Development of in vitro digestion simulation of gastrointestinal tract to evaluate lipolysis and proteolysis: Comparison of infant model digestion of breast milk and adult model digestion of cow milk

This study aims to evaluate the in vitro gastrointestinal lipolysis and proteolysis of milk using a dynamic digestion simulation of infants and a static digestion simulation of adults following INFOGEST 2.0. Human breast milk and cow milk were used as substrates in our two models to evaluate their different digestion behaviors by determining lipolysis and proteolysis production respectively as well as microstructural characteristics. The gastric lipolysis degree at 120 min was 18.72% under infant digestion, higher than that for the adult (10.76%). However, no significant difference was found between human milk (73.69%) and cow milk (76.43%) in the end. The molecular species of lipolysis production were identified and quantified using LC‒MS, which was highly related to their initial lipid compositions. Higher amounts of LCFA-containing lipolysis were detected at the beginning of human milk intestinal digestion under infant model. The proteolysis of human milk under infant digestion was slower than that of cow milk in the adult model, although the former has a nearly 2% lower protein content than the latter. In both models, whey proteins are more resistant to gastric digestion, while caseins are more extensively hydrolyzed. A larger mean fat globule size was observed in human milk during intestinal digestion, compared to the opposite phenomenon of cow milk. The established model is meaningful for evaluating the chemical composition and structure of digestion products for further development of novel infant formulas that are better for infant digestion and functional foods that are easily digested for people with intestine dysfunction.