9D Influence of Phenolics on Wine Organoleptic Properties 557
(Cheynier et al. 2006). In conclusion, and attending to all the information available
concerning this matter, it is more prudentto accept that all the phenomena referred
above are involved altogether in the evolution of the mouth-feel sensation of wine
during aging.
At present the structures of the wine-derived-tannins are practically unknown and
a great part of the structures identified so far have been only demonstrated in wine
model studies. Hence, the influence, or contribution, of wine tannins to astringency
is far from being ascertained. For that reason, it is crucial to make efforts to clarify
those structures and the mechanisms involved in their formation. Moreover, the role
of oxygen is not fully understood and it is important to know how to deal with
it during winemaking to control oxidation, and therefore improve the wine taste
characteristics.
9D.3.6 Polysaccharides and Astringency
Research work performed in the end of the last century by Haslam and co-workers
showed that carbohydrates inhibit the protein-tannin interactions in solution (Luck
et al. 1994; Ozawa et al. 1987). More recently, similar findings have been reported
by de Freitas and co-workers using nephelometric techniques (Fig. 9D.12) for
different carbohydrates and protein-tannin systems (Carvalho et al. 2006a, b; de
Freitas et al. 2003; Mateus et al 2004a).
This inhibition of the interactions between tannins and salivary protein by carbo-
hydrates has been proposed to contribute to the loss of astringency during ripen-
ing of some fruits (Luck et al. 1994; Ozawa et al. 1987; Taira et al. 1997).
<BSA/tannin> <BSA/tannin/carbohydrate>Fig. 9D.12Flow nephelometric analysis of the inhibitory effect of gum arabic on aggregate forma-
tion between procyanidins (tetramers–digallate and pentamers–gallate, 0.034 g/L) and BSA (0.33
g/L) (adapted from Carvalho et al. 2006a)