The second most abundant isomer is the C18:2 trans7, cis9, represents about 10% of the total CLA-isomers. Table 1 Distribution of the main CLA-isomers in milk and dairy products (Adapted from Bauman and Lock (11)).Īs it can been appreciated in Table 1, the cis-9, trans-11-octadecadienoic acid (C18:2 cis9, trans11), also known as rumenic acid, is the predominant isomer, representing between 75 and 90% of the total CLA-isomers (12). The Table 1 presents the predominant distribution of the CLA-isomers in milk and dairy products.
Milk fat is the richest natural source of CLA, with concentrations typically ranging between 2 and 37 mg/g fat 10. The main employed strategies are based on the manipulation of the feed and dietary regimen of the animals, and on the modification of the technological processes used in the manufacture of dairy products 6 )( 7 )( 8.Ĭonjugated linoleic acid is a generic term used for describing the geometrical and positional isomers of linoleic acid (C18:2 cis9, cis12) with a conjugated double bond system 9. Since the concentration of these fatty acids is relatively low for providing health benefits, significant efforts have been devoted to increasing their content in milk and dairy products, in order to produce foodstuffs with improved nutritional value. However, milk's lipid fraction also contains mono and polyunsaturated fatty acids, such as oleic acid (C18:1 cis9), and fatty acids belonging to the omega-3 (C18:3) and omega-6 families (C18:2), which are considered beneficial to human health, especially for reducing the level of triglycerides and LDL cholesterol, and for enhancing the levels of HDL cholesterol 4 )( 5. The high concentration of saturated fatty acids (mainly that of palmitic, myristic and lauric acids) in the milk's lipid fraction has generated some concern, because of their negative effects on human health, especially related to the increased risk of acquiring cardiovascular diseases 3.
Milk fat is mainly composed of triacylglycerols (~98%), minor amounts of mono and diacylglycerols (~2%), phospholipids (~1%), sterols (~0.5%), free fatty acids (0.1%) and traces of fat-soluble vitamins 2. Milk and dairy products are daily consumption foodstuffs, considered as important sources of energy, and of a variety of bioactive substances positively associated with human health, such as proteins and peptides, oligosaccharides, lipids, minerals and vitamins 1.