Systematic study on date palm seeds (Phoenix dactylifera L.) extraction optimisation using natural deep eutectic solvents and ultrasound technique

Natural deep eutectic solvents (NADES) are emerging, environment-friendly solvents that have garnered attention for their application in extracting phenolic compounds. This study investigated the effects of four synthetic NADES on polyphenols extracted from date seeds (DS) using choline chloride (ChCl) as a hydrogen-bond acceptor and lactic acid (La), citric acid (Citri), glycerol (Gly), and fructose (Fruc) as hydrogen-bond donors, in comparison with DS extracts extracted by conventional solvents (water, 70% methanol, and 70% ethanol). The antioxidant activity (DPPH), total phenolic content (TPC) and 6 phenolic compounds were determined using HPLC. The results showed that the ChCl-La and ChCl-Citri systems exhibited a high extraction efficiency regarding TPC, and DPPH in the DS extracts extracted by NADES compare to those DS extracts extracted with conventional solvents (p < 0.001). HPLC results demonstrated that DS extracted by ChCl-La contained all measured phenolic compounds. Also gallic acid and catechin were the major compounds identified in the DS extracts. In addition DS extracted by ChCl-Citri and ChCl-Gly had the highest concentration of catechin. In conclusion, combining NADES is a promising and environment-friendly alternative to the conventional solvent extraction of phenolic compounds from DS.