Résumé
It is well known that one key parameter for food digestion is the rate of emptying of the stomach. However, during its transfer through the stomach, due to the physico-chemical conditions of this compartment (pH, content in digestive enzymes, rate and intensity of contraction), the structure of foodstuff and their rheological properties are strongly modified. This affects the rate of transfer of food into the intestine. The gastric step is particularly essential for colloidal emulsions such as dairy liquids that will gel or precipitate during that step, with changes on their residence time in the stomach. So, our aim is to understand how the structure and the rheology of dairy colloidal emulsion evolve during their digestion and impact the hydrolysis rates of proteins and lipids and the bioavailability of these macro-nutriments. Taking into account these structural and rheological changes is particularly crucial in neonatal nutrition to develop optimized infant formulas. We performed in vitro dynamic gastrointestinal digestions of different infant formulas1. At some specific steps during the digestion, we determined the structure and the rheology of the bolus, together with the hydrolysis rates of proteins and lipids. Rheological measurement can be performed on aliquoted samples by shearing at a low rate. But, only limited sampling can be practiced because digestion systems are limited in volume and sampling the bolus for rheological measurements can introduce bias by applying additional shearing to the sample. Thus, we proposed performing continuous rheological measurements in parallel to the dynamic digestion study.Two continuous rheological methods were tested on different infant formulas, by shearing or small amplitude oscillation. The changes evidenced with these two methods and the one observed in the digestion system were compared.In conclusion, these two methods gave relevant results and were shown to be much simpler than the digestion system. They could be applied to predict the rheological behavior of formulas. Moreover, the methods allowed discriminating the infant formulas in relation with the technological process applied for their manufacture.