  Swallowing disorders deteriorate significantly the quality of life and can be
lifethreatening. Texture modification using shear thinning food thickeners have
proven effective in the management of dysphagia. Some studies have recently
considered the positive role of cohesiveness, but there is still an
insufficient understanding of the effect of the rheological properties of the
liquid bolus on the dynamics of bolus transport, particularly when elasticity
and extensional properties are combined with a shear thinning behaviour. This
study combines steady shear, SAOS and capillary breakage extensional rheometry
with an in vitro method to characterize the oral transport of elastic liquids.
Bolus velocity and bolus length were measured from in vitro experiments using
image analysis and related to the shear and extensional properties. A theory
describing the bolus dynamics shows that the elastic and extensional properties
do not influence significantly the oral transit dynamics. Conversely, in vitro
results suggest that the extensional properties can affect the transition from
the oral to the pharyngeal phase of swallowing, where thin, viscoelastic
liquids lead to a fast transit, lower oral post-swallow residues and more
compact bolus with a smoother surface, which may suggest a lower risk of
fragmentation. This mechanistic explanation suggests that the benefit of the
extensional properties of thin viscoelastic liquids in the management of
dysphagia should be further evaluated in clinical trials.
