Milkfat phospholipids

Norris, C.S., Fong, B.Y., de Bueger, N., MacGibbon, A.K.H. 2003. Phospholipids in dairy products milkfat globule membrane from milk and colostrum. Aust. J. Dairy Technol., 58, 200. 

The composition of milkfat is somewhat complex. Although dominated by triglycerides, which constitute some 98% of milkfat (with small amounts of diglycerides, monoglycerides, and free fatty acids), various other lipid classes are also present in measurable amounts. It is estimated that about 500 separate fatty acids have been detected in milk lipids it is probable that additional fatty acids remain to be identified. Of these, about 20 are major components the remainder are minor and occur in small or trace quantities (4, 5). The other components include phospholipids, cerebrosides, and sterols (cholesterol and cholesterol esters). Small amounts of fat-soluble vitamins (mainly A, D, and E), antioxidants (tocopherol), pigments (carotene), and flavor components (lactones, aldehydes, and ketones) are also present. 

A significant variation in milkfat composition can occur in colostrum milk. Ahren et al. (27) analyzed the content of glycerol ethers in neutral lipids and phospholipids isolated from bovine colostrum and milk (Table 10). Lactone content of butter fat has also been determined (Table 11). 

The phospholipids of milkfat are found in the fat globule membrane in association with proteins and cerebrosides. Phospholipids are amphipolar in nature and are strongly surface active. These properties enable them to stabilize both oU-in-water and water-in-oil emulsions (Table 12) (4-6). 

Large supply of naturally derived lipids can be obtained from plants in which many oils and fatty acids can be readily extracted and purified. Animal sources (e.g., eggs or milkfats) are used to derive complex lipids such as phospholipids and cholesterol. Yield from natural sources is dependent on the weight-percent composition and the efficiency of the extraction procedure. The constitution of fatty acids in vegetable oils varies widely from different sources. For example, oleic acid is present at 64.6% by weight in olive oil but is present at only 0.7% in palm kernel oil. Similarly, castor oil triglyceride is comprised of almost entirely ricinoleic chains. There are numerous raw material suppliers of oils and oil fractions worldwide. As such, the relative cost of bulk purified... 

Although in fluid milk the phospholipid fraction is more susceptible to oxidation than the triacylglycerol fraction, in dry milk products, the triacylglycerol fraction is more susceptible to oxidation and the phospholipids act as antioxidants. Thus, solvent-extracted milkfat containing phosphohpids is much more stable to oxidation than milkfat free of phospholipids, obtained by melting churned butter (also called butter oil). The susceptibility of milk phospholipids to oxidation appears to be dependent on whether they are suspended in water or fat. This difference of oxidahve stability influences the development of different flavor defects in various dairy products. With butter, which is a water-in-oil emulsion system containing an aqueous phase of phospholipids dispersed in fat, the phosphohpids oxidize more readily than the triacylglycerol components. 

Annison, E.F., LinzeU, J.L., Fazakerlay, S., and Niehols, B.W. (1967) The Oxidation and Utilisation of Palmitate, Stearate, Oleate, and Aeetate by the Mammary Gland of the Fed Goat in Relation to their Overall Metabolism, and the Role of Plasma Phospholipids and Neutral Lipids in Milkfat Synthesis, Biochem. J. L02, 637-647. 

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