An Integrative Approach of an In Vitro Measurement of the Digestibility of Triacylglycerols of Human Milk

Profile of Human Milk Phospholipids at Different Lactation Stages with UPLC/Q-TOF-MS: Characterization, Distribution, and Differences

Human milk phospholipids are important for the regular growth and development of infants. Ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) was employed to qualitatively and quantitatively analyze 277 phospholipid molecular species in 112 human milk samples to obtain a detailed profile of human milk phospholipids along the lactation stage. MS/MS fragmentation patterns of sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine were characterized in detail. Phosphatidylcholine is the most dominant group, followed by sphingomyelin. PC(18:0/18:2), SM(d18:1/24:1), PE(18:0/18:0), PS(18:0/20:4), and PI(18:0/18:2) showed the highest average concentration among all of the phosphatidylcholine, sphingomyelin, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol molecular species, respectively. The fatty acids attached to the phospholipid molecules were mainly palmitic, stearic, oleic, and linoleic acids, and the plasmalogens decreased along the lactation stage. The increase of sphingomyelins and phosphatidylethanolamines and the decrease of phosphatidylcholines are the key changes from colostrum to transitional milk; the increase of lysophosphatidylcholines and lysophosphatidylethanolamines and the continuous decrease of phosphatidylcholines are the vital changes from transitional milk to mature milk.

Efficient in vitro digestion of lipids and proteins in bovine milk fat globule membrane ingredient (MFGMi) and whey-casein infant formula with added MFGMi

The relative immaturity of the infant digestive system has the potential to affect the bioavailability of dietary lipids, proteins, and their digested products. We performed a lipidomic analysis of a commercial bovine milk fat globule membrane ingredient (MFGMi) and determined the profile of lipids and proteins in the bioaccessible fraction after in vitro digestion of both the ingredient and whey-casein-based infant formula without and with MFGMi. Test materials were digested using a static 2-phase in vitro model, with conditions simulating those in the infant gut. The extent of digestion and the bioaccessibility of various classes of neutral and polar lipids were monitored by measuring a wide targeted lipid profile using direct infusion-mass spectrometry. Digestion of abundant proteins in the ingredient and whey-casein infant formula containing the ingredient was determined by denaturing PAGE with imaging of Coomassie Brilliant Blue stained bands. Cholesterol esters, diacylglycerides, triacylglycerides, phosphatidylcholines, and phosphatidylethanolamines in MFGMi were hydrolyzed readily during in vitro digestion, which resulted in marked increases in the amounts of free fatty acids and lyso-phospholipids in the bioaccessible fraction. In contrast, sphingomyelins, ceramides, and gangliosides were largely resistant to simulated digestion. Proteins in MFGMi and the infant formulas also were hydrolyzed efficiently. The results suggest that neutral lipids, cholesterol esters, phospholipids, and proteins in MFGMi are digested efficiently during conditions that simulate the prandial lumen of the stomach and small intestine of infants. Also, supplementation of whey-casein-based infant formula with MFGMi did not appear to alter the profiles of lipids and proteins in the bioaccessible fraction after digestion.

Functional Significance of Different Milk Constituents in Modulating the Gut Microbiome and Infant Health

Human milk, the gold standard for optimal nourishment, controls the microbial composition of infants by either enhancing or limiting bacterial growth. The milk fat globule membrane has gained interest in gut-related functions and cognitive development. The membrane proteins can directly interact with probiotic bacteria, influencing their survival and adhesion through gastrointestinal transit, whereas membrane phospholipids increase the residence time of probiotic bacteria in the gut. The commensal bacteria in milk act as the initial inoculum in building up the gut colonization of an infant, whereas oligosaccharides promote proliferation of beneficial microorganisms. Interestingly, milk extracellular vesicles are also involved in influencing the microbiota composition but are not well-explored. This review highlights the contribution of different milk components in modulating the infant gut microbiota, particularly the fat globule membrane, and the complex interplay between host- and brain-gut microbiota signaling affecting infant and adult health positively.