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Rheological studies on the interaction of xanthan and locust bean gum in aqueous dispersions Gatchair, Sonia Denise


Aqueous dispersions of xanthan and locust bean gum, in combination, show a synergistic increase in viscosity. At sufficiently high concentrations, firm gels are formed, although neither component forms true gels when alone. The actual molecular processes resulting in this phenomenon are still incompletely understood and Theological studies can provide some clues to the mechanism of the interaction. Rheological properties of the polysaccharide blend were therefore investigated. Moisture, ash and inorganic elements and protein content as well as the intrinsic viscosity of the individual polysaccharides were determined. Dynamic viscoelastic properties of dispersions prepared from the polysaccharide blend were evaluated in four solvent treatments capable of disrupting weak intermolecular bonds. The effect of polysaccharide concentration, temperature, ionic strength, pH, ratio of mixing of the two gums and urea concentration on steady shear rheological properties were evaluated in a fractional factorial experiment. More detailed studies were carried out on the effects of temperature at two levels of concentration and ionic strength. Solvent treatments significantly affected the viscoelastic properties of xanthan-locust bean gum solutions. At 20°C and under the conditions used, dipole interactions appeared to be the primary force responsible for stabilizing the xanthan-1ocust bean gum interacting system. Hydrogen bonding and hydrophobic interactions seemed to play less important roles. Under conditions of low ionic strength and increased temperature, the interactions were lost and polysaccharide solution behavior passed from that of a viscoelastic solid to that of a viscoelastic liquid. At 60°C and at high ionic strengths, hydrophobic interactions may become important in the stabilization of the three dimensional gel network. Temperature effects on steady shear viscosity of xanthan-locust bean gum solutions were dependent on the concentration and ionic strength of the system. In general, steady flow properties were comparable to the reported behavior of xanthan solutions and so reflected the weakness of the interaction (dipole interactions) between the two polysaccharides.

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