High-pressure induced thermo-viscoelasticity and dynamic rheology of gum Arabic and chitosan aqueous dispersions

Effect of high pressure treatment (200 MPa, 400 MPa, 600 MPa) on rheological properties of aqueous dispersions of gum Arabic (6 g/100 g, 15 g/100 g, and 20 g/100 g) and chitosan (2 g/100 g, 4 g/100 g) was studied. Dynamic properties were assessed using an angular frequency range of 1-25 rad s(-1). Flow properties were measured by applying a programmed shear rate of 0.1-100 s(-1) for 10 min (upward) and 100-0.1 s(-1) for the next 10 min (downward). A power law shift function was used to describe the deviations from the Cox-Merz theory in all samples. Thermo-viscoelasticity was evaluated using a programmed heat/hold/cool cycle (22 degrees C/70 degrees C/20 degrees C). Two term-exponential and a Gaussian model well fitted the thermo-viscoelastic behavior of both gums. The thermal compatibility, regarding a logarithmic phase shift of loss tangent ratios, was also studied. Results showed higher incompatibilities at lower temperatures, while the shift phases tended to zero at higher temperatures. Overall, HP treatment intensified the existence of a stronger and temperature sensitive hydro colloid network for 4 g/100 g chitosan and 20 g/100 g GA. The highest incompatibility was seen in 20 g/100 g gum Arabic which was a 1-1.5 order of magnitude.