Milk fat globule membrane (MFGM) is a complex and unique structure composed primarily of lipids and proteins that surrounds milk fat globule secreted from the milk producing cells of humans and other mammals. It is a source of multiple bioactive compounds, including phospholipids, glycolipids, glycoproteins, and carbohydrates that have important functional roles within the brain and gut.
Preclinical studies have demonstrated effects of MFGM-derived bioactive components on brain structure and function, intestinal development, and immune defense. Similarly, pediatric clinical trials have reported beneficial effects on cognitive and immune outcomes. In populations ranging from premature infants to preschool-age children, dietary supplementation with MFGM or its components has been associated with improvements in cognition and behavior, gut and oral bacterial composition, fever incidence, and infectious outcomes including diarrhea and otitis media.
MFGM may also play a role in supporting cardiovascular health by modulating cholesterol and fat uptake. Clinical trials in adult populations have shown that MFGM could positively affect markers associated with cardiovascular disease including lowering serum cholesterol and triacylglycerol levels as well as blood pressure.
Origin
MFGM secretion process in milk
Milk lipids are secreted in a unique manner by lactocytes, which are specialized epithelial cells within the alveoli of the lactating mammary gland.
The process takes place in multiple stages. First, fat synthesized within the endoplasmic reticulum accumulates in droplets between the inner and outer phospholipid monolayers of the endoplasmic reticulum membrane. As these droplets increase in size, the two monolayers separate further and eventually pinch off. This leads to the surrounding of the droplet in a phospholipid monolayer that allows it to disperse within the aqueous cytoplasm. In the next stage, lipid droplets then migrate to the apical surface of the cell, where plasma membrane subsequently envelops the droplet and extrudes together with it. It fully encases the fat droplet in an additional bilayer of phospholipids. The milk fat globule thus released into the glandular lumen, measuring 3-6 μm in average diameter, is surrounded by a phospholipid trilayer containing associated proteins, carbohydrates, and lipids derived primarily from the membrane of the secreting lactocyte. This trilayer is collectively known as MFGM.
This secretion process occurs in all types of mammalian milk, including human and bovine. However, it is distinct from the lipid secretion mechanism used by all other non-mammary cells. That makes MFGM unique to milk and it is not present in non-dairy food products.
Sources of MFGM
MFGM is a structurally complex bioactive milk component, found in human milk as well as the milk of other mammalian species. The MFGM in human milk contains many bioactive components with diverse functions and has been linked to cognitive and health benefits to infants. Some compositional differences are reported to exist between species, but bovine MFGM, the best-studied non-human source, generally contains a lipid and protein composition, which is similar to that of human MFGM.
MFGM makes up an estimated 2-6% of the total fat globules. As raw milk has an average total fat content around 4%, it therefore contains around 0.08-0.24% of MFGM. In other words, 417–1250 kg of raw milk is needed to supply 1 kg of MFGM. The content of MFGM in dairy products varies depending on the processing involved. During dairy processing such as churning or decreaming, the MFGM is disrupted and preferentially distributed into aqueous phases such as buttermilk, butter serum, or certain type of whey. Thus they can be a good source of MFGM for addition into food products.
For example, infant formulas traditionally were lacking the MFGM because this fraction is lost during regular dairy processing. However, more recent advances in technology have facilitated the separation of MFGM from the fat globule, allowing bovine MFGM to be added in concentrated form. The MFGM fraction is now commercially available and can be added to infant formula or other nutritional products.