2009_Book_FoodChemistry

3.8 Unsaponifiable Constituents 243
Of all C 13 -norisoprenoids, β-damascenone
and β-ionone, smelling like honey and violets
respectively, have the lowest odor threshold
values (Table 3.59). Precursor of β-damascenone
is neoxanthine, out of which the Grasshopper
ketone (I in Formula 3.142) is formed by oxidative
cleavage. The oxygen function migrates
from the C-9 to the C-7 position by reduction
of I to form an allentriol, elimination and attachment
of HO-ions. In acid medium, 3-hydroxyβ-damascone
and β-damascenone result from the
intermediate (II).
Fig. 3.48. Oxidative degradation of capsanthin during
storage of paprika (according to Philip and Francis,
1971)
(3.141)
Besides the Grasshopper ketone, another enindiol
(Formula 3.141) was identified in grape
juices. When heated (pH 3), this enindiol
yields 3-hydroxy- β-damascone as main and
β-damascenone as minor product.
Hydroxylated C 13 -norisoprenoids (i. e. Grasshopper
ketone, 3-hydroxy-β-damascone) often occur
in plants as glycosides, and can be liberated from
these by enzymatic or acid hydrolysis and then
transformed into aroma compounds. Therefore
the aroma profile changes when fruits are heated
during the production of juice or marmalade.
An example is the formation of vitispirane
(II in Formula 3.143) by hydrolysis of glycosidic
bound 3-hydroxy-7,8-dihydro-β-ionol (I)
in wine. The odor threshold of vitispirane is
relatively high (800 µ g/kg, wine) but is clearly
exceeded in some port varieties.
1,2-Dihydro-1,1,6-trimethyl naphthalene (Table
3.59) can be formed by a degradation of
neoxanthin and other carotinoids during the storage
of wine. It smells like kerosene (threshold
20 µ g/kg, wine). It is thought that this odorant
contributes considerably to the typical aroma of
white wine that was stored for a long period in
the bottle. The compound may cause an off-flavor
in pasteurized passion fruit juice.
(3.142)