Systematic Analysis of trans and Conjugated Linoleic Acids in the Milk and Meat of Ruminants

Conjugated fatty acids are defined as fatty acids (FA) in which any two double bonds in the molecule are separated by a single carbon-carbon bond (C=C–C=C). The number of possible conjugated fatty acids is considerable since the FA can differ in chain length, position of the conjugated system within the molecule, up to four possible geometric configurations for each positional isomer, and number of additional double bonds in the molecule. In addition to conjugated dienes, some plant oils have conjugated trienes or tetraenes in which there are three and four double bonds each separated by a single carbon-carbon bond (1). In this chapter we will restrict our discussion to the analysis of conjugated dienes derived mainly from ruminant animals. We will use the term conjugated linoleic acid (CLA) even though this term is somewhat restrictive and incorrect (2). For example, 9c11t15c-18:3 is a conjugated fatty acid but is not derived from linoleic acid. All CLA isomers give rise to unique ultraviolet and infrared absorptions, and their chemical properties and chromatographic behaviors are very different from the more common methylene interrupted unsaturated FA. These characteristic properties have been successfully used for their identification and quantification (2). However, it has not been these chemical and chromatographic differences that have distinguished CLA in the past 20 years with the challenges of handling, identification, and completeness of separation, but their unique biological effects. Systematic Analysis of trans and Conjugated Linoleic Acids in the Milk and Meat of Ruminants