Study on differences in the enzyme hydrolysis induced from lignins from diverse types of lignocellulosic biomass

Abstract

ABSTRACT The content and composition of substrate lignin significantly impacted the enzymatic hydrolysis of the lignocellulosic biomass process, mainly manifested in steric hindrance and non-productive adsorption, which was considered one of the main obstacles affecting enzymatic hydrolysis. Because of the intricate lignin structure, the mechanism of its effect on enzyme hydrolysis was unclear. Hence, this study aimed to inquire into the effect of the lignin structural units on the enzymatic hydrolysis of lignocellulosic biomass. Lignins with different structural units were isolated from non-wood: reed, rice straw, and bamboo. Analyzed the structural differences of lignins using methods like GPC, FT-IR, and NBO. The results showed that bamboo lignins had a higher S/G ratio of 1.7: 1, which was different from reed and rice straw lignin of 0.9: 1. The surface morphology of lignin/cellulose composite films was characterized byAFM. QCM-D was used to monitor the hydrolysis process of lignin/cellulose composite films in situ and in real-time. Bamboo lignin composite film had the slowest enzymatic hydrolysis rate of 0.2 min−1, the longest time (23.6 min) to get the maximum enzymatic hydrolysis, and the lowest maximum hydrolysis frequency of 83.9 Hz. Structural analysis indicated the bamboo lignin had a higher yield of the content of syringyl unit, a higher degree of non-condensation, and contained more aryl ether bonds. Both enzymatic hydrolysis and QCM-D results showed that bamboo had the lowest enzymatic hydrolysis efficiency. This study focuses on how the structural differences of the three isolated lignins affect the enzymatic hydrolysis process. It suggests that the lignin with a higher S/G ratio inhibits the enzyme adsorption to cellulose present in composite and retard enzymatic hydrolysis process of cellulose more obviously.