title: Structural changes in xanthan gum solutions during steam sterilization for sterile preparations.
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.
authors.affiliation: Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Aditya
authors.initials: A
authors.lastname: Bindal
authors.forename: Ganesan
authors.initials: G
authors.lastname: Narsimhan
authors.forename: Stanley L
authors.initials: SL
authors.lastname: Hem
authors.forename: Alok
authors.initials: A
authors.lastname: Kulshreshtha
mesh_terms: D002236:Carbohydrate Conformation; D002626:Chemistry, Pharmaceutical; D004337:Drug Carriers / Q000737:chemistry*; D008970:Molecular Weight; D019999:Pharmaceutical Solutions / Q000737:chemistry*; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D012212:Rheology; D013227:Steam; D013242:Sterilization / Q000379:methods*; D014783:Viscosity
chemical_list: D004337:Drug Carriers; D019999:Pharmaceutical Solutions; D011135:Polysaccharides, Bacterial; D013227:Steam; C002563:xanthan gum