Study on time-dependent rheological behavior of bene butter (Pistacia atlantica)

Bene butter is a paste form product that contains mainly milled, roasted bene kernel with sugar. This product has suitable nutritional properties and knowing about its rheological characteristics can be useful for industries. In this investigation, time-dependent flow properties of pistachio butter were determined using three different models such as Weltman, first-order shear stress decay with zero equilibrium stress value and first-order shear stress decay with a non-zero equilibrium stress value. For this reason for evaluating the correlation between shear stress and time of shearing in a constant rate (150 s-1), samples at two different temperatures (25°C and 45°C) were evaluated for 10 min. Shear stress vs. time of shearing data were then assessed using the three models. R2, RMSEand %E were applied to choose the best modeland among these models the Weltman model was the best fitted to experimental data. It was found that pistachio butter exhibits a thixotropic behavior and its apparent viscosity decreases with increasing the time of shearing.