Ultrasonic Shear Reflectometry to Monitor the Isothermal Crystallization Behavior of Cocoa Butter

Determining and applying the correct crystallization procedure of cocoa butter in chocolate is crucial to obtain the desired quality characteristics, such as a glossy appearance, a pleasant texture and mouthfeel and a stable shelf life. However, most of the currently used techniques to monitor fat crystallization are off-line techniques, while in-line techniques could have important advantages. Here, we propose a shear ultrasonic wave reflection technique based on low intensity ultrasound, and we show that this technique has the potential to measure the crystallization behavior in-line. The implementation involves normally incident shear wave reflectometry and measures a averaged shear wave reflection every 10s while the data is processed in real-time. Furthermore, the measurement is non-destructive and can be performed under shear stirring conditions. An inverse wave propagation model allows to deduce relevant ultrasonic parameters that provide information about the crystallization kinetics and the microstructure development by analyzing the behavior of the measured shear reflection coefficient. In this study, the isothermal crystallization behavior of cocoa butter has been monitored and compared using three techniques: ultrasonic shear reflectometry, Differential Scanning Calorimetry and Polarized Light Microscopy. In order to understand the impact of the crystallization on the measured ultrasonic parameters, limonene was added to cocoa butter and the isothermal crystallization behavior was monitored for different doses. The results suggest that shear reflectometry especially monitors the microstructure development, which makes the technique particularly interesting as a complementary monitoring tool to other techniques that monitor primary crystallization.status: publishe