ABSTRACT
Conjugated linoleic acid (CLA) is a group of positional and geometric isomers of linoleic acid with conjugated double bonds located at positions 8 and 10, 9 and 11, 10 and 12, or 11 and 13, and these double bonds may be of cis and trans con# guration (Eulitz et al., 1999) (Figure 34.1). This group of isomers is synthesized by microbial fermentation (bacteria, Butyrinvibrio brisolvens) occurring in the gut of ruminant animals (such as sheep and cattle) (Kepler et al., 1966). Thus, CLAs are predominantly found in dairy products and meat from ruminants (Chin et al., 1992). The concentration of CLA in these foods can be as high as 30 mg/g depending on the diet of the ruminant animal, and are generally higher if the animal is grazing on fresh, green pasture than feeding a grain (Dhiman et al., 1999). Interestingly, the highest concentration of CLA when compared with other foods is found in Kangaroo meat (Engelke et al., 2004). Kangaroos are not true ruminant animals, but like ruminants, they ferment feed in their foregut. Other foods including vegetable oils, eggs, seafood, poultry, and pork may also contain CLA but at very low levels. The most abundant isomer in food is cis 9, trans 11-18:2 (c9,t11-18:2), followed by t10, c12-18:2. Evidence indicates that different CLA isomers exert different health effects (Ip et al., 1999; Pariza et al., 2001; Li et al., 2006).
