Effects of Fermentative Factors on Biochemical, Microbiological and Sensory Characteristics of Probiotic Iranian Fermented Milk (Doogh)

Background: Doogh is a traditional Iranian fermented milk drink that is currently a very popular product in Iran. In the present study, the combined effects of incubation temperature, type of starter culture, and final pH of fermentation on the viability of two probiotic strains (Lactobacillus acidophilus La-5 (A) and Bifidobacterium lactis Bb-12 (B)) and biochemical and sensory characteristics of probiotic Doogh were investigated. Method: Different treatments were prepared with yoghurt starter culture containing probiotics, using reconstituted skimmed milk with 6% of solid nonfat. They were incubated at 38°C or 44°C until pH 4.0 or pH 4.5 and were kept for 21 days at 4°C or 8°C storage temperature. The biochemical properties of treatments were evaluated during fermentation and refrigerated storage. The viable count and sensory attributes of treatments were studied at the end of fermentation and at the end of storage. Results: Results showed that the greatest mean pH drop rate, mean acidity increase rate and mean redox potential increase rate and the shortest incubation time were observed in treatments incubated at 44°C with final pH of 4.5. The highest survival of both probiotic strains during storage was related to treatments with fermentation temperature of 38°C and final pH of 4.5. Treatments ABY1-38°C-4.0 had the highest sensorial total acceptance at the end of refrigerated storage. Conclusion: It would be concluded that the best treatment was ABY3-38°C-4 stored at 8°C in regards of probiotics’ viability and sensory characteristics of Doogh. Thus, controlling the temperature of refrigerated storage is the most importance factor during storage and distribution.