|Holliday, Russell - FORMER ARS EMPLOYEE|
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 21, 2000
Publication Date: N/A
Interpretive Summary: Liquid vegetable oils are converted to more solid fats by a process called hydrogenation. A new analytical method was used to follow the course of this reaction which has yielded new information about how the hydrogenation reaction affects the types of products produced by this important industrial process. By changing the pressure within the reaction vessel, industry has an opportunity to lower the amounts of undesirable products formed during the hydrogenation of vegetable oils.
Technical Abstract: High pressure liquid chromatography was used to monitor changes in triglyceride structure occurring during the hydrogenation of soybean oil under non-selective conditions: i.e. low temperature, high pressure, high stirring. Soybean oil contains five triglycerides accounting for over 70% of the total. These include LLL, LLO, LLP, LOO, and LOP and their isomers (where L=linoleic, O=oleic, P=palmitic). HPLC analysis of samples taken during a typical hydrogenation run in which the iodine value (IV) was reduced from 130 to about 70 showed that the linoleate containing triglycerides were reduced at a much faster rate than the linolenate containing triglycerides. Results clearly show that hydrogenation proceeds through definite pathways rather than by random saturation of fatty acids within the triglyceride molecules. Pressure has a significant effect on the course of hydrogenation. At higher pressures (500 lbs.), the reaction is truly non-selective, since di- and tri-saturated glycerides are formed at about 70 IV, whereas, at 50 psi, the reaction becomes selective. At higher pressures, fat functionality and solid fat result primarily from di- and tri-saturated fatty acid triglycerides as well as trans fatty acid triglycerides. At lower pressures, functionality results from trans acid triglyceride formation. Although the reactivity of linoleate containing triglycerides followed the pattern 6 double bonds>5 double bonds>4 double bonds, other factors may be important. For example, LLP is reactive and undergoes hydrogenation, while LLS remains unchanged. Triolein, which comprises less than 3% of the total triglyceride in natural soybean oil, is a significant product of hydrogenation, which suggests that LLL and LLO are reduced directly while adsorbed on the catalyst surface.