Due to special properties of fermented milks containing probiotics, such as improving protein and vitamin metabolisms, antibacterial activities, treatment of liver disease and reduction of the risk of colon cancer, in recent years, special emphasize is placed on shelf-life evaluation of these products. The effects of acid-adaptation treatment of bifidobacteria on the viability of these microorganisms in bioyoghurt during storage were evaluated in this research. Also, viability of bifidobacteria in simulated gastric juice and bile solution was assessed. The results showed that while B. breve survived better during storage of refrigerated bioyoghurt, B. infantis strains were more resistant to simulated gastric juice and the survival rate of these strains under alkaline condition of bile solution was approximately 70%. Since the survival of probiotics throughout the shelf-life of the product and at the time of consumption as well as tolerating the extreme pH conditions are important factors for exertion of health benefits in the host, both aspects must be considered in shelf-life evaluation of commercial bioyoghurt.

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