Background:
Due to the complexity of lignocellulosic materials, a complete enzymatic hydrolysis into fermentable sugars requires a variety of cellulolytic and xylanolytic enzymes. Addition of xylanases has been shown to significantly improve the performance of cellulases and to increase cellulose hydrolysis by solubilising xylans in lignocellulosic materials. The goal of this work was to investigate the effect of acetyl xylan esterase (AXE) originating from Trichoderma reesei on xylan solubilisation and enzymatic hydrolysis of cellulose.
Results:
The solubilisation of xylan in pretreated wheat straw and giant reed (Arundo donax) by xylanolytic enzymes and the impact of the sequential or simultaneous solubilisation of xylan on the hydrolysis of cellulose by purified enzymes was investigated. The results showed that the removal of acetyl groups in xylan by AXE increased the accessibilty of xylan to xylanase and improved the hydrolysis of xylan in pretreated wheat straw and giant reed. Solubilisation of xylan led to an increased accessibility of cellulose to cellulases (CEL) and thereby increased the hydrolysis extent of cellulose. A clear synergistic effect between CEL and xylanolytic enzymes was observed. The highest hydrolysis yield of cellulose was obtained with a simultaneous use of CEL, xylanase (XYL) and AXE, indicating the presence of acetylated xylan within the cellulose matrix. Acetylated xylobiose and acetylated xylotriose were produced from xylan without AXE as confirmed by atmospheric pressure matrix assisted laser desorption/ionization ion trap mass spectrometer (AP-MALDI-ITMS).
Conclusions:
The results in this paper demonstrate that supplementation of xylanase with acetyl xylan esterase enhances the solubilisation of xylan to some extent and consequently, increases the following hydrolysis of cellulose. Highest hydrolysis yield was, however, obtained by simultaneous hydrolysis of xylan and cellulose, indicating a layered structure of cellulose and xylan chains in the cell wall substrate. AXE had an important role in the hydrolysis of lignocellulosic materials containing acetylated xylan.Source:
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