Desorption of phenolic compounds bound to lees by combining hydrolytic enzymes and ultrasounds

Abstract

The final concentration of phenolic compounds in the wines is usually lower than what might be expected given the phenolic concentration measured in grapes. One possible cause of this low concentration is the interactions between the suspended mesocarp and skin cell walls and phenolic compounds during the maceration process of red wine [1]. Most of these aggregates that are formed by these interactions are insoluble and end up precipitating forming, together with the yeast cell walls, the lees. Maceration enzymes have the ability to degrade the polysaccharides that represent the major components of the cell wall, which it is why these enzymes could lead to the release of phenolic compounds previously absorbed by the cell walls. Ultrasound (US) has been used in oenology as a technology to break cell structures through cavitation and facilitates the release of compounds of interest from the cell interior [2,3], and, precisely because of this capacity, US could also promote the desorption of phenolic compounds precipitated with lees.The objective of this work is to determine the capacity of two different techniques, the use of enzymes and/or the application of high power ultrasounds (US) to release those anthocyanins and tannins adsorbed in the lees. Both techniques seek the degradation (enzymes) or disruption (US) of the structures of the cell walls, to facilitate the desorption of the phenolic compounds.The lees from a red wine vinification were recovered, dissolved in a model ethanolic solution and treated, at laboratory scale, with enzymes and/or ultrasounds. Three different commercial enzymes were used: two different pectolytic enzymes and glucanase. The best sonication conditions were previously tested in order to find the optimal treatment conditions. The chromatic characteristics of the model solution and anthocyanins and tannins recovery were analyzed after the treatments. Anthocyanins and tannins were quantified and characterized by liquid chromatography. In addition, the soluble polysaccharides and tannins extracted from the lees after the treatments were analyzed by size exclusion chromatography.The results of this study could be of interest for the valorization of the lees, as a winery byproduct, by recovering the adsorbed compounds but also we add light into possible enological procedures for facilitating and accelerating the aging on lees, through the liberation, first of all, of polysaccharides from the lees but also those phenolic compounds lost during vinification.