Effect of different yeast mannoproteins on the interaction between wine flavanols and salivary proteins.

Unbalanced wine astringency, caused by a gap between phenolic and technological grape maturities, is one of the consequences of the global climate change in the vitiviniculture. To resolve it, potential strategies are being currently used, like the addition of commercial yeast mannoproteins (MPs) to wines. In this work, the main interactions responsible for the wine astringent sensation, namely, interactions between human salivary proteins and wine flavanols have been studied by Dynamic Light Scattering (DLS) and liquid chromatography coupled to DAD and MS detectors (HPLC-DAD-MS), in presence or absence of two MPs with different saccharide/protein ratio. The results indicate that there are differences on the substrate specificity for each mannoprotein and that its action mechanism could change not only depending on the mannoprotein composition but also on the flavanol structure. MPs with elevated carbohydrate content could act thought the stabilization of soluble aggregates with human salivary proteins and flavanols, mainly non-galloylated flavanol oligomers, whereas MPs with higher protein percentage mostly could precipitate flavanols (mainly non-galloylated ones with low degree of polymerization) which partially prevents the formation of insoluble flavanol-salivary protein aggregates.

Effect of the addition of mannoproteins on the interaction between wine flavonols and salivary proteins.

It has been suggested that the addition of flavonols (i.e. white grape skins) improves and stabilizes the color of red wines. However, it has been shown that flavonol glycosides produce a mouth-drying and mouth-coating sensation at very low threshold concentrations. Moreover, the addition of polysaccharides to wines is a practice addressed to improve the smoothness and roundness and correct excessive astringency, so we have studied the effect of the addition of yeast mannoproteins (MP) on the interaction between quercetin 3-glucoside and human salivary peptides. Sensory analysis showed the first evidence of the mannoprotein smoothing effect when the flavonol is added to wine. Additionally, MP/SP/polyphenol interactions were studied using fluorescence spectroscopy, dynamic light scattering and isothermal titration calorimetry. Results obtained indicate not only the existence of interactions between mannoproteins and flavonols but also between mannoproteins and salivary proteins (SP), suggesting a possible formation of protein/polyphenol/polysaccharide ternary complex.