The effect of lignin degradation products on the generation of pseudo-lignin during dilute acid pretreatment

Pseudo-lignin is an insoluble material that tends to deposit on acidic pretreated fiber surface and negatively impacts the biological conversion of biomass to valued added products. Employing a laboratory generated acidic hydrolysate solution from dilute acid pretreatment of bamboo residues, we sought to seek an improved understanding of pseudo-lignin formation from fragmented carbohydrates. In addition, we also performed experiments to investigate how lignin model compounds interact with carbohydrates en route to pseudo-lignins formation. The yields of pseudo-lignin generated from xylose (CXPL) were higher than those generated from glucose (CGPL). Gas chromatography-Mass spectrometry and Foloin-Ciocalteau analysis suggested that there were more aromatic compounds in hydrolyzate during CGPL's formation. The presence of lignin phenolic model compounds had both a positive and negative effect upon quantitative yields of pseudo-lignin. Gel permeation chromatography and NMR analysis (P-31 and 2D-HSQC NMR) of the pseudo-lignin samples generated in the presence and absence of 4-hydroxybenzoic acid (4-HA), employed as a lignin model compound, revealed drastic differences in molecular weight, changes in hydroxyl group content, and hydrocarbon bonds, suggesting significant differences in the pseudo-lignin reaction pathways when certain lignin model compounds are present. Our findings demonstrate the effects of both hemicellulose carbohydrate makeup and lignin model compound impact on the formation of pseudo-lignin and its chemical properties, suggesting a potential way to minimize pseudo-lignin formation.