INTEGRATED BIOREFINERY VALORIZATION OF GRAPE POMACE VIA GRADIENT SUBCRITICAL WATER–DES EXTRACTION

The sustainable valorisation of agro-industrial residues is a key objective in green chemistry and circular bioeconomy strategies. This work investigates a semi-continuous gradient subcritical water extraction assisted by deep eutectic solvents (SWH/DES) for the biorefinery valorisation of Vitis vinifera grape pomace. Six deep eutectic solvents composed of choline chloride combined with different hydrogen-bond donors (glycerol, ethylene glycol, malic acid, tartaric acid, lactic acid, and oxalic acid) were evaluated under subcritical conditions (150 °C, 200 bar). The lactic acid–based DES yielded the highest recovery of total phenolics (~275 mg GAE g⁻¹), flavonoids (~170 mg CE g⁻¹), and antioxidant activity (~1600 µmol TEAC g⁻¹, FRAP). In contrast, the malic acid DES maximized sugar extraction (~740 mg g⁻¹), while the tartaric acid DES enhanced protein recovery (~40 mg g⁻¹). The ethylene glycol DES favoured anthocyanin extraction (~2.6 mg C3G g⁻¹). Compared with conventional subcritical water extraction, the combined SWH/DES approach increased the recovery of bioactive compounds by up to fourfold. Additionally, the resulting extracts demonstrated antimicrobial activity against Escherichia coli and Salmonella typhimurium. A sustainability assessment confirmed the strong alignment of this approach with green chemistry principles, highlighting reduced reliance on conventional organic solvents and improved resource efficiency. Overall, the proposed SWH/DES strategy demonstrates significant potential as an environmentally responsible method for the integrated recovery of value-added compounds from winery residues within a biorefinery framework. This work was supported by FAPESP through grants 2021/04096-9 and 2024/04678-6 (L.E.N.C.), 2024/06628-6 (V.C.F) and 2018/14938-4 and 2024/10205-3 (T.F.C.).