ISOTHERMAL CRYSTALLIZATION OF HYDROGENATED SUNFLOWER OIL - I - NUCLEATION

Nucleation kinetics of sunflower seed oil, which was hydrogenated unde r two different conditions, was studied by means of a polarized light microscope and an optical setup with a laser as the light source. When the laser was used, observed induction times were shorter than the on es measured by the microscope. The laser method was found to be more s ensitive and accurate. Two different crystallization behaviors were fo und depending on the chemical composition of the samples. Samples with high content of trielaidin crystallized in the beta form at temperatu res close to the melting points. They exhibited both beta' and beta fo rms depending on crystallization temperature, as happens in natural se misolid fats such as palm oil. Samples with high content of mixed olei c and elaidic triacylglycerols crystallized in the beta' form even at temperatures close to the melting points and they did not show beta fo rm under the conditions used in this study. Activation free energies o f nucleation for hydrogenated sunflower seed oil were low for the two hydrogenation conditions. It can be concluded that nucleation of sunfl ower seed oil is a Cast process and initially needs low supercooling. These results are also important from a practical point of view for pr ocessing design, especially in regards to processes in which fats shou ld be completely crystallized by the end of the production line.