Calculation of activation free energy for different edible fats

This study evaluates the activation free energy of crystallization of three fats by measuring induction times (λ) of crystallization. Three methods were used to measure λ (a) through SFC vs. time (discrete method), (b) fitting SFC vs. time to the Gompertz equation, and (c) using differential scanning calorimetry (DSC).

When measuring SFC as a function of time Tc for IESBO and PKO ranged from 30-38°C, while for IEPO, Tc were between 22-31°C. Induction times for IESBO using the discrete method was between 2 min (Tc=30°C, ΔGc 7.2KJ/mole) and 75 min (Tc=38°C, ΔGc 17.1KJ/mole). While the Gompertz equation resulted in λ=0.23 min (Tc=30°C, with ΔGc 9.2KJ/mole) and λ=25.21 min (Tc=38°C, with ΔGc 21.8KJ/mole). Similar λ were observed for PKO at Tc 30°C (λ=2 min) but lower ΔGc of 1.99KJ/mole. At Tc=38°C longer λ was observed (λ=90 min, ΔGc of 11.5KJ/mole) (discrete value). When using the Gompertz equation a good fit was found for Tc between 31°C-37°C with λ=5-287 min (ΔGc=3.4-12.5KJ/mole). These results show that more energy must be delivered to IESBO samples to crystallize compared to PKO for the same Tc. For IEPO at Tc 22-31°C the λ=1-90 min (ΔGc=6.8-17.8KJ/mole) through the discrete method. While λ=2.6-37.2 min (ΔGc=6.5-14.2KJ/mole) when the Gompertz method was used. When λ were calculated with the DSC method higher Tc were used. Tc were between 37-43°C, 30-35°C, and 33-35.5°C and ΔGc values between 4.1-10.5KJ/mole, 1.4-2.31KJ/mole, and 0.5-0.6KJ/mole for IESBO, IEPO, PKO, respectively. Using the DSC method, for a supercooling of approximately 10.7°C ΔGc were 9.5KJ/mole, 2.31KJ/mole, and 0.5KJ/mole for IESBO, IEPO, and PKO, respectively.  This suggests that even for the same supercooling, more energy is required to crystallize IESBO, followed by IEPO and the least energy is required for the PKO sample.