4 Enzymes in Winemaking 117
the monoterpene alcohol geraniol and its glucoside, both identified in wine, can
both act as precursor to various other terpene aroma compounds, including the
monoterpene alcohol linalool. It has been shown that the rate of formation of
linalool and other volatiles from geraniol during wine aging is much higher for
free geraniol than for its glucoside (Fig. 4.6a) (Skouroumounis and Sefton 2000).
Because linalool is a more powerful odorant than geraniol, this might have positive
consequences for wine aroma. In contrast, in a study on the formation of the
powerful odorant -damascenone, it was found that acid-catalyzed hydrolysis of
the glucoside of megastigm-5-en-7-yne-3,9-diol, one of the possible precursors to
-damascenone during wine aging (Sefton et al. 1989), yielded a higher propor-
tion of -damascenone compared to the aglycone, although the latter reacted more
Enzyme hydrolysisAcid hydrolysisMegastigm-5-en-7-yne-3,9-diol glucoside Megastigm-5-en-7-yne-3,9-diolβ-Damascenoneβ-DamascenoneAcid hydrolysisHigher yield, slower reactionLower yield, faster reactionAcid
hydrolysisEnzyme
hydrolysisAcid
hydrolysis High rate of transformation, large
array of compounds formed,
including linalool, α-terpineol,
nerol, myrcenol, ocimene isomersLow rate of transformation, small
array of compounds formed, mainly
linalool and α-terpineola)
b)
Fig. 4.6Mechanisms of formation of: aterpenes from geraniol and geranyl glucoside;
b -damascenone from megastigm-5en-7yne-3,9-diol and its glucoside