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Vanillin: a promising preservation booster

Vanillin: a promising preservation booster

Link: Vanillin, a promising preservation booster | PCM
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Abstract

Preservation has always been under the spot light; even more so is preservation of natural products.

Traditional substances that have been long used to preserve cosmetic products are undergoing radical reviews by the competent Authorities, which could potentially lead (or already have led) to drastic reductions of the allowed concentration in formula.

This, in conjunction with a growing consumer demand for more natural products, can inspire formulators to ‘borrow’ ingredients from allied industries.

In recent years consumers of personal care products have become increasingly demanding in terms of quality as well as safety of the products they use. It can be argued that some bad press has been pushing customers towards certain directions that are then reflected in various claims found in finished products.

Among these, the ‘free from’ claim has become quite trendy. ’Free from’ can refer to more or less any ingredient, e.g. mineral oils, silicones, preservatives. What once used to be mainly found on labels of natural products is now being claimed by some big names in the industry, with paraben-free on the hot list. This can stimulate some research into novel ways to develop preservation strategies that can help meet the consumer’s demand for more natural cosmetic products.

It goes without saying that number one priority for a cosmetic formulator must be safety. This implies that certain substances need to be used in order to guarantee efficacious preservation of products: Annex V of the European Cosmetic Regulation (EC) N. 1223/2009 defines a list of substances that can be used as ‘preservatives’.

Substances not listed cannot be defined as preservatives and products containing these substances can be claimed ‘preservative-free’. This custom is obviously argued by many in the industry and has generated a flourishing market of new multifunctional ingredients that can be used to preserve a cosmetic product.

Most of these substances are not sufficiently efficacious if used singularly and need to be combined with others. For the weaker molecules the ‘hurdle technology’1 may still be adopted.1

It is anyway acknowledged that combinations of several substances will most likely give a better result than what could be achieved by using only one. The present article describes the use of natural Vanillin as an effective preservation booster.

Preservation systems

Without falling into semantic debates on the use of the word ‘preservative’ and its regulatory implications, ‘preservation system’ will hereafter indicate substances showing some antimicrobial activity. For many years cosmetic formulators have been trying to find the ideal preservation system that could be used in all product types. If this existed it would have some peculiar features:

  • Broad spectrum
  • Low use concentration
  • Compatible with other ingredients
  • Usable within a wide pH range
  • Thermo-stable
  • Good water solubility, poor oil solubility
  • Safe
  • Cheap
  • Colourless and odourless

When formulating natural certified cosmetic products (e.g. in accordance with standards such as Cosmos), organic acids and their salts and esters (e.g. sorbic/sorbate, benzoic/benzoate, etc) are the only preservative substances that can be used as defined in Annex V of the Cosmetic Regulation.

The anti-microbial efficacy of these materials depends on their dissociation: they are active in their undissociated state and show no or little activity when in their dissociated or salt state.

At a pH equivalent to their pKa, the organic acids have lost approximately 50% of their activity, and at 1.5 pH units above the pKa the remaining activity is only 10%. As a consequence natural cosmetic products utilising organic acids tend to be acidic and pH values of 4.5 and even 4.0 are commonly found.

Combinations with other substances are always recommended in order to achieve a satisfactory protection of the system. It is clear that preserving a natural certified cosmetic product is one of the most demanding challenges formulators are requested to face and represents a source of endless worries.

From one side, the number of preservative systems allowed by natural certification bodies is quite limited, mainly restricted to organic acids and their salts. However, on the other side, a huge arsenal of ‘non-listed’ materials showing antimicrobial activity is available and well documented.2

Vanillin

Vanillin (4-hydroxy-3-methoxybenzaldehyde, Fig. 1) is the major constituent of vanilla beans and is produced naturally via a multi-step curing process. However, 90% of vanillin currently in use is synthetically produced (nature-identical) from lignin, eugenol or guiacol.3,4 Vanillin has GRAS (Generally Recognized as Safe) status and is widely used as a flavouring/aroma compound in the food and fragrance industry.

