1/2-2014 English Edition International Journal for Applied Science • Personal Care • Detergents • Specialties
W. Siegert
Boosting the antimicrobial efficiency of multifunctional additives by chelating agents
Cosmet ic s a n t i mi c ro b ia l stab i li s at i o n
W. Siegert*
Boosting the Antimicrobial Efficiency of Multifunctional Additives by Chelating Agents
■■ Introduction The microbial safety of cosmetic products is an important consideration. It is integral to ensuring the stability of the
products for the entire shelf-life and to preventing damage to the health of consumers. The continuing discussions surrounding cosmetic preservation has limited the
Abstract
T
he continuing discussions surrounding cosmetic preservation has limited the number of accepted actives that can be used. As a result, a number of different methods and materials are being used to boost the activity of the remaining acceptable substances for microbial stabilisation. Increasing the permeability of microbial cells to biocides by EDTA helps to optimise the stabilisation, however to avoid the environmental discussions regarding chelating agents, readily biodegradable alternatives to EDTA are indispensable. The antimicrobial stabilisation of multifunctional additives in combination with chelating agents were tested in different cosmetic formulations. The readily biodegradable chelating agent Tetrasodium Glutamate Diacetate is shown to improve performance therefore enabling the reduction in the use concentration of sensiva® SC 10, sensiva® PA 20 , and sensiva® PA 30 and sensiva® PA 40 to pass antimicrobial effectiveness testing.
number of accepted actives that can be used. Over-dosing of antimicrobial actives becomes more clearly a regulatory affair if it results in an adverse risk assessment. The incentive to make biocides more effective at lower concentrations becomes more and more important. The efficacy of EDTA is generally known (1), however modern readily biodegradable alternatives can replace it (2). ■■ The use of chelating agents in
cosmetics
The chelate effect describes the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar non-chelating (monodentate) ligands for the same metal. The key features of chelating agents in cosmetics are: • Chelates calcium and transition metal ions, which helps to enhance the shelf-life of creams • Helps to stabilise and avoid discolouration • Boosts the performance of antioxidants • Boosts the performance of preservatives
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Commonly used chelating agents Ethylenediaminetetraacetic acid
(EDTA) and its salts are commonly used, but this is under environmental discussion in several European countries. Glutamic acid, N,N- diacetic acid
(GLDA) and its salts are readily biodegradable chelating agents that can be used as alternative for EDTA. GLDA has an exceptionally high solubility at high and low pH.
Fig. 1 Trend using EDTA and EDTA salts in cosmetics (3)
Trends in using chelating agents The frequency of use of EDTA in cosmetic products was investigated in Mintel GNPD (3). In the period Jan 2010 to Dec 2012 13.8% of the products contain EDTA or EDTA salts. The analysis of the trend in the last three years shows an increase in the use of EDTA salts in cosmetic formulations (Fig. 1). The use of GLDA is still minor but also increasing (Fig. 2). Based on the trend to more environmentally friendly and natural compounds an increasing substitution of EDTA can be expected. Boosting preservatives – Mode of action Chelating agents can be used to increase the efficacy of antimicrobial substances. They remove multivalent cations from the cell membrane of the microbes by forming complexes, weakening the outer surface by decreases membrane stability and making them more vulnerable to biocidal attack (Fig. 3) (4)(5). Influence of pH on the preservative boosting effect Overall, the chelating agents were found to exhibit a better boosting effect at pH 5.0 for Escherichia coli and Pseudomonas aeruginosa. For Staphylococcus aureus, the result at pH 7.0 was better, especially with GLDA. Finally, the efficacy for Candida albicans was worse at pH 5.0 (6).
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Fig. 2 Trend using GLDA in cosmetics (3)
Fig. 3 Boosting of preservatives - Mode of action (5)
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Fig. 4 PEG-Free Emulsion for Baby Wipes (O/W)
■■ Tests with frame formulations To evaluate the effect of chelating agents cosmetic formulations without microbial stabilisation where tested in comparison to samples with antimicrobial additive and with chelating agent (GLDA). The microbial challenge tests where performed according KoKo Test (7) (8) protocol. For the finished wet wipe the FeuTuKo Test (9) was applied. The results are shown in Fig. 4–7. The schülke KoKo Test In this test (the schülke KoKo Test), a mixture of bacteria, yeast and moulds are inoculated 6 times (once a week) into the test material with the goal of keeping the test material germ free for this period. The inoculum contains pathogenic microorganisms as germs which
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Fig. 5 Natural O/W Cream
are well known for product spoilage. All species have to be cultivated separately and mixed directly before the addition, to ensure a constant composition and germ count of the inoculum. Its germ count is approximately 107–108cfu/ml, which means a germ count of approximately 105cfu/ml in the sample. A sample can be considered to be well preserved according criteria A, if a period of six weeks is passed under the above described laboratory conditions without showing microbial growth on the test batches. This means that even after the sixth inoculation no microbial growth should be observed. From many years of experience in the use of this test method, these results can equate to a microbiological stability of 30 months, as recommended for cosmetic products.
