Formation and Identification of Lignin-Carbohydrate Complexes in Pre-hydrolysis Liquors

The lignin-carbohydrate complexes (LCCs) typicallypresentin the liquors produced in the pre-hydrolysis of biomass cause severedifficulties in downstream fractionation. To address this issue, aseries of LCC samples were accessed from solutions obtained from thepre-hydrolysis of extractive-free pine wood meal (H-LCC) and comparedwith LCC obtained from the corresponding residues (B-LCC). Chromatographicand spectroscopic techniques revealed that 8.2% of the lignins weredegraded at 160 degrees C, resulting from the breakage of beta-O-4 ' linkages during pre-hydrolysis. Meanwhile, (reactive) hemicelluloseswere mainly removed from the fibers' cell walls. Some hemicellulosesin the pre-hydrolysis liquor, such as glucomannans, were associatedwith degraded lignin fragments via ether and ester bonds. However,the newly formed LCCs were pH-labile and underwent rapid hydrolysis.Overall, we reveal details about LCC formation and degradation duringpre-hydrolysis at given temperatures, critically important in effortsto improve biomass processing and valorization.