The lignin–carbohydrate complexes (LCCs) typically
present
in the liquors produced in the pre-hydrolysis of biomass cause severe
difficulties in downstream fractionation. To address this issue, a
series of LCC samples were accessed from solutions obtained from the
pre-hydrolysis of extractive-free pine wood meal (H-LCC) and compared
with LCC obtained from the corresponding residues (B-LCC). Chromatographic
and spectroscopic techniques revealed that 8.2% of the lignins were
degraded at 160 °C, resulting from the breakage of β-O-4′
linkages during pre-hydrolysis. Meanwhile, (reactive) hemicelluloses
were mainly removed from the fibers’ cell walls. Some hemicelluloses
in the pre-hydrolysis liquor, such as glucomannans, were associated
with 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 during
pre-hydrolysis at given temperatures, critically important in efforts
to improve biomass processing and valorization.