Rheological Characterization of Gastric Juices from Bread with Different Amylose/Amylopectin Ratios

Impact of saliva incorporation on the rheological properties of in vitro gastric contents formulated from sour cream

Rheological properties of gastric contents depend on the food ingested, and on the volume and composition of secretions from the host, which may vary. This study investigates the impact of saliva regular incorporation in the stomach after a meal on the rheological properties of gastric contents, considering two levels of salivary flow (low = 0.5 and high = 1.5 mL/min). In vitro chymes were obtained by mixing sour cream, simulated gastric fluid, two different volumes of oral fluid (at-rest human saliva, SSF for Simulated Salivary Fluid or water) and adjusting pH at 3. Chymes samples were characterized at 37°C for their particle size and rheological properties. Overall, particle size distribution was not different between samples: incorporating a larger volume of saliva resulted in more heterogeneity, but the surface area moment D[3,2] and volume moment D[4,3] did not differ significantly with the oral fluid type. Shear viscosity of chyme samples was higher when saliva was incorporated, in comparison with water or SSF. In addition, as shown from data extracted atγ ̇ $$ \dot{\gamma} $$  = 20 s-1 the higher the fluid volume the lower the shear viscosity, which is attributed to a dilution effect. However, this dilution effect was attenuated in the case of saliva, most likely due to its composition in organic compounds (e.g., mucins) contributing to the rheological properties of this biological fluid. In these in vitro conditions, both saliva and the salivation rate had a significant but slight impact on the rheological properties of gastric contents (of the order of 1-5 mPa s atγ ̇ $$ \dot{\gamma} $$  = 20 s-1).

Quantitative visualization study on the physical movement and gastric emptying of diced carrot particle in a transparent rat stomach-duodenum model

In this study, a transparent soft-elastic silicone rat stomach model was prepared to visualize the gastric movement and emptying of one individual diced carrot in a dynamic in vitro rat stomach system. The influences of the viscosity of solution medium, the pattern of gastric peristalsis and the extraction rate of the emptying pump on the location and gastric residence time of the carrot particle were examined. A proper medium viscosity could promote the emptying of the carrot particle. Compared to the combined actions of plate and roller, gastric residence time of the carrot particle was reduced from 32.3 to 19.8 min under the single plate compression. This time was also shortened from 34.8 to 12.3 min when the extraction rate of emptying pump was changed from 100 mL/min to 400 mL/min. Knowledge gained from this work is unique and may provide new insights for optimizing biomimic gastrointestinal models.

Flow and mixing by small intestine villi

Flow and mixing in the small intestine are multi-scale processes. Flows at the scale of the villi (finger-like structures of ≈500 μm length) are poorly understood. We developed a three-dimensional lattice-Boltzmann model to gain insight into the effects of villous movements and the rheology of digesta on flow, mixing and absorption of nutrients at the periphery of the intestinal lumen. Our model simulated the hydrodynamic consequences of villi movements that resulted from folding of the mucosa during longitudinal contractions. We found that cyclic approximation and separation of groups of villi generated laminar eddies at the edges of the group and augmented mass transfers in the radial direction between the inter-villous space and the intestinal lumen which improved the absorption of nutrients and mixing at the periphery of the lumen. This augmentation was greater with highly diffusible nutrients and with high levels of shear-thinning (pseudoplasticity) of the fluid. We compared our results with bulk flows simulations done by previous workers and concluded that villous movements during longitudinal contractions is a major radial mixing mechanism in the small intestine and increases mixing and absorption around the mucosa despite adverse rheology.