EP4701611A1

EP4701611A1 - Colour-stable cosmetic compositions comprising sorbate and 4-isopropyl-3-methylphenol

Info

Publication number: EP4701611A1
Application number: EP23724683.0A
Authority: EP
Inventors: Laura Meunier; Jasmin SALMEN; Florian GENRICH
Original assignee: Symrise AG
Current assignee: Symrise AG
Priority date: 2023-04-28
Filing date: 2023-04-28
Publication date: 2026-03-04
Also published as: CN121038773A; WO2024223064A1; MX2025012838A

Abstract

The present invention relates to cosmetic compositions comprising sorbate and 4- isopropyl-3-methylphenol to prevent discoloration effects induced by the degradation of sorbate.

Description

Colour-stable cosmetic compositions comprising sorbate and 4-isopropyl-3- methylphenol

Technical field

[0001 ] The present invention relates to cosmetic compositions comprising sorbate and 4-isopropyl-3-methylphenol to prevent discoloration effects induced by the degradation of sorbate.

Background Art

[0002] Potassium sorbate is a commonly used preservative in cosmetics and personal care products. The sorbate salt itself is inactive so that a pH lower than 7 is required to generate sorbic acid which can preserve cosmetic formulations.

[0003] Sorbates belong to the unsaturated fatty acid derivatives; therefore, they are sensitive to UV light and can undergo oxidation. It is well known that sorbates are prone to turn yellow in solution.

[0004] The discoloration of a cosmetic formulation is not desirable for several reasons; thus, efforts have been made to prevent such a discoloration effect.

[0005] For example, US 2020/0100995 discloses colour stable compositions of preservatives containing a blend of a dicarboxylic acid and a ketonic acid as active discoloration-inhibiting compounds. The invention also prevents discoloration induced by potassium sorbate.

[0006] According to WO 2018/036625, 4-isopropyl-3-methylphenol belongs to the group of preservatives which are approved for use in cosmetic and household compositions. In addition, a blend containing potassium sorbate and 4-isopropyl-3- methylphenol as well as several other compounds has been examined in a shampoo composition. Technical Problem

[0007] It is commonly known that cosmetic compositions containing potassium sorbate turn yellow after some time, which is especially problematic for cosmetic products that are to be sold to customers.

[0008] The present invention has been made in view of the problem mentioned above and an object of the present invention is to prevent the discoloration of cosmetic compositions induced by potassium sorbate.

Solution to Problem and advantages of the invention

[0009] The present invention is a cosmetic composition comprising sorbate or a sorbate derivative or sorbic acid or sorbic acid derivative, and 4-isopropyl-3- methylphenol. Surprisingly, it was found that 4-isopropyl-3-methylphenol prevents the discoloration induced by the preservative sorbate or sorbic acid compound.

[0010] In a preferred aspect of the invention, the sorbate or sorbate derivative or sorbic acid derivative is a sodium or calcium salt, preferably potassium sorbate. The preferred potassium sorbate is more sensitive to discolouration in aqueous solutions and thus has a more pronounced effect in this medium. However, also preferred is the sorbic acid itself which works together with 4-isopropyl-3-methylphenol in the cosmetic composition to achieve the discoloration effect.

[0011 ] In one aspect, the disclosed cosmetic composition comprises sorbate or sorbate derivative or sorbic acid or sorbic acid derivative and 4-isopropyl-3- methylphenol in a molar ratio of 10:1 to 1 :1 , preferably in a molar ratio of 4:1 to 2:1 , even more preferably 3:1 to 2:1. Outside of this range, the effect of discoloration prevention is limited due to the small amount of 4-isopropyl-3-methylphenol present in the mixture, especially if the ratio is greater than 10:1. Thus, the higher ratio end is preferably 10:1 or less. In the other direction, outside the preferred range, an excess of 4-isopropyl-3-methylphenol versus sorbate, i.e. in a ratio smaller than 1 :1 , is not always preferable, since this can cause solubility issues due to the lower water solubility of 4-isopropyl-3-methylphenol. Thus, the lower ratio end is preferably 1 :1 or higher.

[0012] In practice, the amount of a material in a cosmetic composition is preferably given in wt.-%, however, the amount based on wt.-% is only specifically valid for a certain single component, since other derivatives, in the present case other sorbate compounds, mostly differ in their molar weight. Therefore, the aforementioned compound ratio of sorbate to 4-isopropyl-3-methylphenol is given as a molar ratio.

