Many foods contain microcomponents that have beneficial effects beyond those associated with their traditional nutrient content. These are often referred to as functional foods. One such component in foods derived from ruminants is conjugated linoleic acid (CLA). The initial discovery of a functional food role was in the 1980s when M. Pariza and colleagues identified CLA as the antimutigen present in cooked beef. Subsequent studies with animal models demonstrated that synthetically produced CLA was a potent anticarcinogen.
The major dietary sources of CLA are foods derived from ruminants, with about 70% and 25% coming from dairy products and red meat, respectively. CLA is a fatty acid, and thus is present in milk fat and intramuscular fat. Polyunsaturated fatty acids (PUFA) typically have a methylene group between the double bonds (e.g., see linoleic acid in Fig. 1). However, in the case of CLA, the double bonds are conjugated, or adjacent to each other. The most studied isomers are cis-9, trans-11 and trans-10, cis-12 (Fig. 1). First identified in 1977 by P. Parodi, cis-9, trans-11 is the major CLA isomer, representing about 75 90% of the total CLA in ruminant fat. However, many isomers of CLA are found in trace amounts and these differ by position of the double-bond pair (e.g., 7 9, 8 10, 9 11, 10 12) or geometric orientation of the double-bond pair (cis trans, trans cis, cis cis, and trans trans). The isomer form of CLA can affect its biological activity and the presence of multiple isomers presents an analytical challenge. Frequently, quantifying CLA isomers and related fatty acids requires a combination of analytical methods.
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