Extraction and Functional Characterization of Low and High Molecular Weight Fractions from Post-Distillation Wine Lees using Natural Deep Eutectic Solvents

The wine industry generates large amounts of by-products, among which wine lees remain largely underutilized despite containing yeast biomass and valuable compounds. Post-distillation wine lees still contain proteins, peptides, and other low-molecular-weight compounds after ethanol recovery, making their further valorization of interest from both environmental and economic perspectives. This thesis is part of a broader research project focused on the valorization of post-distillation wine lees using Natural Deep Eutectic Solvents (NADES). Building on extraction systems identified in previous studies, this work focused on the characterization of the recovered high- and low-molecular-weight fractions, with particular attention to peptide content and antioxidant properties of the low-molecular-weight material. Extractions were performed using three acidic betaine-based NADES containing citric, malic, or lactic acid, and were compared with McIlvaine buffer at pH 3.4. High-molecular-weight fractions were characterized for extraction yield, protein content, and polysaccharide profile, while low-molecular-weight fractions were evaluated for peptide content using the Pierce Colorimetric Peptide Assay and RP-HPLC. Antioxidant activity was assessed by DPPH radical scavenging, TPTZ-adapted ferrous ion chelating activity, and catechin oxidation. The extraction solvent affected both the amount and composition of the recovered material. RP-HPLC showed clear differences in peptide concentration among the low-molecular-weight fractions, whereas the Pierce assay appeared to overestimate peptide content. Fractions with higher peptide concentrations generally showed higher DPPH radical-scavenging activity, but the same trend was not observed for ferrous ion chelating activity. Antioxidant activity generally decreased after ultrafiltration. Complementary results from a parallel malolactic fermentation study also showed different effects of the recovered fractions on Oenococcus oeni growth and malic acid consumption, depending on fraction type, solvent, and concentration. Overall, this study contributes to the characterization of fractions recovered from post-distillation wine lees using NADES and shows that different extraction solvents produce materials with distinct compositional and functional properties. These results support the further investigation of post-distillation wine lees for sustainable valorization and potential food and oenological applications.