Synthetic vanillin is also used as an intermediate in the chemical and pharmaceutical industry for the synthesis of herbicides and drugs.5 A rather extensive literature shows that vanillin is indeed a multifunctional molecule, not only providing foodstuff and drinks with a pleasant aroma and taste.

Some reports have shown that vanillin can act as an antioxidant, improving the keeping quality of precooked dried cereal flakes6 and providing significant protection against protein oxidation and lipid peroxidation in rat liver mitochondria.7

Moreover, vanillin exhibits strong broad spectrum antimicrobial properties with activity demonstrated against a number of microorganisms in laboratory media.8–10 Some authors11 have thoroughly investigated the mode of action of vanillin, finding that it was primarily a membraneactive compound.

In recent works12 vanillin solutions were used as antimicrobial coatings for paperboard used as packaging for baked goods. Little or no evidence of the use of vanillin for its antimicrobial activity in the cosmetic industry was found.

Materials and methods

Two multifunctional substances were selected in order to build an ‘alternative’ preservation system that would allow a preservative-free claim yet provide cosmetic products with an efficacious antimicrobial action.

Glyceryl caprylate has long been used for its well-recognised properties, including refatting and moisturising. It shows good activity against bacteria and yeast at relatively low concentration and within a wide range of pH (approx 4.5-7.0). It is classified as a naturally-derived substance as synthesised from vegetable raw materials.

Picea abies extract is extracted from the Norway spruce and shows interesting properties, among which are antioxidation and broad spectrum antimicrobial activity.

A prototype oil-in-water emulsion was developed in accordance to Cosmos Organic Standards. The pH was adjusted to 5.0±0.2 with citric acid. Several combinations of glyceryl caprylate, Picea abies extract and vanillin were tested as shown in Table 1.

Table 1. Combinations used to preserve the prototype formula.
Substanc A B C D E F G
Glyceryl caprylate 1.0 – – 1.0 1.0 – 1.0
Picea abies extract – 3.0 – 3.0 – 3.0 3.0
Vanillin – – 0.1 – 0.1 0.1 0.1
Citric acid QS to pH +/- 0.2

Microbial challenge test was performed according to the European Pharmacopoeia guidelines for preservation testing of aqueous liquid cosmetic formulations.

The following test organisms were used in this study:

  • Aspergillus niger.
  • Candida albicans.
  • Escherichia coli.
  • Pseudomonas aeruginosa.
  • Staphylococcus aureus.

Initial microbial content of all prototypes formulated was carried out in order to exclude any sample that could be contaminated. The acceptance criteria for the challenge test were as follows:

  • Bacteria: at least a 2 Log reduction in the total number of organisms must be obtained by Day 2 when compared to the initial inoculum.
    By Day 7 at least a 3 Log reduction in the total number of organisms must be obtained.
    By Day 28, there must be no increase in bacterial number from what was observed in Day 7.
  • Fungi: at least a 2 Log reduction in the total number of organisms must be obtained by Day 14 when compared to the initial inoculum.
    By Day 28, there must be no increase in bacterial number from what was observed in Day 14.

Results and discussion

Table 2 shows results of the initial microbial counts that were conducted on each prototype. It can be seen that none of the formulations were contaminated prior to the commencement of the challenge test.

Table 2. Initial microbial count.
Preservation system Result (growth)
Bacteria Fungi
A No No
B No No
C No No
D No No
E No No
F No No
G No No

Table 3 summarises challenge test results showing Log reduction at day 2 for bacteria and Log reduction at day 14 for fungi. It can be seen that in this particular prototype formula, the three substances used singularly were not efficacious neither against bacteria nor fungi (preservation systems A, B and C) as the minimum acceptability Log reduction was not obtained.

Table 3. Challenge test results at day 2 and 14.
Preservation system Bacteria – Log reduction at day 2 Fungi – Log reduction at day 14
E.coli P.aeruginosa S.aureus A.niger C.albicans
A 0 1 0 1 1
B 1 1 1 1 1
C 0 0 0 0 0
D 2 2 2 2 2
E 5 3 3 5 5
F 3 5 3 5 3
G 5 7 5 7 7

A combination of glyceryl caprylate and Picea abies extract (preservation system D) demonstrated to be efficacious against both bacteria and fungi: in all cases the 2 Log reduction was obtained. Interesting results were achieved by adding vanillin to the previous preservation systems.

