May 12, 2023

Milk fat globules and milk fat globule membrane

Milk fat globules are formed throughout the mammary epithelial cell, grow in size as they move toward the apical cell membrane, and are extruded into the alveolar lumen. The diameter of milk fat globules ranges from 0.1 μm to 15 μm, with a volumetric average around 4 μm, depending e.g. on cow breed, feed and season,

The MFG is composed of a triglyceride-rich core surrounded by a tri-layer membrane, also known as the milk fat globule membrane (MFGM) that originates from mammary gland epithelia. Milk fat globules (MFG) contains a wide range of fatty acids in its core. Milk fat globule membrane (MFGM) surrounds this core and is a complex mixture made up of 60% protein and 40% fat, which stabilizes the globule.

The MFGM is composed mainly of phospholipids, glycolipids, proteins (25 - 60% of MFGM mass), lipoproteins and enzymes such as butyrophilin and xanthine oxidase. This membrane, about 10–20 nm in cross-section, acts as an emulsifier and protects the globules from coalescence and enzymatic degradation.

MFGM is highly structured and contains unique polar lipids and membrane-specific proteins. Sphingolipids (highly bioactive molecules, mainly present in polar lipids from animal origin) account for up to one third of the MFGM polar lipid fraction. MFGM protects fat globules from lipolysis catalyzed by lipase activity, mainly linked to the casein micelles.

Total fat content and fat globule size distribution affects the viscosity of milk and has applications in the processing and manufacture of milk products. Smaller fat globules are usually better dispersed and provide a more homogeneous mixture of fat in milk.

The small size of fat globules means high phospholipid content because of greater surface area.

Research has shown that MFGM plays an important role in the development of brain and nerve tissues and also play a vital role in the absorption and digestion of fat.

Due to their origin, composition and structure, MFGM polar lipids and proteins could be used as an emulsifier or stabilizer, combining technological and nutritional functionality.

The main factor responsible for rapid formation of a cream layer on cow milk has been shown to be a heat denaturable protein adsorbed on cold fat globules, which has the characteristics of a euglobulin. This protein, known as fat agglutinin, promotes clustering of globules.
Milk fat globules and milk fat globule membrane

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