Wine Chemistry and Biochemistry

4 Enzymes in Winemaking 115

Although genetic engineering techniques have the potential to generate yeasts with

enhanced ability to liberate glycosidically-bound aroma compounds, the use of

genetically modified organisms in the wine industry is currently not allowed in the

majority of wine-producing countries.

Lactic Acid Bacteria (LAB), particularly the speciesOenococcus oeni,havealso

been studied for their ability to hydrolyze glycosidic aroma precursors in the course

of malolactic fermentation. Studies in model systems have shown that different

O. oenistrains possess enzymatic activities that can catalyze thehydrolysis of gly-

cosides (Guilloux-Benatier et al. 1993; Grimaldi et al. 2000; Ugliano et al. 2003;

D’Incecco et al. 2004). During the production of red wine, these activities have

been shown to catalyze the hydrolysis of glycosides of different volatile compound

(Boido et al. 2002; Ugliano and Moio 2006), the extent of the hydrolytic process

mainly depending on the chemical structure of the aglycone moiety and on the bac-

terial strain employed for the induction of MLF (Fig. 4.5). Nevertheless, precursor

hydrolysis during MLF does not result in a proportional increase in the concen-

tration of the corresponding volatile compounds (Boido et al. 2002; Ugliano and

Moio 2006), indicating the occurrence of other processes causing a partial loss of

the liberated aglycons, such as adsorption on macromolecules or metabolisation by

the bacteria (Boido et al. 2002; D’Incecco et al. 2004).

MLB 1 MLB 2

MLB 3 MLB 4

0

10

20

30

40

%

50

60

70

C6 alcohols

Total aliphatic alcohols

Aromatic alcoholsAromatic adehydes

Vinyl phenols

Total benzene derivativesTertiaty terpene alcoholsPrimary terpene alcohols

Linalool dervatives

Terpene diolsTotal terpenes

Total C13 Norisoprenoids

Total

MLB 1 MLB 2

MLB 3 MLB 4

a b c d e b f g h i b b b

Fig. 4.5Extent of hydrolysis of glycoside of different volatile compounds during MLF with
four strains of malolactic bacteria (MLB). Values are calculated as a percentage ratio between
the concentration of glycosides in MLF samples and in a non-MLF control.aSum of 1-hexanol,
trans-andcis-3-hexenol,trans-andcis-2-hexenol;bsum of isoamyl alcohols, heptanol, and 4-
hydroxy-4-methyl-2-pentanol;csum of benzyl alcohol and 2-phenylethanol;dsum of vanillin and
benzaldehyde;esum of 4-vinylphenol and 4-vinylguaiacol;fsum of linalool andα-terpineol;gsum
of nerol and geraniol;hsum ofcis-andtrans-linalool oxides (pyranic and furanic);isum of
3,7-dimethyl-1,5-octadien-3,7-diol and the two 2,7-dimethyl-2,7-octadien-1,6-diol isomers (from
Ugliano and Moio 2006, reproduced with permission)