Lipids in milk

The membrane contains 0.5-1.0% of the total lipid in milk and is composed principally of phospholipids and neutral lipids in the approximate ratio 2 1, with lesser amounts of other lipids (Tables 3.9 and 3.10) contamination with core lipid is a major problem. The phospholipids are principally phosphatidylcholine, phosphatidylethanolamine and sphingomyelin in the approximate ratio 2 2 1. The principal fatty acids and their approximate percentages in the phospholipids are Cl4 0 (5%), C16 0 (25%), C18 0 (14%), C,8 1 (25%), C18 2 (9%), C22 o (3%) and C24 0 (3%). Thus, the membrane contains a significantly higher level of polyunsaturated fatty acids than milk... 

Lipids As the capacity of the stomach of newborns is very limited, lipids and fat are necessary to provide the large amounts of energy required by the newborn s high body growth rate. Milk fat is the major source of lipid that mammalian newborns use for accumulating body adipose tissue and for the development of their nervous system. The major lipids in milk fat are triglycerides, which represent more than 98 percent of the neutral lipids. From a quantitative point of view, there is no difference in the fat content in cow s (3.8 percent) and human milk (3.7 percent), but they do differ in their qualitative composition in fact, in cow s milk the predominant fatty acids are saturated acids, while polyunsaturated acids are the main fatty acids in human milk, as shown in Table 13.3. 

Among the biological lipids, few exceed bovine milk fat in the complexity of fatty acids present and triacylglycerol (TAG) structure. This, together with its importance commercially as a human food, has generated very large data bases on the synthesis and composition of milk fat. In spite of this, Jensen (2002) lamented the paucity of new information on the content of trace fatty acids and complex lipids in milk fat. 

The complex lipids in milk fat are comprised of the phosphoglycerides, phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidylinositol and plasmalogens. Also, the non-glyceride phospholipid, sphingomyelin, occurs in important amounts (Jensen, 2002). Bitman and Wood (1990) described the distribution of phospholipid classes in bovine milk and their fatty acid composition. The phospholipids comprise about 1% and cholesterol 0.4—0.5% of the total milk fat. These occur almost completely in the milk fat globule membrane. 

Annison, E.F., Linzell, J.L., Fazakerley, S., Nichols, B.W. 1967. The oxidation and utilization of palmitate, stearate, oleate and acetate by the mammary gland of the fed goat in relation to their overall metabolism, and the role of plasma phospholipids and neutral lipids in milk-fat synthesis. Biochem. J. 102, 637-647. 

Factors that Affect the Oxidation of Lipids in Milk and Milk Products... 

To a certain extent, the composition (including lipid composition) of cows milk reflects feed composition (Bugaud et al., 2001 Ramaswamy et al., 2001). Certain feeding regimes have the potential to increase the level of polyunsaturated lipids in milk and the potential for oxidation (Barrefors et al., 1995 Charmley and Nicholson, 1995 Hermansen, 1995 Focant et al., 1998 Morales et al., 2000 Bugaud et al., 2001 Timmons et al., 2001 Havemose et al., 2004). 

A wide study was carried out on the PCB content in milk samples from marine mammals (Table 9.4). In particular, milk samples from Antarctic fur seals, Australian sea lions, northern fur seals (Arctic), northern elephant seals (California) and California sea lions were analyzed. Total PCB content ranged from about 40 to 2100 ng g extractable lipids in milk samples of Antarctic fur seals and California sea lions, respectively (48). The highest value is comparable with the concentration found in human milk (1300 ng g extractable lipids). 

Table 9.4. Total PCB content and individual congener concentrations (ng g extractable lipids in milk)...

The polar lipids in milk fat are richer in PUFA than neutral lipids and are... 

Major factors affecting the oxidation of lipids in milk and dairy... 

The lipids in milk exist as microscopic globules in an oil-in-water (OAV) emulsion. On the interface between globules and milk plasma is a membrane that stabilizes the emulsion. Many factors can affect the milk lipid content, particularly genetics, feed, stage of lactation, and climate. Cow s milk contains approximately 2.8 to 6% total lipids, 3.5 to 4% on average. 

PL represent up to 1.0% of the total lipids in milk. The lactation stage has a significant influence on the content of PL. The major types of milk PL and their... 

Granelli, K. 1996. The oxidative stability of lipids in milk and milk powder in relation to some pro- and antioxidants. Doctoral thesis, Swedish University of Agricultural Sciences, Uppsala, 1-82. 

Morrison, WR. (1968). Surface-active lipids in milk and miUc products, Surface-Active Lipids in Foods. SCI Monograph No. 32. London. Soc Chem Ind, pp 75-91. 

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