Novel Green Extraction Technique Combining Subcritical Water Hydrolysis and Natural Deep Eutectic Solvents (SWH/NADES) for Recovering Anthocyanins from Grape Pomace (Vitis vinifera L.) within a Biorefinery Framework

Grape pomace, a winemaking byproduct, presents a sustainable source of bioactive compounds. This study introduces an innovative extraction technique combining subcritical water hydrolysis with natural deep eutectic solvents (SWH/NADES) to efficiently recover phenolic compounds. By applying this method within a biorefinery framework, the process aligns with green chemistry principles, adding value to agricultural waste. The study evaluated various NADES compositions coupled with a subcritical water system to enhance anthocyanin recovery from lyophilized grape pomace (GPL). Four NADES were synthesized by combining different hydrogen bond donors (lactic acid – “SWH 1,” tartaric acid – “SWH 2,” malic acid – “SWH 3,” and oxalic acid – “SWH 4”) with choline chloride, a hydrogen bond acceptor, under an inert atmosphere at 60 ºC for 4 h at 500 rpm. Diluted to 80:20 (v/v) with water, the NADES solutions were fed into the SWH reactor at a flow rate of 5 mL/min, with conditions set at 180 ºC and 200 bar for 40 min. Each NADES/SWH extraction was compared to subcritical water extraction alone (“SWH 5”) to determine NADES impact. Results indicated that NADES/SWH significantly increased anthocyanin concentration in extracts. The SWH 2 extract yielded approximately 12.52 ± 0.03 mg of C3G/g of GPL, compared to 3.15 ± 0.01 mg of C3G/g of GPL for SWH 5, representing a 4-fold increase. Other NADES/SWH extracts showed yield enhancements of at least 2.5-fold. In conclusion, combining subcritical water hydrolysis with NADES enhances anthocyanin recovery from grape pomace, outperforming traditional subcritical water extraction. This sustainable approach maximizes bioactive compound yield, contributing to high-value product development from agricultural residues within a green biorefinery framework.