Mannoproteins extraction from wine lees using natural deep eutectic solvents

Abstract

Wine lees can be a good source of yeast mannoproteins for both food and wine applications [1,2]. However, mannoprotein extraction from wine lees has not yet been scaled up to an industrial scale, mainly because of the limited cost-effectiveness ratio of the methods employed at the laboratory scale [2].

In order to improve solubilization of the cell wall components of wine lees taken before and after distillation, this study explores the potential of Natural Deep Eutectic Solvents (NADES) combined with autoclave treatment. Three food-grade NADES formulations [3,4] including citric acid/betaine (pH 1.42), tartaric acid/betaine (pH 1.13), urea/choline chloride (pH 9.65) were used. Firstly, the stability of the NADES was confirmed by comparing their physicochemical properties before and after the autoclave treatment, as indicated by FTIR analysis. However, urea/choline chloride showed changes in pH and water content, likely due to evaporation.

Then, 5 g of wine lees were suspended in 40 mL of the different NADES and subjected to the autoclave treatment (121°C, 20 min). Extracts were analyzed for their composition and tested as surfactants in model conditions at different pHs (3.4, 5.4, 7.0), comparing the results to those achieved by extracting the lees with the solvent employed in previous research (McIlvaine buffer at pH 3.4, MIB) [1,2,5]. The type of solvent strongly influenced the yield and composition of the extracts. Treatment with Citric acid/betaine resulted in the highest polysaccharide content (33.16 g/100g of lees) and cell wall destabilization (as assessed by microscopy), whereas urea/choline chloride maximized protein (6.63 g/100g of lees) and high molecular weight (> 250 kDa) mannoproteins extraction. When tested as emulsifiers in model systems, extracts exhibited distinct behaviors. At all pHs tested, the sample obtained using urea/choline chloride was the best, showing emulsifying activity (volume of the emulsion/total volume x 100) of 56–62% after 7 days. These emulsions also showed the highest viscosity (>900 Pa·s) and viscoelastic moduli. In terms of foaming properties, although MIB extracts performed significantly better, NADES-based extracts also produced foams with high stability (foam volume of 5.8 cm² lasting after 4 hours), particularly at pH 3.4, indicating the potential use of these extracts as foam enhancers in wines.

Results from this study, the first to combine NADES and autoclave treatment for the extraction of mannoproteins from wine lees, indicate that NADES can enhance the efficiency of mannoprotein extraction, paving the way for a scalable and sustainable valorization of wine lees, an underexploited by-product of the winemaking industry.