Effect of storage time and some chemical properties of probiotic yogurts on probiotic viability

Various factors affect viability of probiotic bacteria. In this investigation, the effect of some chemical specifications and the storage time on probiotic bacterial count in 30 samples of probiotic yogurts stored at 4ºC was studied. The samples were evaluated in 7 days interval for viable cell count, coli count, pH and acidity during refrigerated storage. The pour plate method of Culture with MRS-bile agar was used for enumeration of probiotic bacteria. Total coliform was enumerated in VRBA and BGB culture. Acidity of samples was determined with titration method and the values of pH were measured by a digital pH meter. The obtained results showed that the number of probiotic bacteria and titrable acidity in all of the samples were significantly decreased and increased, respectively. Also, the level of pH was decreased during the storage time. There were significant relationship between probiotic bacterial count and the amount of pH and acidity. A brief increase of probiotic bacterial counts was measured during the initial days, but there was sever declining during the final days of storage. 46.67% of examined samples had probiotic bacterial counts less than the minimum dose of 106 cfu per gram of yogurt in day 28. This study indicated that the deadline for storage and consumption of probiotic yogurts is 21 days after production. In addition, the decline in viability was dependent on the amount of pH and acidity.