Biorefinery Valorization of Grape Pomace via Gradient Subcritical Water–DES Extraction

This study reports a semicontinuous subcritical water extraction assisted by deep eutectic solvents (SWH/DES) for valorizing Vitis vinifera grape pomace. Six DES based on choline chloride with different hydrogen bond donors (glycerol, ethylene glycol, malic, tartaric, lactic, and oxalic acids) were evaluated at 150 °C and 200 bar. The lactic acid DES showed the highest recovery of total phenolics (∼275 mg GAE g–1), flavonoids (∼170 mg CE g–1), and antioxidant capacity (∼1600 µmol TEAC g–1 FRAP). Malic acid DES maximized sugar extraction (∼740 mg g–1), tartaric acid DES enhanced protein recovery (∼40 mg g–1), and ethylene glycol DES favored anthocyanin extraction (∼2.6 mg C3G g–1). Compared to conventional subcritical water, SWH/DES increased bioactive recovery up to fourfold. Extracts exhibited antimicrobial activity against E. coli and S. typhimurium. Sustainability assessment was performed using the Path2Green tool, yielding scores of 0.262 and 0.256, which confirm strong alignment with green chemistry and circular economy principles, demonstrating that SWH/DES is an efficient and sustainable extraction strategy.