Zemea Propanediol: Potential for Boosting Preservative Efficacy

Published: 1-Jan-2011


Introduction

The potential for boosting preservative efficacy by using Zemea propanediol in an aqueous-based cosmetic and personal care formulation was studied. The testing was conducted using standardized microbiology guidelines, known as preservative efficacy testing or challenge tests.


Background

Previously the bactericidal and fungicidal properties of Zemea propanediol were evaluated using the Cosmetic, Toiletry, and Fragrance Association (CTFA) Microbiology Guidelines. Neat samples of Zemea, Propylene glycol (PG) and Butylene glycol (BG) were tested, as well as three oil-water emulsions using a combination of Zemea, PG, and BG, and three different preservative systems. The preservative systems included phenoxyethanol, methylparaben, propylparaben, and ethylparaben; caprylyl glycol, phenoxyethanol and ethylhexylglycerin; cetearyl alcohol, dimethicone DC 200-100 and caprylyl glycol. The test results concluded that the bactericidal and fungicidal performance for Zemea was comparable to PG and better than BG, both as neat solutions and as an ingredient in the o/w emulsion.

Market feedback suggests that Zemea propanediol boosts preservative efficacy when used in cosmetic and personal care formulations, and further testing was conducted. The results of the additional testing is the focus of this bulletin.


Experimental Design

A. Formulation
A generic oil-in-water skin care emulsion formula was chosen as the base material and prepared by Cosmetech Laboratories, Inc., Fairfield, NJ (Table 1). The formula was prepared to minimize performance impact and allow measurement of preservative boosting effectiveness.

Table 1: Formulation used in challenge test

IngredientINCI NameWeight, %
Water, deionizedWaterqs to 100%
Zemea propanediolPropanediol0 to 6.0
Xanthan gumXanthan gum0.3
Liponate GCCaprylic Capric Triglyceride10.0
Sesame oilSesamum Indicum(Sesame)seed oil5.0
Lipomulse 165Glyceryl Stearate2.0
Promulgen DCetearyl Alcohol and Ceteareth 201.5
DC 200-100Dimethicone1.0
NaOH /Citric acid (20% sol)Sodium hydroxide/citric acidqs to pH 5.0-6.0
PreservativePreservative(Table 2)

B. Preservatives

The following preservatives (Table 2) were chosen to represent combinations commonly used for their effectiveness to protect products. The four phenoxyethanol-based and three natural-based systems were tested at one-half their recommended use level and evaluated in four separate emulsions with varying levels of Zemea (0.0, 2.0, 4.0 and 6.0 wt%).

Table 2: Preservative systems used in the challenge test

PreservativeINCI NameSuggested Weight %Tested Weight %Zemea, Wt %
Microcare PM3Phenoxyethanol, Methylparaben, Propylparaben, Ethylparaben0.3 – 0.70.150.0/2.0/4.0/6.0
euxyl PE 9010Phenoxyethanol, Ethylhexylglycerin0.5 – 1.00.250.0/2.0/4.0/6.0
Neolone PEPhenoxyethanol, Methylisothiazolinone0.60.30.0/2.0/4.0/6.0
Jeecide CAP-4 OptiphenPhenoxyethanol, Caprylyl glycol0.5 – 1.50.250.0/2.0/4.0/6.0
Lexgard NaturalGlyceryl Caprylate, Glyceryl Undecylenate1.0 – 1.50.50.0/2.0/4.0/6.0
Dermosoft 688 ECOAnisic acid, Parfum0.20.10.0/2.0/4.0/6.0
Geogard ULTRAGluconolactone, Sodium benzoate1.00.50.0/2.0/4.0/6.0

C. Test Methods & Organisms

The challenge testing was conducted by Clinical Research Laboratories, Piscataway, NJ. The methods employed were CTFA Microbiology Guidelines, Section 20, M-3, A Method for Preservation Testing of Water Miscible Personal Care Products and USP 33, Section 61, Neutralization/Removal of Antimicrobial Activity.

