view - Department of Reproduction, Obstetrics and Herd Health

CHAPTER 2
double bond at the sixth and third position respectively from the methyl end (Mattos et
al., 2000; Calder and Yaqoob, 2009).
Figure 2. The spatial model (top) and chemical structure (bottom) of 18:2 cis-9, cis-12 or 18:2n-6 linoleic
acid (left) and 18:3 cis-9, cis-12, cis-15 or 18:3n-3 linolenic acid (right).
Within the PUFA and uniquely found in the adipose tissues and milk of ruminant
animals, conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers
of LA with two conjugated (one single bound in between) double bonds at various
carbon positions in the FA chain (Nagpal et al., 2007; Crumb and Vattem, 2011). Each
double bond can be cis or trans, but especially those with one trans double bond are
bioactive (Jensen, 2002).
The presence of conjugated double bonds in FA was first demonstrated in food
products derived from ruminants by Booth and Kon (1935), working with milk fat from
cows turned out to spring pasture. Due to their wide range of physiologic effects in
animal models, various CLA isomers ever since have gained a lot of interest (Pariza et al.,
2000; Crumb and Vattem, 2011). More specifically for dairy products, a specific CLA
isomer, i.e. cis-9, trans-11 has been proposed as a functional food (Bauman and Lock,
2010). In the dairy cow, this isomer is formed as an intermediate during ruminal
biohydrogenation of 18:2n-6 to 18:0 by Butyrivibrio fibrisolvens (Kepler and Tove, 1967)
and other rumen bacteria (Kritchevsky, 2000), or via endogenous conversion in the
mammary gland by delta-9 desaturase enzymes from 18:1 trans-11 and other 18:1
intermediates of biohydrogenation of 18:2n-6 or 18:3n-3 (Griinari and Bauman, 1999;
Corl et al., 2001). Recently however, the formation of CLA from biohydrogenation of
18:3n-3 has been reported as well (Lee and Jenkins, 2011).
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