GC–MS Metabolomic Profiling of Sheep and Goat Milk Infant Formulas During Simulated In Vitro Digestion

Human milk is the gold standard for infant nutrition; however, infant formulas (IFs) remain the main alternative when breastfeeding is not possible. Cow and goat milk-based IFs are well established, whereas sheep milk IFs have attracted increasing interest. IFs are among the most studied food products; nevertheless, little is known about the evolution of small molecules during digestion. This study monitored the metabolomic changes in sheep and goat IFs during simulated digestion using the dynamic in vitro gastrointestinal digestion system (DIDGI®). Using an untargeted GC–MS approach, a total of 51 metabolites were identified in samples collected throughout the digestion process. The results of multivariate statistics indicated that the gastric and the intestinal digestion stages, rather than milk origin, were the primary sources of metabolic variation. However, different sheep and goat IF metabolite fingerprints were detected and persisted throughout digestion. Temporal profile analysis showed limited amino acid release during gastric digestion followed by a rapid increase during intestinal transition, reflecting extensive proteolysis. Similarly, massive lipolysis led to the accumulation in the intestine of free fatty acids, including medium-chain fatty acids derived from milk fat. These findings provide the first untargeted GC–MS characterization of the metabolomic evolution of sheep and goat milk IFs during dynamic in vitro gastrointestinal digestion.