Shear and Extensional Flow Rheology of Mucilages Derived from Natural Foods

Abstract

Food bolus cohesiveness plays an important role to suppress miss-swallowing in swallowing disorder. The cohesiveness of masticated particles can be enhanced by binding liquids, which often represent high spinnability similarly as oral saliva does. Thus, in addition to shear viscosity, the extensional viscosity is important to control the bolus swallowing. Using a capillary thinning extensional viscometer, this study measured the extensional viscosity of natural okra, yam, and kelp mucilage in addition to whole saliva and a thickener solution for liquid care foods. The mucilages showed very high extensional viscosity, which was two or three orders of magnitude higher than the shear viscosity. The rheological characteristics for shear and extensional flow were found to be described by a Giesekus model approximately. The results obtained here can be applied to simulate the bolus swallowing numerically and to improve care foods for swallowing disorder.

Numerical simulation of pharyngeal bolus flow influenced by bolus viscosity and apparent slip

“…The wall layer is thin compared with the pipe radius R, and thus the wall layer shear rate is high for the viscous core fluid. Saliva viscosity is low at a high shear rate and approaches the viscosity of the solvent (water) (Stokes & Davies, 2007;Zhu & Mizunuma, 2017). increases with η c in contrast to the decreasing _ γ core of the first term.…”

Optimizing Texture Modified Foods for Oro-pharyngeal Dysphagia: A Difficult but Possible Target?

“…Bearing in mind the fact that for a Newtonian fluid G ′ = 0 occurs, it is evident that the elastic component plays a fundamental role with respect to the extensional behaviour of a non Newtonian fluid, even if it is not possible to consider separately the viscous and elastic effects due to the non-linearity of the materials ( 41 ). Although extensional viscosity has not been much discussed so far for dysphagia, an additive that can provide a high extensional viscosity may contribute to bolus cohesiveness during the swallowing process ( 42 ).…”

Influence of Rheological Characteristics on Liquid Residue in Stagnant Free Surface Flow (Rheological Approach for the Suppression of Post-swallow Residue in Pharynx)

“…The mucilage was extracted in a similar manner as in our previous study. 9) The thickener used was a commercial product for care foods (Neo high toro meal, Food-care Inc., Kanagawa). The ingredients are dextrin, polysaccharide, and acidity regulator.…”

“…The method was same as that used by Zhu and Mizunuma. 9) The measurements of extensional viscosity were conducted in a temperature-controlled room of 20 °C.…”