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Abstract
In vitro gastrointestinal (GI) models that simulate the physiological and biochemical conditions of human GI tract have emerged as a promising tool to understand digestive behavior and fate of food and bioactive compounds. The simulation of GI motility is among the most challenging parts and often oversimplified in the current simulations. The mechanism of how digesta viscosity affect food digestion and absorption has not been fully understood. The overall research goal of this dissertation was to investigate the effect of digesta viscosity on digestive process of selected food in originally developed in vitro GI models that are capable of simulating human gut motility and the resultant fluid mechanical events. In the first study, the impact of chyme viscosity on gastric emptying was investigated in a Gastric Simulator Model (GSM) with peristalsis function. Results showed that chyme viscosity affected gastric emptying primarily by influencing diffusion of nutrients, suspension capacity and flow resistance of solids food. In the second study, the effect of digesta viscosity on intestinal mixing and transit was investigated in a Small Intestinal Simulator (SIS) with intestinal segmentation function. The mixing time was exponentially increased with the logarithm of consistency index. Results also indicated that higher digesta viscosity was associated with longer residence time, but shorter travelling distance and lower contact frequency with the intestinal wall which was less favorable for digestion and absorption. In the third project, the effect of cinnamon on starch hydrolysis of rice pudding was investigated during in vitro digestion, and the digestion process was compared between a static model and a dynamic digestion model consisting of GSM and SIS. Results revealed that significant inhibitory effect of cinnamon on starch hydrolysis was observed during the gastric and intestinal phases in the dynamic model (p < 0.05), but no such effect was found in the static model. The difference was attributed to their distinct physiological conditions. In the fourth part, ex vivo porcine intestinal and in vitro dialysis model were developed to estimate intestinal effective permeability (Peff) of nutrients. The Peff of D-glucose obtained from the porcine model (2.37 ± 0.04 × 10−4 cm/s) and dialysis model with 8,000 Da dialysis membrane (2.16 ± 0.03 × 10−4 cm/s) were comparable to the human reports (11.0 ± 8.2 × 10−4 cm/s). The Peff of gallic acid was 1.70 ± 0.004 × 10−4, 1.35 ± 0.004 × 10−4, and 1.33 ± 0.007 × 10−4 cm/s, respectively, which was consistent with that reported in rat in situ model (2.73 × 10−4 cm/s) and rat Ussing chamber model (1.23 × 10−4 cm/s). Both models exhibited potential for use in intestinal permeability assessment of nutrients. Overall, the GI models capable of simulating GI motility developed in this dissertation can serve as an effective tool to study food digestion.