Sensory discrimination of the viscosity of thickened liquids for dysphagia management

Thickened water and thickened milk are frequently used in dysphagia management. However, there is still lack of information regarding the correlation between their measured viscosity and sensory viscosity. In this work, the relationship was investigated by rheological measurements and a series of tactile sensory tests. Both magnitude estimation (ME) and triangle protocols were used for the evaluation. The rheological data indicated that both thickened water and thickened milk were shear thinning, but the shear viscosity of thickened milk was obviously higher than that of thickened water for the same amount of thickeners. For the participants considered, the perception of thickened water and thickened milk both obeyed the Stevens' power law according to the results of ME. It was found in the triangle assessments that within the proposed nectar‐ and honey‐thick viscosity ranges, participants were able to correctly discriminate a 0.83‐fold and a 1.05‐fold increase in shear viscosity for thickened water and thickened milk, respectively. Results of both ME and triangle tests suggested that human abilities in detecting the viscosity changes of thickened water and thickened milk by finger tactile sensory were similar within nectar‐ and honey‐thick viscosity range in spite of their different compositions and rheological properties. PRACTICAL APPLICATIONS: Thickened water and thickened milk are commonly used in the management of individuals with dysphagia to improve their quality of life. However, it is difficult to determine the optimal thickening degree in clinical practice because there is a lack of information of the perception of their rheological properties. To investigate the human sensory ability in detecting viscosity differences of thickened water and thickened milk is essential to improve our understanding of the perception of thickened liquids. Moreover, it provides significant information for manufacturing high quality thickened liquids products and for setting guidelines for effectively preparing and serving thickened liquids to individuals with dysphagia.