Investigation of the effects of adding hydrochlorides (Guar and Xanthan) on rheological behavior of low fat doogh

Doogh is a fermented beverage that is prepared by mixing yoghurt with water and some salt. There are resembling beverage basis of yogurt in neighboring countries around Iran. For example, dilution ratio, fat content, rheological characteristics and taste like doogh, however, they all contain aggregated casein Serum separation is one of the main problems of this product during storage period. In this study, the effect of the additional of guar gums (0.3%), and xanthan (0.3%) and a mixture of two gums (0.15%- 0.15%) on the rheological properties and serum separation of low fat doogh was examined. Rheological behavior of doogh samples was fitted with Ostwald-de Waele model. Mathematical calculations of data based Ostwald-de Waele model, showed that the low-fat doogh is non-Newtonian and shear thinning (Pseudo plastic) fluid type. Also, using the Arrhenius equation dependence of the apparent viscosity to temperature is determined and the activation energy between 11.09 to 19.07 kJ/mol is calculated.