POLYMORPHIC BEHAVIOR OF HIGH-MELTING GLYCERIDES FROM HYDROGENATED CANOLA OIL

Canola oil was hydrogenated with a commercial nickel catalyst at 175-degrees-C and 15 psi hydrogen pressure. Samples were taken during the reaction starting at 15 min and thereafter at ten-minute intervals. The reaction was stopped after two hours. The high-melting glycerides (HMG) were obtained by fractional crystallization at 15-degrees-C with acetone as solvent. The HMG were analyzed for fatty acid and triglyceride composition by gas liquid chromatography and trans was determined by infrared spectroscopy. In the first 45 min of hydrogenation of canola oil, the 18:0 fatty acid increased at a low rate while the trans fatty acid content increased at a much faster rate. The 16:0 and 18:0 content of the HMG was highest and trans content the lowest during the period in which the triglyceride composition was the most diverse. The 54-carbon triglyceride content of the HMG increased from 64% to 78% during the two hours of hydrogenation. The short spacings for the HMG showed the presence of beta crystals as well as several intermediate forms. The number of short-spacings increased with hydrogenation time. The differential scanning calorimetry (DSC) melting profile of the HMG showed one broad peak between 20 and 30-degrees-C and two peaks around 60-degrees-C and above. Crystallization temperatures of the HMG were in the range of 40-45-degrees-C.