The gel nature and structure of the carbohydrate of ispaghula husk ex Plantago ovata Forsk

Abstract

Mucilage from the seed husk of Plantago ovata Forsk is an arabinosyl(galactosyluronic acid)rhamnosylxylan. A wide range of molecular sizes was revealed by chromatography of the methylated mucilage on Sephadex LH-60, and the resulting 12 fractions were homologous. Partial hydrolysis with acid and enzymic hydrolysis variously of the mucilage and carboxyl-reduced mucilage led to identification of the β- d-xylosyl residues forming the xylan backbone of the polymer. Similarly, the arabinose, rhamnose, and galacturonic acid residues were shown to be α- l, α- l, and α- d, respectively. A structure for the polysaccharide is proposed and related to gel formation. Electron microscopy of the gel revealed a co-linear association. This association is reversible, and therefore not the result of covalent bonding.