Abstract
It is known that composition of positional and geometrical isomeric acids in hydrogenated oils varies with hydrogenation conditions, fatty acid composition of original oils and by catalysts.
In this paper, hydrogenation of an olive oil, oleic safflowerseed oil, safflowerseed oil and soybean oil were carried out with 0.15% of a commercial nickel catalyst under different conditions, one under relatively felective (180°C, 1.5kg/cm2, 200rpm) and the other under relatively non-selective (150°C, 3.0kg/cm2, 500rpm) conditions. The hydrogenation was continued until the trans- and cis-monoenoic acids came to a content which was able to be isolated by TLC. Samples of hydrogenated olive oils were taken at different stages of hydrogenation, the iodine values of the corresponding samples being approximately same for both runs. Each sample was analyzed for its trans-isomer % and fatty acid composition. Further, each methyl ester of hydrogenated samples was separated by argentation-TLC into saturated, trans-monoene, cis-monoene and diene fractions. Each sample of trans- and cis-monoenoic fractions was subjected to permanganate oxidation in acetone-acetic acid and relative amounts of isomers were calculated from GLC of dibasic dimethyl esters.
From the results of experiments it can be observed as follows. In the case of olive oil and oleic safflowerseed oil major double bond in cis-monoene retained its original position (Δ9) with both hydrogenation runs, and also the double bond in trans-monoene retained most its original position under non-selective conditions, but it was mostly migrated to the Δ10 position under selective conditions. In the case of safflowerseed oil and soybean oil the double bond in cis-monoene mostly retained at Δ9 and Δ12 positions in both runs, and trans-monoene contained chiefly Δ10 and Δ11 isomers in both runs.
