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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
COSMETICS
2 SOFW-Journal | 140 | 1/2-2014
ANTIMICROBIAL STABILISATION
number of accepted actives that can
be used. Over-dosing of antimicrobial
actives becomes more clearly a regula-
tory affair if it results in an adverse
risk assessment. The incentive to make
biocides more effective at lower con-
centrations 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 en-
hanced 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
W. Siegert*
Boosting the Antimicrobial Efficiency of
Multifunctional Additives by Chelating Agents
Abstract
The continuing discussions surrounding cosmetic preservation has li-
mited 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.
Introduction
The microbial safety of cosmetic prod-
ucts 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
COSMETICS
SOFW-Journal | 140 | 1/2-2014 3
ANTIMICROBIAL STABILISATION
Commonly used chelating agents
Ethylenediaminetetraacetic acid
(EDTA) and its salts are commonly used,
but this is under environmental discus-
sion in several European countries.
Glutamic acid, N,N- diacetic acid
(GLDA) and its salts are readily biode-
gradable chelating agents that can be
used as alternative for EDTA. GLDA has
an exceptionally high solubility at high
and low pH.
Trends in using chelating agents
The frequency of use of EDTA in cos-
metic products was investigated in Min-
tel 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 cos-
metic 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 sub-
stitution 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 out-
er surface by decreases membrane sta-
bility 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 Can-
dida albicans was worse at pH 5.0 (6).
Fig. 1 Trend using EDTA and EDTA salts in cosmetics (3)
Fig. 2 Trend using GLDA in cosmetics (3)
Fig. 3 Boosting of preservatives - Mode of action (5)
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ANTIMICROBIAL STABILISATION
Fig. 4 PEG-Free Emulsion for Baby Wipes (O/W) Fig. 5 Natural O/W Cream
Tests with frame formulations
To evaluate the effect of chelating
agents cosmetic formulations without
microbial stabilisation where tested in
comparison to samples with antimicro-
bial 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 keep-
ing the test material germ free for this
period. The inoculum contains patho-
genic microorganisms as germs which
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 approxi-
mately 105cfu/ml in the sample.
A sample can be considered to be well
preserved according criteria A, if a pe-
riod 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 micro-
bial 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 cos-
metic products.
Criteria B is fulfilled if the sample
showed slight microbial growth (+)
during the 6 inoculation cycles. If the
formulation meets criteria B, the mi-
crobiological risk analysis should dem-
onstrate the existence of control fac-
tors not related to the formulation; for
example, a protective package such as a
pump provides a higher level of protec-
tion than a jar and /or following strong
demands on Good Manufacturing Prac-
tice (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 microor-
ganisms as germs which are well known
for product spoilage. All species have to
be cultivated separately and mixed di-
COSMETICS
SOFW-Journal | 140 | 1/2-2014 5
ANTIMICROBIAL STABILISATION
Fig. 6 Cosmetic Wipes – Self-Preserving Fig. 7 Tutti Frutti Body Scrub
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 differ-
ent mould types.
A sample can be considered to be well
preserved, if it passes a period of three
weeks under the above described labo-
ratory conditions without showing mi-
crobial 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.
Summary
Chelating agents can improve the anti-
microbial 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) Ethylhexyl-
glycerin) (2).
Internal challenge tests showed the ben-
efit 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 formula-
tions. 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 counter-
act 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 po-
lymyxin and to EDTA, Journal of Antimicrobi-
al Chemotherapy 1/1975
(2) W. Siegert, Can New Biodegradable Comple-
xing Agents Replace Tetrasodium EDTA to
boost Preservatives, SOFW Journal 1/2 2008
(3) Mintel’s Global New Products Database
(GNPD), Search criteria: »Household, Beau-
ty & Personal Care, Global (49 countries)«,
search for products where Ingredient Search
matches one or more of »EDTA, Disodium ED-
TA, Tetrasodium EDTA, Trisodium EDTA« as the
Ingredients and Date Published is between
Jan 2010 and Dec 2012. www.mintel.com
COSMETICS
6 SOFW-Journal | 140 | 1/2-2014
(4) E. C. Hill, Biocides for the future, International
Biodeterioration Vol. 26/1990
(5) J. Seetz, New Environmental benign che-
lating agent GLDA, International Nonwo-
vens Symposium, May 2013, St. Peters-
burg, Russia
(6) W. Siegert, Influence of pH on the Preser-
vative Boosting Effect of Chelating Agents,
http://www.cosmeticsandtoiletries.com
/formulating/function/preserva-
tives/102957044.html
(7) H.Brill, Prüfverfahren zur Bestimmung der
mikrobiologischen Wirksamkeit von che-
mischen Konservierungsmitteln für Kosme-
tika, Jahrbuch für den Praktiker 1987
(8) W. Siegert, ISO 11930, Cosmetics – Microbi-
ology – Evaluation of the antimicrobial pro-
tection of a cosmetic product, SOFW-Journal
7/2012
(9) W. Siegert, Microbiological quality ma-
nagement 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: wolfgang.siegert@schuelke.com
www.schuelke.com
ANTIMICROBIAL STABILISATION
