Monitoring the isothermal crystallization behavior of cocoa butter by low intensity ultrasound

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 a production environment, non-destructive techniques, such as ultrasonic waves, are especially interesting as these methods allow for in-line measurements. The aim of this research is to study 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, has already proven to be sensitive to changes in microstructure (Saggin and Coupland, 2004). Measurements were performed within a centre frequency range of 1MHz to 3MHz and frequency dependent oscillations were observed in the measured reflection coefficient during crystallization of the cocoa butter sample. These oscillations may be explained by constructive as well as destructive interference, caused by the gradually increasing thickness of the crystallized fat layer. This hypothesis was confirmed by a quasi-analytical theoretical model. A non-linear least squares inversion model has been developed to deduce relevant parameters from the experimental shear reflectivity measurements, such as the shear velocity and attenuation of the cocoa butter sample and the evolution of the thickness of the crystallized fat layer. To study experimentally the impact of the fat crystallization process on the ultrasonic parameters in more detail, the crystallization process was modified by adding Mycryo to the cocoa butter substrate. The addition of such seed crystals accelerates the crystallization process of cocoa butter and this can also be observed in the measured reflection coefficient.status: publishe