Natural deep eutectic solvent-based ultrasonic-assisted extraction of Euphorbia hirta L.: Total flavonoid content, total phenolic content, and antioxidant activity

Euphorbia hirta L. was identified as containing secondary metabolite compounds like terpenoid, coumarin, lignin, flavonoids, and phenolic compounds. The plant also has pharmacological activity as an antioxidant, antiinflammatory, and antibacterial. In this study, extraction is using natural deep eutectic solvent (NADES). NADES can be tailored concerning polarity, so this solvent is selective to extract secondary metabolite compounds. Ultrasound-assisted extraction (UAE) is often combined with extraction using NADES. This study aims to obtain the best NADES composition to extracting flavonoid and phenolic compounds as well as those with the strongest antioxidant activity and found out the correlation between TFC and TPC values with IC50 in extracts. The NADES was prepared with heating and stirring methods. The NADES was used is choline chloride : citric acid (ChCa), choline chloride: maleic acid (ChMla), choline chloride : malic acid (ChMa), choline chloride : lactic acid (ChLa), and choline chloride : oxalic acid (ChOa). NADES ChMla is the best composition for extracting flavonoid and phenolic compounds. The TFC and TPC values of ChMla extract were 9.613±0.0258 mg QE/g DW and 125.105±0.9674 mg GAE/g DW. Extracts from NADES ChMla also have the strongest antioxidant activity with an IC50 value of 30,438 mL/L. There is a strong correlation between the total flavonoid content with IC50 values, as well as a very strong correlation between the total phenolic content and the IC50 value.