Optimization of antioxidant extraction from agro-industrial wastes using ultrasound & response surface methodology

Extracting antioxidants from agro-industrial residues represents a promising waste management strategy. This study assessed the total polyphenol content (TPC) and antioxidant activity (DPPH^• and ABTS^•+) of under-researched materials : hempseed hulls (HH), oat bran (OB), sea buckthorn pomace with (SBPS) and without seeds (SBPW), and sea buckthorn leaves (SBL) using conventional solvent extraction (CSE) and ultrasound-assisted extraction (UAE). The effects of different drying methods (freeze- and oven-drying) and solvents (70 % and 96 % ethanol, distilled water) were analyzed in CSE. In UAE, response surface methodology (RSM) was adopted to optimize extraction time (5–30 min), amplitude (20–50 %), and drying methods. Optimal UAE conditions were identified for each material, while the significance of individual parameters differed across samples. UAE consistently outperformed CSE, however the difference was only statistically significant for SBPW across all three analyses. Freeze-dried samples yielded higher results in both extraction techniques, while 70 % ethanol yielded highest results in CSE for all samples except SBPS, where 96 % ethanol performed most efficiently. Findings from this study underscore the importance of tailoring extraction process to the unique properties of each material. Obtained optimized extraction conditions are expected to enhance the value of these materials, contributie to their sustainable utilization and support circularity.