A principal component analysis‐supported optimization study for green extraction of phenolic and flavonoid compounds from <i>Urtica dioica</i> leaves using deep eutectic solvents

Abstract In this study, a green extraction strategy was developed for the recovery of antioxidant phenolics and flavonoids from Urtica dioica leaves using deep eutectic solvents (DESs). Seven DESs consisting of lactic acid (La) and ethylene glycol (Eg) at different molar ratios (1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1) were prepared and screened based on the total phenolic content (TPC) and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging activity. Principal component analysis (PCA) identified La:Eg (1:4) as the best‐performing DES. The homogenizer‐assisted extraction process using La:Eg (1:4) was subsequently optimized using a Box–Behnken design with four variables (solid mass, water content, homogenization speed, and extraction time). Bioactivity was evaluated using TPC, total flavonoid content (TFC), and antioxidant activity determined by DPPH and 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) assays. In addition to modeling and experimental validation, PCA was applied to evaluate the relationships between the optimized extraction conditions and bioactivity indicators, including TPC, TFC, DPPH, and ABTS.