Fragrance is an important ingredient in most cosmetic formulations, as it is a key driver in consumer assessment and sensory perception of products¹. Fragrance is a complex blend of natural and/or synthetic odorant molecules of great chemical diversity². When added to a cosmetic formulation, individual fragrance molecules partition between the different phases and can interact with other ingredients, impacting the structure, stability, texture, and odour of the final product^3,4. There is a growing demand for the use of new natural and multifunctional cosmetic ingredients. Essential oils are a good example, as they can serve the roles of both fragrance and active⁵. However, the impact of the incorporation of these new ingredients on the textural and sensorial properties of lamellar emulsions is poorly documented. This presentation aims to understand the interactions between fragrance molecules and lamellar emulsion matrices, from microstructure to sensory perception. First, the effects of fragrance on emulsion microstructure, stability, and texture will be presented. Then, the effects of emulsion structure on fragrance release will be discussed.

An alkyl polyglucoside/fatty alcohol mixture was used as an emulsifier. In previous works, we demonstrated that we are able to control the formation of lamellar emulsions and to link the emulsion composition, its microstructure and the type of lamellae with its texture and applicative properties⁶. In this study, emollients highlighting different chemical structures were used as the dispersed oil phase and fragrance molecules with different polarities were selected. Emulsions microstructure was investigated using microscopy, wide-angle X-ray scattering (WAXS) and static light scattering (SLS). Viscoelastic properties were determined by rheology. Emulsion texture and consistency were investigated using a texture analyser. Fragrance release was investigated using headspace gas chromatography. Sensory analyses were carried out to evaluate the impact of fragrance on emulsions textural properties before and after topical application. Fragrance intensity was also evaluated after topical application, to investigate the impact of emulsion structure on fragrance release.

The results suggest a link between emulsion properties, fragrance release and perception. The presence of lamellar phases and onion rings was observed by microscopy under polarized light for all the emulsions. The results of characterization methods suggest that emollient and fragrance have a significant impact on emulsion microstructure. Differences in microstructure organization and droplet size were observed using microscopy and SLS respectively. This impact is also noticeable on the viscoelastic properties and texture properties of the emulsions. Sensory analyses also highlighted differences in emulsions appearance and textural properties, depending on the emollient and fragrance used. Moreover, emulsion microstructure has a significant impact on fragrance release. Trained panellists found differences in fragrance intensity for emulsions containing different emollients. This was confirmed by fragrance release kinetics using gas chromatography.

Previous work of our team showed that the nature of the emollient used as the oil phase influences the lamellar organization of the emulsion microstructure⁷. Depending on the liquid crystalline phases present and on their nature, fragrance molecules partition between different parts of the emulsion. Consequently, emulsion microstructure, texture, and stability are altered.

This work proposed an innovative methodology combining the use of liquid crystalline phases in emulsions, their interactions with fragrance components and extensive analytical analyses to elucidate them at the microscopic and macroscopic scales. In the end, this work will provide new knowledge for optimal control of fragrance incorporation in the design of future emulsions. Indeed, understanding the interactions between fragrance molecules and dermo-cosmetic emulsion matrices is crucial, to predict how fragrance can alter the physicochemical properties of emulsions, and to optimize fragrance release. New knowledge will also be found on the behaviour of scented cosmetics on the skin and will be used to better protect consumers.

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