Green extraction of phenolic compounds from grape pomace by deep eutectic solvent extraction: physicochemical properties, antioxidant capacity

Herein, new function-oriented deep eutectic solvents (DESs) with on l-proline or betaine and DL-lactic acid were designed extraction of polyphenol compounds from grape pomace. The formations of new hydrogen between the two components of DESs were evidenced by FTIR and H-1 NMR spectra. Physicochemical characteristics of deep eutectic solvents under the effect of water on density, viscosity, electrical resistance have been revealed. The betaine-based DES could changes the electrical resistance depending on the concentration of water. The feasibility of using ultrasound-assisted extraction of phytochemicals combined with betaine-based and proline-based DES as a green chemistry technique to improve extraction of green (polyphenols) compounds from grape pomace was evaluated. Grape pomace extracts were analyzed by LC-DAD-MS to identify extracted compounds and analyze the impact of type DES on compound chemical profile. LC results indicated that ultrasound-assisted extraction of phytochemicals using betaine-based and proline-based deep eutectic solvent application allowed enhanced hydroxycinnamic acids extraction, while the use of proline-based DES resulted in a more diverse compound profile. The highest recovery efficiencies were recorded with DESs giving the highest total phenolic content (80-92 mg EGE//g d.w), total flavonoid content (47-51 QUE/g d.w), antiradical activity (80% at 100 mg/ml) and reducing power (310-468 mg ASE/g extract). Scanning electron microscope (SEM) results further verified DESs intensified the destruction of cell wall structure, and thereby allowed greater release of polyphenolic from grape pomace.