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The DIDGI® System

Olivia Ménard, Daniel Picque, and Didier Dupont

Abstract A simple two-compartment in vitro dynamic gastrointestinal digestion system allowing the study of the disintegration of food during digestion has been recently developed at INRA. As a first application, it has been used for understanding the mechanisms of infant formula disintegration in the infant gastrointestinal tract. The developed system was validated by comparing the kinetics of proteolysis obtained in vitro towards in vivo data collected on piglets. Results showed a good correlation between in vitro and in vivo data and prove the physiological relevance of the newly developed system.

Keywords Two-compartment in vitro dynamic gastrointestinal digestion system • Disintegration of food • In vitro • Digestion • Infant gastrointestinal tract

Origins and Design of the DIDGI® System

At the French National Institute for Agricultural Research (INRA), several groups are trying to improve our understanding of the fate of different foods (dairy, egg, meat, bakery products, etc.) in the gastrointestinal tract. Our first objective is to unravel the mechanisms of food disintegration in the gastrointestinal tract and identify the molecules (nutrients, bioactive compounds, contaminants etc.) that are released during digestion (Barbé et al. 2013). A second objective is to determine how the structure of food matrices affects food digestion and nutrient bioaccessibility and bioavailability (Barbé et al. 2014). Finally, we model digestion and translate this cascade of events into mathematical models (Le Feunteun et al. 2014) in order to design new foods through a reverse engineering approach i.e. starting from the bioactivity we want to deliver to the body and going back to the most adapted structure.

Since dynamic digestion devices are not very available on the market or quite expensive, we decided to build our own system. The system developed had to be cheap, simple, robust and applicable to all kind of foods INRA is working on. This model was built in order to monitor the disintegration and the kinetics of hydrolysis of the food occurring during a simulated digestion. It focuses on the upper parts of the digestive tract, i.e. the stomach and the small intestine. To be physiologically realistic, the computer-controlled system reproduces the gastric and intestinal transit times, the kinetics of gastric and intestinal pH, the sequential addition of digestive secretions and the stirring of the stomach and small intestine contents.

The gastrointestinal digestion system (Fig. 8.1) consists of two consecutive compartments simulating the stomach and the small intestine. Each compartment is surrounded by a glass jacket filled with water pumped using a temperature-controlled water bath. The system is equipped with temperature, pH and redox sensors and variable speed pumps to control the flow of meal, HCl, Na2CO3, bile, enzymes and the emptying of each compartment. Flow rates are regulated by specific computercontrolled peristaltic pumps. Anaerobic conditions can be simulated by purging air with nitrogen. A Teflon membrane with 2 mm holes is placed before the transfer pump between the gastric and the intestinal compartment to mimic the sieving effect of the pylorus in human, as described previously (Kong and Singh 2008).

The computer program was designed to accept parameters and data obtained from in vivo studies in animals or human volunteers, such as the quantity and duration of a meal, the pH curves for the stomach and small intestine, the secretion rates into the different compartments and the gastric and small intestine emptying rates. The system is controlled by software named StoRM for Stomach regulation and monitoring (Guillemin et al. 2010). To control the transit time of the chyme in each compartment, a power exponential equation for gastric and intestinal delivery is used f = 2-(t / t 1/ 2)b where f represents the fraction of the chyme remaining in the stomach, t is the time of delivery, t½ is the half time of delivery and β is the coeffi describing the shape of the curve, as described previously (Elashoff et al. 1982).

Fig. 8.1 Presentation of the gastro-intestinal dynamic digestion system

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