PhD defence: Parveen Kumar Deralia – Københavns Universitet

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PhD defence: Parveen Kumar Deralia

Parveen Kumar Deralia defends his thesis,

Lignin- and Hemicellulose-derived Biomass Recalcitrance - Chemistry of lignin and hemicellulose and physiochemical characterizations of hydrothermally pretreated poplar and wheat straw in relation to enzymatic saccharifiability

Supervisors:
Professor Claus Felby, IGN
Senior Researcher Lisbeth Garbrecht Thygesen, IGN

Assessment Committee:
Professor Gunnar Lidén, Department of Chemical Engineering, Lund University
Associate Professor Ib Johannsen, Department of Engineering – Biorefining, Aarhus University
Associate Professor Henning Jørgensen (chair), Department of Plant and Environmental Sciences, University of Copenhagen

Summary:
How a biocomposite assembly of cellulose, hemicellulose, and lignin in form of a plant cell wall forms the basis of recalcitrance towards enzymatic deconstruction is something of a mystery and is still being resolved. Among many factors of recalcitrance, lignin and hemicellulose and their associations at the molecular level are primary obstacles when cellulose is saccharified enzymatically to monomeric sugars, limiting the extent of saccharification.
In this thesis, the main objective is to understand how the structure and composition of lignin and hemicellulose interact with pretreatment technology bringing the multitude of chemical and physical changes, which govern the level of biomass recalcitrance. The lignocellulosic biomasses in question are wheat straw and poplar and the hydrothermal pretreatment is used as pretreatment technology.
The 2D HSQC NMR and wet chemistry chemical composition techniques are applied to reveal the structural and compositional modifications in lignin and hemicellulose. The scission of β-aryl ethers and concomitant generation of repolymerized structures (β-5 and β-β) and removal of different subsets of hemicellulose (in terms of different groups, e.g. acetyl etc.) differ. This reflects in enzymatic saccharifiability at different pretreatment severities between poplar and wheat straw.
While investigating the extent of lignin migration and reorganization mode using multi-technique analysis, it can be concluded that poplar lignin migrates in a higher degree to the biomass surface, giving a proportional increase in the specific surface area opposite to wheat straw, which has a marked increase in the specific surface area. The distinctly different chemistry of lignin and hemicellulose and different lignin migration and reorganization appear to be correlative, helping explain differences in enzymatic saccharification performance across the pretreatment severities and between two biomasses.
The main contribution of this work to the current state-of-the-art in the field is the revelation of distinct behaviors of generation of different repolymerized lignin structures at different pretreatment severities and their identification for these biomasses, illustration the molecular basis of the disparity in repolymerization behavior. The work presented in this thesis has contributed to better understanding of the fundamental mechanisms of recalcitrance. This work also has implications for better pairing up different biomasses with pretreatment conditions and for the design of commercial enzyme preparations for effective enzymatic conversion.

The thesis is available for inspection from the PhD administration office, 04.1.413, at Øster Voldgade 10