The role of human saliva on the elongational properties of a starch-based food product

In the medical context of swallowing disorders, human saliva may play an essential role, affecting the rheological properties of starch-based thickened products, due to the effect of the alpha-amylase, a protein enzyme naturally present in saliva. The aim of this work was to compare the effect of three different salivary solutions on the uniaxial properties of a starch-based food product (SBFP). Extensional rheology properties of SBFP after addition of solution containing a commercial alpha-amylase, mechanically stimulated saliva, or in-vivo stimulated whole human saliva, were measured by using a CaBER (Capillary Break-up Extensional Rheometer) device. Extensional and oscillatory shear results for the different types of salivary solutions were then analysed. These results showed that in-vivo stimulated whole human saliva provides an increased SBFP elasticity, while the alpha-amylase dramatically decreases its viscoelastic functions in oscillatory shear. The results obtained also suggest that mechanically stimulated saliva and alpha-amylase aqueous solutions do not offer adequate information concerning the real extensional properties of the bolus when blended with whole human saliva.