Wine Chemistry and Biochemistry

152 R. Marchal and P. Jeandet

cloudy under the effect of heat; correlatively, protein stability requires a lower

dosage of bentonite. Thus, it has been observed that a racked Sauvignon wine

with a turbidity of 38 NTU after completion of the alcoholic fermentation requires

a bentonite treatment of 120g/hL to avoid protein haze. Within 10 months aging

on lees, the same wine shows a turbidity of 12 NTU and remains stable follow-

ing a bentonite treatment of only 30–40 g/hL. In further work, Moine-Ledoux and

Dubourdieu (1999, 2007) demonstrated that proteins responsible for protein haze

in a Sauvignon wine straight after fermentation can be separated by capillary elec-

trophoresis into six main fractions already present in the must (Fig. 5.7), while,

in the same wine kept on lees, an additional protein fraction (peak 7) was shown

to appear 10 months after aging (Fig. 5.7). In contrast to proteins originating from

grapes, this compound is thermostable and cannot be adsorbed by bentonites. Peak

7 which seems to play a key role in the improvement of protein stability in wines

aged on lees was further purified and characterized as an invertase fragment ofMr

32 kDa, known as MP32 (Moine-Ledoux and Dubourdieu 1999). This protein frag-

ment can be extracted from yeast cell walls by using Glucanex©R, leading to various

mannoproteins enriched in fraction 7.

Enzyme-extracted mannoproteins from the yeast cell wall added at a dose of

25 g/hL, can reduce by half the bentonite dosage necessary for protein stabilization

of a very hazy wine (Table 5.3). During lees autolysis, MP32 is released from the

1

2

5

6

1

2

3

4

5

6

7

Fig. 5.7Electrophoresis diagram of proteins in a Sauvignon wine after alcoholic fermentation
(left) and after 10 months aging on lees (right) (redrawn with permission from Moine-Ledoux and
Dubourdieu 2007)