Effect of incubation and storage temperatures and final pH on the viability of probiotic bacteria and sensory characteristics in probiotic Doogh

The viability of Lactobacillus acidophilus and Bifidobacterium lactis was monitored during the storage of probiotic Doogh for 21 days as influenced by incubation and storage temperatures and product’s final pH value. Samples were fermented at various temperatures (37، 40 and 44°C) till the pH value dropped to 4. 6، 4. 4 or 4. 0. The highest viability of probiotics was achieved at fermentation temperature 37°C and final pH values 4. 4 and 4. 6. Storage of these two best treatments in various temperatures (5، 10 and 15°C) for 21 days resulted a rapid decrease in B. lactis population in the first 7 days after which the bacteria became compatible with the harsh condition. The highest viability occurred for L. acidophilus merely at pH lower than 4. 05 ± 0. 05 and its growth was observed in first week of storage. Samples stored at 5°C showed the highest viability and samples at 15°C had the best sensory properties.