Isolation and structural characterization of the water-extractable polysaccharides from Cassia obtusifolia seeds

The seed of Cassia obtusifolia is a food or herbal medicine used for improving eyesight, treating constipation and other disorders, and polysaccharides have been implicated in these pharmacological activities. The endosperm of the seeds, Cassia gum, is a commercial thickening or gelling agent, composed mainly of galactomannans. However, the whole seeds of C. obtusifolia, rather than the endosperm, are used in folk medicine or food, which might contain more complex constituents of polysaccharides. In this study, the whole seeds of C. obtusifolia were extracted with boiling water, and from the water extract, three homogeneous fractions were isolated, designated CFAA-1, CFAA-3, and CFBB2, respectively, after treatment with Fehling solution followed by anion-exchange and gel permeation chromatography. Using chemical and spectroscopic methods, CFAA-1, and CFAA-3 were elucidated to be both branched galactomannans with different molecular weights, consisting of 1,4-linked β-d-mannopyranosyl backbone with single-unit α-d-galactopyranosyl branches attached to O-6 of mannose, while CFBB2 was shown to be a linear (1 → 4)-α-polygalacturonic acid.