Orientation and phase transitions of fat crystals under shear

Crystalline orientation and phase transition acceleration induced by shear are demonstrated to occur in different edible fats using synchrotron X-ray diffraction. Cocoa butter, milk fat, stripped milk fat, and palm oil were crystallized statically and under shear (90 s(-1) and 1400 s(-1)) from the melt (50 degreesC) to 18 degreesC at a constant rate of 3 degreesC min(-1). The 2D diffraction patterns clearly showed crystallite orientation imposed by the flow in the different phases. A dramatic reduction in phase transition times was also evident. These effects of shear on crystallizing fats are of great importance for the industrial processes carried out in chocolate, dairy, margarine, and shortening production, since temperature and shear treatments are the tools for tailoring the desired crystalline structures.