Liu, Claire Ann; (2001) An investigation into the gel characteristics of xanthan gum-locust bean gum mixes. Doctoral thesis (Ph.D.), University College London.

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Abstract

Xanthan gum and locust bean gum are two naturally occurring polysaccharides which do not form gels in isolation, but undergo a positive synergy to form thermoreversible elastic gels in combination. The aim of this project was to investigate the interaction between the two polysaccharides and factors affecting the gel characteristics of the mixes, with a view to developing their pharmaceutical uses. The individual polysaccharides were characterised using flame emission spectrometry and nuclear magnetic resonance spectroscopy for xanthan gum and fractionation for locust bean gum. The gel strengths of the mixed systems were studied using oscillatory rheology and texture analysis with respect to temperature, fractionated locust bean gum and the inclusion of either sodium chloride or sucrose as additives. Conformational changes of xanthan gum which are thought to contribute to the mechanism of the interaction were studied using a combination of high sensitivity differential scanning calorimetry and synchrotron circular dichroism. The findings from these studies led to the development of methods for formulating controlled release tablets using a wet granulation process. The results show that maximum synergy occurs for the 1:1 ratio between xanthan gum and locust bean gum, in which the gelation process is temperature dependent and is enhanced by heating and cooling between 20°C to 90°C. The effects of sucrose and locust bean gum fractions with a high mannose:galactose ratio increase the gel strength, whereas the inclusion of sodium chloride has no effect on the gel strength of xanthan gum-locust bean gum mixes. The thermoanalysis techniques used to determine xanthan gum conformation suggest that xanthan gum interacts with locust bean gum both in the disordered coil and ordered helical forms. These findings were employed for the formulation studies, which showed that xanthan gum conformation which is affected by different factors, depends upon an aqueous environment which in turn affects the synergy with locust bean gum and hence the release properties from the gel matrix. This work suggests that the techniques chosen for this project are highly complimentary and a useful approach for studying the behaviour of mixed polysaccharide gel systems, which may exhibit different properties when formulated into tablet dosage forms.

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