36D-24 |
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A. E. OZEN and M. Kilic. Dept. of Food Engineering, Istanbul Technical Univ., Faculty of Chemical and Metallurgical Engineering, Maslak, Istanbul, 34469, Turkey Non-Newtonian fluids might exhibit time-dependent flow behavior. Fermented milk products such as yogurt exhibit thixotropy which is defined as the time-dependent decrease in shear stress or apparent viscosity at constant shear rate. The objective of this study was to investigate time-dependent flow behavior of a commonly consumed fermented and salted milk beverage in Turkey, ayran. Rheological properties of the beverage were measured with a rheometer at constant shear rates (25-350 s-1) and a temperature of 10° C. Time-dependent changes in shear stress were modeled by using Weltman, power law and Hahn models. The viscosity of the beverage decreased with time and an equilibrium value was not reached after 60 min of continuous shearing at shear rates higher than 100 s-1. The Weltman model gave the best fit followed by Hahn and power law models. All of the models gave better fit at higher shear rates (≥200 s-1) that was attributed to the structure being destroyed more rapidly and becoming more homogeneous compared to that at lower shear rates. Weltman model gave the best prediction of the thixotropic behavior of the fermented milk beverage. This model can be utilized for the design of equipment used in the processing of this beverage.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |