Determination of a Suitable Shear Rate for Thickened Liquids Easy for the Elderly to Swallow

Abstract

Thickening agents are usually added to thin liquids administered to dysphagic patients to prevent aspiration. In this study, we aimed to identify the viscosity best suited for easy swallowing in elderly people and to examine the optimal shear rate for measuring, through sensory evaluation, these thickening liquids. Ten elderly participants were selected for sensory evaluation of diluted solutions for ease of swallowing and stickiness. Diluted solutions containing > 2.0% xanthan gum-based product were judged to be significantly more difficult to swallow than solutions containing < 2.0%. Fifty-two healthy panelists were selected for sensory evaluation of oral viscosity to compare sensory evaluation with instrument-based viscosity measurement. We found that the optimal shear rate was approximately 100 s^-1. These findings indicate that the thickening agent-diluted solutions that the elderly found difficult to swallow exceeded 120 mPa·s at a shear rate of 100 s^-1.