Valorization of agro-food waste by converting it into a renewable resource plays a crucial role in a bio-based circular economy. Therefore, this study was designed to evaluate the suitability of distillery stillage (DS), which comes from alcohol production from cereals, for producing value-added products that can be used synergistically. The main objective was to investigate the usefulness of two substances for the recovery of phenolic acids, which have antioxidant activity, from the liquid fraction of DS: namely, tetrahydrofurfuryl alcohol (THFA) as a solvent and biochar as an adsorbent, both produced from the solid fraction of cereal processing waste. The effect of THFA concentration (80 and 100%) on phenolic acid yield in ultrasound-assisted extraction was studied. The solubilization predictions of phenolic compounds by the Hansen solubility parameters were in accordance with the experimental results: the yield of phenolic acids in the extracts was highest (3.76 μg g-1 dry mass) with 80% THFA. Among the extracted phenolic acids, hydroxycinnamic acids predominated over hydroxybenzoic acids, which may affect the bioactive properties of the extracts and their future applications for industrial purposes. Phenolic acids from the extracts were adsorbed on 17-170 g biochar L-1 and desorbed into water at 40-60 °C. The phenolic acid recovery was highest (∼92%) when the biochar dose was 85 g L-1 and when desorption was performed at 50 °C. After adsorption/desorption, ∼95% of the antioxidant activity of the phenolic acids in the extracts was maintained. As biochar has a smaller specific surface area than commercial powdered activated carbon (PAC), the biochar dose should be about 5 times higher than an equivalent PAC dose for adsorption efficiency above 90%.
Keywords: Biochar; Circular bioeconomy; Distillery stillage; Phenolic acids; Tetrahydrofurfuryl alcohol; Waste-to-profit.
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