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Abstract:

Monitoring the isothermal crystallization behavior of cocoa butter by low intensity ultrasound Annelien Rigolle, Jan Descheemaeker, Koen Van Den Abeele, Imogen Foubert KU Leuven KULAK, Kortrijk, Belgium In the production of fat containing food products, insight in the crystallization behavior of fats is of utmost importance to obtain the desired product functionality and product quality. Several methodologies exist to follow the crystallization. In particular non-destructive techniques, such as ultrasonic waves, are interesting in a production environment since these allow for in-line measurements. The aim of the research is to study in detail the potential of an advanced ultrasonic shear reflection technique to monitor fat crystallization. The main advantages of this experimental set-up are that no problems with excessive attenuation of the fat arise and that shear ultrasonic reflectance, unlike longitudinal measurements, seems sensitive to changes in microstructure. Measurements were performed within a centre frequency range of 500kHz to 5 MHz, whereby different frequencies provide complementary information on the crystallization process. We conjecture that several particular effects observed in the evolution of the reflection coefficient are due to the various crystallization phases of the cocoa butter. Frequency dependent oscillations were observed in the reflection coefficient. The current hypothesis is that the oscillations are caused by local gradients and variations of parameters, such as the shear wave velocity and attenuation, during the crystallization of the bulk fat substrate. To verify this hypothesis, we are constructing a quasi-analytical theoretical model to calculate the evolution of the reflection coefficient during the crystallization. To study experimentally the impact of the fat crystallization process on the ultrasonic parameters in more detail, the crystallization process is modified and the effect on the relevant parameters is inferred. The crystallization process is modified in two ways: by changing the crystallization temperature and by adding minor components, such as limonene and lecithin, to the cocoa butter substrate. These minor components are used to modify the crystallization parameters in the ultrasonic experiments and these are compared with the parameters in conventional techniques, like DSC, using the same sample and the same processing conditions.