Chemical modification and fractionation of pea stem polysaccharides

Pea stem tissue was fractionated by chemical and enzymatic methods and the water soluble fractions analyzed by NMR spectroscopy and high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The obtained results indicate that arabinogalactoxyloglucan in similar purity could be isolated by one-step extraction with 2% NaOH or 5% ZnCl 2, as well as by two-step treatment with pronase and α-amylase. By quaternization under alkaline conditions with 3-chloro-2-hydroxyprophyltrimethylammonium chloride (CHMAC), a mixture of arabinogalactan and galacturonan modified with trimethylammoniumhydroxypropyl (TMAHP) group (10.8% yield) could be isolated. By extraction with 2% NaOH, a fraction in 19.0% yield could be obtained, contrary to 2.4% yield of polysaccharide when treated with 5% ZnCl 2. Treatment with pronase and amylase have given 1.5 or 4.5% yields of soluble frations, while the subsequent residue extracted with ammonium oxalate gave galacturonic acid oligomers (2.1% yield). Direct extraction with (NH 4) 2(COO) 2 and without enzymatic pretreatment solubilized only a small part of the material (0.9% yield) consisting of three polysaccharide fractions having the highest molecular weight from all obtained fractions.