A proposed method of evaluating the yield stress of a thickened liquid using a simplified inclined plane test

Managing the thickening index of food is important for dysphagia and helps in recognizing the static and dynamic rheological properties of the thickening agent. One dynamic property is the viscosity under a shear rate of 50 s^-1 , and one static property is the yield stress at a shear rate of 0 s^-1 . The purpose of this study is to design a simplified inclined plane test to identify the yield stress of a thickened liquid by observing flow behavior on an inclined plate. The yield angle (stress) is defined as the inclination angle of the plate just before the thickened liquid flows. The concentrations (yield stresses, yield angles) of a thickening agent containing xanthan gum are 1.0 (1.2, 3°), 1.5 (5.6, 13°), 2.0 (7.5, 26°), 2.5 (12.5, 26°), and 3.0 (19.1, 42°) wt% (Pa, degrees). We measured the time course of the displacement of the downstream edge (DDE) of the thickened liquid on the inclined plate. The discrete inclination angles were in the range of 0° to 42°. The DDE after 10 s was more than 4.5 mm for all concentrations of the thickening agent at an inclination greater than the yield angle of the plate. We confirmed that the yield angle identifies the yield stress for the thickened liquid via the DDE using the simplified inclined plane test with discrete inclination angles.