[0013] According to a further aspect of the invention, the cosmetic composition preferably comprises 0.1 to 1.0 wt.-%, more preferably 0.2 to 0.5 wt.-%, most preferably 0.3 to 0.4 wt.-% of the sorbate or sorbate derivative or sorbic acid or sorbic acid derivative, preferably potassium sorbate. Also independently preferably, the cosmetic composition comprises 0.01 to 0.5 wt.-%, more preferably 0.02 to 0.2 wt.-%, most preferably 0.05 to 0.1 wt.-% 4-isopropyl-3-methylphenol. A higher concentration of the components sorbate or sorbate derivative or sorbic acid or sorbic acid derivative, preferably potassium sorbate, and 4-isopropyl-3-methylphenol can result in solubility issues in the aqueous solvent system of the composition. Lower concentrations than those given in the ranges above, may render the cosmetic composition ineffective in respect to preservation.

[0014] Preferably, the cosmetic composition further comprises 3-phenyl-1 -propanol. This component improves solubility factors in the formulation.

[0015] Further preferably, the cosmetic composition comprises an alkanediol or alkanediol mixture, preferably where the alkanediol or alkanediol mixture comprises at least one 1 ,2-alkanediol. Preferably the alkanediol or alkanediol mixture is selected from the list consisting of 1 ,2-hexanediol, 1 ,2-octanediol and 1 ,2-decanediol, most preferably the alkanediol is 1 ,2-decanediol.

[0016] More preferably, the alkanediol is decylene glycol. For the preparation of the composition according to the present invention, 4-isopropyl-3-methylphenol may be used in substance and dissolved upon mixing of the composition. Alternatively, 4- isopropyl-3-methylphenol may be used as a solution in 3-phenyl-1 -propanol and an alkanediol, preferably decylene glycol, without any disadvantageous effects. In contrast, applying 4-isopropyl-3-methylphenol in the form of a solution in 3-phenyl-1- propanol and decylene glycol improves solubility of the solid IPMP upon formulation of the cosmetic composition.

[0017] Preferred alkanediols of the cosmetic composition are selected from the group consisting of linear 1 ,2-diols, 2, 3-diols or 4, 5-diols having five to twenty carbon atoms. Preferably, the alkanediol is selected from the group consisting of 1 ,2-hexanediol, 1 ,2- heptanediol, 1 ,2-octanediol, 1 ,2-nonanediol, 1 ,2-decanediol, 1 ,2-undecanediol and

1 .2-dodecanediol, also preferably the alkanediol is 2,3-hexanediol and/or 2,3- heptanediol and/or 2,3-octanediol. Further preferably the alkanediol is a combination of 1 ,2-hexanediol and 2,3-hexanediol, or 1 ,2-heptanediol and 2,3-heptanediol, or 1 ,2- octanediol and 2,3-octanediol. More preferably, the alkanediol comprises 1 ,2- octanediol or 1 ,2-decanediol, also preferably or 1 ,2-hexanediol, 1 ,2-octanediol and/or

1 .2-decanediol. The alkanediols have advantage of improving mixability of the other components, thus bridging different lipophilic/hydrophilic components. At the same time, these components have antimicrobial functions or also can stabilise formulations and support the discoloration prevention.

[0018] In a further more preferred variant, the above alkanediol is selected from the group consisting of alkanediols having a lower number of carbon atoms of 5 to 8, i.e. pentanediol, hexanediol, heptanediol, octanediol, and any mixture thereof, or is selected from the group consisting of alkanediols having a number of carbon atoms of 6 to 8, i.e. hexanediol, heptanediol, octanediol, and any mixture thereof, or is selected from the group consisting of alkanediols having a number of carbon atoms of 7 and 8, i.e. heptanediol, octanediol, and any mixture thereof.

[0019] In a still more preferred variant, the alkanediol is selected from the group consisting of alkanediols having a higher number of carbon atoms of 9 to 12, i.e. nonanediol, decanediol, undecanediol, dodecanediol, and any mixture thereof, or is selected from the group consisting of alkanediols having a number of carbon atoms of 9 to 11 , i.e. nonanediol, decanediol, undecanediol, and any mixture thereof, or is selected from the group consisting of alkanediols having a number of carbon atoms of 9 and 10, i.e. nonanediol, decanediol, and any mixture thereof. [0020] In a still more preferred variant, the alkanediol is either pentanediol, hexanediol, heptanediol or octanediol, or any mixture thereof. In a still more preferred variant, the alkanediol is either nonanediol, decanediol, undecanediol or dodecanediol, or any mixture thereof. In a most preferred variant, the alkanediol is decanediol.

