Chemical and colorimetric study of the influence of grape soluble polysaccharides on the color and stability of malvidin 3-O-glucoside solutions

Red wine color is mainly due to anthocyanins' flavylium cation. In wine, these pigments are involved in a pH-dependent equilibrium involving other forms, both colored and non-colored. This equilibrium is affected by the presence of other phenolic compounds, the so-called copigments. Moreover, other non-phenolic compounds that can be found in wine, such as polysaccharides, can also affect wine color. In this work, molecular dynamics simulations, tristimulus colorimetry and HPLC-DAD analyses have been performed to assess the effect of soluble polysaccharides (P) on the color and stability of malvidin 3-O-glucoside (Mv) solutions at different pH values, both in presence and absence of other compounds that can establish copigmentation interactions with the pigment. Results showed that P shifts the color of flavylium solutions towards a more intense color with bluer hues, which can be related to a stabilization of the blue quinoidal forms of anthocyanins. This effect is similar to that observed for quercetin 3-beta-glucopyranoside (QG), although, in the case of P, it seems to be more relevant. This behavior could be due to the presence of hydrophobic regions in P that allows the interaction with the quinoidal forms, which in the case of the polysaccharide might be related to the type I rhamnogalacturonans.