A new emulsifier-free w/o system based on a triterpene extract from the outer bark of birch

Surfactants are critically seen due to their impairment of skin barrier function. Therefore surfactant-free emulsions become more and more important. Here we present a new w/o emulsion system based on a triterpene dry extract from the outer bark of birch (TE) that is supposed to be emulsifier-free. Beside the galenic properties the TE display various pharmacological activities also important for dermatology [1]. 80% of TE is betulin, a pentacyclic triterpene with a polar group (alcohol) on each side of the molecule, respectively [1].

Investigations on the surface tension were done using axisymmetric drop shape analysis (ADSA) method. To further clarify the stabilizing action of TE on emulsions, Raman microscopy was carried out and the solubility of the TE was determined in the Jojoba oil by gas-chromatography [1].

In comparison to classical emulsifiers, the TE reduces the interfacial tension between oil and water by only 5 mN/m. 2–6% (w/w) of TE are necessary to prepare a stable emulsion. Only 0.28% (w/w) of TE are soluble in Jojoba oil and less than <0.0001% (w/w) are soluble in water [3]. Thus TE-particles are present in the lipid phase forming a Pickering emulsion [2]. Accordingly, Raman microscopy shows that the TE particles surround the water droplets and they additionally form a network like structure in the lipid phase. The surface of the water droplets is not completely covered in contrast to a classic Pickering emulsion showing long term stability. Presumably, the stability of the w/o emulsions is enhanced by the lipophilic gel phase which is formed by the TE.

In conclusion the TE allows to formulate a plant based and long-term stable emulsifier-free w/o system without any further ingredients.

References: [1] Laszczyk, M.N. et al. (2006) Planta Med. 72:1389–1395.

[2] Stiller, S. et al. (2004) Colloid Surface A 232:261–267.

[3] Jäger, S. et al. (2008) Molecules 13:3224–3235.