Comparison of nonproductive adsorption of cellulase onto lignin isolated from pretreated lignocellulose

Abstract

Lignin, as a main factor inhibiting the enzymatic hydrolysis of lignocellulose, was investigated by comparing lignin isolated from untreated and pretreated lignocellulose to elucidate the differences in the enzyme adsorption ability. The nonproductive adsorption of cellulase on lignin was investigated by using a quartz crystal microbalance with dissipation. The results indicated that more cellulase adsorbed on the lignin isolated from autohydrolysis and green liquor-pretreated lignocellulose than on protolignin. Higher temperature and enzyme concentration increased the initial adsorption rate and the amount of enzyme adsorbed on lignin. A dynamic equation for enzyme adsorption on lignin was established. The adsorption of enzymes on lignin increased as the content of phenolic hydroxyl groups, and β-β and β-5 linkages in the lignin increased, attributed to enhanced hydrogen bonding and hydrophobic interaction. Consequently, inhibition of the enzymatic hydrolysis of cellulose was promoted by a higher phenolic hydroxyl group, β-β, and β-5 content. The adsorption of the enzyme components on lignin followed the order: β-glucosidase > xylanase > endo-glucanase > cellobiohydrolase, as revealed by polyacrylamide gel electrophoresis analysis. Electrostatic interaction increased the adsorption of β-glucosidase and xylanase on lignin, while synergistic hydrophobic interaction and hydrogen bonding increased the adsorption of endo-glucanase and cellobiohydrolase on lignin. The results indicate that the adsorption of enzymes on lignin is affected by the structure of lignin and the composition of the enzymes. The findings of the current study provide fundamental knowledge for improving the enzymatic conversion of lignocellulose.