Caprylyl Glycol/Phenethyl Alcohol Blend for Alternative Preservation of Cosmetics

Aug 1, 2013 | Contact Author | By: Paola Ziosi, Stefano Manfredini, Alberta Vandini and Silvia Vertuani, University of Ferrara; and Massimo Fraternali, Akema Fine Chemicals
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Title: Caprylyl Glycol/Phenethyl Alcohol Blend for Alternative Preservation of Cosmetics
antimicrobialx self-preserving cosmeticsx caprylyl glycolx phenethyl alcoholx complexing agentsx
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Keywords: antimicrobial | self-preserving cosmetics | caprylyl glycol | phenethyl alcohol | complexing agents

Abstract: In recent years, the safety of traditional preservatives has been called into question. Therefore, there is a need for alternatives that are effective, safe and sustainable—and that are non-controversial. In response, the present work investigates a mixture of caprylyl glycol and phenethyl alcohol, which is shown to provide antimicrobial activity in various skin and hair care formulations.

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P Ziosi, S Manfredini, A Vandini, S Veruani and M Fraternali, Caprylyl Glycol/Phenethyl Alcohol Blend for Alternative Preservation of Cosmetics, Cosm & Toil 128(8) 538 (2013)

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The attitudes and perception of cosmetic preservatives have undergone significant changes in recent years. Traditional preservatives such as parabens, thiazolinones, formaldehyde-releasers and organic halogens have come under scrutiny, and, consequently, there is growing interest in alternative means of preservation with other antimicrobial choices; for example, organic acids and aromatic alcohols. This also follows a demand for milder and more natural ingredients. The use of alternative antimicrobials and the claim preservative-free have become popular in today’s cosmetics market as well, the latter thought to be due in part to current consumer beliefs that a product containing preservatives may pose a higher risk than “unpreserved” or “self-preserved” options.

In many formulations, “preservatives” have been replaced by cosmetic ingredients with one or more specified purposes that have the added benefit of preserving the formulation. To some, this raises controversy, as these are not officially classified as preservatives, and do not require labelling as such. The antimicrobial activity of plant oils and extracts, for example, has been recognized for years, together with other functional activities, i.e., lenitive, antioxidant, etc.1 Regardless of an ingredient’s classification, cosmetics on the market must be self-preserving or well-preserved.

Various aldehydes and alcohols, aromatic and aliphatic compounds, or terpenes and organic acids are among the most active molecules that can be used to reduce the levels of traditional preservative needed—or, in combination with other substances, replace them altogether.2 Regardless of an ingredient’s classification, microbial contamination leads to product deterioration, and can result in serious risks for consumer health; thus, cosmetics placed on the market must be either self-preserving or well-preserved.

The presented study investigates the antibacterial and antifungal activities of a blend of caprylyl glycol and phenethyl alcohol, referred to here as blend 1, in comparison with another composed of caprylyl glycol, glyceryl caprylate, glycerin and phenylpropanol, referred to here as blend 2. This blend was chosen for comparison for its preservation properties, and because it is based on a similar combination of caprylyl glycol with an aromatic alcohol; it also has the same suggested use range of 1.0–1.5%.

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Figure 1. Unpreserved tonic lotion

Figure 1. Unpreserved tonic lotion

All unpreserved formulations were susceptible to bacterial and fungal contamination, and supported a high level of viable microorganisms during the test period (see Figures 1-3).

Table 1. Serial dilutions of the antimicrobial blends tested

Table 1. Serial dilutions of the antimicrobial blends tested

Microbial suspensions of single microorganisms, i.e., bacteria and fungi, from ATCC culture collection were prepared in suitable nutrient broths, and serial dilutions of the test samples were made in 96-well sterile micro-titer plates (see Table 1).

Table 2. Concentration of preservative system in tested formulations

Table 2. Concentration of preservative system in tested formulations

Challenge tests were performed using three different formulation types (see Formulas 1-3): an o/w emulsion, a shampoo and a tonic lotion, into which blend 1 was incorporated at various concentrations (see Table 2).

