New insights on structure of lignin-carbohydrate complex from hot water pretreatment liquor.

To understand the lignin-carbohydrate linkages and the structure changes in hot water pretreatment process, lignin-carbohydrate complex (LCC) fraction was extracted from hot water pretreatment liquor of poplar for the first time. Various structural analyses of LCC fraction were performed by different methods including high performance anion exchange chromatography, gel permeation chromatography, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy and two-dimensional nuclear magnetic resonance spectroscopy. The results show that the lignin in LCC fraction mainly composed of syringyl unit, which was connected with β-O-4´ linkage. The above lignin linked to glucomannan in the initial phase of hot water pretreatment, then gradually connected with glucuronoxylan. Compared with ball-milling LCC, LCC fraction from hot water pretreatment liquor presented advantageous hydrophilia and biocompatibility based on higher contents of acid-soluble lignin and galactose. Various LCCs would be obtained by hot water pretreatment design, which was attractive for boosting its applicability in the field of biomaterial.