Upcycling orange waste biomass into bio-aerogels

The orange juice industry produces large amounts of by-products. In this work, we demonstrate for the first time a strategy to upcycle orange juice side streams into high-added-value materials, bio-aerogels. Bulk biomass and its fractions (peels, bagasse and pulp) were first subjected to citric acid hydrolysis, a “green” water-based treatment. Processing parameters (washing with water, biomass fraction, and biomass and citric acid concentrations) were tuned to maximize suspensions’ kinetic stability and produce homogenous aerogels. Removing soluble sugars during biomass washing and increasing biomass and citric acid contents led to higher stability of the suspensions, bearing mainly soluble pectin as a continuous phase with dispersed swollen insoluble fraction. Suspensions’ rheological properties, insoluble fraction contents, and swelling capacities were evaluated. The prepared suspensions were subjected to non-solvent-induced phase separation and solvent exchange with ethanol, followed by drying with supercritical carbon dioxide. The obtained bio-aerogels possessed low densities (< 0.1 g/cm³) and high specific surface areas (190 - 235 m²/g). The insoluble swollen fibers were porous and embedded in an open-pore nanostructured network.