RHEOLOGICAL BEHAVIOR OF COCOA DISPERSIONS WITH COCOA BUTTER REPLACERS

The steady shear viscosity and yield stress of cocoa powder dispersed in three cocoa butter replacers (CBRs) are measured over a wide range of powder concentration and temperature. The flow activation energies of the three CBRs are nearly the same, and close to that of cocoa butt er. Values of intrinsic viscosity of cocoa powder dispersed in corn oi l and Socolate 36-38 are in the range of 4.0-5.0, (similar to that in cocoa butter), suggesting that these two CBRs are good cocoa replacers . A lower value of intrinsic viscosity is found for the powder dispers ed in Super YZ-2. Viscosity measurements indicate that all three CBR d ispersions exhibit Newtonian behavior at low volume fraction, but non- Newtonian shear thinning characteristics when the volume fraction phi > 0.3 at 60C. The non-Newtonian behavior can be described by the Casso n model when phi exceeds a critical value, phi(mo), the maximum packin g fraction at zero shear. The yield stress can be related to the powde r volume fraction using a four-parameter equation originally proposed by Zhou et al. (1995).