Modelling two-step isothermal fat crystallization

Since fats are complex mixtures of triglycerides, multiple steps may be identified in their crystallization curves, due to polymorphism or crystallization of different fractions. This kind of curve, which was already observed in several studies, is more complex to model than single step crystallization curves. Therefore it is the aim of this research to present an extension of the Foubert model which facilitates the description of two-step processes. The data used in this study are from isothermal crystallization of milk fat (fractions) and cocoa butter examined by time-resolved X-ray diffraction (XRD) where the first crystallization step involves crystallization of part of the melt in the α polymorph while the second step is an α mediated β′ crystallization with no β′ crystals formed directly from the melt. The model is built based on these assumptions, that are based on the occurrence of an isosbestic point. Simulation experiments are performed to show the role of the different model parameters. Parameter estimation on the different data sets is performed with a very good fit as a result.