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  • Title: Structural changes in xanthan gum solutions during steam sterilization for sterile preparations.
    Author: Bindal A, Narsimhan G, Hem SL, Kulshreshtha A.
    Journal: Pharm Dev Technol; 2007; 12(2):159-67. PubMed ID: 17510887.
    Abstract:
    Steam sterilization of xanthan gum solutions at 121 degrees C caused a decrease in the helix conformation as well as the molecular weight distribution with a corresponding increase in the coil structure. The effect was directly related to the exposure time and inversely to the xanthan gum concentration, thus suggesting a two-step mechanism of disentanglement followed by degradation with the first step being predominant at higher concentrations. Mark-Houwink exponent of 0.9002 for the intrinsic viscosity of xanthan gum compared favorably with reported values in the literature. The model for intrinsic viscosity of a free draining coil yielded an expansion coefficient of 1.2 (independent of molecular weight) and a root mean square radius of unperturbed chain in the range of 189.5-368 nm. The root mean square unperturbed chain length increased with molecular weight without reaching an asymptotic value, thus indicating that the xanthan molecule behaved as a stiff chain.
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