Zemea Propanediol: Potential for Boosting Preservative Efficacy
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
Ingredient | INCI Name | Weight, % |
Water, deionized | Water | qs to 100% |
Zemea propanediol | Propanediol | 0 to 6.0 |
Xanthan gum | Xanthan gum | 0.3 |
Liponate GC | Caprylic Capric Triglyceride | 10.0 |
Sesame oil | Sesamum Indicum(Sesame)seed oil | 5.0 |
Lipomulse 165 | Glyceryl Stearate | 2.0 |
Promulgen D | Cetearyl Alcohol and Ceteareth 20 | 1.5 |
DC 200-100 | Dimethicone | 1.0 |
NaOH /Citric acid (20% sol) | Sodium hydroxide/citric acid | qs to pH 5.0-6.0 |
Preservative | Preservative | (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
Preservative | INCI Name | Suggested Weight % | Tested Weight % | Zemea, Wt % |
Microcare PM3 | Phenoxyethanol, Methylparaben, Propylparaben, Ethylparaben | 0.3 – 0.7 | 0.15 | 0.0/2.0/4.0/6.0 |
euxyl PE 9010 | Phenoxyethanol, Ethylhexylglycerin | 0.5 – 1.0 | 0.25 | 0.0/2.0/4.0/6.0 |
Neolone PE | Phenoxyethanol, Methylisothiazolinone | 0.6 | 0.3 | 0.0/2.0/4.0/6.0 |
Jeecide CAP-4 Optiphen | Phenoxyethanol, Caprylyl glycol | 0.5 – 1.5 | 0.25 | 0.0/2.0/4.0/6.0 |
Lexgard Natural | Glyceryl Caprylate, Glyceryl Undecylenate | 1.0 – 1.5 | 0.5 | 0.0/2.0/4.0/6.0 |
Dermosoft 688 ECO | Anisic acid, Parfum | 0.2 | 0.1 | 0.0/2.0/4.0/6.0 |
Geogard ULTRA | Gluconolactone, Sodium benzoate | 1.0 | 0.5 | 0.0/2.0/4.0/6.0 |
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:
Organism | Inoculation | Incubation temp |
Staphylococcus aureus (ATCC#6538) | 1x106 CFU/g | 30-37oC |
Escherichia coli (ATCC#8739) | 1x106 CFU/g | 30-37oC |
Pseudomonas aeruginosa (ATCC#9027) | 1x106 CFU/g | 30-37oC |
Candida albicans (ATCC#10231) | 1x105 CFU/g | 30-37oC |
Aspergillus niger (ATCC#16404) | 1x105 CFU/g | 20-25oC |
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
Preservatives | Challenge Organisms | ||||
gram-positive | gram-negative | gram-negative | yeast | mold | |
Staphylococcus aureus | Escherichia coli | Pseudomonas aeruginosa | Candida albicans | Aspergillus 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 Zemea | 2% | 2% (1 Log reduction) | ||
Geogard ULTRA(0.5%) | Preservative levels provided sufficient reduction to <1.00 CFU/g without addition of Zemea | 2% | 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.