Fenton Reaction-Oxidized Bamboo Lignin Surface and Structural Modification to Reduce Nonproductive Cellulase Binding and Improve Enzyme Digestion of Cellulose

Abstract

Nonproductive adsorption of cellulase on lignin was a major inhibitory mechanism reducing the enzymatic saccharification efficiency of lignocellulosic material. The surface and structural properties of Fenton reaction-oxidized lignins (FRLs) and their effects on the nonproductive binding of enzymes to lignin and enzymatic saccharification of Avicel were examined. The Fenton chemistry pretreatment not only decreased the ratio of syringyl to guaiacyl units and the phenolic OH group content in lignin preparations but increased the carboxylic content and the negative zeta potential of lignin, all of which could be responsible for reducing the unproductive adsorption of cellulase on lignin. And Langmuir adsorption isotherms also proved that FRLs were provided with a lower binding ability to the cellulase enzyme when compared with untreated milled bamboo lignin (MBL). Finally, when the nonproductive binding of cellulase to FRLs was reduced significantly, the 72 h glucose yields of Avicel with 3-FRL and 5-FRL were 60.64% and 65.96%, respectively, which were 6.3–15.6% higher than that of Avicel alone, 57.06%. The results can also help to optimize the existing pretreatment technologies and develop new pretreatment methods that could produce less inhibitory lignin.