Challenges to assumptions regarding oral shear rate during oral processing and swallowing based on sensory testing with thickened liquids

Abstract

For people with dysphagia, or difficulty swallowing, thickened liquids are used to slow bolus flow to make them easier to control. For these liquids, the oral shear rate of 50 s−1 has been adopted as the standard at which viscosity measurements are taken. However, there is evidence to suggest that other shear rates may be more appropriate to model the processes in the mouth and throat. This research compared the sensory and rheological properties of xanthan gum, guar gum, and carboxymethyl cellulose thickened liquids that had been matched for apparent viscosity at 50 s−1 to assess the validity of the current shear rate standard. Properties of gums were observed at various viscosity levels based on the International Dysphagia Diet Standardisation Initiative (IDDSI) framework. Textural sensory characteristics of samples were quantified using magnitude estimation scaling and a trained descriptive panel, while rheological measurements were taken at shear rates of 1 to 1000 s−1. Perceived slipperiness of the gums was found to be driven by thickness level at low viscosity levels, but affected by the shear thinning behavior of the gums at higher viscosity levels. Although the liquids had been matched for apparent viscosity at 50 s−1, panelists could distinguish both the perceived viscosities of the gums and their ease of swallowing, suggesting that 50 s−1 is neither appropriate to model the oral nor pharyngeal shear rates. A single oral shear rate could not be predicted from the data, and it is proposed that panelists evaluated oral viscosity using different methods at different viscosity levels. Based on the sensory data, the pharyngeal shear rate during swallowing appears to lie above 50 s−1.

Gellan gum: A new member in the dysphagia thickener family

“…Figure 2 shows the behaviour of the 5 wt% commercial dysphagia thickeners (MS and NT) and 0.5-1.0 wt% xanthan gum. In absence of artificial saliva or the buffer, both the starch-based Apparent viscosity was examined over a large shear rate range, although the discussion will be focusing on a range of shear rate from 1 to 100 s -1 corresponding to the orally relevant shear rate range established in recent studies [6,36]. All the commercial starch-based thickeners showed typical pseudoplastic behaviour as their apparent viscosity decreased with an increase in shear rate (Figure 2Ai).…”

Bolus rheology and ease of swallowing of particulated semi-solid foods as evaluated by an elderly panel

“…The list of sensory attributes was prepared based on previous studies. [16][17][18][19] During the familiarisation session, the protocol and the different sensory attributes were explained and discussed with the panellists to ensure that they were familiar with the samples and the vocabulary used to define the sensory attributes. Reference samples were also evaluated to understand the scales for rating the attributes.…”

The role of extensional rheology in the oral phase of swallowing: an in vitro study

“…Under the IDDSI framework, thickened beverages are classified via a simple gravity discharge test 13 . This flow test has already been considered by several authors [14][15][16][17] , but a relationship between the liquid rheology and the IDDSI scale has not yet been comprehensively investigated. While there is general agreement that texture modified liquids reduce aspiration, but the mechanistic reasons why this occurs are still debated.…”