Fungal pretreatment of sweet sorghum bagasse with supplements: improvement in lignin degradation, selectivity and enzymatic saccharification

Vartika Mishra,Antriksh Gupta,Asim K Jana,Mithu Maiti Jana

doi:10.1007/s13205-017-0719-4

Vartika Mishra, Antriksh Gupta + Show 2 more

Open Access

https://doi.org/10.1007/s13205-017-0719-4

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Abstract

Sweet sorghum bagasse (SSB) from food processing and agricultural industry has attracted the attention for uses in production of biofuel, enzymes and other products. The alteration in lignocellulolytic enzymes by use of supplements in fungal pretreatment of SSB to achieve higher lignin degradation, selectivity value and enzymatic hydrolysis to fermentable sugar was studied. Fungal strain Coriolus versicolor was selected for pretreatment due to high ligninolytic and low cellulolytic enzyme production resulting in high lignin degradation and selectivity value. SSB was pretreated with supplements of veratryl alcohol, syringic acid, catechol, gallic acid, vanillin, guaiacol, CuSO4 and MnSO4. The best results were obtained with CuSO4, gallic acid and syringic acid supplements. CuSO4 increased the activities of laccase (4.9-fold) and polyphenol oxidase (1.9-fold); gallic acid increased laccase (3.5-fold) and manganese peroxidase (2.5-fold); and syringic acid increased laccase (5.6-fold), lignin peroxidase (13-fold) and arylalcohol oxidase (2.8-fold) resulting in enhanced lignin degradations and selectivity values than the control. Reduced cellulolytic enzyme activities resulted in high cellulose recovery. Enzymatic hydrolysis of pretreated SSB yielded higher sugar due to degradation of lignin and reduced the crystallinity of cellulose. The study showed that supplements could be used to improve the pretreatment process. The results were confirmed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric/differential thermogravimetric analysis of SSB.

Highlights

Increasing agro-industrial activity has led to the production of large quantities of lignocellulosic residues composed of cellulose, hemicellulose and lignin
CuSO4 increased the activities of laccase (4.9-fold) and polyphenol oxidase (1.9-fold); gallic acid increased laccase (3.5-fold) and manganese peroxidase (2.5-fold); and syringic acid increased laccase (5.6-fold), lignin peroxidase (13-fold) and arylalcohol oxidase (2.8fold) resulting in enhanced lignin degradations and selectivity values than the control
CuSO4, gallic acid and syringic acid resulted in higher selectivity value (SV) 1.15, 0.75 and 0.89, respectively, than the control, and we further studied the effect on lignocellulolytic enzyme activities, lignin degradations and SV in pretreatment

Summary

Introduction

Increasing agro-industrial activity has led to the production of large quantities of lignocellulosic residues composed of cellulose, hemicellulose and lignin. Sweet sorghum bagasse (SSB) derived from food processing and agricultural industry has recently attracted much attention for its uses in the production of biofuel, enzymes and other useful products. The major problem associated with utilization of SSB is the rigid barrier of lignin that sandwiches the cellulose underneath its recalcitrant structure. There is need for an efficient pretreatment process of biomass to degrade lignin and expose the cellulose for hydrolysis by hydrolytic enzymes. The physical and chemical treatments of lignocellulosic biomass have potential problems, like high energy consumption and environmental pollution (Thakur et al 2013; Zhang et al 2007). The uses of biological pretreatments have advantages of being cheaper, safer, less energy consuming and environment-friendly

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