S. Ghosi Hoojaghan - of Food Science and Technology, Faculty of Biological Sciences, North Tehran Branch, Islamic Azad University, Tehran, Islamic Republic of Iran.
M. Sedaghati - of Food Science and Technology, Faculty of Biological Sciences, North Tehran Branch, Islamic Azad University, Tehran, Islamic Republic of Iran.
N. Mooraki - Department of Fisheries Science, Faculty of Marine Sciences and Technology, North Tehran Branch, Islamic Azad University, Tehran, Islamic Republic of Iran.

The effect of gum tragacanth (۰, and ۰.۱۵%) and Fennel (Foeniculum vulgare) (۰, ۲.۵, and ۵%) on the chemical and rheological properties, phase separation, Lactic Acid Bacteria (LAB) viability, and sensory characteristics of an Iranian dairy drink "Doogh" was investigated during ۲۰ days of storage. Results cleared the stability of Dooghs prepared with Gum Tragacanth Dispersions (GTD) was significantly higher than samples without this hydrocolloid (P< ۰.۰۵). Doogh samples’ viscosity in the presence of Fennel Extract Powder (FEP) was increased significantly (P< ۰.۰۵). Power-law and Herschel-Bulkley rheological models were appropriate models for describing the flow behavior of control and treated Doogh samples, respectively. The results showed that by increasing the amounts of FEP, LAB viability increased while the fungi population decreased significantly (P< ۰.۰۵). Therefore, this herbal powder could stimulate LAB growth and control the fungi population in treated samples. Finally, adding GTD to the Doogh sample was proper for improving stability, and enrichment with Fennel was suitable for increasing LAB viability and microbial spoilage control.

Herschel-Bulkley rheological model, Microbial spoilage control, Lactic acid bacteria, Power-law model.