Exploring why sodium lignosulfonate influenced enzymatic hydrolysis efficiency of cellulose from the perspective of substrate\u2013enzyme adsorption

Wenqiu Zheng,Hui Li,Guojun Yue,Tianqing Lan,Haifeng Zhou

doi:10.1186/s13068-020-1659-5

Abstract

BackgroundCellulase adsorbed on cellulose is productive and helpful to produce reducing sugars in enzymatic hydrolysis of lignocellulose; however, cellulase adsorbed on lignin is non-productive. Increasing productive adsorption of cellulase on cellulose would be beneficial in improving enzymatic hydrolysis. Adding lignin that was more hydrophilic in hydrolysis system could increase productive adsorption and promote hydrolysis. However, the effect mechanism is still worth exploring further. In this study, lignosulfonate (LS), a type of hydrophilic lignin, was used to study its effect on cellulosic hydrolysis.ResultsThe effect of LS on the enzymatic hydrolysis of pure cellulose (Avicel) and lignocellulose [dilute acid (DA) treated sugarcane bagasse (SCB)] was investigated by analyzing enzymatic hydrolysis efficiency, productive and non-productive cellulase adsorptions, zeta potential and particle size distribution of substrates. The result showed that after adding LS, the productive cellulase adsorption on Avicel reduced. Adding LS to Avicel suspension could form the Avicel–LS complexes. The particles were charged more negatively and the average particle size was smaller than Avicel before adding LS. In addition, adding LS to cellulase solution formed the LS–cellulase complexes. For DA-SCB, adding LS decreased the non-productive cellulase adsorption on DA-SCB from 3.92 to 2.99 mg/g lignin and increased the productive adsorption of cellulase on DA-SCB from 2.00 to 3.44 mg/g cellulose. Besides, the addition of LS promoted the formation of LS–lignin complexes and LS–cellulase complexes, and the complexes had more negative charges and smaller average sizes than DA-SCB lignin and cellulase particles before adding LS.ConclusionsIn this study, LS inhibited Avicel’s hydrolysis, but enhanced DA-SCB’s hydrolysis. This stemmed from the fact that LS could bind cellulase and Avicel, and occupied the binding sites of cellulase and Avicel. Thus, a decreased productive adsorption of cellulase on Avicel arose. Regarding DA-SCB, adding LS, which enhanced hydrolysis efficiency of DA-SCB, increased the electrostatic repulsion between DA-SCB lignin and cellulase, and therefore, decreased non-productive adsorption of cellulase on DA-SCB lignin and enhanced productive adsorption of cellulase on DA-SCB cellulose.Graphical abstract

Highlights

Cellulase adsorbed on cellulose is productive and helpful to produce reducing sugars in enzymatic hydrolysis of lignocellulose; cellulase adsorbed on lignin is non-productive
Enzymatic hydrolysis of Avicel. For pure cellulose (Avicel) and dilute acid (DA)‐sugarcane bagasse (SCB) In order to investigate the influence of LS on the enzymatic hydrolysis efficiency of pure cellulose and lignocellulose, the enzymatic hydrolysis of Avicel and dilute acid-treated sugarcane bagasse (DA-SCB) was carried out
Avicel and DA-SCB arrived at the equilibrium of enzymatic hydrolysis at 120 and 72 h, respectively

Summary

Introduction

Cellulase adsorbed on cellulose is productive and helpful to produce reducing sugars in enzymatic hydrolysis of lignocellulose; cellulase adsorbed on lignin is non-productive. Increasing productive adsorption of cellulase on cellulose would be beneficial in improving enzymatic hydrolysis. Pretreatment can remove lignin and destroy lignocellulosic structure to improve the cellulose accessibility to cellulase and enzymatic hydrolysis of cellulose [7, 8]. Many pretreatment technologies such as physical, chemical and biological treatments have been developed [9]. It was found in many studies that adding surfactants into enzymatic hydrolysis system could reduce adsorption of cellulase on lignin and improve enzymatic hydrolysis [11, 12]. LS can influence enzymatic hydrolysis efficiency of lignocellulose via electrostatic and hydrophobic interactions [17]

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