Shear-Induced Crystal Formation and Transformation in Cocoa Butter

We investigated shear-induced crystal formation and phase transformation of cocoa butter fora wide range of temperatures and shear rates. By simultaneously monitoring the wide-angle X-ray scattering pattern and the viscosity evolution, we characterized different crystallization events. The initial formation of polymorph form alpha and the transformation into the beta(V) polymorph was confirmed up to 24 degrees C. We quantified the acceleration of phase trans formation by shear in cocoa butter. We also demonstrated that the same crystallization events are found in a highly concentrated model suspension at low macroscopic shear, which represents the now conditions of chocolate in a temperer. There is strong evidence for fraction formation and compositional changes during growth of the crystallites. This led to the proposition of phase III being a mixture of cocoa butter in form alpha and a fraction of trisaturated triacylglycerols in form beta'. Moreover, we investigated the gradual formation of a beta(VI)-like diffraction pattern during conditioning of beta(V) crystals under shear. Changes similar to single components transforming into their most stable form were all indication of local accumulation of higher melting triacylglycerols for the experimental conditions used.