Rheological characterisation of cocoa creams

Rheological properties of four commercial cocoa creams (A, B, C and D) were investigated under steady and oscillatory shear conditions in the temperature range 25-45°C. Calorimetric measurements (DSC) were also performed. Samples exhibited marked shear-thinning behaviour characterised by high-viscosity Newtonian plateau at low shear stresses and a complex yielding process. An approach based on three consecutive critical stresses (elastic, static and dynamic yield) was proposed. Large differences in viscosity, yield stresses and flow temperature dependence were observed among samples. Generally, viscosity and yield stress decreased with increasing temperature, and the higher the viscosity of the samples, the greater was the decreasing rate. Mechanical spectra showed gel-like behaviour due to interactions of particle aggregates. Temperature increase determined different changes of linear viscoelastic properties. Relaxation spectra at 25°C ranked samples into two groups (A-B) and (C-D), while all four creams showed similar behaviour at 45°C. No substantial thermal transition occurred in the temperature range investigated.