Mannoproteins extraction from Wine Lees Using Natural Deep Eutectic Solvents

Wine lees can be a good source of yeast mannoproteins for both food and wine applications. However, such extraction has not yet been scaled up to an industrial scale. One of the reasons limiting this valorisation is the limited cost-effectiveness offered by current physical and enzymatic extraction methods that only partially exploit the yeast biomass. In order to increase the solubilisation of the yeast cell wall, this study explores the potential of natural deep eutectic solvents (NADES) combined with autoclave extraction (121°C, 20 min) for extracting mannoproteins and other yeast polysaccharides from wine lees sampled before and after distillation. Three food grade NADES formulations with different acidity (citric acid/betaine, tartaric acid/betaine, urea/choline chloride) were used. Being the first extraction combining NADES and autoclave, the stability of the solvents during the treatment was studied by assessing their physicochemical properties before and after extraction. The obtained extracts were then characterized and tested as surfactants in model conditions at different pHs (3.4, 5.4, 7.0), and the results were compared to those achieved using pH 3.4 McIlvaine buffer, the solvent employed in previous research. The autoclave treatment did not significantly affect the physicochemical properties of NADES, except for urea/choline chloride, which showed changes in pH and water content, likely due to evaporation. FTIR analysis revealed that the wavenumbers of bond absorptions remained nearly unchanged thus indicating that NADES could be applied in these conditions. Conversely, the type of solvent strongly influenced the yield and composition of the obtained extracts. Treatment with Citric acid/betaine achieved the highest polysaccharide extraction (33.16 g/100g of lees) and cell wall destabilization, whereas using urea/choline chloride maximized protein extraction (6.63 g/100g of lees), yielding glycosylated proteins with high molecular weight (> 250 kDa) as shown by SDS-PAGE electrophoresis. Extracts exhibited distinct technological properties, with the ones obtained using urea/choline chloride performing better as emulsifiers, showing emulsifying activity of 56–62% after 7 days. These extracts, along with those obtained using citric acid/betaine, also produced emulsions with higher viscosity (>70 Pa·s) and viscoelastic moduli compared to those obtained using McIlvaine buffer’s extracts. NADES-based extracts also demonstrated good foaming properties (foam volume of 5.8 cm² lasting after 4 hours), particularly at wine pH (3.4). Nevertheless, McIlvaine buffer extracts performed significantly better in terms of foaming stability. Results from this study, the first to combine NADES and autoclave for such extraction, indicate NADES as sustainable and effective solvents for the complete exploitation of wine lees, paving the way for the green valorization of this underexploited by-product of the winemaking industry.