A MUltiREactor DIgestion approach to study digestion kinetics in a semi-dynamic way

Generally, our research group aims to study the influence of food parameters (food design, food processing, food composition) on the digestive kinetics of diverse nutrients throughout the upper gastrointestinal tract. For this, we use in vitro digestion protocols. The current method is a semi-dynamic in vitro digestion protocol simulated using a multireactor system. This multireactor system is a custom-made automated system with four independent syringe pumps (BioXplorer 100, H.E.L Group). It consists of multiple, small-scale reactors allowing to study digestion as a function of time and thus to determine digestion kinetics. The digestion conditions used in the oral, gastric, and small intestinal are currently based on the digestion protocols published by the INFOGEST consortium (Brodkorb et al., 2019). Briefly, food is first mixed with simulated salivary fluids to simulate the dilution and potential starch digestion of the oral compartment. Hereafter, the gastric phase is simulated by gradually decreasing the pH from the original food pH to a pH of 2 over 2h. Additionally, pepsin was added gradually as well over 2h. If wanted, also the small intestinal phase can be mimicked. For this, the pH is increased to pH 7 and small intestinal fluids (e.g. bile salts) and enzymes (e.g. (chymo)trypsin, pancreatic lipase and αamylase) are added dynamically over 2h. Enzymes are inactivated in different reactors at different pre-determined digestion moments to study the kinetic evolution of nutrient hydrolysis and metabolite formation throughout the upper gastrointestinal tract. A kinetic study can be performed both in the gastric and small intestinal phase, depending on the research question. Quantification of the digestive metabolites is mostly done by chromatographic techniques. Our analytical platform allows characterization of starch, lipid and protein macronutrient digestion (substrate, intermediate products and metabolites) as well as bioaccessibility of a range of micronutrients (minerals, vitamin C, carotenoids, etc.). Besides, we structurally characterize our digested food during digestion by the evaluation of particle size, microstructure and/or particle charge.