Using the organisms listed below, the formulations were inoculated with approximately 1x106 bacteria per gram of product, 1x105 yeast cells per gram of product, or 1x105 mold spores per gram of product:

OrganismInoculationIncubation temp
Staphylococcus aureus (ATCC#6538)1x106 CFU/g30-37oC
Escherichia coli (ATCC#8739)1x106 CFU/g30-37oC
Pseudomonas aeruginosa (ATCC#9027)1x106 CFU/g30-37oC
Candida albicans (ATCC#10231)1x105 CFU/g30-37oC
Aspergillus niger (ATCC#16404)1x105 CFU/g20-25oC

The microbial count was measured at 1, 2 and 7 days to determine the survival ability of the microorganisms in the preserved test formulations.


D. Acceptance Criteria

For this type of formulation, the preservative is effective in the sample examined if a). The concentrations of viable bacteria demonstrate no less than a 3.0 log reduction (99.9%) from the initial count at 7 days, and no increase for the duration of the test period and b). The concentration of viable yeast and molds demonstrate no less than a 1.0 log reduction (90.0%) from the initial count at 7 days, and no increase for the duration of the test period.


Results

Shown below is the minimum percentage of Zemea propanediol needed to boost the preservatives efficacy when used at one-half their recommended use level. These percentages are based on the concentrations of viable bacteria and yeasts reduced to <1.00 CFU/g at Day 7, and concentrations of viable molds with a 1 Log reduction at Day 7.

Table 4: Minimum percentage of Zemea needed to boost preservative efficacy

PreservativesChallenge Organisms
gram-positivegram-negativegram-negativeyeastmold
Staphylococcus aureusEscherichia coliPseudomonas aeruginosaCandida albicansAspergillus niger
Phenoxyethanol-based
Microcare PM3(0.15%)2%2%2%4%2% (1 Log reduction)
euxyl PE 9010(0.25%)4%4%2%6%2% (1 Log reduction)
Neolone PE(0.3%)2%2%6%2% (1 Log reduction)
Jeecide CAP-4 Optiphen(0.25%)2%2%6%2% (1 Log reduction)
Lexgard Natural(0.5%)2% (1 Log reduction)
Natural
Dermosoft 688 ECO(0.1%)Preservative levels provided sufficient reduction to <1.00 CFU/g without addition of Zemea2%2% (1 Log reduction)
Geogard ULTRA(0.5%)Preservative levels provided sufficient reduction to <1.00 CFU/g without addition of Zemea2%2% (1 Log reduction)

Organisms reduced to <1.00 CFU/g at Day 7


Conclusion

- Zemea worked well with the phenoxyethanol-based preservatives and boosted the preservative efficacy for gram-positive, gram-negative, and yeast organisms.
- Zemea consistently boosted the efficacy of each preservative tested with Aspergillus niger.
- Zemea worked well with the natural based preservatives and boosted the preservative efficacy for yeast and molds.
- Zemea may allow the use of less preservatives in formulations while providing additional performance benefits such as no skin irritation, increased humectancy and excellent aesthetics.
- Zemea is not a preservative nor is it considered an active ingredient.


Summary

The potential for Zemea to boost preservative efficacy in aqueous-based cosmetic and personal care formulation was studied. An o/w skin care emulsion formula was chosen as the base material.

Seven preservative systems (four phenoxyethanol-based and three natural-based) were tested at one-half their recommended use level and evaluated in four separate emulsions with varying levels of Zemea (0.0, 2.0, 4.0 and 6.0 wt%).

Challenge testing was conducted using Cosmetic, Toiletry, and Fragrance Association (CTFA) Microbiology Guidelines and the results are expressed as the minimum percentage of Zemea needed to boost preservative efficacy.

Zemea may allow the use of less preservatives in formulations while providing additional performance benefits such as no skin irritation, increased humectancy and excellent aesthetics.

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