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Numbers and Types of Starter Bacteria in Fermented Milks and Dried Products in Relation to Claims Concerning Probiotic Properties


Production of probiotic products, including dried supplements and fermented milks (especially yoghurt) has increased as consumers become more interested in possible heath benefits from the microflora they contain. There is a need to ensure these foods maintain an acceptable level of viable probiotic bacteria at the time of ingestion and conform to designations on product labels. <p>There have previously only been limited methods for the detection and enumeration of these bacteria. Therefore the main objective of this work is to develop methodology to identify and quantify the numbers of specific bacteria, incuding Lactobacillus acidophilus and some species of Bifidobacterium, in probiotic fermented milks and dried supplements during distribution and at point of consumption.

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Samples were examined on the day of delivery into distribution and up to four times during storage until the 'Best before' date. Dried products were assessed after removal of any possible confounding elements (vitamins/herbal extracts) where possible.
Different media were evaluated for isolation of starter cultures. Suitability of media was determined on sensitivity, selectivity, and practicality. Presumptive recognition of bacteria was on the basis of colony and cell morphology. This could then be followed by the use of existing confirmatory tests if appropriate. For example, X-GLU for Lb. acidophilus.
The feasibility of developing a fructose-6-phosphoketolase enzyme assay for the confirmation of presumed bifidobacteria colonies was investigated. This enzyme is genus specific and used by bifidobacteria during carbohydrate breakdown.
Genetic fingerprinting was used to identify strains of bacteria from products. Using known isolates and AFLP (amplified fragment length polymorphism) 50-100 fragments are amplified per strain, creating a comprehensive profile.
The final goal of the project is the development of a protocol for enumeration and strain identification of probiotic bacteria in fermented milks and dried supplements.
Find more about this project and other FSA food safety-related projects at the <a href="; target="_blank">Food Standards Agency Research webpage</a>.

University of North London
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