The impact of saliva on digestion is described through its enzymatic content1, antioxidant properties2 or the effect it may have on emulsions3. In such studies, however, the concept of interindividual variability in saliva flow rate or composition is not considered. Our own results of in vitro digestion of cheese in presence of saliva or water showed that saliva decreased slightly proteolysis in the gastric phase, which we attributed partly to a modification of the chyme (i.e., gastric content) physical properties. The objective of this work was therefore to evaluate specifically the impact of saliva incorporation on the rheological properties of in vitro chymes. The model food used was whole milk. Based on the definition of gastric emptying half-time of foods4, and on the range of non-pathological salivary flow rates5, we produced in vitro chymes representing gastric conditions in subjects with low and high salivary flow rates, using either human saliva or an ionic solution (SSF for Simulated Salivary Fluid). The four different chymes also contained an ionic solution simulating gastric secretions (SGF for Simulated Gastric Fluid) and pH was adjusted at 3. A flow test was performed on the chymes (n=3 per condition) at 25°C: stress (Pa) was measured as a function of shear rate (1/s) from 10 to 200 s-1. From these data were extracted values of threshold and plastic viscosity. The main result of interest is that both the type of oral fluid and the incorporation rate had a significant effect on plastic viscosity: it was higher in presence of saliva, and with high rates of incorporated fluid regardless of the type of fluid. Concerning the latter, a higher dilution may have been expected to reduce plastic viscosity. On-going experiments therefore aim at investigating the impact of ionic strength on the chyme microstructure and its rheological properties. Eventually, the chymes will be subjected to an in vitro model of digestion to assess the impact of structural and rheological differences on digestive hydrolyses.