Effect of Source and Amount of Total Solids Content on the Rheological Properties and Stability of Non-Fat Doogh

As a native fermented dairy drink, doogh is an important industrial product in Iran. However, its characteristics have not been completely evaluated. This study evaluated the flow behavior, particle size distribution and stability of non-fat doogh as affected by the row material employed (fresh skim milk or skim milk powder) and the total solids (TS) content of the final drink. The viscosity of samples produced using fresh skim milk was 1.73 ± 0.24cPs. Those produced using skim milk powder exhibited higher viscosity resulting from bigger particle size. Increasing the TS content caused the viscosity of the doogh to increase, but the volume of the separated serum was reduced. Flow behavior became non-Newtonian at higher TS contents. Evaluations indicated that the colloidal particles existing in doogh were distributed among a wide range of sizes. Different particle shapes with complex structures were observed.