[0021 ] The term “alkanediol” within the context of the present invention also includes its constitutional isomers or position isomers. Constitutional isomers are compounds that have the same molecular formula and different connectivity. Position isomers, a particular form of constitutional isomerism, are structural isomers that can be viewed as differing only on the position of a functional group on a parent structure, which in this case, in particular, is the position of the two alcohol functions.

[0022] Depending on the number of the carbon atoms of the carbon chain of the alkanediol, there are various position isomers of the alkanediol: (x,x+1 ) constitutional isomers; (x,x+2) constitutional isomers; (x,x+3) constitutional isomers; etc. and alpha, omega constitutional isomers when the alcohol functions are at the terminal ends of the carbon chain, wherein x stands for the number of the carbon atom in the alkanediol chain, to which the OH groups of the alkanediol are chemically bonded. For example: if x is 1 , the two OH groups of the alkanediol are chemically bonded to the C1 and C2 carbon atoms in the alkanediol chain; if x is 2, the two OH groups of the alkanediol are chemically bonded to the C2 and C3 carbon atoms in the alkanediol chain, etc.

[0023] In the (x,x+1 ) constitutional isomers, the two OH functional groups are vicinal attached to two different adjacent carbon atoms in the chain. In the (x,x+2) constitutional isomers, the two OH functional groups are attached to two different carbon atoms in the chain where the two carbon atoms are separated by one C atom. In the (x,x+3) constitutional isomers, the two OH functional groups are attached to two different carbon atoms in the chain where the two carbon atoms are separated by two C atoms. In the alpha, omega constitutional isomers, the two functional groups are attached to the first C atom and to the terminal C atom. [0024] In a preferred variant of the cosmetic composition, the alkanediol having a carbon chain of 5 to 12 carbon atoms, is preferably a vicinal (x,x+1 ) diol, selected from the group consisting of a 1 ,2-diol, 2,3-diol, 3,4-diol, 4,5-diol, further (x,x+1 ) diols, and mixtures thereof, preferably an alpha, beta-1 , 2-constitutional isomer.

[0025] Thus, according to a preferred variant of the cosmetic composition, the alkanediol is an (x,x+1 ) constitutional isomer, wherein x stands for the number of the carbon atom in the alkanediol chain, to which the OH groups of the alkanediol are chemically bonded, in particular a 1 ,2-alkanediol, a 2,3-alkanediol, a 3,4-alkanediol, or mixtures thereof, preferably a 1 ,2-alkanediol or a 2,3-alkanediol.

[0026] In a further preferred variant of the cosmetic composition according to the present invention, the alkanediol having a carbon chain of 5 to 12 carbon atoms, is preferably a non-vicinal (x,x+2) diol, selected from the group consisting of a 1 ,3-diol, 2,4-diol, 3,5-diol, further (x,x+2) diols, and mixtures thereof, preferably an alpha, gamma-1 ,3-constitutional isomer.

[0027] In a preferred variant of the cosmetic composition, the alkanediol having a carbon chain of 5 to 12 carbon atoms is a non-vicinal (x,x+2) diol, selected from the group consisting of a 1 ,3-diol, 2,4-diol, 3,5-diol, 4,6-diol, further (x,x+2) diols, and mixtures thereof, preferably an alpha, gamma-1 ,3-consitutional isomer.

[0028] In a further preferred variant of the cosmetic composition the alkanediol having a carbon chain of 5 to 12 carbon atoms, is preferably a non-vicinal (x,x+3) diol, selected from the group consisting of a 1 ,4-diol, 2,5-diol, further (x,x+3) diols, and mixtures thereof, preferably an alpha, delta-1 ,4-constitutional isomer.

[0029] In a preferred variant of the cosmetic composition, the alkanediol is preferably an alpha, omega alkanediol, more preferably, 1 ,7-heptanediol or 1 ,8-octanediol.

[0030] According to the present invention, vicinal (x,x+1 ) diols are most preferred, such as alpha, beta or beta, gamma or gamma, delta etc. [0031 ] In a still more preferred variant of the cosmetic composition, the alkanediol is a 1 ,2-alkanediol, a 2,3-alkanediol, a 3,4-alkanediol, or mixtures thereof, more preferred 2,3-alkanediol.

