Sequential extraction of antioxidants from paulownia petioles with sc-CO2 and with subcritical water and formulation of hydrogels with the residual solids

Abstract Attention must be paid to the valorization of forest residues to advance towards a circular economy maximizing the use of resources. Petioles of paulownia were subjected to sequential extraction using green technologies to obtain extracts with antioxidant properties. Firstly, supercritical CO2 extraction was performed for 90 min at 45 °C at different extraction pressures (20 and 30 MPa) and ethanol concentrations (0. 5 and 10%). Subsequently, the solid residue remaining after supercritical extraction was subjected to microwave heated autohydrolysis for 3 min at different temperatures in the range 120-220 °C. The combination of both extraction technologies led to an extraction yield of 39%, and generated extracts with 10 g gallic acid equivalents (GAE)/100 g extract, and antiradical capacity against the ABTS radical ranging between 30-50 g/100 g extract. The waste solids remaininig after conventional extraction and microwave heated autohydrolysis of paulownia petioles were used in different mass proportions (1-9%) for the preparation of hydrogels with potential application in personal care products. Starch based gelling matrices enriched with the selected residual solids exhibited strong viscoelastic properties.