Fractionation of wheat and barley straw to access high-molecular-mass hemicelluloses prior to ethanol production.

The cost efficiency of the biorefining process can be improved by extracting high-molecular-mass hemicelluloses from lignocellulosic biomass prior to ethanol production. These hemicelluloses can be used in several high-value-added applications and are likely to be important raw materials in the future. In this study, steam pretreatment in an alkaline environment was used to pretreat the lignocellulosic biomass for ethanol production and, at the same time, extract arabinoxylan with a high-molecular-mass. It was shown that 30% of the arabinoxylan in barley straw could be extracted with high-molecular-mass, without dissolving the cellulose. The cellulose in the solid fraction could then be hydrolysed with cellulase enzymes giving a cellulose conversion of about 80-90% after 72 h. For wheat straw, more than 40% of the arabinoxylan could be extracted with high-molecular-mass and the cellulose conversion of the solid residue after 72 h was about 70-85%. The high cellulose conversion of the pretreated wheat and barley straw shows that they can be used for ethanol production without further treatment. It is therefore concluded that it is possible to extract high-molecular-mass arabinoxylan simultaneously with the pretreatment of biomass for ethanol production in a single steam pretreatment step.