Multi-scale characterization of the evolution of the food structure during digestion
Résumé
Digestion of nutrients is an essential function for human to allow normal growth and development. During digestion, the structure of the food is strongly modified and detailed characterization of the digestion products is essential for a better understanding on how food is disintegrated in the gastro-intestinal tract. It appears therefore crucial to have methods for characterizing the evolution of the matrix at different scales, from the macroscopic to the molecular level. Different methods such as biochemical techniques (SDS-PAGE, mass spectrometry) but also molecular immunology (ELISA) have been developed and allowed the monitoring of the proteolysis throughout the gastro intestinal tract at a molecular level. Evolution of the food at the microscopic level was evaluated by confocal microscopy and light scattering. In order to characterize the rheological properties and the clotting ability of a liquid dairy sample in the stomach, an infant formula was placed in an AR 1000 rheometer (TA Instrument) and glucono-delta lactone (GDL) was added in order to mimic the decrease in pH that will occur in the stomach of the neonate after meal ingestion. Formation of the acid gels was monitored using low-amplitude dynamic oscillation by measuring the elastic modulus (G’), the loss modulus (G”) and the loss tangent of the sample under acidification at 37◦C. The applied deformation was 0.1%, frequency was 1Hz, and gel formation was followed for at least 4h. The onset of gelation was defined as the time when G’ > 1Pa. Combination of this set of techniques allowed demonstrating that an increase in the intensity of the heat-treatment applied to the milk concentrate during infant formula manufacture increased significantly the firmness of the bolus in gastric conditions and modified the kinetics of proteolysis of the milk proteins. We also demonstrated that the presence of insoluble particles in a rehydrated infant formulas lead to the absence of gel formation in the stomach.