Steady and dynamic shear rheological properties of açai pulp (Euterpe oleraceae Mart.)

The aim of this work was to study the rheological behavior of açai pulp at different temperatures (10, 25, 40, 55 and 70 °C) under steady and dynamic shear conditions. The measurements were carried out using a stress-controlled rheometer with stainless steel plate-plate geometry and smooth or grooved surfaces. In the tests performed with smooth surface geometry, the slip effect was shown at low shear rates under steady and dynamic shear conditions, while the use of grooved surface geometry minimized this effect. At any given temperature, the açai pulp showed shear thinning behavior with yield stress in the steady shear measurements. However, an increase in temperature led to an increase in thixotropy and a decrease in yield stress. In addition, the açai pulp viscosity at 100 s−1 showed Arrhenius type temperature dependence, with activation energies of 4.18 and 6.21 kJ/mol for smooth and grooved surfaces, respectively. With respect to the dynamic shear measurements, the açai pulp showed weak gel-like behavior, and the storage and loss moduli decreased with increasing temperatures.