(604a) Assessing Changes on Plant Cell Wall Recalcitrance Associated with Alkaline Oxidative Pretreatments

Plant cell walls represent the majority of the terrestrial plants by mass and mainly consist of polysaccharides and lignin. These constituents are considered as an abundant and renewable carbon resource providing great potential for the production of petroleum-displacing biofuels and biochemicals.  However, the complex, rigid and heterogeneous plant cell wall structure are difficult deconstruct, and typically a combination of biological and chemical treatments are required in order to break down the cell wall and maximize the yield of the products. Pretreatments are thermal or chemical processes that facilitate the subsequent sugar-releasing enzymatic hydrolysis.  Alkaline pretreatments and alkaline-oxidative pretreatments are one of the main categories of pretreatments that function well on monocot grasses, which include the cereal stovers and the energy crops.  These pretreatments target esters cross-links between lignin and xylans within the grass cell walls formed by the hydroxycinnamates, and release the hemicelluloses by cleaving the ester linked side chains such as acetyl groups, to significantly increase the hydrophilicity of the cell walls, and the enzymatic accessibility to the polysaccharides constituents.

Structural assessment of the cell wall is important to fundamentally understand the cell wall changes associated with these biomass conversion processes. However, commonly performed analysis methods only provides limited information on the cell wall structures such as the total content and composition of the structural carbohydrates and lignin. Structural characteristics including higher order structures within the cell wall, covalent and non-covalent cross-linking, and porosity may all impact the conversion process but require attention.  Additionally, plant cell walls can exhibit substantial heterogeneity between plant cell type and tissue. Novel and practical characterization tools are desired to identify how properties of diverse cell walls are impacted by pretreatments and how this correlates to reduced cell wall “recalcitrance”, which is important for both plants design with properties suited for deconstruction and the design of deconstruction strategies.

The overall goal of the research is to fundamentally understand the structure of diverse plant cell walls from multiple levels to investigate the impact of pretreatment on cell wall recalcitrance and develop multivariate models to predict the hydrolysis yield from those properties. Specifically, this work will firstly understand the roles that lignin and glycans play in the plant cell wall recalcitrance, as well as the mechanism of enhanced hydrolysis yield, through characterization on the structural changes of diverse cell walls associated with alkaline oxidative pretreatment. Secondly, grass cell wall features including xylan, β-glucan, hydroxycinnamates, enzyme accessibility and hydrophilicity/porosity are characterized, and their correlations with the cell wall digestibility are analyzed to further understand how those features may impact recalcitrance. Thirdly, multivariate models are developed to predict the cellulolytic digestibility by cell wall properties, and the chemometric models are developed in order to provide high-throughput tool for characterization.