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1 Department of Chemical and Biochemical Engineering, Technical University of Denmark 2 Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark 3 University of Copenhagen 4 Department of Civil Engineering, Technical University of Denmark 5 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
Background: Biomass recalcitrance is affected by a number of chemical, physical and biological factors. In this study we looked into the differences in recalcitrance between two major anatomical fractions of wheat straw biomass, leaf and stem. A set of twenty-one wheat cultivars was fractionated and illustrated the substantial variation in leaf-to-stem ratio between cultivars. The two fractions were compared in terms of chemical composition, enzymatic convertibility, cellulose crystallinity and glucan accessibility. The use of water as a probe for assessing glucan accessibility was explored using low field nuclear magnetic resonance and infrared spectroscopy in combination with hydrogen-deuterium exchange. Results: Leaves were clearly more degradable by lignocellulolytic enzymes than stems, and it was demonstrated that xylose removal was more linked to glucose yield for stems than for leaves. Comparing the locations of water in leaf and stem by low field NMR and FT-IR revealed that the glucan hydroxyl groups in leaves were more accessible to water than glucan hydroxyl groups in stems. No difference in crystallinity between leaf and stem was observed using wide angle x-ray diffraction. Hydrothermal pretreatment increased the accessibility towards water in stems but not in leaves. The results in this study indicate a correlation between the accessibility of glucan to water and to enzymes. Conclusions: Enzymatic degradability of wheat straw anatomical fractions can be indicated by the accessibility of the hydroxyl groups to water. This suggests that water may be used to assess glucan accessibility in biomass samples. © 2014 Zhang et al.; licensee BioMed Central Ltd.
Biotechnology for Biofuels, 2014, Vol 7, Issue 1
cellulose crystallinity; glucan accessibility; recalcitrance; water; Wheat straw anatomical fractions; Biomass; Cellulose; Enzymes; Infrared spectroscopy; Water; X ray diffraction; Cellulose crystallinity; Hydrogen-deuterium exchange; Hydrothermal pretreatment; Low field nuclear magnetic resonance; Wheat straws; Wide angle Xray diffraction; Straw
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