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(1999) Biosynthesis of Conjugated Linoleic Acid and Its Incorporation into Meat and Milk in Ruminants, in Advances in Conjugated Linoleic Acid Research (Yurawecz, M.P., Mossoba, M.M., Kramer, J.K.G., Pariza, M.W., and Nelson, G.J., eds.), Vol. (1977) Conjugated Octadecadienoic Acids of Milk Fat, J. (1998) A New Conjugated Linoleic Acid Isomer, 7 trans,9 cis-Octadecadienoic Acid, in Cow Milk, Cheese, Beef, and Human Milk and Adipose Tissue, Lipids 33, 803–809. Yurawecz, M.P., Roach, J.A.G., Sehat, N., Mossoba, M.M., Kramer, J.K.G., Fritsche, J., Steinhart, H., and Ku, Y. (2000) Quantitative Determination of Conjugated Linoleic Acid Isomers in Beef Fat, Eur. Comparison of Chromatographic Elution Sequences, Lipids 33, 963–971.įritsche, J., Fritsche, S., Solomon, M.B., Mossoba, M.M., Yurawecz, M.P., Morehouse, K., and Ku, Y. (1998) Identification of Conjugated Linoleic Acid Isomers in Cheese by Gas Chromatography, Silver Ion High Performance Liquid Chromatography, and Mass Spectral Reconstructed Ion Profiles. Sehat, N., Kramer, J.K.G., Mossoba, M.M., Yurawecz, M.P., Roach, J.A.G., Eulitz, K., Morehouse, K.M., and Ku, Y. (2000) Conjugated Linoleic Acid: Implications for Human Health, Pharm. Whigham, L.D., Cook, M.E., and Atkinson, R.L. Results indicate this isomer in milkfat is derived almost exclusively from endogenous synthesis via Δ 9-desaturase. In contrast, trans-7, cis-9 CLA was not present in rumen fluid in significant amounts. Thus, milkfat cis-9, trans-11 CLA was primarily from endogenous synthesis with a minor portion from rumen escape. Similar corrected values were 77 and 58% for endogenous synthesis of cis-9, trans-11 CLA. Correcting for the extent of treatment-induced inhibition of Δ 9-desaturase based on changes in myristic and myristoleic acids, endogenous synthesis of trans-7, cis-9 CLA represented 85 and 102% in Experiments 1 and 2, respectively. In Experiment 2, the 10,12 CLA supplement decreased milkfat content of trans-7, cis-9 CLA and cis-9, trans-11 by 44 and 25%, respectively. In Experiment 1, SO decreased milkfat content of trans-7, cis-9 CLA by 68 to 71% and cis-9, trans-11 CLA by 61 to 65%. Samples were analyzed by GC and Ag +-HPLC to determine FA. Experiment 2 treatments (four cows) were 0 or 14.0 g/d of 10,12 CLA supplement milk and plasma were collected. Milk, plasma, and rumen fluid were collected. Experiment 1 (four cows Latin square) involved four treatments: control, SO, partially hydrogenated vegetable oil (PHVO), and PHVO+SO. We tested the hypothesis that trans-7, cis-9 CLA originates from endogenous synthesis by inhibiting Δ 9-desaturase with a source of cyclopropene FA (sterculic oil: SO) or with a trans-10, cis-12 CLA supplement. The majority of cis-9, trans-11 CLA is synthesized endogenously by Δ 9-desaturase. Cis-9, trans-11 and trans-7, cis-9 CLA are the most prevalent CLA isomers in milkfat.