Hydrogenation,isomerization and migration of unsaturated acyl moieties in natural triacylglycerols

Triacylglycerols of soybean were partially hydrogenated with a copper chromite catalyst, which reduced the octadecadienoyl and octadecatrienoyl moieties selectively to octadecenoyl moieties. Composition of the acyl moieties, including the distribution of positional isomers of cis- and trans-octadecenoyl moieties, both in 1,3- and 2-positions of triacylglycerols, was determined after hydrolysis with pancreatic lipase. The results show that the octadecadienoyl, but not the octadecatrienoyl moieties are reduced at a faster rate in the 1,3-positions than in the 2-position, whereas the accumulation of trans-octadecenoyl moieties is much higher in the 2-position than in the 1,3-positions. On the other hand, the distribution of positional isomers, both in cis- and trans-octadecenoyl moieties, is essentially the same in 1,3- and 2-positions. Practically no acyl migration occurs during hydrogenation under the conditions described.