Lignin—Carbohydrate Complexes from Poplar Wood

Abstract

Four distinct lignin-carbohydrate complexes (LCCs) were isolated from a thermal hydrolysate of Populus deltoides wood by a preparative sequence involving extraction with ethyl acetate, ethyl alcohol, and exhaustive fractionation on a variety of gel filtration media. Purified LCCs presented peaks of superimposable carbohydrate content and ultraviolet absorption when subjected to gel filtration chromatography wherein each given species eluted within the included gel volume. While LCCs of apparent high molecular size were typified by high ultra-violet absorption, lower total carbohydrate, and critical micelle concentrations in the range of 20 to 35 micrograms dry weight, LCCs of apparent low molecular weight possessed less ultraviolet absorbance, significantly more carbohydrate, and critical micelle concentrations that were 10-fold greater on average than the larger sized species. All LCC preparations were highly O-acetylated, and contained varying proportions of glucose, xylose, mannose, and uronic acids. Treatment of purified LCCs with a variety of enzymes including acetyl xylan esterase, xylanase, β-mannanase, and β-glucosidase independently and in combination, while not producing monomeric (carbohydrate) components, generated products of altered gel permeation and critical micelle concentration properties.