Production of fungal plant cell wall degrading enzymes on wet-oxidised wheat straw xylan

In Denmark, the wet-oxidation (WO) process has been used for fractionating wheat straw [10], where most of the hemicellulose is solubilised mainly as oligomers and polymers and the cellulose retained as a solid. In wheat straw, hemicellulose is an arabino-4-O-methylglucurono xylan, which, in addition to xylose, contains arabinose, 4-O-Me-D-glucuronic acid, and acetic acid substituents [9]. Some arabinosyl groups may be esterified with ferulic or p-coumaric acids. Most micro-organisms used for lactate, ethanol or xylitol production do not produce enzymes for hemicellulose hydrolysis. Acid or enzymatic hydrolysis is needed to convert the sugar polymers to monomers. A problem associated with dilute acid hydrolysis is the poor fermentability of the produced hydrolysates compared with enzymatic hydrolysis. This study investigated the utilisation of wet-oxidised wheat straw xylan (WO-xylan) for production of enzymes for hydrolysis. Three fungal strains (Aspergillus oryzae, Aspergillus fumigatus, and Trichoderma reesei) were cultivated on WO-xylan using xylan (Lenzig AG) as a supplementary carbon-source. A. oryzae was selected for production of enzymes in larger scale.