Rheological characterization of milled sesame (tehineh)

Tehineh (semi solid paste) is a local food in the Middle East, which is pro duced from dehulled sesame seeds. A major concern facing the tehineh indust ry is the production and maintenance of the product while preserving the pr oper 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-Newton ian 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- (increa sing shear rate) and backward-measurements (decreasing shear rate), the con sistency coefficient, in, significantly decreases with temperature, while t he flow behavior index, n, slightly increases with temperature. As far as t he effect of steady shearing on the flow properties of tehineh is concerned , two models were used to predict the flow behavior, namely; the first-orde r shear stress decay and Weltman models. It was found that tehineh paste ex hibits a thixotropic behavior that increases with increasing shear rate and is mitigated by increasing temperature. An equilibrium time of about 25 mi n 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. (C) 2001 E lsevier Science Ltd. All rights reserved.