8F Interactions Between Wine Matrix Macro-Components and Aroma Compounds 427
such as yeast used in winemaking orBotrytis cinerea,a parasitic mould of the
vine. Micro-organisms can release exocellular and cell wall polysaccharides dur-
ing fermentation.Sacharomyces cerevisiaeexocellular manoproteins have structural
features in common with cell wall mannoproteins but have lower protein contents
(Saulnier et al. 1991). This diversity of origins leads to wines differing in polysac-
charides, i.e. different in composition and structure.
Dufour and Bayonove (1999a) reported twocriteria for polysaccharide discrimi-
nation: acidity and protein content. Neutral peptic substances (type II arabinogalac-
tans and arabinogalactans-proteins) represent 40% of the polysaccharides in wine
and acidic pectic polysaccharides, (e.g.homogalacturonans and rhamnogalacturo-
nans) account for 20% of them. Because of the difficulty in purifying wine polysac-
charides, most of the studies on interactions between wine polysaccharides and
aroma compounds have been carried out with exocellular and cell wall mannopro-
teins (thus mainly glycoproteins) of Saccharomyces (see effect of yeast and deriva-
tives in the next section).
Nevertheless, Dufour and Bayonove (1999a) studied the effect of different wine
polysaccharides isolated from wine, specifically arabinogalactan proteins (AGPs),
monomeric and dimeric rhamnogalacturonans II (mRG-II, dRG-II) and manno-
proteins (MPs), on the activity coefficients of some volatile compounds (isoamyl
acetate, ethyl hexanoate, 1-hexanol, diacetyl). They founddifferent effects depend-
ing on the type of polysaccharide and the nature of the aroma compound. They
observed that the volatilities of isoamyl acetate and ethyl hexanoate were not
affected by a range of polysaccharides at concentrations from 5 to 20 g/L. However,
at higher concentrations, the volatilities of these two esters were decreased by pro-
tein rich polysaccharides and AGP0 (withthe lower uronic acid content) and weakly
salted out in the presence of the uronic acid rich fractions (AGP4). They did not find
the effect in the presence of monomeric and dimeric rhamnogalacturonans. They
also observed that the volatility of 1-hexanol in water was reduced in the order:
AGP0>dRG-II>mRG-II>AGP4 while it was strongly salted out in presence of
MP0 (mannoprotein rich in polysaccharides).Regarding diacetyl, its activity coef-
ficient in water was not modified, increasing only at high concentration of AGP4.
Proteins are present in wines at very low and wide range of concentrations
(between 30 and 269 mg/L) (Feuillat et al. 2000). Their concentration depends on
the winemaking technology and grape type. Must and wine proteins have a molec-
ular weigh between 25 and 35 kDa (Pueyo et al. 1993) and most are glycoproteins
(Yokotsuka et al. 1991).
Other than studies on the role of proteins released by yeast during autolysis
(mannoproteins) on wine aroma, little work has been reported on interactions of
other proteins with aroma compounds. One study investigating such interactions
was published by Druaux et al. (1995). They used synthetic wines and bovine serum
albumin (BSA) as a model protein. This protein was found to bindδ-decalactone and
there was greater binding when in water than in a model wine environment (pH 3.5
and 10% ethanol). To our knowledge this is the only study focused on elucidating
the effect of proteins (others than mannoproteins) on the aroma release in wine or
model wine.