Tailoring flow behavior and texture of water based cocoa suspensions

Abstract

The microstructure of low fat food suspensions must be carefully adjusted to meet customer expectations. Here, we discuss how appropriate heat treatment or the addition of an adequate immiscible secondary fluid can be used to tailor the texture and flow of water based cocoa suspensions in a wide range. By comparing suspensions of untreated and organic solvent (n-hexane and ethanol) extracted cocoa particles, we demonstrate that the residual cocoa butter is decisive for the control of the structure and flow behavior of these suspensions. The low shear viscosity and apparent yield stress of suspensions from untreated particles increases by more than two orders of magnitude when heated to 30–35 °C. This is attributed to the formation of a particle network held together by the sticky, semi-crystalline cocoa butter leaking from the interior of the particles. This structure remains stable upon cooling to 20 °C, but it vanishes when the suspension is heated to temperatures T > 40 °C. At high temperatures the cocoa butter detaches from the cocoa particles forming separate emulsion droplets as confirmed by fluorescence microscopy. A similar structure formation can be achieved at room temperature if trace amounts of a polar organic solvent like oleic acid is added. This is attributed to the partial solubility of cocoa butter in these solvents resulting in the formation of a sticky surface layer formed by these butter/solvent mixtures. This hypothesis is further supported by small angle neutron scattering experiments. The solubility rate determines the kinetics of particle network formation.