Ultrasound-Assisted Extraction of Apple Pomace: Statistical Optimization and Antioxidant Activity Evaluation

Apple pomace, produced by the apple processing industry, is a raw material rich in bioactive compounds with a broad spectrum of biological activity, yet it remains underutilized. Both the method of raw material stabilization and the extraction technique influence the quality of the final apple pomace extract. The aim of this study was to select the most effective stabilization method and to determine optimal conditions for ultrasound-assisted extraction (UAE) of total phenolic compounds (TPC) from apple pomace. The extraction process was optimized using mathematical methods of experimental design. Input parameters included extraction temperature and time, solvent composition (ethanol concentration), and the raw material-to-solvent mass ratio. Output variables included total phenolic content and antioxidant activity of the extracts. Total phenolic content was determined using the Folin-Ciocalteu method, and antioxidant activity was determined using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. The conditions enabling maximum extraction of phenolic compounds (total phenolic content: 8.207 mg GAE/mL and 88.09% DPPH inhibition) were achieved at 90 min, a temperature of 45 °C, an ethanol concentration of 50%, and a raw material-to-solvent ratio of 8 g.