A first step towards a consensus static in vitro model for simulating full-term newborn digestion: application to infant formulas

Studying food digestion in humans through clinical trials is difficult for economical, ethical and technical reasons. In vitro alternatives are thus used for screening different foods and for a better understanding of the mechanisms of the digestive process. To date, there are only few models for simulating infant digestion and most of them lack of physiological relevance. Thanks to an extensive literature review of the in vivo infant digestive conditions, a gastrointestinal static in vitro model was developed for infants born at term and aged of 28 days. The oral phase was omitted due to the liquid nature of infant formula but also because carbohydrate digestion was not monitored here. The following parameters were determined: pH, ratio of meal to secretions, enzyme units of pepsin and gastric lipase (added as rabbit gastric extract) and of pancreatin (porcine source), and biliary salt molarity. Gastric and intestinal phases lasted 60 min each. The model was applied to the digestion of a commercial infant formula. Kinetics of digestion and end-points were compared with those obtained while submitting the same formula to the adult standardised protocol of in vitro static digestion1.Gastric and intestinal digesta were sampled regularly. Proteolysis kinetics were followed by SDS-PAGE and NMR and lipolysis kinetics by thin layer and gas chromatography. The structure evolution during the gastric phase was evaluated by confocal laser scanning microscopy and laser light scattering. As a result, the kinetics of proteolysis and lipolysis differed according to the physiological stage likely due to the reduced level of enzymes in the infant model and the higher gastric pH at the infant stage. This model is of interest for scientists or companies studying the digestion of infant food.