Separation of polyphenolic compounds from Citrus aurantium L. peel by deep eutectic solvents and their recovery using a new DES-based aqueous two-phase system

Abstract

This study aims to investigate the extraction of polyphenolic compounds (PCs) from Citrus aurantium L. peel using Deep Eutectic Solvents (DESs) and ultrasound-assisted extraction (UAE). A screening process evaluated various DESs based on Choline Chloride (ChCl) with polyol, acids, and amides. ChCl-1,4-butanediol performs highest among the tested DESs and the benchmark solvent (70 % ethanol and water). The extraction efficiency, measured by total phenolic content (TPC) using the Folin − Ciocalteu method, was influenced by temperature, time, liquid-to-solid ratio, and water content. Optimal conditions were found at a temperature of 40 °C, extraction time of 30 min, water content of 49.95 %, and 18.97:1 solvent to biomass ratio with a yield of 7.85 mg gallic acid equivalent per gram of peel.Under these conditions, we employed an Aqueous Two-Phase System (ATPS) consisting of salt and DES to recover polyphenols from DES extracts. Various salts (K2HPO4, K3PO4, Na2SO4, LiCL, BaCl2, Na3cit, and NaCl) were assessed for their potential to form the ATPS. Among them, only K2HPO4, and K3PO4 demonstrated the ability to induce phase separation. The effect of the salt concentration was carefully investigated on the partitioning of the PCs. K3PO4 demonstrated a higher performance compared to K2HPO4 with an extraction efficiency of 88.54 %. An ATPS containing DES (0.67 % w/w) and K3PO4 (0.32 % w/w) proved advantageous for back-extraction. Water-immiscible organic solvents, including n-hexane, ethyl acetate, n-butanol, and isoamyl alcohol, were assessed as back-extraction agents. Notably, n-butanol achieved an impressive polyphenol recovery efficiency of 98.11 %.