Comparison of physical properties of fats at high and low crystallization temperatures

The objective of this study was to evaluate the physical properties of three fats: interesterified soybean oil (IESBO), interesterified palm olein (IEPO), and fully hydrogenated palm kernel oil (FHPKO) at high and low crystallization temperatures (T_c) to generate low and high activation free energy of crystallization (∆G_c), respectively. T_c tested were 37°C and 30°C; 29.5°C and 24°C; 36.5°C and 31°C for IESBO, IEPO, and FHPKO, respectively. The ∆G_c at high T_c for IESBO, IEPO and FHPKO were respectively 21.5 KJ/moles, 17.8 KJ/moles and 8.6 KJ/moles and at low T_c 10.3 KJ/moles, 9.9 KJ/moles and 2.8 KJ/moles. The physical properties measured were hardness, SFC, melting behavior, and polymorphism. Hardness at highest and lowest T_c for IESBO was 0.2±0.02N and 0.4±0.04N, for IEPO was 0.07±0.03N and 0.9±0.07N, for FHPKO was 1.2±0.1N and 7.5±1.2N respectively. The significantly harder material (p< 0.05) obtained for the FHPKO was due to the lower ∆G_c of these samples.  SFC at lower T_c were 57.3%, 76.6%, and 62.5% and the SFC at higher T_c was 56.2%, 58.6% and 56.0% respectively. Though FHPKO has lower ∆G_c and resulted in a harder sample, it didn’t contain more solid fat than IESBO at high Tc. The melting enthalpy for the high and low T_c for IESBO was 10.8±11.7 J/g and 17.7±6.3 J/g, for IEPO 15.8±5.6 J/g and 24.5±2.2 J/g and for FHPKO 5.2±7.6 J/g and 45.5±6 J/g. IESBO and IEPO exhibited β and β’ polymorphic forms at their highest and lowest Tc, while FHPKO only exhibited β’ polymorphism.

Overall, despite the low ∆G_c observed for the FHPKO that resulted in a high hardness, SFC and melting enthalpy values did not always follow the ∆G_c trend suggesting that other factors such as polymorphism, crystal morphology, and viscosity might affect the crystallization behavior of the fats and their physical properties.