On the assessment of shear and extensional rheology of thickened liquids from commercial gum-based thickeners used in dysphagia management

Abstract

In order to promote safe swallowing in dysphagia patients, it is of interest to study the rheological properties of thickened liquids from various commercial gum-based thickening powders using small amplitude oscillatory shear, steady shear and extensional measurements. The active hydrocolloid of the studied samples included xanthan gum, guar gum or tara gum. Shear rheology measurements showed that all samples exhibited shear thinning behaviour that can be described by the Cross model. With comparable viscosity at shear rate 50 s −1 , the xanthan gum-based samples exhibited higher zero shear viscosity and longer relaxation time than the guar gum and tara gum-based samples. Furthermore, they behaved as weak gels while the other samples showed viscoelastic liquid behaviour at IDDSI (International Dysphagia Diet Standardisation Initiative) level 1 to 3. Extensional rheology revealed that the breakup time of these samples were xanthan gum > guar gum > tara gum, suggesting more superior cohesiveness of xanthan gum-based compared to the others. • Water thickened with different types of thickeners can have similar shear viscosity at shear rate 50 s -1 but very different extensional viscosity. • Xanthan gum-based thickened water behaves as concentrated solutions with higher extensional viscosity than guar gum and tara gum-based samples. • Xanthan gum-based thickened water is less likely to fracture during swallowing compared to the guar gum and tara gum-based samples. • The characteristic fluid relaxation time (λ E ) may be used to describe the cohesiveness of thickened fluid/bolus. • Extensional rheology may be an essential tool to define a safe-swallow bolus.