Improvement of simplified inclined plane test for evaluation of thickened liquids by using optical sensor

The thickening management index for food for dysphagia is important in enabling recognition of the rheological properties of thickened liquids, including their static and dynamic properties. One of the static properties of these liquids is the yield stress. An improvement to the simplified inclined plane test is proposed here that involves use of an automatic system for measurement of the displacements of thickened liquids on an inclined plate. The aim of this study is to investigate the relationship between the displacements of the thickened liquids and the variable thickener concentrations using an optical sensor. To measure the displacement of each thickened liquid on a clear inclined plate, an optical sensor that has a 12-mm-long light receiving surface is selected to form a one-dimensional position-sensitive detector (1D-PSD) under the clear inclined plate. The relationship between the angle of inclination of the plate θ at which the maximum voltage occurred in the 1D-PSD and five thickener (xanthan gum) concentrations c, ranging from 1.0 to 3.0 wt% in steps of 0.5 wt%, was investigated. It was confirmed that an approximately linear plot was obtained under the condition that θ = 8.24 c + 0.18, with the correlation R = .99 (for n = 7). This result indicated that the optical sensor composed of the 1D-PSD can measure the displacements of thickened liquids with various thickener concentrations on the clear inclined plate automatically.