PRESERVATIVES 71
phenethyl alcohol and sorbitan caprylate (Velsan SPA) for fragrance and preservation support of a wide range of cosmetics and toiletries. It provides an alternative to phenoxyethanol.
Efficacy tests & findings Using the synergistic effects shown in Table 1, the efficacy of the preservative options should be proven in industry relevant tests. Each was therefore investigated in formulation challenge tests at two different pH levels in accordance with the European Pharmacopoeia (Ph. Eur.) requirements. In addition to the four strains Pseudomonas aeruginosa (Pa, gram neg. bacteria), Staphylococcus aureus (Sa, gram pos. bacteria), Candida albican (Ca, yeast), and Aspergillus brasiliensis (Ab, mold) that are mandatory for Ph. Eur., the gram-negative bacteria Escherichia coli (Ec) was also tested as this is a requirement in the US market. Standardised formulations of a shampoo and leave-on oil/water cream gel were developed specifically to represent the typical preservation challenges faced by a formulator. The formulations were tested unpreserved, with the aforementioned blends and one well-known benchmark preservative system of phenoxyethanol and parabens. Table 2 and Table 3 detail the sample
Rinse-off Shampoo and Leave-on O/W Cream Gel Challenge Test formulations. For both Challenge Tests, traffic light
colours are used to indicate preservation suitability. Green denotes passed A-criteria of Ph. Eur., which is sufficient for preservation even of eye and baby care applications. Yellow denotes passed B- criteria of Ph. Eur., which is sufficient for preservation of a cosmetic product expect for eye and baby care. Red denotes failed criteria of Ph. Eur., which means that the formulation has high risk of microbiological contamination.
Results challenge test rinse-off In a rinse-off application, the blend sorbitan caprylate, potassium sorbate, and capryloyl/caproyl methyl glucamide and the blend sorbitan caprylate and benzyl alcohol showed excellent efficacy at low pH. Both of these blends are especially suited for low pH formulations. The phenethyl alcohol and sorbitan caprylate blend preservative system also passed at ph 5, while the benchmark blend of phenoxyethanol + parabens failed against mold. At high pH of 7, the use of potassium sorbate as a preservative does not make sense, as organic acids perform only in the low pH-range. The combination of benzyl alcohol and phenethyl alcohol with sorbitan
caprylate respectively, resulted in a pass in the challenge test that is again not achieved with phenoxyethanol + parabens.
Results challenge test leave-on For a typical leave-on cream formulation with low pH and high pH, all preserved blends passed the Challenge Test. Regarding the results for Aspergillus brasiliensis (Ab), it has to be noted that the criteria in the EP challenge test is targeting specific log-reduction. A B-criteria, as seen for the blend of sorbitan caprylate and benzyl alcohol and the blend phenethyl alcohol and sorbitan caprylate, means no growth of the organism, a finding that would allow a pass in the similar tests of USP challenge test and ISO 11933.
Preservative load The Challenge Test findings indicate that the preservation need of rinse-off and leave-on formulations is fulfilled by all three blends at a low in-use level. When the actual preservative load is assessed, all formulations pass with max. 1.0 % active.
Features & applications The tests shown here reinforce the findings of further internal tests, including additional internal testing demonstrating broad spectrum microbial activity (see overview
NEW
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November 2017
PERSONAL CARE ASIA PACIFIC
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