108 M. Ugliano
need further microbial stabilization against post-MLF bacterial spoilage. Sulfur
dioxide is normally added to the wine to inhibit MLF as well as to prevent the devel-
opment of other spoilage microorganisms. In an effort to reduce the concentrations
of sulfur dioxide employed in winemaking, alternative strategies for wine stabiliza-
tion have been explored. Lysozyme is an enzyme present in hen egg white, which
can lyse Gram-positive bacteria, includingwine lactic acid bacteria. Its application
to stabilize the wine against bacteria, including those responsible for MLF, has been
recently investigated. Although it has beenproven that lysozyme can inhibit MLF
and growth of other microbial species (Gerbaux et al. 2007), unwanted side effects
have been observed in association with its use, namely loss of color in red wines and
formation of haze in whites (Bartowsky et al. 2004). Furthermore, lysozyme has no
inhibitory action against spoilage yeasts.
4.5 Pectolitic Enzymes
Grape berry skin and pulp contain significant amounts of pectic compounds that,
along with other constituents such as cellulose, hemicellulose and lignin, contribute
to the structure of cell walls (Vidal et al. 2003). Grape pectins are a heterogeneous
group of compounds characterised by a structure consisting of linear chains of -
dgalacturonic acid joined through 1→4 linkages, partially esterified with methanol
on the carboxylic function and with aceticacid in position O-2 and O-3. Insertion
of rhamnose residues in alternate positions in this structure results in rhamnogalac-
turonanes, which also contain side chains of arabinose or galactopyranose (Doco
et al. 1995).
During the production of white wines, part of pectic compounds from the berry
is released into the juice with grape crushing and pressing, and forms a colloid that
slows or prevents sedimentation of solid particles, particularly skin fragments. It has
been reported that wines made from juice rich in suspended solids have increased
levels of higher alcohols masking fruity aromas (Klingshirn et al. 1987) and higher
concentration of sulphur compounds potentially responsible for off-flavors (Single-
ton et al. 1975; Lavigne-Cru`ege 1996). Therefore, elimination of solid particles is
a key step in the production of quality whitewines. Enzymatic hydrolysis of pectic
structures is generally considered the most efficient way to break down their col-
loidal state and permit the separation of the entrapped solid particles. Due to the vari-
ety of possible structures, different enzymatic activities, particularly pectinesterases,
polygalacturonases, pectin lyases, and pectate lyases can hydrolyse grape pectins.
The occurrence of polygalacturonase and pectinesterase activities in grape berries
has been reported (Usseglio-Tomasset 1978), which indicates that grape enzymes
have the potential to promote juice clarification following crushing. Nevertheless,
the activity of these enzymes is often insufficient, so that the time required to
obtain an optimal degree of clarification thorough the action of grape pectinase can
be incompatible with normal winery operations. To improve the efficiency of the
clarification process, commercial preparations of pectinases can be added. These