Abstract
Shear viscosity is the main property linked to the therapeutic effect of thickening products (TP) and can be reduced by the effect of salivary α-amylase during the oral phase and shear thinning during the pharyngeal phase of swallowing. The main aim of this study was to determine the time-effect salivary α-amylase. The study solutions were prepared with three types of TP: modified starch (MS), xanthan gum (XG), and mixture (MX), and two viscosity levels: 250 and 800 mPa·s at 50 s(-1). Five volunteers performed oral incubations from 5 to 60 s to assess the time-effect of α-amylase. The results revealed that MS-TP presented a sudden reduction in shear viscosity >99% at 5 s at both viscosity levels. In contrast, XG-TP showed only a slight reduction (1-20%) to α-amylase for all the time intervals. MX-TP viscosity exhibited a reduction of 25% for 250 and 13% for 800 mPa·s. The immediate and extreme reduction in shear viscosity of MS-TP in contact with α-amylase contrasted with the amylase resistance presented by TPs that contained XG. These findings improve the description of the full rheological behavior of TP and provide valuable insights into optimizing the choice of TP in the management of patients suffering from swallowing disorders.