Applying Subcritical Water Extraction to Fractionate Grape Pomace into Functional Ingredients

Grape pomace (GP) is the main residue of the winemaking process; it is rich in phenolics with great bioactive potential. This study applied subcritical water extraction (SWE) to GP at 120, 140, and 160 °C to fractionate it into value-added products. The extraction performed at 120 °C and 1.3 bar (E-120) was the most efficient, resulting in the highest soluble fraction yield (61 g/100 g GP) with high phenolic content (4.1 g GAE (gallic acid equivalent)/100 g extract solids) and strong antioxidant capacity (EC50: 0.79 mg extract/mg DPPH (2,2-Diphenyl-1-picrylhydrazyl)), while it inhibited the growth of Listeria innocua at 325 mg/mL. The insoluble extraction residue (38 g/100 g GP) also retained substantial phenolic content (10 g GAE/100 g), with high antioxidant activity (EC50: 1.5 mg residue/mg DPPH) and a fibre-rich composition, supporting its value as a functional ingredient. To improve handling and stability, the E-120 extract was encapsulated in maltodextrin or pectin. For both polymers, a 40% polymer ratio with respect to the extract solids yielded a stable, single-phase, glassy powder (Tg ~50 °C), with thermal stability extending up to 200 °C. Therefore, SWE constitutes an efficient and sustainable technique for obtaining functional ingredients from GP, allowing for its valorisation.