Physicochemical characterization of mechanically modified xanthan gum solutions

Mechanical modification of xanthan gum through application of high shear conditions was investigated in order to understand the reason underlying physicochemical changes of hydrocolloid solutions after they were subjected to dynamic high pressure conditions. Two different pressures were applied (69 MPa and 276 MPa) to a 1 % XG solution by using a Nano Debee Homogenizer (B.E.E International, Inc.). Both treated and control (untreated xanthan gum) solutions were stored at two different temperatures (4 °C and 25 °C) for 11 weeks. Results showed decreased viscosity and elasticity upon treatment compared to the control. Decrease in viscosity and viscoelasticity was attributed to the increase of the maximum packing of the dispersion due to the wider distribution of molecular weight and sizes of the treated samples, which were measured by SEC-MALS. The stress relaxation behavior, which changed from a viscoelastic to a liquid-like material along with an observed increased sensitivity on material viscoelasticity with temperature clearly indicates the loss of structured network of xanthan with the shear treatment. Circular Dichroism spectra of treated samples further support the less structured and more disordered network upon high pressure homogenization. Measurements on time stored samples showed unperturbed rheological characteristics suggesting the structural modifications in the xanthan gum molecules after treatment are not purely intermolecular and are irreversible