Advanced NADES-based extraction processes for the recovery of phenolic compounds from Hass avocado residues: A sustainable valorization strategy

Natural Deep Eutectic Solvents (NADES) are eco-friendly solvents with considerable potential for extracting bioactive compounds. In this study, we aimed to extract phenolic compounds from Hass avocado residues (epicarp and seed) using NADES in combination with ultrasound-assisted extraction (UAE) and pressurized liquid extraction (PLE) as advanced processes. Ten eutectic mixtures, consisting of choline chloride (ChCl) or betaine as hydrogen bond acceptors (HBA), as well as fructose (Fru), glucose, lactic acid (Lac), citric acid, or glycerol as hydrogen bond donors (HBD), were prepared through stirring and heating. The estimated values for total phenol content (TPC), proanthocyanidin content (PAC), monomeric anthocyanin content (MAC), and antioxidant capacity of the extracts demonstrated a noticeable influence of these solvents. The PLE process significantly enhanced the extraction of phenolic compounds from the epicarp, as evidenced by TPC (185 ± 9 mg gallic acid equivalent/g dry sample) and PAC (77.8 ± 6 mg proanthocyanidin B2/g dry sample) values. Phytochemical characterization conducted via HPLC-QTOF-MS/MS revealed the great extraction capacity of ChCl:Fru and ChCl:Lac, and the improvement of extraction efficiency through PLE. The results suggest that employing these innovative solvents along with advanced extraction processes, especially under high pressures, provides a sustainable approach to recover extracts with high content of phenolic compounds from Hass avocado agro-industrial waste, thus enabling their valorization.