Chemistry and Prevalence of CA Isomers in Animal Systems
The chemistry of conjugated fatty acids, specifically octadecadienoic acids (18:2) (commonly referred to as conjugated linoleic acid or CLA), has provided many challenges to lipid analysts because of their unique physical properties, and the many possible positional and geometric isomers. After overcoming their acid labile properties during analytical procedures, it became evident that natural products, specifically dairy fats, contain one dominant (9c,11t-CLA), 3 intermediate (7t9c-, 9t11c- and 11t13c-CLA) and up to 20 more minor CLA isomers. The best analytical techniques todate include a combination of GC using 100 m highly polar capillary columns, silver-ion HPLC, and a combination of silver-ion TLC and GC to analyze also the 18:1 trans isomers that serve as precursors of CLA in biological systems. These analytical techniques have assisted commercial suppliers to prepare pure CLA isomers, and have made possible the evaluation of individual CLA for their nutritional and biological activity in animal and human models. It is increasingly evident that different CLA isomers have distinctly different physiological and/or biochemical properties. These techniques have also been essential to evaluate dairy fats for their CLA content, to design experimental diets to increase the level of CLA in dairy fats, and to determine the CLA profile in these CLA enriched dairy fats. These improved techniques were used to evaluate the CLA profile in pork products from pigs fed different commercial CLA mixtures.