Ultrasonic wave propagation in cocoa butter during crystallization

In the production of fat containing food products, insight in the crystallization behaviour of fats is of utmost importance to obtain the desired product functionality and product quality. The aim of this research is to study the potential of advanced ultrasonic techniques to monitor fat crystallization. For reasons of sensitivity and signal quality during the entire process, we concentrate on shear wave reflectivity measurements at the interface between a fat sample and a plexiglass delay line. Preliminary experiments show that interesting evolutions can be observed in the experimentally obtained reflection coefficient during the crystallization process of cocoa butter, and we conjecture that the observed features can be linked to particular phases in the process. Additional measurements have been performed to check the influence of sample properties and of the experimental set-up, such as the viscosity or thickness of the cocoa butter layer. It is found that the thickness of the layer influences the reflection coefficient up to a frequency dependent limiting thickness value. In order to eliminate this influence and avoid its contamination in the analysis of the crystallization phases, it is required to use sufficiently thick fat layers. To support the experiments, a shear reflectivity simulation model is proposed, which is coupled to the evolution of sample parameters.