Ultrasound assisted extraction of phenolic compounds from Tunceli walnut varieties using deep eutectic solvents

This study aimed to improve a green way to enhance extraction of bioactive compounds from walnut, and to evaluate the effect of altitude on walnut bioactive content. Total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity were evaluated as bioactive compounds of walnut. In comparison with conventional solvents (water, ethanol and methanol), three DESs (Deep eutectic solvents) were formed from choline chloride, zinc chloride, and sorbitol as HBA and ethylene glycerol as HBD. The DESs (DES-1 and DES-2) generated from choline chloride and zinc chloride exhibited better extraction efficiencies for any bioactive compound than that of conventional solvents. Especially, the DES formed from the choline chloride: ethylene glycerol demonstrated the highest extraction efficiency. However, sugar-based DES showed the worst extraction efficiency. The altitude significantly affected extracted bioactive contents from walnuts (Hozat 1000m, Ovacik 1300m and Nazimiye 1550m). Walnut’s extracted bioactive content ordinarily decreased as the altitude increased, regardless of solvent type used in extraction. The result is a light to enhancing knowledge as to DES usage and its extraction efficiency of bioactive compounds for food applications. In addition, it gives better understanding of altitude effect on the content of bioactive compounds in walnuts.