[0032] In a preferred variant of the cosmetic composition, the alkanediol is selected from the group consisting of:

1 .2-pentanediol, 2,3-pentanediol, 3,4-pentanediol,

1 .2-hexanediol, 2,3-hexanediol, 3,4-hexanediol,

1 .2-heptanediol, 2,3-heptanediol, 3,4-heptanediol,

1 .2-octanediol, 2,3-octanediol, 3,4-octanediol,

1 .2-nonanediol, 2,3-nonanediol, 3,4-nonanediol,

1 .2-decanediol, 2,3-decanediol, 3,4-decanediol,

1 .2-undecanediol, 2,3-undecanediol, 3,4-undecanediol,

1 .2-dodecanediol, 2,3-dodecanediol, 3,4-dodecanediol, and any mixture thereof.

[0033] According to a preferred variant, in the cosmetic composition, the alkanediol is selected from the group consisting of 1 ,2-pentanediol, 2,3-pentanediol, 1 ,2-hexanediol,

2.3-hexanediol, 1 ,2-heptanediol, 2,3-heptanediol, 1 ,2-octanediol, 2,3-octanediol, 1 ,2- nonanediol, 2,3-nonanediol, 1 ,2-decanediol, 2,3-decanediol, 1 ,2-undecanediol, 2,3- undecanediol, 1 ,2-dodecanediol, 2,3-dodecanediol, and any mixture thereof.

[0034] Of the aforesaid linear alkanediols, the following (x,x+1 ) constitutional isomers are preferred: 1 ,2-pentanediol, 2,3-pentanediol, 1 ,2-hexanediol, 2,3-hexanediol, 1 ,2- heptanediol, 2,3-heptanediol, 2,3-octanediol, 2,3-nonanediol, 2,3-decanediol, 2,3- undecanediol, 2,3-dodecanediol, or mixtures thereof. Said alkanediols are liquid at a purity of 90 to 99 %.

[0035] Of the aforesaid liquid alkanediols 1 ,2-pentanediol, 2,3-pentanediol, 1 ,2- hexanediol, 2,3-hexanediol, 1 ,2-heptanediol, 2,3-heptanediol, 2,3-octanediol, 2,3- nonanediol, or mixtures of said liquid alkanediols are particularly preferred.

[0036] In a further preferred variant of the cosmetic composition, the alkanediol is selected from the group consisting of: 1 .2-pentanediol, 2,3-pentanediol,

1 .2-hexanediol, 2,3-hexanediol,

1 .2-heptanediol, 2,3-heptanediol,

1 .2-octanediol, 2,3-octanediol,

1 .2-nonanediol, 2,3-nonanediol,

1 .2-decanediol, 2,3-decanediol,

1 .2-undecanediol, 2,3-undecanediol,

1 .2-dodecanediol, 2,3-dodecanediol, and any mixture thereof.

[0037] More preferred, the alkanediol mixture is selected from the group consisting of 1 ,2 and 2,3 mixtures:

1 .2-pentanediol and 2,3-pentanediol,

1 .2-hexanediol and 2,3-hexanediol,

1 .2-heptanediol and 2,3-heptanediol,

1 .2-octanediol and 2,3-octanediol,

1 .2-nonanediol and 2,3-nonanediol,

1 .2-decanediol and 2,3-decanediol,

1 .2-undecanediol and 2,3-undecanediol,

1 .2-dodecanediol and 2,3-dodecanediol, and any mixture thereof.

[0038] Further preferred in the cosmetic composition the alkanediol mixture is a combination of 1 ,2-heptanediol and 2,3-heptanediol, or 1 ,2-decanediol and 2,3- decanediol.

[0039] Further preferred in the cosmetic composition, the alkanediol is selected from the group consisting of 1 ,2-pentanediol, 2,3-pentanediol, and mixtures thereof, or is selected from the group consisting of 1 ,2-hexanediol, 2,3-hexanediol, and mixtures thereof. However, the linear alkanediol or the first linear alkanediol can also preferably be selected from the group consisting of 1 ,2-octanediol, 2,3-octanediol, and mixtures thereof. [0040] One important factor for the cosmetic composition is the solubility of its components. The cosmetic composition is preferably based on an aqueous solvent system wherein the components sorbate and 4-isoporopyl-3-methylphenol need to be soluble. Indeed, potassium sorbate is dissolved in water in a range up to 30 wt.-%, preferably up to 25 wt.-%, more preferably up to 20 wt.-%. A hydrophilic additive or cosolvent is helpful to dissolve 4-isopropyl-3-methylphenol and the active form of sorbate, i.e. , sorbic acid. Thus, in a preferred aspect, the solubility of potassium sorbate and 4- isopropyl-3-methylphenol in an aqueous solvent system is increased upon addition of a hydrophilic additive or co-solvent.

