The hypothesis that galactose and arabinose pectic substances are disributed with lignin throughout wood cell walls was tested by analyzing a high-yield loblolly pine kraft pulp that had been separated into middle-lamella-rich and secondary-wall-rich fractions. The fractions were first treated with a polysaccharidase enzyme mixture to obtain #x201C;enzyme lignins.#x201D; The structures of the galactose and arabinose oligomers remaining attached to the lignin were determined by methylation analysis. The 1#x2192;4 linked galactose structure, characteristic of pectic materials, was present in significant amounts in the middle-lamella-rich fraction, but to only a very small extent in the secondary-wall-rich fraction. In contrast, the pectic arabinan 1#x2192;5 linked structure was a significant proportion of the arabinose from both fractions. The 1#x2192;5 linked arabinose structure can arise from a linkage of arabinoxylan to lignin through the 5 position of the arabinose substituent as well as from pectic structures. After partial acid hydrolysis, approximately half the remaining arabinose in the secondary-wall-rich fraction was attached as monomeric units to lignin through the 5 position.
展开▼