Table 3. Inhibitory (MIC) and biocidal (MBC) activity of blends 1 and 2

Table 3. Inhibitory (MIC) and biocidal (MBC) activity of blends 1 and 2

 Blend 2 was required at a higher 1% concentration to inhibit both bacteria and fungi (see Table 3).

Table 4. Inhibitory (MIC) and biocidal (MBC) activity of blend 1 (in black) plus sodium phytate and tetra-sodium glutamate diacetate (in red)

Table 4. Inhibitory (MIC) and biocidal (MBC) activity of blend 1 (in black) plus sodium phytate and tetra-sodium glutamate diacetate (in red)

When combined with 0.05% sodium phytate and tetra-sodium glutamate diacetate, blend 1 exhibited a bactericidal action against Gram-positive bacteria at 0.2%, and a complete fungicidal activity against yeasts and molds at 0.3% and 0.4%, respectively (see Table 4).

Table 5. Inhibitory (MIC) and biocidal (MBC) activity of blend 2 (in black) plus sodium phytate and tetra-sodium glutamate diacetate (in red)

Table 5. Inhibitory (MIC) and biocidal (MBC) activity of blend 2 (in black) plus sodium phytate and tetra-sodium glutamate diacetate (in red)

Blend 2, combined with 0.1% sodium phytate, exhibited full bactericidal and fungicidal activity at 0.4%, whereas in combination with 0.2% tetra-sodium glutamate diacetate, it was required at a concentration of 0.7% (see Table 5).

Figure 3. Unpreserved shampoo

Figure 3. Unpreserved shampoo

All unpreserved formulations were susceptible to bacterial and fungal contamination, and supported a high level of viable microorganisms during the test period (see Figures 1-3).

Figure 2. Unpreserved o/w emulsion

Figure 2. Unpreserved o/w emulsion

All unpreserved formulations were susceptible to bacterial and fungal contamination, and supported a high level of viable microorganisms during the test period (see Figures 1-3).

Figure 4. Tonic lotion with 0.8% blend 1

Figure 4. Tonic lotion with 0.8% blend 1

A particularly good result was seen in the test with the tonic lotion, see Figures 4-8, where all five test microorganisms were completely inactivated in 48 hr at all concentrations tested, with and without chelating agents.

Figure 5. Tonic lotion with 1% blend 1

Figure 5. Tonic lotion with 1% blend 1

A particularly good result was seen in the test with the tonic lotion, see Figures 4-8, where all five test microorganisms were completely inactivated in 48 hr at all concentrations tested, with and without chelating agents.

Figure 6. Tonic lotion with 1.2% blend 1

Figure 6. Tonic lotion with 1.2% blend 1

A particularly good result was seen in the test with the tonic lotion, see Figures 4-8, where all five test microorganisms were completely inactivated in 48 hr at all concentrations tested, with and without chelating agents.

Figure 7. Tonic lotion with 1.4% blend 1

Figure 7. Tonic lotion with 1.4% blend 1

A particularly good result was seen in the test with the tonic lotion, see Figures 4-8, where all five test microorganisms were completely inactivated in 48 hr at all concentrations tested, with and without chelating agents.

Figure 8. Tonic lotion with 0.8% blend 1 + 0.1% sodium phytate

Figure 8. Tonic lotion with 0.8% blend 1 + 0.1% sodium phytate

A particularly good result was seen in the test with the tonic lotion, see Figures 4-8, where all five test microorganisms were completely inactivated in 48 hr at all concentrations tested, with and without chelating agents.

Figure 9. O/W emulsion with 1% blend 1

Figure 9. O/W emulsion with 1% blend 1

When evaluating the results from the o/w emulsion, blend 1 at 1% was sufficient to protect the formulation against contamination, inactivating P. aeruginosa, S. aureus, C. albicans in 48 hr, and E. coli (2.4 x 103) and A. brasiliensis (1.0 x 104) in 7 days without chelating agents (see Figure 9).