[0041 ] In general, hydrophilic additives or co-solvents for the aforementioned purpose are preferably selected from the group consisting of alcohols, diols, polyols, phenols or esters with good solubilizing properties, preferably selected from the group consisting of ethanol, 1 -propanol, isopropanol, phenoxyethanol, benzyl alcohol, ethylene glycol, propylene glycol, 1 ,3-propanediol, butylene glycol, pentylene glycol, 1 ,2-hexanediol, hexylene glycol, dipropylene glycol, ethoxydiglycol, propylene carbonate, glycerine carbonate, butylene carbonate, triethyl citrate, ethyl lactate, butyl lactate, ethyl acetate, diethylmalonate, diacetin, dimethyl isosorbide, diethylene glycol, PPG-3 methyl ether or any of their mixtures. Most preferably, the hydrophilic additive or co-solvent comprises propylene glycol.

[0042] The solubility of the cosmetic composition may be improved using any of the solubilizers of the aforementioned list. However, in some cases solubilizers have been found to reduce the effect of the present invention, so that the use of a hydrophilic additive or co-solvent, such as a glycol, is preferred.

[0043] For production of the cosmetic composition, preferably 4-isopropyl-3- methylphenol is premixed with a hydrophilic compound, comprising more preferably propylene glycol. This can be prior to addition to an aqueous solution of sorbate.

[0044] According to a further aspect of the invention, the cosmetic composition is acidified with 0.1 to 1 wt.-% aqueous citric acid (w = 5 to 15 %). It is further preferable to adjust the pH of the aqueous composition to from 5 to 7, preferably from 5 to 6. The preservative potassium sorbate can be activated if it is acidified and thus is then present in form of the corresponding sorbic acid. In addition, acidification improves the stability of the composition.

[0045] A further preferred component is hydroxyacetophenone, which is also preferably comprised in the cosmetic composition. This component shows further secondary effects which can support discoloration prevention.

[0046] The composition of all the samples prepared and investigated is found in Tab. 1 in the Experimental part along with a description of the production method of the samples.

[0047] The degradation of potassium sorbate in aqueous solutions is typically accompanied by a yellow discoloration and may be explained in terms of oligomerization or polymerization reactions. It is important to prevent these. Surprisingly it was found that the addition of the components described above could prevent these effects. In particular, it was possible to achieve a composition with improved colour properties as described below.

[0048] In most cases, the discoloration is clearly visible by eye (see Fig. 3 to 9). For quantification of the discoloration properties, the corresponding L* a* and b* values of the samples are measured.

[0049] The L*a*b* concept exactly describes the colour depending on parameters, where L* represents the brightness of a sample, a* represents the green/red distribution and b* represents the blue/yellow distribution. In case of a clear and colourless sample, L* ideally adapts a value equal or close to 100, whereas a* and b* should both be equal or close to zero. In the present case, a special focus lies on b* where positive values would indicate a yellow discoloration.

[0050] For the evaluation of a colour change of a sample, it is more convenient to have only one parameter instead of three. Therefore, based on changes in the L*a*b* values of a sample, the parameter AE is calculated according to the following equation: Since AE is defined as a function depending on the sum of the squared changes in the parameters L* a* and b* a low AE will indicate colour stability, i.e. no or only minor changes in the colour of a sample.

[0051 ] The results of the L*a*b* measurements and the AE calculations are summarized in Tab. 2. Each of the sample compositions 1 to 8 was stored under different conditions for the indicated period and then analysed regarding discoloration represented by changes in the L*a*b* values, especially b* For a more convenient analysis, the corresponding AE values were compared to each other. The most representative data was additionally selected and plotted in Fig. 1 and Fig. 2 to visualize differences in the colour stability of the sample compositions. Surprisingly, only the compositions according to the present invention, i.e., those containing 4- isopropyl-3-methylphenol, can effectively prevent discoloration induced by potassium sorbate.

[0052] Preferably, the cosmetic composition is such that the colour of the composition is stable, as described by AE values calculated from measured L*a*b* values, where AE remains below 3.0.

[0053] The cosmetic composition of the present invention is preferably stable against discoloration at temperatures up to 50 °C for more than six months as measured by L*a*b* values, where L* does not decrease by more than 0.3 units. Preferably also a* does not change by more than 0.8 units and further preferably b* does not increase by more than 2.0 units.

