Formation of conjugated linoleic acids in soybean oil during hydrogenation with a nickel catalyst as affected by sulfur addition.

The effects of sulfur addition on the formation of conjugated linoleic acid (CLA) isomers were studied during the hydrogenation of soybean oil with a nonselective type nickel catalyst. Sulfur addition greatly promoted CLA formation in soybean oil during hydrogenation. As the amount of sulfur increased to a certain level, the maximal quantity of CLA in soybean oil during hydrogenation increased greatly. However, further increase in sulfur addition above the certain level decreased CLA formation. The optimal sulfur level for the promotion of CLA formation differed greatly with the amount of nickel used. It was of great interest to find that the optimal ratio of sulfur to nickel for the promotion of CLA formation was always 0.06:1, regardless of the nickel amount used. At the same ratio of sulfur to nickel, higher nickel content induced significantly higher production of CLA (p < 0.05). At the optimal sulfur to nickel ratio, an increase in the nickel amount from 0.05 to 0.15% produced approximately 1.5 times higher levels of CLA during hydrogenation under the tested conditions. The CLA isomer compositions were greatly affected by both sulfur addition and amounts of nickel used for treatment. This is the first report of the possibility that the total quantity of CLA and their isomer composition could be manipulated during hydrogenation by controlling the amounts of sulfur and nickel.