6B Peptides 207
The amino acid composition of sparkling wine peptides depends on the aging
time (Moreno-Arribas et al. 1998b). The action of both types of proteases, but
mainly of the exocellular ones, that areactive in wines for months or even years,
causes large variations in peptide contents as happen during the aging of wines with
yeasts. Figures 6B.1 and 6B.2 illustrate these process showing the chromatograms
corresponding to the peptide fractions larger and smaller of 700 Da molecular mass,
respectively, of one must and the corresponding base wine and sparkling wines made
by thetraditionalmethod. It can be observed that, although the must hardly contains
any peptides in the fraction studied, their content increases during the production of
the base wine. The variation in the peptide content observed in the sparkling wines is
due to the successive and simultaneous degradation of some peptides and the release
of others during the aging with yeast.
Some of the lactic acid bacteria strains of wines have also shown proteolytic
activity in wine-making conditions (Feuillat et al. 1980; Manca de Nadra et al. 1997;
Leit ́ao et al. 2000). This activity has been found even in the presence of ethanol and
SO 2 (Manca de Nadra et al. 2005). It has been shown that this activity is greater in
red than in white wines (Manca de Nadra et al. 1999). The proteolytic activity is
a very important characteristic for some bacteria strains, allowing them to growth
in nitrogen-deficient media, and also favouring them to carry out malolactic fer-
mentation. According to Remize et al. (2005 and, 2006), peptides from 0.5 kDa to
10 kDa seem to be more favorable for the growth of wine lactic acid bacteria than
other nitrogen sources (<0.5 kDa). Alcaide-Hidalgo et al. (2008) have observed
a reduction in peptides during the malolactic fermentation of red wines followed
by an increase during the aging in barrels that was more evident when the aging
was in the presence of lees. The occurrence of proteolytic activity in all the stages
of wine manufacture can explain the wide range of peptides that can coexist in
a wine at any time and the discrepancies in most of the studies related to their
identification.
Glutathione is a peptide of non-proteic origin, present in grapes and wines that
merits a special mention. It was described for the first time in grapes by Cheynier
et al. (1989). Because of its strong antioxidant properties, it has been recommended
as an additive to prevent the enzymatic browning of white wines (Vaimakis and
Roussis 1996). Nevertheless, neither its evolution during wine manufacture nor its
precise role in wine manufacture are fully understood.
In an analysis of 29 varieties of grapes, Cheynier et al. (1989) detected glu-
tathione, mostly in a reduced form, GSH, at levels of 56.3–371.8μmol/kg in grapes
and of 41.9–332.7 mM in musts. According to Okuda and Yokotsuka (1999) and
Park et al. (2000), the glutathione content decreases during the firsts days of fer-
mentation, rising afterwards to reach values of 0.1–5.1 mg/L. According to Lavigne
et al. (2007), the amount of glutathione present in a wine at the end of the alcoholic
fermentation depends on the yeast strain, and decreases as the lees are removed and
also during the aging in barrels. In yeast, GSH accounts for about 1% of dry weight
ofSaccharomyces cerevisiaeand represents more than 95% of the low molecular
thiol pool (Elskens et al. 1991); thereby some of this glutathione could possibly be
released into the wine.