[0054] Preferably the discolouration stability as indicated above is at temperatures of 30 °C to 100 °C, more preferably 40 °C to 60 °C.

[0055] Further preferably the stability indicated above is achieved for a period of 6 months or more, more preferably 1 year or more, even more preferably for 2 years or more, most preferably for 5 years or more.

[0056] The cosmetic composition of the present invention is furthermore preferably stable against UV-light of a wavelength from 300 to 800 nm with an energy of 550 to 600 W/m² over a period of at least 8 hours, where L* does not decrease by more than 0.3 units, a* does not change by more than 0.2 units and b* does not increase by more than 0.5 units.

[0057] The cosmetic composition of the present invention may preferably be submitted to freeze-thaw processes without showing any discoloration over at least five cycles, wherein L* does not decrease by more than 0.7 units, a* does not change by more than 0.1 units and b* does not increase by more than 0.2 units. A freeze-thaw cycle includes cooling a sample to -20 °C and warming it up to +40 °C.

[0058] Furthermore, it was surprisingly found that the pH and the appearance of the composition do not change within six months if stored at temperatures up to 50 °C. Thus, the formulations have further stability attributes and long-term degradation is prevented.

[0059] The cosmetic composition is preferably furthermore stable regarding its odour. The odour is preferably stable over a period of at least six months.

[0060] The cosmetic composition of the present invention is designed to prevent discoloration in cosmetic formulations induced by a sorbate, preferably potassium sorbate, such as by a degradation process comprising oxidation or polymerisation condensation.

[0061 ] Thus, the invention also relates to the use of 4-isopropyl-3-methylphenol or a composition as described above, to prevent discoloration in cosmetic formulations induced by sorbate, potassium sorbate or sorbate derivatives.

[0062] Preferably, the use of 4-isopropyl-3-methylphenol or a composition as described above relates to the use in skin creams, skin lotions or other personal care products, preferably wet wipes.

[0063] The composition of all the samples prepared and investigated is found in Tab.

1 in the Experimental part along with a description of the production method of the samples. The results of the L*a*b* measurements and AE calculations are summarized in Tab. 2.

Brief description of Drawings

[0064] Fig. 1 is a plot of the measured b* values of the tested samples 1 to 8 stored under different conditions.

[0065] Fig. 2 is a plot of the calculated AE values of the tested samples 1 to 8 stored under different conditions.

[0066] Fig. 3 shows the samples 1 to 8 after storage at 40 °C for 12 weeks.

[0067] Fig. 4 shows the samples 1 to 8 after storage at 40 °C for 24 weeks.

[0068] Fig. 5 shows the samples 1 to 8 after storage at 50 °C for 12 weeks.

[0069] Fig. 6 shows the samples 1 to 8 after storage at 50 °C for 24 weeks.

[0070] Fig. 7 shows the samples 9 to 12 and 15 to 17 after storage at 40 °C for 4 weeks.

[0071 ] Fig. 8 shows the samples 9 to 12 and 15 to 17 after storage at 40 °C for 12 weeks.

[0072] Fig. 9 shows the samples 9 to 12 and 15 to 17 after storage at 50 °C for 4 weeks. Experimental part

[0073] Initially, the solubility of potassium sorbate and sorbic acid in 1 ,2-hexanediol and water was tested. The material was dissolved in the respective solvent by stirring and only heated if necessary. Assessment of the solubility was performed at ambient temperature after the samples were stored at 5 °C for 72 hours. Potassium sorbate is poorly soluble in 1 ,2-hexanediol (1 wt.-% with heating to 60 °C) and moderately soluble in water (20 wt.-% are soluble, 30 wt.-% are not). In contrast, sorbic acid is soluble in 1 ,2-hexanediol (5 wt.-% with heating to 60 °C) and insoluble in water.

[0074] A variety of wet wipe juice samples comprising potassium sorbate was prepared according to Tab. 1 and the following general procedure. Phase A was mixed, and Phase B was premixed, which required slight heating (~40 °C) for Phase B of sample 3 and 5. Phase B was then added to phase A and stirred, then the pH was checked and adjusted to approximately 5.5 with Phase C.

[0075] Tab. 1 : Composition of wet wipes juice comprising potassium sorbate (concentrations in wt.-%)

[0076] For evaluation of the stability, the sample formulations 1 to 8 (see Tab. 1 ) were stored under different conditions and analysed afterwards. As a first indication, the colour of the solutions was checked by eye, and the appearance, odour and pH were analysed. In addition, the corresponding L*a*b* colour values of the samples were measured using an instrument HACH Lange LICO 690. For L*, a value close to 100 needs to be reached to indicate a bright colour. Both a* and b* should ideally adapt values close to 0 to indicate the absence of any coloration effect. This especially holds for b* where positive values represent yellow discolorations which would be expected to be caused by sorbate degradation. The measured L*a*b* values are summarized in Tab. 2 below.

