Técnicas bioquímicas y físicas para limitar la interacción o promover la desorción de polifenoles ligados a las paredes celulares de la uva

Abstract

The phenolic composition of red wines is one of the principal factors of their quality. Compared to its concentration in grapes, the concentration of phenolic compounds in wines is low. Among other causes, this low transfer is due to the adsorption of part of these phenolic compounds by the cell walls of the pulp and skin, which, at the beginning of the vinification, are in large quantities, suspended in the must. Therefore, an effective extraction of phenolic compounds will depend on the ability to limit these adsorptions or to release the adsorbed compounds. For all these reasons, the overall objective of this thesis is to study the application of biochemical and physical techniques (addition of enzymes, addition of soluble polysaccharides and high power ultrasound) to limit the interactions of tannins and anthocyanins with the cell walls present in the freshly crushed must or promote their desorption when the bindings have already taken place. Each of these techniques was initially tested in wine model solution, with the aim of selecting the best working conditions and the most effective techniques that could later be applied in real vinifications. In this way, we conducted the following tests in model solution: - Studies of adsorption and desorption of skin and seed tannins with cell walls of Monastrell and Syrah grape skins in the presence of enzymes that degrade the plant cell wall. - Study of the reactivity of tannins and cell walls in the presence of soluble polysaccharides (mannan and pectin with a high degree of esterification). - Studies of desorption of anthocyanins and tannins from freeze-dried lees from a red vinification with the application of ultrasound and enzymes (pectin lyase and β-glucanase). In the same way, in real vinifications: - Vinifications in which enzymatic cockails with different predominant enzymatic activities were added. - Vinifications in which soluble polysaccharides were added before the maceration stage. - Vinifications in which US and enzymes were applied, alone or in combination at different times of the vinification period. The tannin composition of the wines and the assays in model solutions were analysed by phloroglucolysis (HPLC) and size exclusion chromatography (GPC), in addition to soluble polysaccharides by GPC and the chromatic and polyphenolic composition of the wines by spectrophotometry. The enzymes were able to reduce the interactions between cell walls and tannins, especially when these enzymes were used individually, pectin lyase being the enzyme that produced the largest degradation of the cell wall and the one that limited the most the adsorption of tannins. However, the enzymes were barely able to release tannins already bound to the cell walls. The combined use of an enzyme rich in pectin lyase activity and high-power ultrasound were able to both increase the extraction of phenolic compounds during the maceration of a red wine, and decrease the interactions between them and the cell walls in suspension during this stage. In addition, the use of this enzyme generated a large amount of lees and phenolic material attached to them, a phenomenon that unexpectedly had a positive effect on the chromatic and phenolic composition of the wine, since it favoured the generation of a more pronounced gradient of phenolics from the grape to the must/wine, thus increasing its extraction. On the other hand, the combination of enzymes (β-glucanase and pectin lyase) and ultrasound can release anthocyanins and tannins linked to plant and yeast cell walls present in red wine lees. The addition of soluble polysaccharides both in model solutions and in real vinifications achieved that more phenolic compounds remained in solution, therefore, they are capable of competing with cell walls by interacting with them. In conclusion, all the techniques used were able to limit the interactions between the phenolic compounds and the cell walls, however, all of them had to be applied with specifications to increase their effectiveness.