranosyl-β-D-glucopyranoside (II) have
been found in wine grapes and in wine (cf.
20.2.6.9):(5.27)Terpene glycosides hydrolyze, e. g., in the
production of jams (cf. 18.1.2.6.11), either
enzymatically (β-glucosidase) or due to the
low pH of juices. The latter process is strongly
accelerated by a heat treatment. Under these
conditions, terpenes with two or three hydroxyl
groups which are released undergo further
reactions, forming hotrienol (IV) and nerolox-
ide (V) from 3,7-dimethylocta-1,3-dien-3,7-diol
(cf. Formula 5.28) in grape juice, or cis- and
trans-furanlinalool oxides (VIa and VIb) from
3,7-dimethylocta-1-en-3,6,7-triol in grape juice
and peach sap (cf. Formula 5.29).