Rheological characterization of milled sesame (tehineh)

Tehineh (semi solid paste) is a local food in the Middle East, which is produced from dehulled sesame seeds. A major concern facing the tehineh industry is the production and maintenance of the product while preserving the proper consistency, stability, color, and texture properties. In this study, the flow curves and time-dependent flow properties of tehineh were assessed at different temperatures. It was found that tehineh behaves as non-Newtonian pseudo-plastic foodstuff. The power-law model was found to be the most appropriate to fit the flow curves of tehineh. Both in the forward- (increasing shear rate) and backward-measurements (decreasing shear rate), the consistency coefficient, m, significantly decreases with temperature, while the flow behavior index, n, slightly increases with temperature. As far as the effect of steady shearing on the flow properties of tehineh is concerned, two models were used to predict the flow behavior, namely; the first-order shear stress decay and Weltman models. It was found that tehineh paste exhibits a thixotropic behavior that increases with increasing shear rate and is mitigated by increasing temperature. An equilibrium time of about 25 min or less is needed by tehineh paste, under the action of steady shearing, such that no further breakdown of 3-D fat polymer is pronounced.