Time Dependent Stress Decay Rheology of Stirred Yogurt

Stress decay behavior of two stirred yogurt samples was evaluated at various shear rates (100-500 s(-1)) and selected temperatures (10-25 degrees C) using a Haake rotational viscometer. Time-dependent shear thinning (thixotropy) was evident under all testing conditions, and an equilibrium shear stress was not reached even after 60 min of continuous shearing. Weltman's logarithmic time model accurately described the stress decay behavior at each shearing condition, and the temperature influence on Weltman parameters showed a linear trend. The temperature influence could also be evaluated using the Arrhenius model: resulting activation energies ranged from 4.9 to 14.6 kcal mol(-1).