Extraction of phenolic compounds from hazelnut shells by green processes.

Abstract

The nut industries generate a high amount of by-products that can be valorized as feedstocks for new processes using green technologies. Hazelnut shells have potential as source of antioxidant compounds with commercial interest in cosmetic, pharmaceutical and food industries. Antioxidants from hazelnut shells can be solubilized in autohydrolysis processes and recovered using resins. The autohydrolysis study led to achieve the highest solid solubilization of 26.7 g of non-volatile compounds (NVC)/100 g of hazelnut shells at 220 °C. Higher temperatures improved the release of phenolic compounds in the aqueous phase up to 3.37 g of gallic acid equivalents (GAE)/100 g of hazelnut shells. The DPPH free radical scavenging capacity allowed to determine the potential activity of the extracted phenolic compounds, and increasing temperatures improved the antioxidant capacity of extracts up to 1.64 g GAE/100 g of NVC in the range 210–230 °C. The phenolic compounds in aqueous phase after autohydrolysis were recovered by adsorption, and the sorption kinetics and the equilibrium isotherms were evaluated. The maximum sorption capacities of assayed resins were 8.9 and 7.7 mg GAE/g resin for Amberlite XAD4 and XAD16HP, respectively. The knowledge provided for this study should be helpful to further exploit and apply phenolic compounds from hazelnut shells as source of natural antioxidant compounds.