A biomechanical model of swallowing for understanding the influence of saliva and food bolus viscosity on flavour release

TL;DR

This study develops a biomechanical model of swallowing to analyze how saliva and food viscosity influence mucosa coating and flavor release, revealing conditions where viscosity effects are significant or negligible.

Contribution

It introduces a new elastohydrodynamic model that predicts mucosa coating dynamics considering saliva flow, viscosity ratios, and elasticity, explaining in vivo flavor release phenomena.

Findings

Food viscosity impacts flavor release when saliva film is thin.

Thick saliva films dilute food coating, reducing viscosity effects.

Predicted mucosa coating thickness aligns with experimental data.

Abstract

After swallowing a liquid or a semi-liquid food product, a thin film responsible for the dynamic profile of aroma release coats the pharyngeal mucosa. The objective of the present article was to understand and quantify physical mechanisms explaining pharyngeal mucosa coating. An elastohydrodynamic model of swallowing was developed for Newtonian liquids that focused on the most occluded region of the pharyngeal peristaltic wave. The model took lubrication by a saliva film and mucosa deformability into account. Food bolus flow rate and generated load were predicted as functions of three dimensionless variables: the dimensionless saliva flow rate, the viscosity ratio between saliva and the food bolus, and the elasticity number. Considering physiological conditions, the results were applied to predict aroma release kinetics. Two sets of conditions were distinguished. The first one was obtained when the saliva film is thin, in which case food bolus viscosity has a strong impact on mucosa coating and on flavour release. More importantly, we demonstrated the existence of a second set of conditions. It was obtained when the saliva film is thick and the food bolus coating the mucosa is very diluted by saliva during the swallowing process and the impact of its viscosity on flavour release is weak. This last phenomenon explains physically in vivo observations for Newtonian food products found in the literature. Moreover, in this case, the predicted thickness of the mix of food bolus with saliva coating the mucosa is approximately of 20 $\mu$m; value in agreement with orders of magnitude found in the literature.