Pretreatment of sweet sorghum straw and its enzymatic digestion: insight into the structural changes and visualization of hydrolysis process

Miaoyin Dong,Fuqiang Xu,Jihong Chen,Junkai Wang,Qiaoqiao Li,Ning Yang,Wenjian Li,Shuyang Wang

doi:10.1186/s13068-019-1613-6

Abstract

BackgroundThe efficient utilization of lignocellulosic biomass for biofuel production has received increasing attention. Previous studies have investigated the pretreatment process of biomass, but the detailed enzymatic hydrolysis process of pretreated biomass remains largely unclear. Thus, this study investigated the pretreatment efficiency of dilute alkali, acid, hydrogen peroxide and its ultimate effects on enzymatic hydrolysis. Furthermore, to better understand the enzymatic digestion process of alkali-pretreated sweet sorghum straw (SSS), multimodal microscopy techniques were used to visualize the enzymatic hydrolysis process.ResultAfter pretreatment with alkali, an enzymatic hydrolysis efficiency of 86.44% was obtained, which increased by 99.54% compared to the untreated straw (43.23%). The FTIR, XRD and SEM characterization revealed a sequence of microstructural changes occurring in plant cell walls after pretreatment, including the destruction of lignin–polysaccharide interactions, the increase of porosity and crystallinity, and reduction of recalcitrance. During the course of hydrolysis, the cellulase dissolved the cell walls in the same manner and the digestion firstly occurred from the middle of cell walls and then toward the cell wall corners. The CLSM coupled with fluorescent labeling demonstrated that the sclerenchyma cells and vascular bundles in natural SSS were highly lignified, which caused the nonproductive bindings of cellulase on lignin. However, the efficient delignification significantly increased the accessibility and digestibility of cellulase to biomass, thereby improving the saccharification efficiency.ConclusionThis work will be helpful in investigating the biomass pretreatment and its structural characterization. In addition, the visualization results of the enzymatic hydrolysis process of pretreated lignocellulose could be used for guidance to explore the lignocellulosic biomass processing and large-scale biofuel production.

Highlights

The efficient utilization of lignocellulosic biomass for biofuel production has received increasing attention
This work will be helpful in investigating the biomass pretreatment and its structural characterization
The visualization results of the enzymatic hydrolysis process of pretreated lignocellulose could be used for guidance to explore the lignocellulosic biomass processing and large-scale biofuel production

Summary

Introduction

The efficient utilization of lignocellulosic biomass for biofuel production has received increasing attention. We found that the heavy-ion beam irradiation caused the transformation of polymorphs (Iα → Iβ) of cellulose I, thereby increasing the enzymatic digestibility of the biomass [9]. This irradiation pretreatment requires a sophisticated accelerator device, which means high cost and limits its industrial application. Biological pretreatment is a relatively time-consuming process, and its hydrolysis rate was lower as compared to other technologies [10, 11] Chemical pretreatment, such as using dilute alkali, acid and oxidant, is an economical and efficient pretreatment process that uses relatively low temperatures and pressures [10, 12]

Methods

Results

Conclusion