Sugarcane Bagasse Saccharification by Enzymatic Hydrolysis Using Endocellulase and β-glucosidase Immobilized on Different Supports

Wilson G Morais Junior,Thályta F Pacheco,Shipeng Gao,José M Guisán,Nídia S Caetano,Pedro A Martins

doi:10.3390/catal11030340

Abstract

The saccharification of sugarcane bagasse by enzymatic hydrolysis is one of the most promising processes for obtaining fermentable sugar to be used in the production of second-generation ethanol. The objective of this work was to study the immobilization and stabilization of two commercial enzymes: Endocellulase (E-CELBA) in dextran coated iron oxide magnetic nanoparticles activated with aldehyde groups (DIOMNP) and β-glucosidase (E-BGOSPC) in glyoxyl agarose (GLA) so that their immobilized derivatives could be applied in the saccharification of pretreated sugarcane bagasse. This was the first time that the pretreated sugarcane bagasse was saccharified by cascade reaction using a endocellulase immobilized on dextran coated Fe2O3 with aldehyde groups combined with a β-glucosidase immobilized on glyoxyl agarose. Both enzymes were successfully immobilized (more than 60% after reduction with sodium borohydride) and presented higher thermal stability than free enzymes at 60, 70, and 80 °C. The enzymatic hydrolysis of the sugarcane bagasse was carried out with 15 U of each enzyme per gram of bagasse in a solid-liquid ratio of 1:20 for 48 h at 50 °C. Under these conditions, 39.06 ± 1.18% of the cellulose present in the pretreated bagasse was hydrolyzed, producing 14.11 ± 0.47 g/L of reducing sugars (94.54% glucose). In addition, DIOMNP endo-cellulase derivative maintained 61.40 ± 1.17% of its enzymatic activity after seven reuse cycles, and GLA β-glucosidase derivative maintained up to 58.20 ± 1.55% of its enzymatic activity after nine reuse cycles.

Highlights

In recent years, due to the shortage of non-renewable energy resources and increasing environmental pressure from greenhouse gases released by burning of fossil fuels, there has been an increase in the number of studies searching for alternative production of cleaner fuels compared to petroleum-based fuels
Almost 90% of E-CELBA was immobilized on dextran coated iron oxide magnetic nanoparticles (DIOMP) in the first hour, but after reduction, the derivative presents only 37.7% of immobilized activity representing 11.72 ± 0.21 U/g of support
An enzyme immobilization hardly occurs at slightly alkaline pH values due to the instability generated by the Schiff bases formation between the enzyme and support

Summary

Introduction

Due to the shortage of non-renewable energy resources and increasing environmental pressure from greenhouse gases released by burning of fossil fuels, there has been an increase in the number of studies searching for alternative production of cleaner fuels compared to petroleum-based fuels. Sugarcane bagasse is one of the most abundant and promising biomass sources in the world, obtained from the processing of sugarcane with an estimated global yield of 510.3 million tons per year [2]. Cellulose and hemicellulose are polysaccharides that cannot be directly converted into ethanol but can be hydrolyzed to obtain monosaccharides such as glucose and xylose that, in turn, can be fermented to produce ethanol [4,5]. Enzymatic hydrolysis is applied to convert cellulose to glucose (substrate used in the classic production of first-generation ethanol) [6]. Once pre-treated, lignocellulosic biomass presents less hemicellulose and lignin, which makes cellulose more accessible to enzymes, increasing the hydrolysis efficiency [7,8]

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