Interactions of the Beechvood Xylan Component with Other Cell Wall Polymers

ABTRACT

Sodium chlorite holocellulose of beechwood was extracted in succession with aqueous ammonia solutions of increasing concentration (1–26% NH₄OH), and finally with 5% sodium hydroxide. The polymeric fractions obtained were composed mainly of 4-0-methylglucuronoxylan polymers which occur in two distinct molecular populations. The 1% NH₄OH-extract contained the most accessible polysaccharide fraction which represents a mixture of O-acetylated 4-0-methylglucuronoxylan, residual lignin, cellulose fragments and pectic polysaccharides of the rhamnogalacturonan type containing arabinan and galactan chains. A 4-0-methylglucuronoxylan-polygalacturonan complex with a minor proportion of neutral sugars and residual lignin was isolated from the 10% NH₄OH-extract. The results suggest that some of the residual lignin and pectic polysaccharides are bound by alkali-stable linkages to xylan and/or cellulose chains in the cell-wall complex.