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05.12.2017 - Cosmetics
Preservative Efficacy Tests (PET) according to DIN EN ISO 11930
The following section provides general information on the execution and assessment of a preservative efficacy test according to DIN EN ISO 11930.
The test procedure is as follows:
- Inoculation of a product with specified microorganisms (each germ individually) and determination of the germ count
- Storage of the inoculated product under defined conditions
- Determination of germ counts at defined time points and tracking germ count development
Verification that germ counts are reduced in accordance with specifications. This provides an indication regarding the microbial stability of the cosmetic product.
Test strains according to ISO 11930
- Pseudomonas aeruginosa ATCC 9027
- Staphylococcus aureus ATCC 6538
- Escherichia coli ATCC 8739
- Candida albicans ATCC 10231
- Aspergillus brasiliensis ATCC 16404
ISO 11930 indicates that, depending on the operation and case, it may be sensible to include additional strains, often involving microorganisms that have already caused problems within the company.
In non-standardized challenge test methods, there are procedures for reducing practicality concerns or examination effort, where two or more test strains are mixed together in a microorganism suspension. However, the issue with using mixed cultures is that mutual interactions between microorganisms during the test cannot be excluded. Additionally, it's disadvantageous as there are no standardized procedures and criteria for evaluating results from tests with mixed cultures or multiple inoculations.
Test time points according to ISO 11930
- 7 days exception: A. brasiliensis
- 14 days
- 28 days
Depending on the results, it may be advisable to continue the challenge test after 28 days to gather further insights into the long-term germ count development in the product. This is particularly relevant in cases where germs are reduced slowly and/or there is a risk of germ resurgence.
Acceptance criteria
Table 2: Acceptance criteria according to ISO 11930
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