[0077] Based on the measured L* a* and b* values, AE values were calculated according to the following equation:

The AE values of the samples are also summarized in Tab. 2. However, since b* mainly contributes to the discolouration effect in the present case, the resulting AE values do not differ significantly from the measured b* values.

[0078]

Tab. 2: Measured L*a*b* and calculated AE values of sample formulations after storage for indicated time periods and storage conditions, at the beginning all formulations are colourless.

[0079] The L*a*b* and AE values summarized in Table 2 confirm the results of the visual check (Fig. 3 to 6). After 4 weeks a tendency towards different colour changes can already be seen after storing the samples at 40 or 50 °C, respectively. After 12 weeks, the effect of 4-isopropyl-3-methylphenol to prevent discoloration induced by potassium sorbate is more prominently visible, since samples 2 and 3, both containing o-cymen-5-ol, show no (40 °C) or hardly visible (50 °C) discolorations, whereas all other samples are visibly discoloured. The same result is observed after 24 weeks but in a more intense way, since no (40 °C) or hardly visible (50 °C) discolorations are found for samples 2 and 3, whereas all others are significantly discoloured. Interestingly, the negative discoloration effect is even more pronounced for sample 6 containing EDTA compared to “placebo” formulation 1 . Thus, EDTA had a detrimental effect.

[0080] The trends in colour stability are also visible in Fig. 1 and Fig. 2, where the measured b* values and the calculated AE values, respectively, are plotted against the different sample compositions. Notably, samples 2 and 3 show only minor changes in the b* and AE value, whereas all other samples indicate significant discoloration.

[0081 ] The effect of 4-isopropyl-3-methylphenol to prevent discoloration induced by potassium sorbate is achieved if the compound is used alone or in combination with the additives 3-phenylpropanol and decylene glycol. As was also found, the additives alone (Samples 4 and 5) do not prevent the discoloration. Furthermore, the phenolic antioxidant hydroxyacetophenone (Sample 8) was tested to find out, if the discoloration process induced by potassium sorbate is an oxidative one. Since hydroxyacetophenone did not prevent discoloration, an oxidative discoloration is not probable. The same holds for a chelating metal ion effect, as both EDTA and sodium gluconate did not prevent the discoloration either (Samples 6 and 7) [0082] Comparative tests

[0083] It is known that discoloration problems can also occur with compositions containing sodium dehydroacetate. Therefore, samples 9 to 11 were prepared according to Tab. 3 and the following general procedure. Phase A was mixed, and Phase B was premixed, which required slight heating (~40 °C) for Phase B of sample 11 . Phase B was added to phase A and stirred, then the pH was checked and adjusted to approximately 5.5 with Phase C.

[0084] Tab. 3: Composition of wet wipes juice containing sodium dehydroacetate (concentrations in wt.-%)

[0085] Compositions containing hydroxyacetophenone are also known to show discoloration problems. Therefore, samples 12 to 17 were additionally prepared according to Tab. 4 and the following general procedure. Phase A was mixed, heated to 40-50 °C until hydroxyacetophenone was completely dissolved and then cooled down. Phase B was premixed, which required slight heating (~40 °C) for Phase B of samples 14 and 17. Phase B was added to phase A and stirred, then the pH was checked and adjusted to approximately 7.0 with Phase C.

[0086] Tab. 4: Composition of wet wipes juice containing hydroxyacetophenone (concentrations in wt.-%)

[0087] The stability of samples 9 to 11 was examined and it was tested if 4-isopropyl- 3-methylphenol can analogously suppress the discoloration induced by dehydroacetate. The results of the L*a*b* measurements are summarized in Tab. 5.

[0088] Furthermore, samples 12 to 17 were examined regarding their stability and it was checked if 4-isopropyl-3-methylphenol is also capable of preventing a discoloration resulting from hydroxyacetophenone. The discoloration induced by hydroxyacetophenone typically occurs above pH 7 so that the samples were adjusted to pH 7 accordingly. In addition, urea was added to the samples 15 to 17 because the combination of urea and hydroxyacetophenone significantly increases the probability for the occurrence of discolorations. The results of the L*a*b* measurements are summarized in Tab. 5 below.

