Effects of phosphoric acid/hydrogen peroxide, ammonia/hydrogen peroxide and deep eutectic solvent pretreatments on component separation and enzymatic saccharification of Glycyrrhiza residue

Glycyrrhiza glabra residue (GR), the fibrous industrial byproduct of glycyrrhizin extraction, and its conversion to sugars are of high potential value in biorefinery. To depolymerize GR and to separate its glucan, xylan and lignin components, three pretreatment agents were applied: PHP (phosphoric acid/hydrogen peroxide), AHP (ammonia/hydrogen peroxide) and DES (deep eutectic solvent). PHP removed the most lignin (81.7 %), while AHP recovered the most sugar (97.2 %). DES pretreatment gave a balanced 78.4 % lignin removal and 83.9 % sugar recovery. GR component separation for each pretreatment was verified by SEM, XRD, and FT-IR. Enzy-matic saccharification of DES pretreated GR gave a higher sugar yield than that from PHP or AHP pretreatment, explained by fractal-like kinetic analysis of the rate constant and fractal dimension parameters. Overall, sugar yield was dependent on a combination of component separation and substrate size distribution and morphology.