Green Extraction of Antioxidants from Hazelnut By-products Using Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, and Pressurized Liquid Extraction

This study investigates the green extraction of antioxidants from hazelnut by-products (specifically hazelnut meal and skin) using microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and pressurized liquid extraction (PLE). The process optimization was conducted via response surface methodology (RSM), with key operational parameters of each process. The extracts were characterized for their total antioxidant capacity (TAC), free radical scavenging capacity (FRC), ABTS radical scavenging capacity (ARC), and total phenolic content (TPC) using spectrophotometric assays. Among the methods, UAE was most effective for hazelnut meal, achieving a TAC of 53.1 µmol trolox (TR)/g, while MAE excelled for hazelnut skin with a TAC of 3.12 mmol TR/g. Phenolic profiling by HPLC–PDA revealed catechin, gallic acid, and protocatechuic acid as predominant compounds. These three extraction processes were evaluated using AGREE-Analytical greenness metric software. These findings demonstrate the potential of hazelnut by-products as sustainable sources of natural antioxidants, with implications for food, nutraceutical, and cosmetic applications. The research underscores the role of advanced extraction technologies in valorizing agricultural waste and contributes to a circular economy.