A New Concept to Boost the Preservative Efficacy ... - Schülke & Mayr

COSMETICSPRESERVATIVESThe maximum allowed concentrationaccording to EU Cosmetic Directive is1.1%, due to the limit of 1.0% for phenoxyethanol.At the recommended useconcentrationof 0.5 to 1.0% Euxyl® PE9010 is soluble in most cosmetic formulations.The low surface tension ofEuxyl® PE 9010 solutions assures gooddispersion in various systems, even atlow temperature.As phenoxyethanol and ethylhexylglycerinare alcohols, the product isstable to hydrolysis, to higher temperatures(e.g. 100 °C) and to low as well ashigh (pH 2 - 12) pH values. Furthermore,it remains liquid with a moderate viscosityat temperatures as low as -20 °C.In general, Euxyl® PE 9010 displays goodcompatibility with other cosmetic ingredients.No discolourations have been detected.The product shows no interactionswith sulphite ions or with pigmentslike TiO 2. It can tolerate high salt content.Cationic and amphoteric substances donot adversely affect the preservative activity.However, it is yet not recommendedfor formulations containing comparativelyhigh amounts of ethoxylated surfactantsbecause these surfactants areable to neutralise the boosting activityof ethylhexylglycerin.Due to its high solvency, Euxyl® PE 9010can serve as a solvent for lipophilic additiveslike perfumes, vitamins and essentialoils. Formulas containing naturalraw materials are particularly susceptibleto microbial growth. Fast-actingEuxyl® PE 9010 can eliminate microorganismsquickly, making it more effectivethan slower acting preservatives.Designed as a substitute for parabencontainingpreservative systems, it alsooffers an alternative to formaldehydereleasersand isothiazolinones. Its use isrecommended in leave-on preparations,such as lotions, creams, sun care products,transparent gels and others, as wellas cosmetic wet wipes. Microbiological efficacyEuxyl® PE 9010 is equally effective againstbacteria, yeasts and fungi. It is effectivewithin a broad pH range, up to pH 12. Itshows higher activity, e.g. in preservativeefficacy tests (S&M KoKo test) (8,9) or ingerm count reduction tests, comparedSpecies ATCC- Euxyl® PE 9010 Phenoxy-Nr.: [%] ethanol [%]Gram-negative:Enterobacter gergoviae 33028 0.5 0.5Escherichia coli 11229 0.5 0.5Klebsiella pneumoniae 4352 0.25 0.5Pseudomonas aeruginosa 15442 0.5 0.5Pseudomonas fluorescens 17397 0.25 0.5Pseudomonas putida 12633 0.5 0.5Gram-positive:Staphylococcus aureus 6538 0.5 1.0Staphylococcus epidermidis 12228 0.5 1.0Mould fungi:Aspergillus niger 6275 0.25 0.5Penicillium funiculosum 36839 0.25 0.25Yeast:Candida albicans 10231 0.25 0.5Table 2 MIC values (dilution test) of Euxyl® PE 9010 compared to phenoxyethanolagainst different microorganismswith phenoxyethanol and ethylhexylglycerinindividually. The efficacy can beillustrated by the determination ofthe Minimum Inhibitory Concentration(MIC) values and by performing germcount reduction tests.MIC valuesTo compare the MIC values of Euxyl® PE9010 with phenoxyethanol, the minimuminhibitory concentration againstdifferent microorganisms in a serial dilutiontest was determined (Table 2).While ethylhexylglycerin alone has noappreciable effect on microorganisms,the enhanced phenoxyethanol in Euxyl®PE 9010 is proven to have better efficacyagainst many microorganisms thanphenoxyethanol alone.Germ count reduction testTo show the effect of ethylhexylglycerinon the performance of phenoxyethanolas a preservative, germ count reductiontests on Pseudomonas aeruginosa (ATCCno. 15442) and Aspergillus niger (ATCCno. 