Effect of bolus viscosity on carbohydrate digestion and glucose absorption processes: an in vitro gastrointestinal study and development of a mathematical model
Creators: name: Jagadeesan Sankaran, Karthikeyan
Publisher: name: No Publisher Supplied
Year: 2019

description: Digestion is the process of breaking down food into smaller nutrient components which can be easily absorbed in the intestinal tract. Research in human digestion is limited due to the complex multistage process of digestion and technical difficulties in completely understanding the process. This dissertation research was aimed at analyzing carbohydrate digestion and glucose absorption processes in the human small intestine using in vitro experimental procedure in a gastrointestinal model system and by subsequently developing a mathematical model to simulate and predict these processes. Based on prior research it could be inferred that the viscosity of gastrointestinal content plays a significant role in reducing the amount of nutrients available for absorption. In this study, the aim of in vitro experiments was to investigate the influence of bolus (gastric content) viscosity on digestion and nutrient absorption processes, using an in vitro gastrointestinal model, the TIM-1 system. Two types of simple carbohydrates, namely glucose and maltodextrin, were used as simple food bases. The initial bolus viscosity was varied (~1 mPa·s, ~15 mPa·s, and ~100 mPa·s) using different glycerol-water proportions. A fluorescence emitting dye (Fast Green) was used to monitor the changing patterns of the viscosity of gastrointestinal content during digestion in the stomach and in the small intestine. By analyzing the nutrient absorption data, it was found that the bolus viscosity did not significantly affect the nutrient absorption process in the small intestine. An increase in the initial bolus viscosity from ~1 mPa·s to ~15 mPa·s, significantly reduced the maltodextrin to glucose conversion by 35%. However, increasing the initial bolus viscosity further from ~15 mPa·s to ~100 mPa·s did not significantly reduce the maltodextrin to glucose conversion.The aim of the numerical simulation was to develop a fluid flow-based numerical model mimicking human small intestine to predict the glucose absorption process during carbohydrate digestion. COMSOL Multiphysics® software was used to numerically simulate two-dimensional axisymmetric fluid flow induced by peristaltic movement. From the literature, the intestinal geometry parameters, motility parameters, and amylase enzyme kinetics were obtained. To predict the glucose absorption process, it was assumed that the intestine is enclosed in a cylindrical casing with an intermediate diffusive wall. The numerical predictions were experimentally validated by analyzing in vitro digestion of 5 g glucose and 5 g maltodextrin. The numerical model with the intermediate diffusive wall of thickness 2 mm and glucose diffusivity value of 5.25ձ0-9 m2/s for the jejunal section and 2.5ձ0-8 m2/s for the ileal section, predicted the experimental cumulative glucose absorption value with an average error of 0.1 g.This research elucidates the influence of viscosity on the digestion of food. This work also demonstrates the possibility of numerically simulating the human digestive process. Research in this direction could guide the food researchers to engineer novel food products with an optimal viscosity behavior for controlled caloric intake/release which might eventually reduce obesity-related risks.