Viscosity of Liquid Nutrition Products with Thickeners in Association with Temporal Changes Evaluated via the Syringe Test

Abstract

　In the Japanese Dysphagia Diet defined based on 2021 guidelines, the “syringe method” was newly introduced as a simple and low-cost method for measuring viscosity. To our knowledge, viscosity assessments using the syringe test to evaluate the thickening of liquid nutrition products have not been described in prior research or in any medical guidelines to date. We evaluated four kinds of liquid nutrition products and six kinds of thickeners. Thickeners were dissolved in liquid nutrition products. Changes in viscosity were determined based on the dissolution amount and stationary time evaluated via the syringe test and were compared with viscometer measurements and organoleptic evaluations. Liquid viscosity was scored and categorized into five levels based on the residual amount of liquid via the syringe test, as was objectively measured viscosity (i.e., measured via a viscometer) and the results of organoleptic evaluations. We verified the consistency of these scores across evaluation methods. When liquid nutrition products were thickened with thickeners, viscosities evaluated via the syringe test were lower than objectively measured viscosity values. The differences between syringe and viscometer assessments were especially large for high-viscosity liquids. However, the viscosity scores assessed via organoleptic evaluation tended to be similar to scores obtained via simple tests and the syringe tests. It is preferable to understand these properties when measuring the thickness of liquid nutrition products using the syringe test or other methodologies.