Polysaccharides in selected industrially important softwood species

The content and composition of carbohydrates comprising polysaccharides in sapwood and heartwood of 12 industrially important pulpwood species were analysed. The total polysaccharide content was between 60 and 80% (w/w) for all species. The main non-cellulosic polysaccharides in the wood samples were galactoglucomannans, except in larch heartwood where arabinogalactans were predominant. The amount of xylans was high in red pine heartwood and northern white-cedar heartwood and sapwood. The main acidic carbohydrate unit in all species was galacturonic acid from pectins. The largest amounts of pectins were found in northern white-cedar and in balsam fir wood. The amount and composition of water-soluble carbohydrates from ground wood samples were also analysed. The main polysaccharides released from the spruce species were mannans, together with starch from sapwood. Especially balsam fir stemwood, but also Siberian fir heartwood, released considerable amounts of pectins, suggesting that more detrimental anionic polysaccharides can be released from fir than from spruce species in mechanical pulping. The heartwood of several species released substantial amounts of acidic arabinogalactans. A recently developed method for recovering galactoglucomannans from mechanical pulp of spruce could also be used for recovering water-soluble polysaccharides from other tree species. The recovered polysaccharides could be used in papermaking to improve runnability and to increase the final paper strength, or in food and pharmaceutical applications.