Comparative Study of Human Milk and Infant Formulas at Different Stages Based on Dynamic <i>In Vitro</i> Infant Gastrointestinal Digestion: The Effect of Polar Lipids on Lutein Digestion

The efficiency of the absorption and digestion of lutein in infant formulas (IFs) is remarkably lower than that in human milk. This work compared the simulated <i>in vitro</i> dynamic digestive characteristics of lutein in three stages of human milk and six IFs, with a special emphasis on how polar lipids affect lutein digestion. Compared with colostrum (CM), IF2 had a significantly higher lutein loss rate but significantly lower micellarization and bioaccessibility rates. In CM, the morphology of milk fat globules (MFGs) remained visible after digestion; the phospholipid globular membrane structure can be observed after 180 min of intestinal digestion, and MFGs remained in a spherical form in micelles. Lipidomic analysis precisely quantified 18 significantly different lipids, including cholesterol, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidic acid, and phosphatidylglycerol, between CM and IF2 micelles, suggesting that these lipids may influence the micellarization of lutein. In summary, polar lipids play an important role in the protection of lutein and the facilitation of lutein micellarization. These findings also provide a certain reference for the adjustment of IF formulations.