6275) were performed with dilutionsof Euxyl® PE 9010 in sterile tap waterand compared to the single components.Fifty-ml portions of the end solutions areeach inoculated with 0.5 ml microorganismsuspension and stirred. The initialmicroorganism count of the test solutionsis approximately 10 8 cfu/ml.These solutions are streaked out ontotryptone soya agar (Pseudomonas aeruginosa)or sabouraud-dextrose 4.0% agar(Aspergillus niger) after 3, 6, 24, 48, 72and 168 hours depending on the test organism.The cultures are incubated for48 hours at 37 °C or 72 hours at 25 -27 °C.The evaluation is made on the basis ofsemi-quantitative assessment of the microbialgrowth of the streaks.As Fig. 3 clearly demonstrate, ethylhexylglycerin,without having any efficacyagainst Pseudomonas aeruginosa or Aspergillusniger alone (green line), booststhe efficacy of phenoxyethanol as thepreservative active in Euxyl® PE 9010 (blueline) compared to phenoxyethanol alone(red line). The improved efficacy of thecombination can be seen after a shortperiod of time.4 SÖFW-Journal | 131 | 11-2005

COSMETICSPRESERVATIVES Mode of actionEthylhexylglycerin has a chemical structurecomparable to surfactants. A calculatedHLB-value of 7.4 means that it belongsto the group of wetting agents orwater-in-oil emulsifiers. It is able to reducethe surface tension of water significantly(Fig. 4a).In combination with phenoxyethanol inEuxyl® PE 9010 an additional reductionof the surface tension can be observed.For a 1.0% solution of Euxyl® PE 9010 inwater the surface tension is 32.1 mN/m(water: 72.6 mN/m). This is even lowerthan the surface tension of 0.1% ethylhexylglycerin,as the contact angles ofthe corresponding water drops on materialslike polyethylene clearly demonstrate(Fig. 4b).Although Euxyl® PE 9010 significantly reducesthe interfacial tension in a foamingtest according to DIN 53 902, a 1.0% solutionin demineralised water proved tobe non-foaming.It is postulated that the addition of ethylhexylglycerinaffects the interfacial tensionat the cell membrane of microorganisms.This improves the contact ofphenoxyethanol with the cell membraneresulting in a better interaction of phenoxyethanolat the cell membrane andan improved antimicrobial efficacy.Fig. 3 Germ count reduction in tap water achieved by Euxyl® PE 9010 comparedto the single components against Pseudomonas aeruginosa and Aspergillus niger Practical experienceThe effectiveness of this system in cosmeticformulations has been tested inthe S&M KoKo test. This is a multiple-inoculation,preservative efficacy test designedand validated by Schülke & Mayr.A mixed suspension of Gram-positive andGram-negative bacteria, yeast and mouldis used for inoculation. At weekly intervals,a sample of the test product isstreaked out onto nutrient media, incubatedand evaluated semi-quantitatively.The longer the time before the occurrenceof the first microbial growth, themore effective the preservative. Experiencehas shown that a well-preservedproduct should remain growth-free for4a4bFig. 4a Surface tension [mN/m] of 1.0% Euxyl® PE 9010 in water compared to 0.9% phenoxyethanol, 0.1% ethylhexylglycerinand water as well as 4b the corresponding water drops on a polyethylene surfaceSÖFW-Journal | 131 | 11-2005 5

COSMETICSPRESERVATIVESsix inoculation cycles to ensure the shelfliferequired in practice (30 months inthe original packaging).Oil-in-water and water-in-oil systemspreserved with use-concentrations ofbetween 0.5 and 1.0% Euxyl® PE 9010proved to be well preserved even afterthree months storage at +40 °C.Fig. 5 shows the result of the S&M KoKotest on a Moisturizing Soothing Balmpreserved with 1.0% Euxyl® PE 9010, aswell as with the single components.Only the sample preserved with 1.0%Euxyl® PE 9010 was proved to be wellpreserved after 6 inoculation cycles,while 0.9% phenoxyethanol as