The Role Of Shear Rheology And Extensional Rheology In Controlling A Swallowing Process

Aging is an unprecedented challenge in human history.Physiological function is weakened for many elderly people,especially chewing and swallowing.How to provide safe and healthy food to elderly is a major challenge to food industry,not only in developed countries but also in many developing countries.In this work,shear and extensional rheological properties of few common food thickeners have been studied in relation to their roles in bolus swallowing.Main conclusions are listed below:(1)The rheological properties of guar gum,carrangeenan,xanthan and CMC-Na are the main commercial thickening agents used for dysphagia diets.Both shear and extensional viscosity of these thickeners increases with the increasing of concentrations.All the thickeners show behaviour of shear thinning and extensional thinning.Guar gum solutions also show time dependent.Its shear viscosity decreases gradually with the time at the same deformation rate,showing the behaviour of thixotropy.(2)Correlations between objectively measured viscosity and sensory perceived viscosity have been investigated for guar gum and CMC-Na solutions.It was found that human perception is significantly more sensitive in discriminating extensional viscosity than in discriminating shear viscosity.Stevens' law provides an adequate description of both shear and extensional viscosity,with n values reaching 1.24 and 0.54 for extensional and shear viscosity respectively.Further JND(Just Noticeable Difference)analysis revealed that humans could on average perceive an extensional viscosity difference of only 6.20%,but for shear viscosity this figure increases to 9.33%.(3)Volunteers were invited to swallow a series of solutions of commercial products with different shear viscosity and extensional viscosity,and then to evaluate ease of swallowing.Correlations were analysized between shear viscosity and sensory score,and also between extensional viscosity and sensory score.It was found that extensional rheology played a more dominated role in the swallowing process,while shear rheology also played a role,but relatively minor.