Arabinoxylan, a polysaccharide composed of xylose and arabinose, is part of the water soluble and insoluble fibre present in cereals, in particular in the cell walls. Hydrolysis of arabinoxylan is an important prerequisite for improved utilization of cereal hemicellulose, e.g. in the ethanol fermentation industry and other cereal-based industries.
Arabinoxylan consist of alpha-L-arabinofuranose residues attached as branch-points to a beta-(1-4)-linked xylose polymeric backbone. The xylose residues may be mono-substituted in the C2- or C3-position or di-substituted at both the C2- and C3-position. In addition, ferulic acid and p-coumaric acid may be covalently linked to arabinoxylan via esterification at the C5 position of some of the arabinosyl units. These substitutions on the xylan backbone retard the actions of xylanases and the complete hydrolysis of arabinoxylan thus requires both side-group cleaving and depolymerising activities. The major products of hydrolysis of arabinoxylan are the C5 sugars xylose and arabinose.
A process for hydrolysis of arabinoxylan using synergistic interactions amongst enzymes present commercial enzyme compositions from Humicola insolens and Trichoderma reesei has previously been described by the present inventors in Sørensen, H. R. et al. (Biotechnology and Bioengineering, Vol. 81, No. 6, March 20, 726-731, 2003). Enzyme catalyzed hydrolysis of >50% of the soluble part of the wheat endosperm arabinoxylan could be achieved, but only low monosaccharide yields were obtained with similar enzymatic treatments on insoluble wheat arabinoxylan. However, since the arabinoxylan degrading enzyme activities are present as side-activities in commercial preparations having other enzyme activities as their main activity, high dosage levels of 5-10 wt % of the enzyme preparation per weight of the substrate has to be added for obtaining efficient hydrolysis. Such high enzyme addition levels are not feasible for use in full scale production applications and improved processes for hydrolysis of arabinoxylan are thus needed.