Cosmetics Testing - Schülke-Koko preservative efficacy (Challenge) test.
There are several types of tests to evaluate the effectiveness of preservatives incorporated into a cosmetic product and European legislation does not specify which of them should be used (Regulation EC No. 1223/2009 of the European Parliament and the Council of Europe of 30 November 2009 on cosmetic products). The most used tests in our area are the test carried out according to the ISO 11930 standard, or the one carried out according to the European Pharmacopoeia (European Pharmacopoeia).
Three microorganisms are used in all preservative efficacy tests: Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. In addition, other microorganisms that can cause alteration of the cosmetic product are usually included (see below). Unlike the European Pharmacopoeia method that uses only pathogenic microorganisms, the Schülke-KoKo test includes degrading microorganisms, chosen according to the experience of Schülke´s service to cosmetics manufacturers.
In this test, an inoculum is used with a mixture of microorganisms (unlike tests based on the European Pharmacopoeia and ISO 11930, in which the test microorganisms are inoculated independently) and with a volume, with respect to the inoculated product, of 0.4% per microorganism making a total of 2.4% with the 6 microorganisms (lower inoculum compared to the 1% inoculated per microorganism in the ISO 11930 standard and European Pharmacopoeia), and 6 weekly inoculations are carried out throughout performing the test.
The microorganisms used are: Enterobacter gergoviae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas putida, Burkholderia cepacia, Kocuria rhizophila, Staphylococcus aureus, Candida albicans, Aspergillus niger (= Aspergillus brasiliensis), and Penicillium funiculosum (= Penicillium pinophilum).
This test is designed to simulate conditions more comparable to the conditions in which a cosmetic product is used. Thus, by inoculating a mixture of microorganisms, it is possible to obtain symbiotic growth similar to that which could occur under natural conditions.
Reductions of test microorganisms are evaluated weekly. If a sample meets criterion A (reduction ≥4 log for bacteria and ≥3 log for fungi), it means that even after the sixth inoculation no microbial growth can be observed, the product can be considered well preserved. Thanks to many years of experience in using this test method, if a product meets criterion A, the microbiological stability of 30 months can be affirmed, which is recommended for cosmetic products. If the formulation meets criterion B (≥3 log reduction for bacteria and ≥2 log for fungi), the microbiological risk analysis must demonstrate the existence of control factors unrelated to the formulation; for example, protective packaging and/or following strong requirements for good manufacturing practices.