[0089] Tab. 5: Measured L*a*b* values and calculated AE values of sample formulations after storage for indicated time periods and storage conditions, at the beginning all formulations are colourless.

[0090] The L*a*b* and AE values summarized in Table 5 confirm the results of the visual check (Fig. 7 to 9). At the beginning, all formulations were colourless. Samples 9 to 11 containing sodium dehydroacetate show almost the same discoloration for the samples that were stored at 40 °C and 50 °C. Thus, 4-isopropyl-3-methylphenol cannot prevent a discoloration induced by sodium dehydroacetate.

[0091 ] The L*a*b* and AE values summarized in Table 5 furthermore confirm the results of the visual check (Fig. 7 to 9) for samples 12 to 17, where all formulations were colourless at the beginning. Samples 12 to 14 containing hydroxyacetophenone show a slight discoloration for the samples stored at 40 °C, 50 °C. When the samples additionally contain urea (Samples 15 to 17), very strong discoloration is observed at early time. Thus, 4-isopropyl-3-methylphenol is not capable of preventing a discoloration induced by hydroxyacetophenone. This observation becomes even more prominent if urea is additionally present in the composition.

Claims

1 . A cosmetic composition comprising a sorbate or sorbate derivative or sorbic acid or sorbic acid derivative, and 4-isopropyl-3-methylphenol.

2. The cosmetic composition according to claim 1 , wherein the sorbate or sorbate derivative is a sodium, potassium or calcium salt or the corresponding sorbic acid.

3. The cosmetic composition according to claim 1 or 2, wherein the ratio of the sorbate or sorbate derivative or sorbic acid or sorbic acid derivative to 4- isopropyl-3-methylphenol is in the range of 10:1 to 1 :1 , preferably 4:1 to 2:1 , by molar ratio.

4. The cosmetic composition according to any one of claims 1 to 3, comprising 0.1 to 1.0 wt.-% of the sorbate or sorbate derivative or sorbic acid or sorbic acid derivative, preferably potassium sorbate and/or 0.01 to 0.5 wt.-% 4-isopropyl-3- methylphenol, each by weight of the total weight of the formulation.

5. The cosmetic composition according to any of the preceding claims 1 to 4, further comprising 3-phenyl-1 -propanol.

6. The cosmetic composition according to any of the preceding claims 1 to 5, further comprising an alkanediol or alkanediol mixture, preferably where the alkanediol or alkanediol mixture comprises at least one 1 ,2- alkanediol which is preferably selected from the list consisting of 1 ,2-hexanediol, 1 ,2-octanediol and 1 ,2-decanediol, most preferably the alkanediol is 1 ,2- decanediol.

7. The cosmetic composition according to any of the preceding claims 1 to 6, further comprising a hydrophilic additive and/or a solubilizer, preferably propylene glycol.

8. The cosmetic composition according to any of the preceding claims 1 to 7, further comprising aqueous citric acid solution, preferably having an aqueous concentration of 5 to 15 wt.-%, preferably in an amount of from 0.1 to 1.0 wt.-%.

9. The cosmetic composition according to any of the preceding claims 1 to 8, comprising water as a solvent, wherein the pH is from 5 to 7.

10. The cosmetic composition according to any of the preceding claims 1 to 9, wherein the colour of the composition is stable, as measured by L*a*b* values, where L* does not decrease by more than 0.3 units, preferably a* does not change by more than 0.8 units and preferably b* does not increase by more than 2.0 units.

11. The cosmetic composition according to any of the preceding claims 1 to 10, wherein the colour of the composition is stable, as described by AE values calculated from measured L*a*b* values, where AE remains below 3.0.

12. The cosmetic composition according to any one of the preceding claims 1 to 11 , wherein the colour of the composition is stable in a temperature range from 30 to 100 °C, preferably in a range from 40 to 60 °C.

13. The cosmetic composition according to any one of the preceding claims 1 to 12, wherein the colour of the composition is stable for a period of 6 months or more, preferably for 1 year or more, even more preferably for 2 years or more.

14. Use of 4-isopropyl-3-methylphenol or a composition according to any of the preceding claims 1 to 13, to prevent discoloration in cosmetic formulations induced by sorbate or sorbate derivatives.

15. The use of 4-isopropyl-3-methylphenol or of the composition according to any of the claims 1 to 13 in skin creams, serum, hair leave-on products, deodorants, mouthwashes, toothpastes, surfactant-based cosmetic compositions, and wet wipes.