EFFECT OF MANNOPROTEIN-RICH EXTRACTS FROM WINE LEES ON PHENOLICCOMPOSITION AND COLOUR OF RED WINE

Abstract

In 2022, wine production was estimated at around 260 million hl. This high production rate implies to generate a large amount of by-products, which include grape pomace, grape stalks and wine lees. It is estimated that processing 100 tons of grapes leads to ~ 22 tons of by-products from which ~ 6 tons are lees [1]. Wine lees are a sludge-looking material mostly made of dead and living yeast cells, yeast debris and other particles that precipitate at the bottom of wine tanks after alcoholic fermentation. Unlike grape pomace or grape stalks, few strategies have been proposed for the recovery and valorisation of wine less [2]. Nevertheless, this by-product could become a source of interesting compounds, such as mannoprotein rich extracts (MRE). Therefore, the aim of this work was to obtain MRE from different lees, to characterize them, and to evaluate their effect on wine colour and on the phenolic composition of red wines.

Red, rosé and white wines were used as sources of lees, which were collected after the alcoholic fermentation with different Saccharomyces cerevisiae commercial varieties. The extraction of MRE was performed by physical extraction (autoclave) followed by a purification with ethanol. The protein and polysaccharidic moieties of the purified extracts were characterized by SDS-PAGE, Lowry method, HR-SEC-RID and HPLC-DAD-MS. The obtained MRE were added to a red wine (Vitis vinifera L. cv Tempranillo) and the changes in the phenolic composition and colour were analysed by HPLC-DAD-MS and triestimulus colorimetry, respectively, before and after the stabilization of the wine (involving cold treatment). Results obtained showed that the extraction yield of MRE was efficient (~ 40 mg/g wet lees) for all types of lees assayed, which supports the valorisation of wine lees as a sustainable source of MRE. Interestingly, MRE presented important structural and compositional differences, both in the protein content and in the polysaccharidic profile, although the source of lees, namely red, white and rosé wines, was not the main factor determining these differences, but the winemaking techniques or the S. cerevisiae strain employed. Furthermore, the addition of the MRE to red wine had an effect on the stabilization of wine colour and its phenolic content that rely mainly on the saccharidic characteristics of each MRE. These results pointed out that MRE from wine less could be a potential tool to improve the colloidal stability of wine phenolic compounds.