Relationship between activity of some fat globule membrane enzymes and the lipidic fraction in ewes' milk: Preliminary studies

Variation in milk fat globule size and composition: A source of bioactives for human health

Milk fat globules (MFGs) are secreted from the mammalian gland and are composed of a triacylglycerol core surrounded by a triple membrane structure, the milk fat globule membrane (MFGM). The MFGM contains complex lipids and proteins reported to have nutritional, immunological, neurological and digestive functions. Human and ruminant milk are shown to share a similar MFG structure but with different size, profile and abundance of protein and polar lipids. This review summarizes the reported data on human, bovine, caprine and ovine MFG composition and concentration of bioactive components in different MFG-size fractions. A comprehensive understanding of compositional variations between milk from different species and MFG size fractions may help promote various milk sources as targeted supplements to improve human development and health. MFG size and MFGM composition are species-specific and affected by lactation, diet and breed (or maternal origin). Purification and enrichment methods for some bioactive proteins and lipids present in the MFGM have yet to be established or are not scaled sufficiently to be used to supplement human diets. To overcome this problem, MFG size selection through fractionation or herd selection may provide a convenient way to pre-enrich the MFG fraction with specific protein and lipid components to fulfill human dietary and health requirements.

The sheep milk fat globule membrane proteome

Milk fat globule membranes (MFGM) are three-layered structures that enclose fat droplets, and are composed by an internal monolayer of endoplasmic reticulum origin, surrounded by a bilayer derived from the apical membrane of the lactating cell. In this work, an optimized protein extraction method was applied to sheep MFGM, and extracts were subjected to SDS-PAGE separation followed by shotgun LC tandem mass spectrometry (GeLC-MS/MS) for identification and characterization. In total, 140 unique sheep MFGM proteins (MFGMPs) were identified. All protein identification data were subjected to Gene Ontology (GO) classification for localization and function. Moreover, the relative abundance of all identified MFGMPs was estimated by means of the normalized spectral abundance factor (NSAF) approach, and GO abundance classes were obtained. The data gathered in this work provide a detailed picture of the proteome expressed in healthy sheep MFGs, and lay the foundations for future studies on sheep lactation physiology and on its alterations in pathological conditions.