PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF SESAME PASTES (TAHIN) PROCESSED FROM HULLED AND UNHULLED ROASTED SESAME SEEDS AND THEIR BLENDS AT VARIOUS LEVELS

ABSTRACT In this study, proximate composition, certain quality and rheological properties of sesame pastes (tahin) produced from hulled roasted sesame seeds (without hull), called simply tahin, from unhulled roasted sesame seeds (with hull), so-called Bozkir tahin, and their blends (25–75%) were determined at temperatures ranging from 15 to 65C and shear rates from 0.5 to 100 1/s. Tahin, Bozkir tahin and their blends were found to exhibit non-Newtonian, pseudoplastic behavior at all temperatures. Apparent viscosity versus shear rate data were successfully fitted to the power law model. The flow behavior index, n, varied in the range of 0.4587–0.6830. The consistency coefficient, K, was in the range of 3.97–28.08 Pa·sn. Both parameters were significantly affected by temperature. The increase in levels of unhulled sesame seeds in tahin resulted in higher viscosity (K) for all temperatures. Temperature sensitivity of the consistency coefficient was assessed by applying an Arrhenius-type equation, and Ea value appeared in the range of 17.87–24.92 kJ/mol. PRACTICAL APPLICATIONS Roasting of sesame seeds is the most significant step in tahin processing that causes important physical, chemical, structural and sensorial changes. The sesame roasting is carried out to promote more flavor, desired color and texture changes that ultimately increases the overall palatability. A major concern facing the tahin industry is the production of a product with proper consistency, emulsion stability, color and textural properties. Reliable and accurate rheological data are necessary for the design of flow process and to evaluate heating and cooling rate during different engineering operations. So, this work is very important in terms of the estimation of physicochemical and rheological properties of sesame paste containing hulls.