XANTHAN-LIKE WEAK GEL RHEOLOGY FROM DISPERSIONS OF ISPAGHULA SEED HUSK

Dispersions of isabgol, the milled seed husk from Plantago ovata Forsk (alternatively known as ispaghula), show 'weak-gel' properties broadl y similar to those of xanthan and related polysaccharides with rigid, ordered structures in solution. The origin of this behaviour is attrib uted to tenuous association of fibrillar assemblies visualised by ligh t microscopy. The network structure is retained to approximately 80-de grees-C, but decreases steeply at higher temperatures. The melting pro cess is accompanied by a sharp change in optical rotation of the extra cted polysaccharide component of isabgol. An earlier change in optical rotation at lower temperature is tentatively attributed to conformati onal rearrangement of xylan chains within an ordered, intermolecular s tructure. Aqueous solutions of the extracted polysaccharide form gels which gradually contract on prolonged storage, consistent with progres sive re-formation of the fibrillar structure seen for intact isabgol. Loss of gel-like character in isabgol dispersions occurs over the same temperature range as thermogelation of hydroxypropylmethylcellulose, suggesting opportunities for combined use of the two materials as a su bstitute (or supplement) for gluten in baked products.