High Quality Content by WIKIPEDIA articles! Vaccenic acid is a naturally occurring trans fat found in the fat of ruminants and in dairy products such as milk and yogurt. It is also the predominant 'trans-fat' in human milk.Its IUPAC name is (E)-11-octadecenoic acid, and its lipid shorthand name is 18:1 trans-11. The name was derived from the Latin vacca (cow).Vaccenic acid was discovered in 1928 in animal fats and butter. It is the main trans fatty acid isomer present in milk fat. Mammals convert it into rumenic acid, a conjugated linoleic acid, where it shows anticarcinogenic properties.