Factors affecting the hydrolytic action of xylanase during pennisetum saccharification: role of lignin

Inhibition of cellulose hydrolysis has been reported extensively, however, there is a paucity of information describing the effect of lignin on xylan hydrolysis by endo-xylanase and β-xylosidase. In this report, the effects of two different lignins on enzymatic hydrolysis of isolated xylan and NaOH-pretreated pennisetum by endo-xylanase and β-xylosidase were assessed. Both acid insoluble lignin (AIL) and enzymatic hydrolysis lignin (EHL) were found to inhibit hydrolysis of endo-xylanase and β-xylosidase, and AIL had a stronger negative effect on enzymatic hydrolysis when compared with that of EHL. Results from inhibitory kinetics experiments showed that the inhibition of AIL and EHL on xylanase did not follow Michaelis–Menten kinetics. The higher adsorption capacity of AIL toward xylanase arose from its higher hydrophobicity and lower absolute zeta potential, and this likely explains the higher inhibitory effect of AIL than that of EHL. The results aid our understanding of the role of lignin in xylan hydrolysis by xylanolytic enzymes.