Elucidation of the Structure of Cellulolytic Enzyme Lignin from Loblolly Pine (pinus taeda)

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Title: Elucidation of the Structure of Cellulolytic Enzyme Lignin from Loblolly Pine (pinus taeda)
Author: Hu, Zhoujian
Advisors: Sederoff, Ronald R., Committee Member
Peszlen, ILona M., Committee Member
Chang, Hou-min, Committee Chair
Abstract: Milled Wood Lignin (MWL) preparation has long been used as a standard method for the studies of lignin structure. However, ball milling reduces the degree of polymerization, creating new free-phenolic hydroxyl groups through cleavage of β-aryl ether linkages as well as increasing a-carbonyl groups via side-chain oxidation. In addition, the maximum yield of MWL from protolignin is about 50%. Therefore, to what extent is milled wood lignin representative of total lignin in situ? Cellulolytic Enzyme Lignin (CEL) preparation has not been used as widely as MWL in the studies of lignin structure. CEL has higher molecular weight, lower condensation and higher b-O-4 interlinkage compared to MWL. The significant higher yield of CEL extracted from wood could help us understand the lignin structure as a whole. To use CEL preparation routinely for lignin chemistry and understand the lignin structure of loblolly pine as a whole, CEL and MWL were prepared by three different ball-milling methods. The structure of CEL at various yields was compared with MWL using wet chemical analysis, FTIR and solution-state NMR techniques. Ball milling of wood degrades b-O-4 structures in lignin. However, even after extensive ball milling, less than 25% of the b-O-4 structures are degraded. The extent of degradation is less for softwood than for hardwood lignin. The yield of extractable lignin, either MWL or CEL, is the best way to access the extent and effect of ball milling. CEL is preferred over MWL as it can be isolated in higher yield with less degradation. CEL was isolated with yields ranging from 20-86%. Over this range CEL has similar structures, suggesting that the major fraction of lignin in the secondary wall is uniform in structure. The residual enzyme lignin (REL) is structurally different from CEL and may originate mainly from the middle lamella. In present study, we propose a new procedure for the isolation of lignin for use in structural studies where the wood is sufficiently milled and successively extracted to produce three lignin fractions representing the total lignin in wood.
Date: 2006-09-25
Degree: MS
Discipline: Wood and Paper Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/26

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