Study on viability of probiotic bacteria in retail samples of fermented milks

43 samples of fermented milks with probiotic bacteria (L. acidophilus and/or Bifidobncterium) belonging to different brands were selected to evaluate the microbial concentrations throughout the shelf life at 4 degrees C and the agreement between isolated species and reported species on the product labels. Three different media (NPNL agar; TPY agar with bile salts at 30 g/l; TPY agar added with nalidixic acid 15 mg/l, neomycin sulfate 100 mg/l, lithium chloride 3 gill were used in order to compare the recovery of the Bifidobncterium genus. NPNL agar resulted the most suitable cultural medium. A concentration value of 10(6) CFU/g for each microorganism was considered the minimum acceptable limit to deem the product promoting a real health effect. Only two out of six fermented milks showed to keep the bacterial counts above this limit until the expiry date; in one product Bifidobacterium was not found, even at low concentrations and near the production time; in two products the isolated strains could not be ascribed to the declared species; samples of different lots belonging to the same brand pointed out remarkable differences in microbial concentrations.