Characterisation of water-soluble galactoglucomannans from Norway spruce wood and thermomechanical pulp

Different fractions of water-soluble polysaccharides, all composed mainly of acetyl-galactoglucomannans, from native Norway spruce wood and thermomechanical pulp were isolated and characterised. About 65% of the mannose units in the glucomannan backbone were acetylated at either the C-2 or C-3 positions in a ratio of 2.2:1.0. Mainly the mannose units, but also some glucose units, were also partly substituted at C-6 by galactopyranose units. The number of galactose side groups at C-6 was considerably lower for acetyl-galactoglucomannans from TMP than from wood. The molar sugar unit ratios of the different fractions of dissolved acetyl-galactoglucomannans differed only slightly. Acetyl-galactoglucomannans dissolved at room temperature, as well as at 90 °C and during prolonged treatment time, contained a large proportion of mannose units. Acidic arabinogalactans were also dissolved at room temperature, while some xylans, pectins, and (1→5)-bonded arabinans were dissolved at higher temperatures and longer treatment times. Also the water-soluble xylans contained acetyl groups, about 0.6 per xylose unit, all attached to C-3.