A comparative study of total colony count of the lactobacilli strains during the shelf-life in some samples of commercial probiotic yoghurts

Lactobacilli are one of the major microorganisms in the probiotic yoghurt. The therapeutic potentials of these microorganisms are due to their variations and rates of survival during the shelf life of probiotic yoghurt. This study aimed to assess the total colony counts of lactobacillus strains in some examples of typical commercial probiotic yoghurt. In this cross-sectional survey، 50 samples of probiotic yoghurts (10 samples derived from 5 dairy brands) were collected and coded. The variations of all lactobacilli strains were counted after the preparation of surface cultures in 2 stages (1: Mid–day of shelf-life، and 2:1 day before the expiration date of yoghurt); additionally، the pH of all samples was measured in the latter stage. Data were analyzed using the SPSS program. The average lactobacilli colony count was lower in the second culture as compared to the first one in 4 out of 5 probiotic yoghurt brands (p≤ 0. 002). Amongst all estimated samples، the highest number of colony counts was less than the minimum recommended dose (2. 9×105 vs. 106، p<0. 0001). The mean pH of samples was significantly lower than the optimum pH at the end of the shelf life (p<0. 0001). Underrated total colony counts of lactobacilli strains during shelf life، and increased acidity of samples at the end of storage period would exacerbate the potential efficacy and clinical merits of evaluated commercial probiotic yoghurts. Implementing regular quality controls in accordance with national standardized protocols، as well as further extended research are warranted.