Protection of conjugated linoleic acids from ruminal hydrogenation and their incorporation into milk fat

In vitro incubations were used to assess the hydrogenation of conjugated li noleic acid (CLA) isomers 9-cis 11-trans and 10-trans 12-cis present in syn thetically produced CLA-60. About 80-90% of the unprotected CLA was hydroge nated when incubated at 38 degrees C for 24 h anaerobically with sheep rume n fluid, the main end product of hydrogenation being trans-octadecaenoic ac id (C-18:1). Encapsulation of the CLA in a matrix of protein provided a pro tection of about 70% with a 30% hydrogenation of the CLA isomers, resulting in no significant change in the trans-C-18:1 but an increase in the level of stearic acid (C-18:0). Feeding sheep with unprotected CLA or protected CLA increased the proportio n of isomers 9-cis 11-trans and 10-trans 12-cis in abomasal digesta. The co ncentration of the CLA isomers leaving the abomasum and available for absor ption at the small intestine was about 3.5-4% higher for the protected CLA, confirming protection imparted by encapsulation. Feeding lactating goats with protected CLA increased the proportion of isom ers 9-cis 11-trans and 10-trans 12-cis in milk fat. The total CLA levels we re enhanced by about 10-fold above the control levels present in milk fat w ith an efficiency of transfer into milk fat of 36-41% and 21-30%, respectiv ely, for the two isomers. (C) 2000 Published by Elsevier Science B.V.