Optimization of Solvent Concentration in Phenolic Compound Extraction from Inula helenium L. Leaves Using D-Optimal Mixture Design

nula helenium L. (Elecampane) leaves are an underutilized source of natural antioxidants due to their rich phenolic content. Although most studies have investigated roots or other aerial parts, limited information is available on phenolic extraction from I. helenium leaves. This study aimed to optimize the solvent concentrations for phenolic compound extraction from I. helenium leaves using D-Optimal Mixture Design and to evaluate the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities of the extracts. Various solvent mixtures (ethanol, methanol, and water) were tested, and the optimal composition was determined as 42.40% ethanol, 0.00% methanol, and 57.60% water. Under these conditions, TPC and TFC were found to be 28.12 mg gallic acid equivalent (GAE)/g dry sample and 27.74 mg quercetin equivalent (QE)/g dry sample, respectively. Antioxidant activities measured by ABTS, DPPH, and FRAP assays were 19.73, 1.42, and 6.10 mg Trolox equivalent (TE)/g dry sample, respectively. These results indicate that I. helenium leaf extracts, with high phenolic content and potent antioxidant activity, represent a promising natural antioxidant source, particularly for applications in the food industry.