Sep 24, 2004 - Department of Food Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, ... the rheology of tahin as a function of shear rate and.
Effects of temperature, shear rate and constituents on rheological properties of tahin (sesame paste) Filiz Lokumcu Altay and M Mehmet Ak∗ Department of Food Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
Abstract: In this paper, rheological properties of tahin are reported at temperatures from 20 to 70 ◦ C and shear rates in the range 0.13–500 s−1 . Temporary hysteresis loops were observed in the first cycle of the flow curves. The steady shear behaviour of tahin was pseudoplastic and described by a power law model. The consistency coefficient exhibited strong temperature dependence for which the activation energy of flow was 21.6 kJ mol−1 . The flow behaviour index of tahin tended to increase whereas the consistency coefficient tended to decrease during storage at room temperature. Tahin oil exhibited Newtonian behaviour with a strong dependence of viscosity on temperature. The activation energy of flow for tahin oil was 35.7 kJ mol−1 . While reconstituted suspensions containing up to 20% solids exhibited Newtonian behaviour, those with more solids and the original tahin showed pseudoplastic behaviour. The Krieger–Dougherty model fitted the suspension viscosity data well. Below 20% solids level there was no effect of particle size on the viscosity of the reconstituted suspensions. It was shown that for the same amount of solids the viscosity of a ‘polydisperse’ suspension was lower than that of a ‘monodisperse’ suspension. 2004 Society of Chemical Industry
INTRODUCTION Tahin (roasted sesame paste) (also called tehina, tehineh, tehinah, tahinah or tahina) is widely used in baked goods, confectionery products and some local dishes in different parts of the world. It is, for instance, the key ingredient of helva (also called halaweh, halawa or halva), a sweet that is quite popular in the Middle East, Saudi Arabia and Turkey. Tahin is also mixed with other ingredients (eg honey, syrups) to prepare a spreadable dessert.1 – 4 Several reports exist in the food literature on chemical and nutritional properties of tahin and sesame oil.1 – 3,5,6 The higher stability of sesame oil against oxidation as compared with other vegetable oils is well known.7,8 This aspect facilitates the incorporation of sesame paste into spreadable products (eg peanut butter)9 to extend their shelf life. There has recently been a marked increase in research on rheological properties of tahin and blends containing tahin.4,10,11 Early work in this area was done by Lindner and Kinsella.12 They reported significant changes in physical properties of tahin (including viscosity at a constant shear rate of 19 s−1 ) as a result of hydration. Their results showed a large increase in viscosity upon addition of small amounts of water (
