Bovine milk lipids triacylglycerols

The composition and structure of bovine milk fat have been reviewed extensively. There are early reviews by Morrison (1970), Christie (1978, 1995), Jensen and Clark (1988), and Jensen and Newberg (1995) recent articles include a comprehensive review of recent research by Jensen (2002) and two book chapters by Vanhoutte and Huyghebaert (2003), and Zegarska (2003). Bovine milk lipids are similar to the milk lipids of other species as they are largely composed of triacylglycerols however, there are also minor amounts of diacyl-glycerols, monoacylglycerols, free (unesterified) fatty acids, phospholipids and... 

Bovine milk fat is made up of 97-98 (wt% of total lipids) triacylglycerols accompanied by much smaller amounts of diacylglycerols (0.36%) and monoacylglyc-erols (0.03%), free cholesterol (0.31%), trace amounts of cholesteryl esters, phospholipids (0.60%), and minor amounts of free fatty acids. For reviews of the composition of bovine milk lipids, the reader is referred to Christie (4) and Jensen and Clarke (5). More than 400 fatty acids have been identified in milk fat, although it is generally accepted that 15 major and 12 minor fatty acids dominate the fatty acid spectrum. The major fatty acids found in milk are long chain (Cj. , myristic Ci6-o. palmitic Cjg., stearic Cjg.j, oleic) and the minor fatty acids are short chain... 

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. 

Human and bovine milks contain about 3-5% total lipid, existing as emulsified globules, 2—4 pm in diameter, covered with a phospholipid-protein membrane derived from the secreting cell. About 98% of the lipids are triacylglycerols, which are found in the fat globules. Phospholipids are about 0.5-1% of total lipids and sterols are 0.2-0.5% the phospholipids are found mostly in the globule membrane (Jensen et a ., 1992). (See Chapters 4 and 6). 

The major differences between the lipids of bovine and human milk are in fatty acid composition and triacylglycerol structure. Bovine milk contains substantial quantities of C4 o-Ci0 o, about 2% Cis 2 and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. Human milk contains very little C4 o-C10 o, 10-14%i (w/w of fat) Ci8 2, and small quantities of other polyunsaturates. The triacylglycerol structure differs, with much of the sn-2 position in human milk lipids occupied by C16 0 and the sn-2 position of bovine milk-fat occupied by C4 o-Ci0 o-... 

The principal lipids of milk are triacylglycerols which may represent up to 98% of the total lipids (Table 3.219). Human milk contains significant quantities of phospholipids, sterols, sterol esters, unesterified fatty acids and monoacylglycerols. In contrast, the proportion of phospholipids in bovine milk is low (Table 3.219). 

Milk fat contains a number of different lipids, but is predominately made up of triacylglycerols (TAG) (98%). The remaining lipids are diacylglycerols (DAG), monoacylglycerols (MAG), phospholipids, free fatty acids (FFA) and sterols. Milk fat contains over 250 different fatty acids, but 15 of these make up approximately 95% of the total (Banks, 1991) the most important are shown in Table 19.1. The unique aspect of bovine, ovine and caprine milk fat, in comparison to vegetable oils, is the presence of high levels of short-chain volatile FFAs (SCFFA), which have a major impact on the flavor/aroma of dairy products. Most cheeses are produced from either bovine, ovine or caprine milk and the differences of their FFA profile are responsible for the characteristic flavor of cheeses produced from such milks (Ha and Lindsay, 1991). 

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