title: Visualization of Miscanthus × giganteus cell wall deconstruction subjected to dilute acid pretreatment for enhanced enzymatic digestibility.
abstract: BACKGROUND
  The natural recalcitrance of lignocellulosic plant cell walls resulting from complex arrangement and distribution of heterogeneous components impedes deconstruction of such cell walls. Dilute acid pretreatment (DAP) is an attractive method to overcome the recalcitrant barriers for rendering enzymatic conversion of polysaccharides. In this study, the internodes of Miscanthus × giganteus, a model bioenergy crop, were subjected to DAP to yield a range of samples with altered cell wall structure and chemistry. The consequent morphological and compositional changes and their possible impact on saccharification efficiency were comprehensively investigated. The use of a series of microscopic and microspectroscopic techniques including fluorescence microscopy (FM), transmission electron microscopy (TEM) and confocal Raman microscopy (CRM)) enabled correlative cell wall structural and chemical information to be obtained.
  
  
  RESULTS
  DAP of M. × giganteus resulted in solubilization of arabinoxylan and cross-linking hydroxycinnamic acids in a temperature-dependent manner. The optimized pretreatment (1% H2SO4, 170°C for 30 min) resulted in significant enhancement in the saccharification efficiency (51.20%) of treated samples in 72 h, which amounted to 4.4-fold increase in sugar yield over untreated samples (11.80%). The remarkable improvement could be correlated to a sequence of changes occurring in plant cell walls due to their pretreatment-induced deconstruction, namely, loss in the matrix between neighboring cell walls, selective removal of hemicelluloses, redistribution of phenolic polymers and increased exposure of cellulose. The consequently occurred changes in inner cell wall structure including damaging, increase of porosity and loss of mechanical resistance were also found to enhance enzyme access to cellulose and further sugar yield.
  
  
  CONCLUSIONS
  DAP is a highly effective process for improving bioconversion of cellulose to glucose by breaking down the rigidity and resistance of cell walls. The combination of the most relevant microscopic and microanalytical techniques employed in this work provided information crucial for evaluating the influence of anatomical and compositional changes on enhanced enzymatic digestibility.
authors.affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Ji
authors.affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.
authors.forename: Xun
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Ling
authors.affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.
authors.forename: Xia
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Department of Bioproducts and Biosystems Engineering, Kaufert Laboratory, University of Minnesota, Saint Paul, MN 55108 USA.
authors.forename: Shri
authors.initials: S
authors.lastname: Ramaswamy
authors.affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
keywords: Cell wall anatomy; Components distribution; Dilute acid pretreatment; Enzymatic hydrolysis; Miscanthus × giganteus