Intracellular Origin of Milk Fat Globules, Composition and Structure of the Milk Fat Globule Membrane Highlighting the Specific Role of Sphingomyelin

Abstract

Milk fat globules are unique biological assemblies with a composition and structure resulting from the mechanisms of their secretion from the mammary epithelial cells. They are enveloped by a biological membrane, the milk fat globule membrane (MFGM), which is rich in polar lipids, cholesterol, and membrane (glyco)proteins. Milk fat globules and the MFGM have gained much interest due to their functional properties and claimed health benefits. This chapter highlights new scientific advances such as the concept of patchwork in the MFGM, based on compositional and structural heterogeneities, which has emerged in the last years. The lateral phase separation of the saturated high-phase-transition temperature (Tm) polar lipids, mainly sphingomyelin, induces the formation of ordered microdomains that are higher and more rigid than the surrounding fluid phase composed of the unsaturated low-Tm polar lipids in which the (glyco)proteins are embedded. Attractive interactions between sphingomyelin andcholesterol could be involved in the ordered microdomains. These new findings contribute in the development of emulsions bioinspired from milk and MFGM-enriched food products, for example, infant milk formulae. The unique richness of milk polar lipids in sphingomyelin and thespecificities of the MFGM will be further explored in the future to better understand their functions in dairy products, in the gastrointestinal tract and in human health.