Solubility and molecular weight of hemicelluloses from Alnus incana and Alnus glutinosa. Effect of tree age

The xylems of Alnus incana Moench. and Alnus glutinosa Gaertn. 8-15-year-old trees were subjected to comparative studies regarding the molecular weight (MW) of hemicelluloses. Extraction of hemicelluloses according to the sequence 1% NaOH-10% KOH-18% NaOH, followed by direct analysis of each extract using the SEC/UV method, was applied aiming at simultaneous quantitative and MW analysis. Both the tree age and alder species were found to affect the behaviour of hemicelluloses in alkaline solutions as well as their MW. Under equal extraction conditions, the solubility of xylan increased for A. incana and decreased for A. glutinosa with the tree age. For glucuronoxylan and glucomannan, a cyclic MW oscillation within a certain range throughout the tree growth was found. Both the sinusoid- and impulse-type of MW changes were suggested. The MW of arabinogalactan and xyloglucan decreased to a certain invariant value in the tree age period under investigation.