Authors: Marie de BORT, Elvire MESSINEO, Romain LE NEVE, Abdelkader BOUBETRA, Anne TIRARD.
In order to help laboratories to face with their regulatory requirements, BIPEA (Bureau Interprofessionnel d’Études Analytiques) developed a production of external reference materials (ERM) for microbiology in food. These samples should allow laboratories to check the trueness of their results at any time, outside the regular proficiency-testing schemes (PTS).
For this purpose, stable and homogeneous samples of minced meat spiked with various bacterial strains are produced by BIPEA: Escherichia coli, Clostridium perfringens, Bacillus cereus, Staphylococcus aureus and Listeria monocytogenes, at levels between 102 to 104 microorganisms per gram. Controls were performed by analysing samples all along the production process, at the beginning of the study and regularly during a 6-month period.
The homogeneity was checked by calculating coefficients of variation, which were inferior to 25 % for all the analytical parameters. The stability was characterized by comparing means of three samples to the mean obtained at the beginning of the study. The samples produced were thus considered as being sufficiently homogeneous and stable to meet the ERM requirements: the results of enumeration of the different micro-organisms present in the minced meat after 6 months of storage at (-24 ± 6)°C showed a good stability, with a maximum deviation less than 0.5 log (CFU/g: colony forming unity per gram).
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