Wheat straw delignification by Djerkandera adusta (Willd.) P. Karst. 1879: The effect on enzymatic hydrolysis

Abstract

The use of lignocellulosic materials in the production of biofuels and biochemicals holds a huge prospect since wood and agricultural residues represent the most abundant global source of renewable biomass. However, delignification is an inevitable step in lignocellulose pre-treatment rendering the cellulose and hemicellulose more exposed to enzymatic saccharification. The aim of this study was to assess the potential of different Bjerkandera adusta strains to enhance the efficiency of enzymatic saccharification of wheat straw after solid-state culturing. Three white-rot fungal strains of Bjerkandera adusta (Willd.) P. Karst. 1879, (BEOFB1601, BEOFB1602 and BEOFB1603) were used for partial delignification of wheat straw during solid-state cultivation. Activity of ligninolytic enzymes were measured spectrophotometrically while wheat straw residues were used for determination of hemicelluloses, cellulose and lignin contents. Enzymatic hydrolysis of pre-treated wheat straw was conducted using commercial cellulase in loadings of 60 U g-1 of solid substrate. The content of reducing sugars was measured calorimetrically using 1,4-dinitrosalycilic acid. Enzymes predominantly responsible for lignin degradation by tested fungal strains were peroxidases. The highest rate of lignin degradation was noticed in samples pretreated with the strain BEOFB1601 (42.3 ± 3.7%). The highest reducing sugars yield (8.6 ± 0.3 gGE L-1) was achieved after enzymatic saccharification of samples pre-treated with the strain BEOFB1601, as the most selective lignin degrader. The obtained results suggest that fungal culturing as a bio­logical pre-treatment method can be significantly strain specific. A key mechanism which enhances convertibility of carbohydrates is selective lignin degradation of the biomass.

Keywords

• bjerkandera adusta
• ligninolytic enzymes
• wheat straw
• fungal pre­treatment
• saccharification