Effect of Cooling Rates and Crystallization Temperature on Crystallization Kinetics of Coconut Oil

It has been shown experimentally by many researchers that cooling rate and crystallization temperature affect the rate of crystal formation. In this study, crystallization kinetics of coconut oil was measured by monitoring the solid fraction of the oil using pulsed Nuclear Magnetic Resonance (pNMR). Four levels of cooling rate and crytallization temperature were studied. Parameters of crystallization kinetics are quantified by applying two different models namely Avrami model and Gompertz model. Avrami model was used to explain the mechanism of nucleation (Avrami index), crystallization rate constant and crystallization half-time, while Gompertz model was used to explain the induction time, maximum increase rate in crystallization and crystal polymorphic occurrence. Crystallization was done by heating the oil at a temperature of 70 °C for 10 minutes prior to rapid cooling to 29 °C. Then, rate of cooling from 29 °C to the crystallization temperature (critical cooling rate) was set below 2 °C/minutes. During the process, the oil was stirred at 15 rpm. Solid fraction was measured periodically since the crystallization temperature was reached until maximum solid fraction was achieved. The results showed that Avrami and Gompertz models are able to quantitatively describe coconut oil crystallization kinetics. Lower critical cooling rate decreases Avrami index, crystallization half time and induction time but increases crystallization rate constant and maximum increase rate in crystallization. Crystallization temperature has positive correlation with the crystallization rate contstant and Avrami index but has negative correlation with induction time and maximum increase rate in crystallization. 1) The article has been submitted for publication at Journal of Food Science and Technology Critical cooling rates and crystallization temperatures only effected on the thermodynamics and crystallization kinetics of coconut oil but not on its polymorphic occurrence.