Characterization and Elimination of Undesirable Protein Residues in Plant Cell Wall Materials for Enhancing Lignin Analysis by Solution-State Nuclear Magnetic Resonance Spectroscopy

12 páginas.-- 5 figuras.-- 5 tablas.-- 74 referencias

Protein polymers exist in every plant cell wall preparation, and they interfere with lignin characterization and quantification. Here, we report the structural characterization of the residual protein peaks in 2D NMR spectra in corn cob and kenaf samples and note that aromatic amino acids are ubiquitous and evident in spectra from various other plants and tissues. The aromatic correlations from amino acid residues were identified and assigned as phenylalanine and tyrosine. Phenylalanine's 3/5 correlation peak is superimposed on the peak from typical lignin p-hydroxyphenyl (H-unit) structures, causing an overestimation of the H units. Protein contamination also occurs when using cellulases to prepare enzyme lignins from virtually protein-free wood samples. We used a protease to remove the protein residues from the ball-milled cell walls, and we were able to reveal H-unit structures in lignins more clearly in the 2D NMR spectra, providing a better basis for their estimation

This work was supported by grants from the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DEFC02-07ER64494). We are grateful for Jane Marita for her various helpful discussions on this project. We also thank Steven Karlen for GC/MS experimental support and Kris Niemann (USDFRC) for assistance with nitrogen analysis.

Peer reviewed