Modeling the Time-Dependent Rheological Properties of Pistachio Butter


1 Department of Food Science and Technology, Ferdowsi University Mashhad (FUM),Mashhad PO Box: 91775-1163, Iran

2 Pistachio Research Institute (PRI), Rafsanjan PO Box: 77175-435, Iran


Pistachio butter (semi solid paste), which is made from roasted pistachio kernels, is an appropriate
alternative to work on because of its high nutritional and economical values. In this study, timedependent
flow properties of pistachio butter were determined at two different temperatures (25˚C and
45˚C) for five different formulations (with different levels of emulsifying agents). Forward and
backward flow curves were plotted and the amount of existing hysteresis loop was measured. Also,
shear stress vs. time of shearing data were assessed using three models namely; Weltman, First-order
shear stress decay with a zero equilibrium stress value, and First-order shear stress decay with a nonzero
equilibrium stress value. To evaluate the ability of these models to predict the rheological
characteristics of pistachio butter, three statistical parameters namely; R2
, RMSE, and MRDM were
used and finally the Weltman model was found to be the most appropriate to fit the experimental data.
The results showed that pistachio butter exhibits a thixotropic behavior and its apparent viscosity
decreases with increasing the time of shearing.