well as0.1% ethylhexylglycerin were ineffective.Whereas ethylhexylglycerin alone has noand phenoxyethanol alone shows nosufficient efficacy against microorganismsthe enhanced phenoxyethanol inEuxyl® PE 9010 is proven to preserve thisMoisturizing Soothing Balm very well.In rinse-off products containing highamounts ethoxylated surfactants theproduct is yet not recommended becausethese surfactants are able to neutralisethe boosting activity of ethylhexylglycerin.As the interest is high in usingEuxyl® PE 9010 also in rinse-off productsefforts were made to decrease the loss ofefficacy by adding complexing agents. Inaqueous surfactant solutions (10% a. i.)germ count reduction tests of the combinationof complexing agents withEuxyl® PE 9010 gave better results thanalone. Fig. 6 shows how 0.05% EDTAand 1.0% Euxyl® PE 9010 can reduceFig. 5 Result of preservative efficacy test on the Moisturizing Soothing Balmduring 6 inoculation cyclesFig. 6 Germ count reduction test in ethoxylated surfactant solutions againstPseudomonas aeruginosa in the presence of complexing agentsFig. 7 Carbomer gels, gel 1: unpreserved; gel2: preserved with 1.0% Euxyl® PE 9010; gel 3:preserved with 1.0% of a standard parabenmixture in phenoxyethanolPseudomonas aeruginosa also in frequentlyused ethoxylated surfactant solutions.These results may encourage formulatorsto check if the combination of Euxyl® PE9010 with complexing agents can successfullypreserve surfactant based rinseoffproducts. At this early stage of experienceit is strongly recommended to checkthe individual finished product as the efficacymight depend on the particularformulation.Furthermore Euxyl® PE 9010 is ideal forthe preservation of clear, transparent gels.As Fig. 7 shows, gels preserved with theproduct (gel 2) stay clear and transparentcompared to a standard parabenmixture in phenoxyethanol (gel 3). ConclusionEuxyl® PE 9010 is an answer to the personalcare industry’s increasing demandsfor new preservation concepts. It is anbroad-spectrum preservative based onphenoxyethanol in combination with themultifunctional ethylhexylglycerin. The6 SÖFW-Journal | 131 | 11-2005

COSMETICSPRESERVATIVESaddition of ethylhexylglycerin affects theinterfacial tension at the cell membraneof microorganisms, improving the preservationactivity of phenoxyethanol impressively.It is is a patented liquid concentratewith extensive toxicological dataon its ingredients. Its physical andchemical properties, as well as its microbiologicalefficacy, make Euxyl® PE 9010ideal for the formulation of skin careproducts. It is focused for leave-on productsand ideal for the preservation ofclear, transparent gels. This new preservativesystem is a reasonable alternativeto classical preservation blends.Literature(1) The Merck Index, Thirteenth Ed., Monograph Nr.7341(2) H. P. Fiedler, Lexikon der Hilfsstoffe für Pharmazie,Kosmetik und angrenzenden Gebiete,Editio Verlag Aulendorf, 5. Aufl., 2002, 1305 –1306(3) Hagers Handbuch der pharmazeutischen Praxis,Springer-Verlag Berlin, 5. Auflage, Folgeband 5,1999, 425 – 426(4) H. Eggensperger, Multiaktive Wirkstoffe fürKosmetika, Verlag für chemische Industrie H.Ziolkowsky GmbH Augsburg, 1995, 141 – 159(5) W. Beilfuß, W. Siegert, Cossma, 2003, 6, 54 – 55(6) W. Beilfuß, SÖFW Journal, 1998, 6, 360 – 366(German edition)(7) H. M. Fishman, Happi, 2005, Vol. 42, No. 2, part1 of 2, 35(8) K. Weber, J. Siebert, SÖFW-Journal, 2003, 6, 44 –50 (English); 48 – 55 (German edition)(9) W. Siegert, Cosmetic Science Technology, 2005,189 – 195.* Authors’ address:Dr. Wolfgang BeilfussDr. Marion LeschkeDr. Klaus WeberSchülke & Mayr GmbH22840 NorderstedtGermanyEmail: sai@schuelke-mayr.comSÖFW-Journal | 131 | 11-2005 7