title: Structure and enzymatic accessibility of leaf and stem from wheat straw before and after hydrothermal pretreatment.
abstract: 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.
authors.affiliation: Department of Geosciences and Natural Resource Management, Faculty of Sciences, University of Copenhagen, Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark.
authors.forename: Heng
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Geosciences and Natural Resource Management, Faculty of Sciences, University of Copenhagen, Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark.
authors.forename: Lisbeth G
authors.initials: LG
authors.lastname: Thygesen
authors.affiliation: Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, D-03-3-06, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Kell
authors.initials: K
authors.lastname: Mortensen
authors.affiliation: Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DTU, DK-2800, Kgs, Lyngby, Denmark.
authors.forename: Zsófia
authors.initials: Z
authors.lastname: Kádár
authors.affiliation: Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
authors.forename: Jane
authors.initials: J
authors.lastname: Lindedam
authors.affiliation: Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs, Lyngby, Denmark.
authors.forename: Henning
authors.initials: H
authors.lastname: Jørgensen
authors.affiliation: Department of Geosciences and Natural Resource Management, Faculty of Sciences, University of Copenhagen, Rolighedsvej 23, DK-1958 Frederiksberg C, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Felby
keywords: Wheat straw anatomical fractions; cellulose crystallinity; glucan accessibility; recalcitrance; water