Isothermal crystallization of hydrogenated sunflower oil: I—Nucleation

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Abstract

Nucleation kinetics of sunflower seed oil, which was hydrogenated under 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 ones measured by the microscope. The laser method was found to be more sensitive and accurate. Two different crystallization behaviors were found depending on the chemical composition of the samples. Samples with high content of trielaidin crystallized in the β form at temperatures close to the melting points. They exhibited both β′ and β forms depending on crystallization temperature, as happens in natural semisolid fats such as palm oil. Samples with high content of mixed oleic and elaidic triacylglycerols crystallized in the β′ form even at temperatures close to the melting points and they did not show β form under the conditions used in this study. Activation free energies of nucleation for hydrogenated sunflower seed oil were low for the two hydrogenation conditions. It can be concluded that nucleation of sunflower seed oil is a fast process and initially needs low supercooling. These results are also important from a practical point of view for processing design, especially in regards to processes in which fats should be completely crystallized by the end of the production line.