Reliability in viscosity measurement of thickening agents for dysphagia management: Are results obtained by cone‐and‐plate rheometers reproducible between laboratories?

Viscosity measurement using a cone-and-plate rheometer is considered to provide an objective and reliable evaluation of thickening agents for dysphagia management. Here, we showed its measurement uncertainty in the context of an inter-laboratory study. Eight test samples (i.e., four viscosity standard liquids, one xanthan gum reagent powder, and three commercial thickening agent powders) were distributed to 10 laboratories in a blinded manner. According to the same standard operating procedure, each laboratory dissolved the xanthan gum or thickening agents at four concentrations (0.5-4.0 g/100 g) and then measured their viscosity (35-803 mPa∙s). As for the viscosity of the standard liquids, the grand means were 98-100% of the certified values, and the relative standard deviations for repeatability (RSD