Selective precipitation and characterization of lignin–carbohydrate complexes (LCCs) from Eucalyptus
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Six types of lignin–carbohydrate complex (LCC) fractions were isolated from Eucalyptus. The acidic dioxane treatment applied significantly improved the yield of LCCs. The extraction conditions had a limited impact on the LCC structures and linkages.
Characterization of the lignin–carbohydrate complex (LCC) structures and linkages promises to offer insight on plant cell wall chemistry. In this case, Eucalyptus LCCs were extracted by aqueous dioxane, and then precipitated sequentially by 70% ethanol, 100% ethanol, and acidic water (pH = 2). The composition and structure of the six LCC fractions obtained by selective precipitation were investigated by sugar analysis, molecular weight determination, and 2D HSQC NMR. It was found that the acidic (0.05-M HCl) dioxane treatment significantly improved the yield of LCCs (66.4% based on Klason lignin), which was higher than the neutral aqueous dioxane extraction, and the extraction condition showed limited impact on the LCC structures and linkages. In the fractionation process, the low-molecular-weight LCCs containing a high content of carbohydrates (60.3–63.2%) were first precipitated by 70% ethanol from the extractable solution. The phenyl glycoside (PhGlc) bonds (13.0–17.0 per 100Ar) and highly acetylated xylans were observed in the fractions recovered by the precipitation with 100% ethanol. On the other hand, such xylan-rich LCCs exhibited the highest frequency of β-O-4 linkages. The benzyl ether (BE) bonds were only detected in the fractions obtained by acidic water precipitation.
KeywordsEucalyptus Lignin–carbohydrate complexes (LCCs) Selective precipitation Structure Linkage 2D HSQC NMR
This work was financially supported by the National Natural Science Foundation of China (31430092 and 31400296) and the Fundamental Research Funds for the Central Universities (2015ZCQ-CL-02).
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