Edible Natural Deep Eutectic Solvents (NADESs)-Based Polyphenolic Extracts: An Eco-Sustainable Alternative for Grape Pomace Valorization

Reusing waste materials is a sustainable practice to reduce the impact of human activities on the global ecosystem. In particular, agro-industrial waste can be explored as an innovative and green source of beneficial bioactive compounds. For this purpose, seventeen different varieties of wine grape pomace were collected from the Apulia region (Italy) to perform extractions and qualitative–quantitative phenolic profile characterization. To ensure an environmentally friendly extraction process, natural deep eutectic solvents (NADESs) were used as privileged media. After an initial screening, Merlot (MEA) and Sangiovese (SGA) varieties were then selected for extraction with betaine/lactic acid 1:4 (mol/mol) +40% water (w/w) and choline chloride/ascorbic acid 2:1 (mol/mol) +40% water (w/w). They were further investigated by LC-QTOF-MS for a comprehensive metabolomic evaluation. Betaine-based extracts from both cultivars exhibited higher polyphenol contents than choline chloride-based ones: 175.0 and 161.8 mg/kg compared to 59.6 and 40.4 mg/kg. Qualitative antimicrobial assays confirmed the effectiveness of betaine/lactic acid (MEA) and choline chloride/ascorbic acid (SGA) extracts on B. allii and E. coli, respectively, as well as the NADES themselves, even though it is difficult to discriminate the individual effects. Finally, the evaluation of both antioxidant activity and total polyphenol content led to good results for betaine/lactic acid (2.8 and 3.2 mg TEAC/g DW and 0.92 and 0.93 mg GAE/g DW for SGA and MEA, respectively), while the content of ascorbic acid, used as a component of NADES, substantially influenced the relevant obtained results in choline chloride/ascorbic acid samples. These findings support the potential of combining NADES with polyphenols recovered from grape pomace as a promising approach for further optimization and application-oriented investigation.