430 M.A. Pozo-Bay ́ ́ on and G. Reineccius
Since yeast lees may adsorb some aroma compounds responsible of off-flavours
in wines (volatile phenols), these components have been also proposed such as a
cost-effective and efficient approach to remove or to decrease organoleptic defects
in wine (Chassagne et al. 2005).
In the case of wines aged in oak barrels with lees, aroma interactions with the
lees could modify how the wine interacts with the wood. One would expect a com-
petition between the wood and yeast derivatives for hydrophobic interactions with
aroma compounds (Ram ́ırez-Ram ́ırez et al. 2004). One of the most recent studies in
this field by Jimenez-Moreno and Anc ́ın-Azpilicueta (2007) investigated the effect
of lees extracted from wines on the binding of aroma compounds contributed by the
wood. As one would expect, most of thesewoodyaroma compounds decreased in
the wines when in the presence of lees, independent of their hydrophobicity and con-
centration (same effect for 10 g/L or 50 g/L). This finding suggested the saturation of
the binding sites at 10 g/L, and that the binding was likely due to non-hydrophobic
interactions. A summary conclusion is that wines aged in oak barrels in the presence
of lees could affect wine aroma giving wines with less woody, aromatic character.
Yeast cells can also influence wine flavour by binding aroma precursors such
as glycoconjugated terpenes. Moio et al. (2004) have shown that this binding by
yeast cells during fermentation could have important consequences on wine varietal
aroma.
The interaction between aroma compounds and other wine micro-organisms (e.g.
lactic acid bacteria) or with metabolites produced during malolactic fermentation
has been studied to a limited extent. Interactions between polysaccharides produced
by the most common wine lactic bacteria(Oenoccocus oeni)during malolactic fer-
mentation have been shown to be responsible for the reduced volatility of some
aroma compounds in wines (Boido et al. 2002). The possibility of direct interac-
tions between the surface of the bacteria cells and aroma compounds should also be
considered since this type of interaction has been found for other food lactic bacteria
(Ly et al. 2008).
8F.2.2.5 Other Wine Components
Glycerol is also one of the most abundant components in wine. It is mainly produced
during glycerol-pyruvic fermentation at the beginning of alcoholic fermentation. It
contributes directly to wine flavour giving sweetness (Noble and Bursick 1984) and
imparts some viscosity (Nurgel and Pickering 2005). Thus glycerol could directly
affect flavour perception.
The effect of glycerol-flavour interactions in white wine has been studied by
Lubbers et al. (2001). They found that glycerol at concentrations ranging from
5 to 50 mg/L did not modify the relative volatility of methyl-3-butanol, methyl-3-
propanol, ethyl hexanoate, or methyl-3-butyl acetate. They also carried out sensory
analysis, showing that the overall flavour of a model wine and white wine was not
changed by the addition of glycerol, suggesting that the concentrations in wine are
too low to have a significant effect on flavour perception.
In wines, De La Ossa and Gal ́an (1986) studied the effect of adding different
salts, such as CaCl 2 in a concentration range between 0 and 9.2 mol/L on aroma