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.
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
- Good water solubility, poor oil solubility
- 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 (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.
|Picea abies extract||–||3.0||–||3.0||–||3.0||3.0|
|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.