Preservation systems E and F showed a nice increase in Log reduction for both bacteria and fungi when compared to respectively A and B. When the three substances were combined (preservation system G) a further increase in Log reduction was obtained with complete kill of some microorganisms.

In the prototype emulsions tested, Vanillin showed a remarkable boosting effect of the overall preservation efficacy.

Comments

It must be noted that results shown in the present article were obtained solely on one particular prototype formulation. Despite being extremely encouraging, conclusions on the antimicrobial efficacy of vanillin cannot be generalised.

Vanillin is a substance with some remarkable attributes, e.g. a natural grade can be easily purchased, it is a food ingredient with a GRAS status and provides products with a pleasant, intense yet never overpowering scent.

However, vanillin has some limitations that may stop formulators from using it: one of the main issues is that it easily undergoes oxidation which leads to heavy discolouration. Nevertheless, this does not seem to affect the odour profiles of vanillin.

Oxidation can be triggered by high temperature, UV exposure as well as low pH. A white emulsion or an opaque, pearlescent shampoo can turn yellowish and then brown in a matter of days.

However, some literature has demonstrated that the main oxidation product, vanillic acid (Fig. 1), would be responsible for boosting the antimicrobial activity of vanillin.13

On a more practical side, natural vanillin is quite expensive, a factor that can limit its concentration in formula. In the author’s opinion the present article can stimulate cross-functional research in a field such as preservation which is of great relevance to the cosmetic industry in general and to the natural/organic segment in particular.

References

1 Orth DS, Kabara JJ. Preservative-free and selfpreserving cosmetics and drugs. Cosmetics & Toiletries 1998; 113 (4): 51-8.
2 Ibarra F, Johnson CH. Natural preservation from concepts in nature. Cosmetics & Toiletries 2008; 3: 81-90.
3 Hocking MB. Vanillin: synthetic flavouring from spent sulphite liquor. J Chem Ed 1997; 74 (9): 1055-9.
4 Ramachandra RS, Ravishankar GA. Vanilla flavour: production by conventional and biotechnological routes. J Sci Food Agric 2000; 80: 289-304.
5 Walton NJ, Mayer MJ, Narbad A. Molecules of interest: Vanillin. Phytochem 2003; 63: 505-15.
6 Burri J, Graf M, Lambelet P, Loliger J. Vanillin: more than a flavouring agent – a potent antioxidant. J Sci Food Agric 1989; 48: 49-56.
7 Kamat JP, Ghosh A, Devasagayam TPA. Vanillin as an antioxidant in rat liver mitochondria: inhibition of protein oxidation and lipid peroxidation induced by photosensitization. Mol Cell Biochem 2000; 209: 47-53.
8 Lopez-Malo A, Alzamora SM, Argaiz A. Effect of natural vanillin on germination time and radial growth of moulds in fruit-based agar systems. Food Microbiol 1995; 12: 213-9.
9 Cerruti P, Alzamora SM. Inhibitory effects of vanillin on some food spoilage yeasts in laboratory media and fruit purees. Int J Food Microbiol 1996; 29: 379-86.
10 Fitzgerald DJ, Stratford M, Gasson MJ, Narbad A. The potential application of Vanillin in preventing yeast spoilage of soft drinks and fruit juices. J Food Prot 2004; 67: 391-5.
11 Fitzgerald DJ, Stratford M, Gasson MJ, Ueckert J, Bos A, Narbad A. Mode of antimicrobial action of vanillin against Escherichia coli, Lactobacillus plantarum and Listeria innocua. J App Microbiol 2004; 97: 104-13.
12 Rakchoy S, Suppakul P, Jinkarn T. Antimicrobial effects of vanillin coated solution for coating paper board intended for packaging bakery products. As J Food Ag-Ind 2009; 2 (4): 138-47.
13 Mourtzinosa I, Kontelesb S, Kalogeropoulosa N, Karathanosa VT. Thermal oxidation of vanillin affects its antioxidant and antimicrobial properties. Food Chem 2009; 114 (3): 791-7.

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