The characterization of a viscoelasticity parameter and other rheological properties of various xanthan gum fermentation broths and solutions

Viscoelasticity has important implications in mass transfer and mixing processes. Previous studies regarding to the viscoelastic behaviour of xanthan solutions have been carried out with diluted solutions or they have not covered a wide range of polymer concentrations. In this study, it was shown that the first normal stress difference measured in fermentation broths is highly dependent on shear rate, and this viscoelastic level is modified by the heat treatment to which the broths are subjected as a postfermentative procedure. The viscoelasticity level is different for xanthan solutions prepared with products arising from different sources and for fermentation broths before the heat treatment, if compared with that measured in end-products. In general, the higher the polymer concentration, the higher the viscoelasticity (expressed as first normal stress difference or Weissenberg number). The addition of a biocide, the change in ionic strength and the addition of sucrose to the xanthan solutions, lead to significant changes in the first normal stress difference.List of Symbols A Pa.S^b constant in first normal stress difference power law (N₁=) - b constant in first normal stress difference power law (N₁=) - c kg m^–3 polymer concentration - K Nsⁿ m^–2 consistency index - N₁ Pa first normal stress difference - n flow behaviour index - Wi Weissenberg number,N₁/ - s^–1 shear rate - Pa shear stress - _y Pa Yield stress