US EPA

7117084 

Journal Article 

Trans fatty acids and conjugated linoleic acids in milk fat from dairy cows fed a rumen-protected linoleic acid rich diet 

Hoshi, S; Shu, YJ; Precht, T; Hagemeister, H; Kanitz, W; Voigt, J; , 

2002 

0 

Kieler Milchwirtschaftliche Forschungsberichte
ISSN: 0023-1347 

VERLAG TH MANN 

GELSK-BUER 

225-242 

WOS:000180749200002 

The objective of this study was to determine the effect of a dairy cows diet supplemented with rumen protected fat on the proportions of cis and trans isomers of C16:1, C18:1 and C18:2 in milk fat. Further, the effect of this diet on the level of different conjugated linoleic acid (CLA) isomers should be investigated. Milk fat samples from high yielding Holstein-Friesian cows fed a control diet (n=1 6) or a diet supplemented with rumen protected fatty acids (Ca soaps, CS; n=1 6) were collected weekly during the first 15 weeks of lactation. With argentation thin-layer chromatography followed by low-speed high-resolution-gas chromatography on a 100-m capillary column 11 trans-Cl 6:1, 11 trans-Cl 8:1 isomers, as well as 8 cis-C18:1 isomers including the rarely described cis Delta16-C18:1 isomer were separated and quantified. Furthermore, 8 cis/trans-C18:2 isomers and 7 CLA isomers were determined. With special gas chromatographic conditions it was possible to identify t9t12-C18:2 without overlaps with other isomers. The results show that the content of denovo synthesized fatty acids (FA) in milk fat was reduced by the CS diet and that the dietary lipids were not completely protected from ruminal biohydrogenation. Increases of more than 150% were observed for t6-8, t13-14, cl 2, c9t12 as well as for the CLA isomers t10c12 and t9t11 in the CS group. The relative trans-Cl 8:1 isomeric profile of the milk fats in the CS group corresponded to the typical composition of winter milk fat during the barn feeding period, although the high oleic content as well as the high total content of trans-C18:1 FA pointed to the typical "soft" milk fat from the pasture feeding period in summer. The relative isomeric contributions of trans-Cl 8:1, cis-C18:1, trans-Cl 8:2 and CLA isomers demonstrate that the CS diet had no fundamental influence on biohydrogenation mechanism in the rumen concerning trans octadecenoic acids, besides the increase in the total amount of all these isomers. However, the especially high levels of c 12 or of certain trans-Cl 8:2 and CLA isomers point out that biohydrogenation does play a certain role concerning their origin under CS feeding conditions.