78 PRESERVATIVES
This is demonstrated in Figure 1 comparing the efficacy of a preservative blend by itself, and with the amplified effect. The efficacy is determined by minimum inhibitory concentration (MIC) which is the lowest concentration of a chemical which prevents growth of a bacterium. The MIC help and guide us to determine the level of use of the enhanced blends, as we strive to achieve the lowest MIC possible. For example a commonly used blend of phenoxyethanol with ethylhexylglycerin would normally be used at a level of 1%. Its amplified version would be used at the same product, with a level of use of 0.5%. A successful challenge test result is demonstrated in Figure 2. It is shown that by day 7 the microbial count was already below 10 and remained at that level for the duration of the full 28 days, thus passing USP criteria for category 1 products. Due to the cationic profile of these preservative blends, it was critical to also test its efficacy in a formula with anionic ingredients, common for rinse-off products.
In the optimised blends, we can show
strong broad spectrum protection in anionic based products, as can be seen in Table 1 of the challenge test results. This line was developed further to provide a range of option to answer the industry needs: ‘Phenoxyethanol-free’ alternatives based on methyl propane diol is a good example. The optimisation process is different in every combination. The level of the cationic surfactant that would enhance a blend of phenoxyethanol with ethylhexylglycerin would not be right for another preservative combination. Some preservatives did not demonstrate an amplified effect with the presence of a cationic surfactant. The flexibility of this platform allows a global approach, approved and allowed for use in US, EU, Brazil, Japan and China, and are applicable to all applications.
Solving formulation problems Several joint projects were conducted in cooperation with leading manufacturers in serval countries, with good results. A good test case is the one of company ‘A’, who experienced difficulties to preserve a premium sheet face mask. Sheet masks are
Table 1: Challenge test.
Time of reading
Inoculum 2 days 7 days
14 days 21 days 28 days
E. coli
ATCC 8739 1x106
8.6x102 <10 <10 <10 <10
Staph. aureus ATCC 6538
1.1x106 <10 <10 <10 <10 <10
PERSONAL CARE NORTH AMERICA
P. aeruginosa ATCC 9027
1.1x106 <10 <10 <10 <10 <10
C. albicans ATCC 10231
1x105 <10 <10 <10 <10 <10
A. niger ATCC 16404
1x105 1x104
4.8x105 6x103
8.5x103 1x103
SharoSENSETM
5000 3750 2500 1250 0
Figure 3: SharoSense Plus MIC comparison. S. aureus
E. coli
often hard to preserve, with even more challenges than the already complex wet wipes, due to the high water content, fabric which is susceptible to fungi growth and use on the sensitive face area.
The use of 0.9% of a phenoxyethanol with ethylhexylglycerin blend was not sufficient and the product did not pass a challenge test. When the level of use was increased to 1.1%, the high level caused irritation around eye area, and stinging sensation. The manufacturer changed the preservative system to an ‘amplified’ version, at a level of use of 0.7%, with excellent results, and no side effects. For those scientific reasons, a provisional patent was filed. Additional products are available in this line for low pH products, and more will be added as we continue to explore the needs of the industry for high efficacy and low level of use, or as we like to call it: Less Preservative Delivers More Protection.
Preserving natural formulations In parallel to the development efforts concentrating on enhancing popular mild systems to a new level, the natural route was also on the R&D map, due to the growing trend of natural ingredients in personal care formulations. But the natural route is not always the
answer. The definition of natural is unclear and not regulated. It is highly desired by some, but does not always meet the manufacturers’ demands, for reasons such as compatibility, cost, or availability. When it comes to broad spectrum protection, many natural solutions are less effective as a
P. aeruginosa A. niger C. albicans Plus Maltol
preservative so a higher level of use is required. Take cinnamon bark extract. Even the Indians used it to protect wounds. But the extract is a complex mixture of chemicals and not all of them are active. Only a few have the function we need as a preservative. A new approach comes from natural-like solutions, bringing the best features of a natural ingredient, with the safety, quality and consistency of the lab. We suggest this route may be a key to filling the gaps of the preservation industry, building a bridge between chemical and natural. The task Sharon Laboratories set up to achieve was to create a broad spectrum, high efficacy preservative, which originates from natural compounds, but created in the lab. In the development process, many natural elements were screened for antibacterial and anti-fungi activity. Once a certain compound was identified, it was time to turn to the lab and choose a synthetic homologue. This R&D process resulted in a line of
preservative blends based on the active ingredient maltol, which was identified as a key ingredient in this concept. It is a naturally occurring organic compound, found in several plants. It is not very common in personal care, but we found its properties bring value to the personal care industry as a preservative.
It is used primarily as a flavour enhancer (as a food additive E636), found in the bark of larch tree, Katsura tree (Cercidiphyllum japonicum), in pine needles, and more. It is also used as intermediate in pharmaceuticals. It comes as a white crystalline powder. It has EWG score of 1, is approved as GRAS and has a good solubility in water. It has interesting antimicrobial activity, but not sufficient to be considered as a sole preservative. In the quest to enhance the properties of maltol, the addition of a cationic surfactant component within a specific range was found to be the best solution.
Test results
As described above, a series of cationic surfactants was tested, and throughout an
May 2019
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