550 C. Santos-Buelga and V. de Freitas
λ (nm)pH 1 and3500 nm400 450 500 550 600 650 700AbsorbancepH 4
pH 5Fig. 9D.10Absorption spectra in the visible region of a catechin-pyrylium derived pigment
derived from the reaction between catechin and sinapaldehyde as a function of pH
latter pigments show a -electron conjugation analogous to anthocyanins and have
similar absorption spectra with maximum absorptivity around 480–520 nm, although
their color is less influenced by pH than anthocyanins in the range of values exist-
ing in wines (Fig. 9D.10). Nonetheless, the levels of all these types of pigments
in red wines seem to be very low and their importance for color definition is
unknown. In the particular case of oaklins, some contribution to the color of red
wines aged in oak barrels might be expected but further studies are still required to
conclude about it.
9D.3 Astringency
9D.3.1 Astringency Perception
Phenolic compounds are a very complex group of natural compounds with large
structural diversity that contribute directly to the flavor, namely to the bitterness
and astringency perceived in a variety of food and beverages such as unripe fruits,
wines, teas and beers. While bitterness is a taste felt by specific receptors in the
tongue, astringency is usually defined as the array of tactile sensations felt around
the mouth transduced by the trigeminal nerve (Green 1993). Astringent primary
descriptors include dryness (lack of lubrication or moisture resulting in friction
between oral surfaces), roughness (harsh texture of the oral cavity marked by edges
and projections that are felt when oral surfaces contact with each other) and con-
striction (feeling of puckering and contraction felt in the mouth lips and cheeks)
(Clifford 1997; Lee and Lawless 1991; Gawel et al. 2001).
It is usual amongst experienced tasters to employ general and subjective terms
to define astringency or sub-qualities of astringency. To categorize the vocabulary,