Valorization of post-distillation wine lees using Natural Deep Eutectic Solvents: extraction and characterization of yeast glycoproteins and polysaccharides for potential food applications.

The wine industry produces several by-products, the main ones being grape pomace, grape stalks and wine lees. Among these, wine lees are the ones that have received the least attention for their valorization, making them the most undervalued by-product of the wine industry. Wine lees are a sludge-like material composed mainly of dead and living yeast cells, as well as other insoluble particles, which precipitate at the bottom of the wine tanks after alcoholic fermentation during wine production process. According to Council Regulation (EC) No. 479/2008 wine lees must undergo a distillation process to produce ethanol, which can be further used to produce spirit liquors. The remaining by-product of this process, known as distilled lees or vinasses, contains several high-value extractable compounds such as polyphenols, tartrates, and yeast biomass. Despite this, vinasses are largely underutilized, and they are typically disposed of, representing both an economic burden for wineries and an environmental issue due to their high oxygen demand. The main aim of this thesis is to enhance the value of distilled wine lees. Specifically, it focuses on the extraction and characterization of mannoproteins-rich extracts by treating post-distilled wine lees in autoclave and using 3 different Natural Deep Eutectic Solvents (NADES) prepared with Betaine and respectively Malic Acid, Citric Acid and Lactic Acid. A fourth autoclave extraction, conducted using pH 3.4 McLlvaine buffer, was taken as control. After the extraction process, both protein and polysaccharides concentrations of the extracts were determined using SEC-HPLC (Size Exclusion Chromatography – High Performance Liquid Chromatography). Furthermore the extraction yield and solubility of each extract were determined. The foaming and emulsifying properties of the four extracts were then determined at a pH level of 3.4. Foaming activity was assessed at a concentration of 1mg/mL using sonication (45% amplitude, 5 seconds) to induce the foam. Foam height was then measured periodically, first every minute for the first 10 minutes, then every 5 minutes. Emulsifying activity was assessed in a model system containing corn oil and pH 3.4 Mclvaine buffer containing 10 mg/ml of freeze-dried extract. Overall, the extracts demonstrated effective functional properties, confirming their potential for use in food and beverages.