2 step hydrolytic conversion of orange processing waste into C5-C6 sugars: the “Hemicellulose Ahead” protocol

Practically viable chemical valorization of lignocellulosic biomass requires innovative and selective fractionation strategies. In this study, we present the “Hemicellulose Ahead” protocol: a novel two-step hydrolysis approach for converting industrial orange processing waste into valuable sugars. This strategy targets a first recovery of C5–C6 sugars from hemicellulose via acid hydrolysis with dilute formic acid, followed by glucose recovery from cellulose using dilute hydrochloric acid. The process is carried out in one pot under relatively mild conditions (100 °C, atmospheric pressure). Prior to hydrolysis, orange processing waste needs to be washed with pressurized 50:50 (wt:wt) ethanol:water mixture to remove free sugars, flavonoids and processing residues, which proved essential to prevent the formation of degradation products during the initial hemicellulose conversion. The sequential process was successfully scaled from 100 mL to 500 mL and 5 L batch reactors, with only minor variations in sugar yields across the different scales. The process provides a cost-effective pathway for valorizing citrus processing waste into C5 and C6 sugars. At the same time, the solid residue, rich in pectin, can be utilized for the recovery of this latter polysaccharide.