Molecular Changes in Corn Stover Lignin Resulting from Pretreatment Chemistry

Abstract

Lignin is an amorphous polymer that limits the enzymatic conversion of polysaccharides to fermentable sugars. Thus, a pretreatment that can enhance the accessibility of carbohydrates is a key step of successful biofuel conversion schemes. In this study, corn stover was fractioned into stem, cob, and leaf because their lignin is different. To elucidate the lignin changes, autohydrolysis, diluted acid, and alkali pretreatments were applied on the samples, followed by the isolation of cellulolytic enzyme lignin preparations. Alkaline nitrobenzene oxidation, 13 C-Nuclear Magnetic Resonance (NMR), and 1 H-13 C heteronuclear single quantum coherence NMR were used to profile the lignin changes. The results indicated that corn stover lignin is a p-hydroxyphenyl-guaiacyl-syringyltype lignin that incorporates p-coumarate and ferulate esters. The β-arylether was the most abundant inter-unit linkage, followed by condensed linkages, e.g. pino-/syringaresinol, phenylcoumaran, and spirodienone. As for the non-pretreated samples, leaf lignin was more condensed than stem lignin and cob lignin. More lignin was removed by the alkali pretreatment due to more cleavage of β-aryl-ether linkages. As a comparison, more condensed linkages were generated by the acidic pretreatments. The decrease of the syringyl/guaiacyl ratio indicated that the residual lignin became more condensed and confirmed that guaiacyl and p-hydroxyphenyl units were more stable than syringyl units during the pretreatment.

Study and characterization of enzymes and metabolic pathways involved in the decomposition of lignin and lignin-derived compounds

“…The main substructures found in native corn stover and wheat straw lignin are β-Ο-4' alkylaryl ethers, followed by lower amounts of phenylcoumarans, resinols and spirodienones. The presence of p-coumarates and ferulates in corn stover and wheat straw lignin has also been previously demonstrated (del Rio et al, 2012, Sammons et al, 2013, Min et al, 2017. Further analysis would confirm the estimated assignments of proton NMR signals.…”

Microbial bioprospecting for lignocellulose degradation at a unique Greek environment

“…However, consistent with the assignments in the lignin 1 H NMR spectra is the fact that grass lignins are characterized mostly as guaicyl-type and that substructures found in native corn stover and wheat straw lignin are β-Ο-4' alkylaryl ethers, followed by lower amounts of phenylcoumarans, resinols and spirodienones. The presence of p-coumarates and ferulates in corn stover and wheat straw lignin has also been previously demonstrated (del Río et al 2012;Sammons et al 2013;Min et al 2017).…”

Microbial bioprospecting for lignocellulose degradation at a unique Greek environment

“…However, consistent with the assignments in the lignin 1 H NMR spectra is the fact that grass lignins are characterized mostly as guaicyl-type and that substructures found in native corn stover and wheat straw lignin are β-Ο-4’ alkylaryl ethers, followed by lower amounts of phenylcoumarans, resinols and spirodienones. The presence of p -coumarates and ferulates in corn stover and wheat straw lignin has also been previously demonstrated ( del Río et al., 2012 ; Sammons et al., 2013 ; Min et al., 2017 ).…”