Figure 10. O/W emulsion with 1.2% blend 1

Figure 10. O/W emulsion with 1.2% blend 1

Use of the blend at 1.2% in the o/w emulsion also inactivated E. coli in 48 days (see Figure 10) and at 1.4% blend, all test organisms were inactivated after 48 hr (see Figure 11 ).

Figure 11. O/W emulsion with 1.4% blend 1

Figure 11. O/W emulsion with 1.4% blend 1

Use of the blend at 1.2% in the o/w emulsion also inactivated E. coli in 48 days (see Figure 10) and at 1.4% blend, all test organisms were inactivated after 48 hr (see Figure 11 ).

Figure 12. O/W emulsion with 1% blend 1 + 0.1% sodium phytate

Figure 12. O/W emulsion with 1% blend 1 + 0.1% sodium phytate

Interestingly, with 0.1% sodium phytate, the inactivation at 48 hr was observed with 1% of blend 1 (see Figure 12), showing how the booster reduced the concentration required to reach the same antimicrobial effect.

Figure 13. Shampoo with 0.8% blend 1

Figure 13. Shampoo with 0.8% blend 1

In the case of shampoo, 0.8% and 1% blend inactivated the test organisms in 48 hr, except E. coli (1.0 x 102 CFU/g) and P. aeruginosa (1.0 x 104), which were inactivated at 7 days (see Figures 13 and 14).

Figure 14. Shampoo with 1% blend 1

Figure 14. Shampoo with 1% blend 1

In the case of shampoo, 0.8% and 1% blend inactivated the test organisms in 48 hr, except E. coli (1.0 x 102 CFU/g) and P. aeruginosa (1.0 x 104), which were inactivated at 7 days (see Figures 13 and 14).

Figure 15. Shampoo with 1.2% blend 1

Figure 15. Shampoo with 1.2% blend 1

However, all five organisms were inactivated at < 10 CFU in 48 hr with 1.2% blend 1 (see Figure 15).

Figure 16. Shampoo with 0.8% blend 1 + 0.1% sodium phytate

Figure 16. Shampoo with 0.8% blend 1 + 0.1% sodium phytate

Also observed when analyzing the shampoo results was the fact that the addition of 0.1% sodium phytate significantly increased activity, giving a higher log reduction, in particular of P. aeruginosa and E. coli (see Figures 16 and 17).

Figure 17. Shampoo with 1% blend 1 + 0.1% sodium phytate

Figure 17. Shampoo with 1% blend 1 + 0.1% sodium phytate

Also observed when analyzing the shampoo results was the fact that the addition of 0.1% sodium phytate significantly increased activity, giving a higher log reduction, in particular of P. aeruginosa and E. coli (see Figures 16 and 17).

Footnote (CT1308 Manfredini)

a Stabil (INCI: Phenethyl Alcohol (and) Caprylyl Glycol) is a product of Akema Fine Chemicals S.r.l. (Italy).

Formula 1. Test o/w emulsion

Formula 1. Test o/w emulsion

Challenge tests were performed using three different formulation types (see Formulas 1-3): an o/w emulsion, a shampoo and a tonic lotion, into which blend 1 was incorporated at various concentrations (see Table 2).

Formula 2. Test shampoo

Formula 2. Test shampoo

Challenge tests were performed using three different formulation types (see Formulas 1-3): an o/w emulsion, a shampoo and a tonic lotion, into which blend 1 was incorporated at various concentrations (see Table 2).

Formula 3. Test tonic lotion

Formula 3. Test tonic lotion

Challenge tests were performed using three different formulation types (see Formulas 1-3): an o/w emulsion, a shampoo and a tonic lotion, into which blend 1 was incorporated at various concentrations (see Table 2).

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