Numerical investigation of starch-based granular food digestion in the duodenum: The role of duodenal posture and gastric acidity

Understanding digestion process in the duodenum, a complex bio-system with various unique characteristics, has been a challenge due to experimental restrictions. This work developed a comprehensive duodenal model that takes into account key features including curved geometry, pancreatic secretion and wall peristalsis. It is the first attempt to simulate dense granular flow together with pH-dependent enzymatic reactions of starch-based multicomponent particles under near-real physiological conditions. Numerical experiments enhanced our understanding of the duodenal digestive environment by analyzing the distributions of particles, enzyme and pH as well as the evolution of particle properties. The inclination of the duodenum was found to inhibit the digestive performance, even by half when completely lying down, due to a higher proportion of particles in the proximal acidic region. Additionally, a rise in gastric acidity significantly lowered the digestion rate in a lying posture, while changes in gastric acid concentration below 25 mmol/L had minimal impact in a standing case. The model developed will be valuable for optimizing food formulation, drug delivery and even the design of bio-inspired reactors.