Isolation and identification of lactobacilli from novel-type probiotic and mild yoghurts and their stability during refrigerated storage

A total of 26 Lactobacillus strains were isolated from various mild yoghurts and novel-type probiotic dairy products and from a starter culture preparation and were identified by using DNA–DNA hybridization technique. The species present in those products were found to be Lactobacillus acidophilus, L. johnsonii, L. crispatus, L. casei, L. paracasei and L. rhamnosus. DNA homology analysis revealed that some strains had been misclassified by their investigators. Three strains designated as L. acidophilus (L. acidophilus LA-1, L. acidophilus ATCC 43121 and the Lactobacillus strain from Biogarde® culture) were found to belong to L. johnsonii and L. acidophilus L1 to be L. crispatus. Strains designated as L. casei were found to be members of three separate species: L. casei, L. paracasei and L. rhamnosus. Viable numbers of lactobacilli in mild and probiotic yoghurts varied greatly including some products with very low Lactobacillus counts. The majority of the probiotic yoghurts, however, contained viable counts above 105 per g even at the end of the best before use period.