Saccharification of pre-treated wheat straw via optimized enzymatic production using Aspergillus niger: Chemical analysis of lignocellulosic matrix

Abstract

Bioconversion of lignocellulosic wastes to valuable end-products via multi-enzymatic hydrolysis is a potential low costing process for large-scale application in many industrial sectors. Thus, in this study, among thirty local fungal isolates, Aspergillus niger which gave the highest cellulase production, was identified under the accession number MZ062603 in GeneBank. Three types of pre-treatments (0.0–0.7%) acid, (0.0–2%) alkali, and (70–90 °C) hot water were applied to increase wheat straw (WS) digestibility by A. niger, and 1% NaOH treated WS was superior to the other pre-treatments (acid and hot water). During solid-state fermentation, the total cellulolytic activity of [filter-paper cellulase (FPase), carboxy-methyl cellulase (CMCase), and β- glucosidase (βGase)] increased about 2.8-fold. While reducing sugar was increased by 3.1 times. The optimum values of total cellulases activities and reducing sugar (8907.2 and 92.4 mg/gds) were obtained after 3 days of incubation at 30 °C and pH 5.2 at 75% v/w moisture using 3 days old inoculum (106 spores/mL/gds). The WS substrate which was subjected to alkali pre-treatment subsequent to fungal bioconversion was varied in its chemical composition and detailed structure compared to the raw and alkali pre-treatment ones as indicated by its chemical analysis, Scanning electron microscopy (SEM) observation, Fourier Transform Infra-red Spectroscopy (FTIR), and X-Ray Diffraction (XRD). All these analyses revealed that the lignocellulosic matrix was completely destroyed after the fungal treatment.