52 PRESERVATIVES
Natural multi-functional antimicrobial ingredients
Dr Marina Raynbird, Antony Hudson, Gemma Jones, Georgia Morgan – ISCA UK
With a drive towards simpler, greener, and cleaner cosmetic ingredients and finished products, there is an ever-growing demand for multi-functional ingredients and innovative formulation ideas. ISCA UK’s R&D laboratory has been exploring ingredients that hold fungicidal and bactericidal activities, as well as other properties.
Why do we need preservatives? Microbial growth is limited in formulations with extreme pH levels, usually less than 4 or above 10. However, simply producing formulations of a pH value that will not encounter microbial growth is not a practical option, since such cosmetic products would undoubtedly cause irritation, and damage to the skin’s natural microbiome, which is naturally slightly acidic (pH of 4–6.5). To overcome this issue, and prevent
decomposition by microbial growth, a preservative can be added. Preservatives are essential ingredients of cosmetic formulations as they increase the longevity of finished products, which are subjected to various sources of contamination and are often stored in humid and warm environments, favourable for microbial growth. The choice and dosage of the preservative will depend on several factors, and the formulator should consider these meticulously. Formulation-dependent factors may include how the final product is used, whether it is for rinse-off or leave-on application, and compatibility with other ingredients to avoid inactivation. In addition, the effective pH range of the
preservative must match the final product. Other key points will include an assessment of the level of microbiological risk. For example, anhydrous products, formulations with high alcohol content or extreme pH are unlikely to require preservation, or may simply need relatively mild preservatives at low dosage. Challenge testing is a legal requirement for
most cosmetic products sold within Europe. A challenge test reassures the consumer that the finished product is protected from microbiological contamination under normal conditions of use, for a period after opening (PAO) which should be clearly stated on the packaging. Examples of standard methods are detailed in the European Pharmacopoeia (EP) and the United States Pharmacopeia (USP), both of which are globally accepted.
PERSONAL CARE July 2022
Figure 1: Fully equipped microbiology laboratory at ISCA UK In a challenge test, a finished product
is inoculated with a known number of microorganisms and at set intervals the sample will be analysed for microbial load. If the product is effectively preserved, then microbial growth will be constrained. If the levels of microbial growth are within the defined parameters, this indicates a pass, whereas greater levels of growth will indicate a failed test.
TABLE 1: ANTI-MICROBIAL PROPERTIES Microorganism
Yeasts Candida albicans Malassezia furfur
Moulds Aspergillus brasilliensis
Bacteria (gram-negative) Pseudomonas aeruginsa Escherichia coli
Bacteria (gram-positive) Staphylococcus aureus Propionibacterium acnes
Antimicrobial studies Aevum Vita 406 (AV 406) is a blend of sodium caproyl or lauroyl lactylate with sodium citrate. It is a naturally derived, multi-functional ingredient which is suitable for both leave-on and rinse-off formulations. Sodium lauroyl lactylate is well known to act as an emulsifier and surfactant by altering the interfacial tension between phases. As part of its latest R&D project, ISCA UK began to probe its antimicrobial efficacy. Initial
MIC (%) - pH adjusted
<0.2 0.2
0.8 1.0 0.5
0.25 0.25
Table 1: MIC values for AV 406 against a range of microorganisms using media with & without pH adjustment
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