Valorization of hazelnut shells into natural antioxidants by ultrasound-assisted extraction: Process optimization and phenolic composition identification

The objectives of this study were to optimize the ultrasound-assisted extraction for phenolic compounds from hazelnut shells and to quantify the individual phenolics. A central composite design was used to optimize extraction time, acetone concentration, and solid to liquid ratio (S/L), for the maximal yield of phenolic compounds and antioxidant capacities. The optimal conditions were 4.0 hr extraction time. 61% acetone, and 10 g/L S/L for the maximal total phenolic content (TPC, 11.23 mg gallic acid equivalents/g shell); 3.7 hr. 60.5% acetone, and 12.9 g/L for the highest ferric reducing antioxidant power (FRAP, 106.3 mu mol Trolox equivalents/g shell); and 4.7 hr, 58.3% acetone, and 10 g/L for the highest DPPH radical scavenging capacity (DRSC, 101.83 mu mol Trolox equivalents/g shell). Catechin, epicatechin gallate, and gallic acid were the most abundant phenolic compounds in the hazelnut shells. Ultrasound could be a good tool for accelerated recovery of polyphenols from hazelnut shells.