Criteria B is fulfilled if the sample showed slight microbial growth (+) during the 6 inoculation cycles. If the formulation meets criteria B, the microbiological risk analysis should demonstrate the existence of control factors not related to the formulation; for example, a protective package such as a pump provides a higher level of protection than a jar and /or following strong demands on Good Manufacturing Practice (GMP). The schülke FeuTuKo Test In this test wet tissues in flexible plastic packaging are inoculated with a mixed culture containing 106-107cfu/ml. The inoculum contains pathogenic microorganisms as germs which are well known for product spoilage. All species have to be cultivated separately and mixed di-
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rectly before the addition, to ensure a constant composition and germ count of the inoculum. After inoculation the whole packaging is kneaded properly and, thereafter, incubated for three weeks at 30°C. The evaluation is done by placing pieces of tissue (approx. 3 x 3cm, cut out of the tissue pack in one block) on TS and SA agar. In every case double determinations are done. The growth on the tissues is evaluated after three days of incubation at 30°C (for bacteria) and seven days at 25°C (for moulds). Fungi are classified into yeasts and the different mould types. A sample can be considered to be well preserved, if it passes a period of three weeks under the above described laboratory conditions without showing microbial growth on the test batches. This means that even after inoculation no microbial growth should be observed. From many years of experience in the use of this test method, these results can equate to a microbiological stability of 30 months, which is recommended for cosmetic products.
Fig. 6 Cosmetic Wipes – Self-Preserving
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■■ Summary Chelating agents can improve the antimicrobial efficiency of multifunctional additives. With GLDA even the effect against moulds is improved (Fig. 4). This results confirm the results achieved with the combination of GLDA with euxyl® PE 9010 (Phenoxyethanol (and) Ethylhexylglycerin) (2). Internal challenge tests showed the benefit of chelating agents with euxyl® PE 9010, sensiva® SC 10, sensiva® PA 20 , and sensiva® PA 30 and sensiva® PA 40 in leave-on formulations. The boosting of preservatives with chelating agents performs at its best in simple formulations. Positive results were found in: • wet wipes (best results) • gels • tonics • other high water-based formulations
In complex systems, the boosting effect to preservatives is limited. The addition of chelating agents cannot counteract an inactivation of preservatives by migration into the oil phase or micelle formation. Literature (1) J . E. Finch and M. R. W. Brown, The influence of nutrient limitation in a chemostat on the sensitivity of Pseudomonas aeruginosa to polymyxin and to EDTA, Journal of Antimicrobial Chemotherapy 1/1975 (2) W. Siegert, Can New Biodegradable Complexing Agents Replace Tetrasodium EDTA to boost Preservatives, SOFW Journal 1/2 2008 (3) Mintel’s Global New Products Database (GNPD), Search criteria: »Household, Beauty & Personal Care, Global (49 countries)«, search for products where Ingredient Search matches one or more of »EDTA, Disodium EDTA, Tetrasodium EDTA, Trisodium EDTA« as the Ingredients and Date Published is between Jan 2010 and Dec 2012. www.mintel.com
Fig. 7 Tutti Frutti Body Scrub
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(4) E . C. Hill, Biocides for the future, International Biodeterioration Vol. 26/1990 (5) J. Seetz, New Environmental benign chelating agent GLDA, International Nonwovens Symposium, May 2013, St. Petersburg, Russia (6) W. Siegert, Influence of pH on the Preservative Boosting Effect of Chelating Agents, http://www.cosmeticsandtoiletries.com /formulating/function/preservatives/102957044.html
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(7) H.Brill, Prüfverfahren zur Bestimmung der mikrobiologischen Wirksamkeit von chemischen Konservierungsmitteln für Kosmetika, Jahrbuch für den Praktiker 1987 (8) W. Siegert, ISO 11930, Cosmetics – Microbiology – Evaluation of the antimicrobial protection of a cosmetic product, SOFW-Journal 7/2012 (9) W. Siegert, Microbiological quality management for the production of wet-wipes, Household and Personal Care Today 2/2008
*Author´s address: Wolfgang Siegert Technical Support Manager, International Schülke & Mayr GmbH Special Additives International Tel.: +49 40 52100 528 Email:
[email protected] www.schuelke.com n
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