Determination of survival, identity and stress resistance of probiotic bifidobacteria in bio-yoghurts

AIMS: To determine the level of bifidobacteria in bio-yoghurts in the UK, identify the species, and compare the resistance of common Bifidobacterium spp. to acidity and oxidative stress. METHODS AND RESULTS: A storage trial of bio-yoghurts was carried out to determine the level and survival of bifidobacteria. The 16S rRNA gene targeted PCR was used to identify the species. Acid tolerance was determined by introducing the organisms to pH-adjusted skimmed milk and enumerating during storage at 4 degrees C. Oxidative stress resistance was determined using the H(2)O(2) disc diffusion assay technique. Nine of 10 bio-yoghurts contained bifidobacteria at levels >10(6) CFU g(-1) at the time of purchase. The viability of the organism decreased during storage and on expiry only five products retained viability >10(6) CFU g(-1) while two others were very close to the target population. Bifidobacterium animalis ssp. lactis showed superior survival abilities and stress tolerance compared with Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium bifidum, Bifidobacterium adolescentis and Bifidobacterium longum biotype infantis. CONCLUSIONS: Bifidobacterium animalis ssp. lactis, the only Bifidobacterium spp. found in bio-yoghurts, had the greatest resistance to acidity and oxidative stress. SIGNIFICANCE AND IMPACT OF THE STUDY: The technological properties of B. animalis ssp. lactis make it suitable for inclusion in bio-yoghurts although its putative health benefits need further investigation.