426 M.A. Pozo-Bay ́ ́ on and G. Reineccius
5-hydroxymethylfurfuraldehyde [HMF] and 5-methylfurfuraldehyde [5-OHFA]) and
phenolic aldehydes (vanillin and syringaldehyde) in wine-like model solutions. The
reactivity of both aldehyde families was very different: furanic aldehydes were
more reactive than phenolic aldehydes (HMF was the most reactive, followed by
FA, 5-OHFA, syringaldehyde and finallyvanillin). Dependingupon the aldehyde,
the product formed was very different. Thus, the formation of these condensation
products could play an important role in wine flavour development when aged in
oak barrels.
It has been suggested that anthocyanins can form hydrogen bonds with some
aroma compounds when they are present at high concentrations (Voilley et al. 1991).
Dufour and Sauvaitre (2000) reported that at pH 3.5, malvin, the hemiacetal form
of the anthocyanin 3,5 diglucoside, was primarily responsible for aroma interac-
tions rather than the main anthocyanin, malvidin-3-glucoside. They also reported
that benzaldehyde, furfural, and 2-isobutyl-3-methoxypyrazine did not contribute as
copigments whereas all phenol-based flavour compounds (e.g. vanillin, syringalde-
hyde) led to copigmentation. Although they did not observe any visible effect on
color by increasing the concentration of anthocyanins, the interactions of volatile
compounds with the anthocyanins may affect the sensory characteristics of wines.
Also during the aging of wine in oak casks, Escalona et al. (2002) have shown that
some phenolic compounds extracted from the wood (ellagic tannins) could partici-
pate in polymerization reactions with aroma compounds.
Some NMR studies (Jung et al. 2000) have confirmed that interactions between
some polyphenols (gallic acid and naringine) and some aroma compounds (e.g.
ethyl hexanoate and 2-methylpyrazine) are due toπ-πstacking of the gallic acid
ring with the aromatic ring of a flavour compound. Hydrogen bonding between
functional groups of a flavour compound and a polyphenol provide stability to the
complex and help to orient the molecules in a specific conformation. Nevertheless,
other studies performed with alkyl-methoxypyrazines in wine model systems sup-
plemented with some of these polyphenols (e.g. gallic acid) did not shown any mea-
surable effect (Hartmann et al. 2002), confirming the different effects of polyphenols
depending on the type of aroma compound being considered.
Most of the studies on polyphenol/aroma compound interactions have been based
on analytical determinations but there are few sensory studies documenting the
effect of polyphenols on wine flavour. However, Aronson and Ebeler (2004) have
shown that gallic acid (in 1% ethanol solution) significantly decreased the volatil-
ity of 2-methylpyrazine, while naringin at the same level had little effect. They
also found that ethyl benzoate had little interaction with either polyphenol. One
of the most valuable findings of this work was the agreement between the analytical
and sensory data showing the effect of gallic acid and naringine interactions with
2-methylpyrazine.
8F.2.2.3 Polysaccharides and Proteins
Wine polysaccharides, ranging from 500 to 1500 mg/L (Will and Dietrich 1990),
mainly come from grape primary cell walls, and from autolysis of micro-organisms