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Effectively breaking down its anti-depolymerization barrier is key to the conversion and utilization of biomass resources. The anti-depolymerization barrier is mainly composed of a lignin-carbohydrate complex (LCC), which hinder the high-value utilization of biomass. In an alkaline environment, phenyl glycosidic bonds in LCC exist stably. Therefore, it is of great significance for the structural analysis of LCC in alkaline environment. In this study, LCC rich in carbohydrates was extracted from alkaline hemicellulose by using the xylanase-macroporous resin method, the effects of enzyme dosage and treatment time on LCC enrichment were discussed. The results showed that the LC bond of LCC samples was dominated by phenyl glucoside bond, the composition of lignin showed the rule of S H G. This method could fulfill the requirements of lignin enrichment and structural integrity. This provides a new method for solving the problems of LCC signal masking and low detection sensitivity.

Owing to the existence of lignin-carbohydrate complex (LCC) linkages, the extracted hemicellulose contains lignin, which is difficult to remove. Chlorine dioxide selectively oxidizes lignin without reacting with carbohydrates. In this study, chlorine dioxide was used to remove lignin from the hemicellulose sample. Ion chromatography and 2D-HSQC NMR were used to observe the changes in the LCC. After chlorine dioxide treatment, acid-insoluble lignin was largely degraded, with a removal rate reaching 68%. Furthermore, the 2D-HSQC NMR spectrum showed that guaiacyl (G) lignin underwent dramatic degradation and degradation of syringyl (S) lignin was also obvious. Phenyl glycoside-type LC linkages were also largely degraded. Moreover, the sugar composition and structure of the hemicellulose did not change significantly. This suggests that it is feasible to remove lignin from LCCs through oxidation of hemicellulose using chlorine dioxide. Meanwhile, hemicellulose with high molecular weight and high purity can be obtained by this method.