Variation, viability and validity of bifidobacteria in fermented milk products

- TOS-MUP proved to be the selective medium of choice for enumeration of bifidobacteria in fermented dairy products.
- All except one products contained ≥106 cfu/g Bifidobacterium spp and little reduction was noticed by the expiry date.
- 16S rRNA gene analysis of isolates revealed that all isolates belong to Bifidobacterium animalis subsp. lactis.
- The DNA fingerprint of all isolates showed a similar pattern, indicating no strain variability among the isolates.
- 19 out of 24 products failed to mention the species or strains used and 2 products' species were mislabelled.

A selection of 24 commercial probiotic fermented milk products was evaluated for the numbers, types and viability of Bifidobacterium strains against the stated information on the package. Nineteen out of 24 products claimed to contain Bifidobacterium on their labels and only 3 referred to the species (one Bifidobacterium lactis and two Bifidobacterium longum). No information on the numbers of probiotics was provided on any of the products. Bifidobacteria were recovered using comparative enumeration on two selective media, BIM-25 and TOS-MUP. All products but one met the minimum recommended level of 106 cfu/g at time of purchase and relatively little reduction was observed by the expiry date, except for one product that fell below minimum recommended level. Partial sequence analysis of the 16S rRNA gene revealed that all isolates from tested products belonged to Bifidobacterium animalis ssp. lactis. The potential value of rep-PCR as a faster alternative to other molecular tools to further differentiate the isolates was also examined. The DNA fingerprint of all isolates using two primers, BOXA1R and GTG5, showed a similar pattern, indicating no strain variability among the isolates. It was concluded that despite no variation in bifidobacteria used, in majority of the products good number of bifidobacteria survived to the end of shelflife and may provide health benefits to consumers. A definitive answer as to how many is adequate remains unknown as there is no specific number of probiotic bacteria that can be recommended to ensure a beneficial effect.