Effects of Gleditsia saponin on high-solids enzymatic hydrolysis of furfural residues

•High-solids enzymatic hydrolysis of furfural residues (FRs) was investigated.•A maximum cellulose conversion of 74.88% was achieved with GS.•Carbonyl groups in the lignin facilitated easy binding of GS to the lignin surfaces.•GS could maintain the enzyme activity in the supernatants.

Surfactants are popular additives for the prevention of the inhibitory effect of lignin on cellulolytic enzymes. Saponin is a type of natural surfactant extracted from Gleditsia spp. In this study, the effect of saponin on the high-solids-loading enzymatic hydrolysis of furfural residues (FRs) with a lignin content of 45% was investigated. The optimal dosage of Gleditsia saponin (GS) was determined to be 25-fold greater than its critical micelle concentration (CMC; 0.16 g/L). The addition of GS increased the cellulose conversion by up to 52.63% in high-solids-loading enzymatic hydrolysis. Due to the addition of GS, a maximum cellulose conversion of 74.88% was achieved after FRs had hydrolyzed for 120 h at a solids loading of 20% (w/w) with 30 filter paper unit (FPU)/g-cellulose. The decrease in cellulose conversion was found to exhibit a linear correlation with an increase in the solids loadings from 20.0% to 27.5% (w/w). The surface structural variations of hydrolytic residues were characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the carbonyl groups of lignin facilitated the binding of GS to the surface of lignin, which resulted in a decrease in the adsorption of between the enzyme and lignin. Interestingly, GS could maintain enzymatic activity in the supernatants.