Betaine-Based Deep Eutectic Solvents for Phenolic Compounds Extraction from Vine Shoots: Screening, Optimisation, and Cytotoxicity Assessment

To develop sustainable extraction of bioactive compounds, this study evaluated the potential of betaine-based deep eutectic solvents (DES). Betaine was applied as a natural, safe hydrogen-bond acceptor in fourteen DES, using polyols/sugars/acids as hydrogen-bond donors to extract vine shoots (VS) phenolic compounds. A conventional solvent, 59% (v/v) ethanol/water, was used for comparison. Among the tested DES, the extracts obtained with betaine:ethylene glycol:water (1:3:5) and betaine:sorbitol:water (3:1:10) demonstrated high extraction capacity. The betaine:ethylene glycol:water (1:3:5) DES yielded the extract with the most favourable biocompatibility profile and adequate stability at room temperature. The extraction of VS with this DES was optimised using response surface methodology, varying temperature, time, and solid load. It enabled an increase of both the total phenolic content (up to 2.35 mg GAE/mL) and the antioxidant activity (EC50 of 162.5 mg extract/mL) under 80 °C, 127 min, and L/S 10:1. Moreover, the DES extract was further profiled by HPLC-UV and HPLC-QTOF-MS, highlighting the occurrence of the high-demand antioxidant trans-resveratrol (16 µg/mL) and its dimer trans-ε-viniferin (31 µg/mL). To the best of our knowledge, this is the first study to evaluate betaine-based DES for VS extraction, along with its characterisation and cytotoxicity assessment, while discussing their limitations.