Food Chemistry

3.8 Unsaponifiable Constituents 243

Fig. 3.48.Oxidative degradation of capsanthin dur-
ing storage of paprika (according toPhilipandFran-
cis, 1971)

Of all C 13 -norisoprenoids, β-damascenone
andβ-ionone, smelling like honey and violets
respectively, have the lowest odor threshold
values (Table 3.59). Precursor ofβ-damascenone
is neoxanthine, out of which theGrasshopper
ketone(I in Formula 3.142) is formed by oxi-

dative cleavage. The oxygen function migrates

from the C-9 to the C-7 position by reduction

of I to form an allentriol, elimination and attach-

ment of HO-ions. In acid medium, 3-hydroxy-

β-damascone andβ-damascenone result from the

intermediate (II).

(3.141)

Besides theGrasshopper ketone, another enin-

diol (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.Grasshop-

per 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 glyco-

sidic 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 (Ta-

ble 3.59) can be formed by a degradation of

neoxanthin and other carotinoids during the stor-

age 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)