Combining Carboxylic-Acid-Based Deep Eutectic Solvents and High Temperatures Enhances Phenolic Acid Extraction from Grape Pomace

Phenolic acids are contained in grape pomace, mostly in a conjugate form, and can be a natural source of building blocks if they are efficiently hydrolyzed and extracted from the natural matrix. In this study, a comparative study based on the spectrophotometric evaluation of total phenolic content, hydroxycinnamic acid content, and anthocyanin content was performed on different carboxylic-acid-based NADES with different heating sources. Moreover, a quali-quantitative characterization of the bioactive molecules extracted was performed using UHPLC-ESI-HRMS. We found that the nature of the acidic component of the DES was crucial in selecting the family of molecules to be extracted; ChCl/oxalic acid 1:1 NADES, when combined with MAE at 100 °C, is the best medium for the in situ hydrolysis and extraction of phenolic acids from grape pomace. The ORAC test performed on natural extracts with and without NADES revealed a role for NADES components in antioxidant activity against the ROS of extracted bioactive phenols.