Sensory and instrumental characterization of fast inverting oil-in-water emulsions for cosmetic application

Abstract

ObjectiveThe aim of this study was to perform short-term sensory testing and instrumental (conductivity and rheological) characterization of a fast inverted oil-in-water (o/w) emulsion base, also known as a SWOP (Switch-Oil-Phase) emulsion, and reference o/w and water-in-oil (w/o) emulsion bases under various testing conditions: in the presence of ions and at different temperatures. SWOP emulsions are known as metastable o/w emulsions, which invert into w/o emulsions on application of mechanical energy, while rubbing it onto the skin and due to their properties SWOP emulsion are especially suitable as a cosmetic vehicle in, for example, sun-protection products. MethodsSensory testing, which included the evaluation of twenty attributes of the investigated emulsion bases, was performed by a panel of 20 healthy assessors experienced in the evaluation of cosmetic products. Rheological characterization of the investigated emulsion bases included continuous flow testing and oscillatory measurements under various testing conditions. Additionally, conductivity measurements were combined with rheological characterization to monitor stability changes of investigated emulsions. The instrumental and sensory results were analysed statistically and compared. ResultsThe obtained results indicated that the investigated emulsions behaved differently in the presence of ions (originating from artificial sweat solution) and at different temperatures (under storage and application conditions). Namely, the SWOP emulsion showed similar behaviour to the reference o/w emulsion under storage conditions, but in the presence of ions and at skin temperature, the SWOP emulsion was followed by re-establishment of a stable w/o system, whereas reference o/w emulsion was irreversibly destroyed. The statistical analysis of chosen sensorial attributes indicated that the reference w/o emulsion was significantly different in comparison with the reference o/w and SWOP emulsions, mainly, standing in good agreement with the results of rheological characterization. ConclusionThe study showed that rheological measurements potentially could be related to certain sensory attributes and used for faster development of SWOP emulsions in the future. Finally, SWOP emulsions should be considered for further investigation as suitable vehicles in cosmetic products due to their favourable physicochemical and sensory characteristics which could be partially predicted with instrumental characterization. Resume ObjectifLe but de cette etude etait d'effectuer des essais sensoriels a court terme et de caracterisation instrumentale (conductivite et rheologique) d'une base d'emulsion huile-dans-eau (H/E) a inversion rapide, aussi connue comme emulsion SWOP (Switch- phase huileuse), compares aux references des bases d'emulsion H/E et E/H (w/o) dans diverses conditions d'essai: en presence d'ions et a differentes temperatures. Les emulsions SWOP sont connues comme des emulsions H/E metastable, qui inversent en emulsions E/H suite a l'application d'une energie mecanique, tout en frottant sur la peau et en raison de leurs proprietes les emulsions SWOP sont particulierement appropries en tant que vehicule cosmetique, par exemple, les produits de protection solaire. MethodesDes tests sensoriels, qui comprenaient l'evaluation de vingt attributs des bases d'emulsion d'une enquete, a ete realisee par un panel de 20 evaluateurs sains experimentes dans l'evaluation des produits cosmetiques. La caracterisation rheologique des bases d'emulsion etudiees comprenait les tests de flux continu et les mesures oscillatoires dans differentes conditions de test. En outre, les mesures de conductivite ont ete combinees avec une caracterisation rheologique dans le but de suivre l'evolution de la stabilite des emulsions etudiees. Les resultats instrumentaux et sensoriels ont ete analyses statistiquement et compares. ResultatsLes resultats obtenus indiquent que les emulsions etudiees se sont comportee differemment en presence d'ions (originaires d'une solution de sueur artificielle) et a differentes temperatures (dans des conditions de stockage et d'application). savoir, l'emulsion de SWOP a montre un comportement similaire a l'emulsion H/E de reference dans des conditions de stockage; mais en presence d'ions et a la temperature de la peau, l'emulsion de SWOP a ete suivie par le retablissement d'un systeme stable E/H, tandis que l'emulsion de reference H/E a ete detruite de maniere irreversible. L'analyse statistique des attributs sensoriels choisis indiquait que le RWOE etait sensiblement different en comparaison avec le ROWE et SE, principalement, en bon accord avec les resultats de la caracterisation rheologique. ConclusionL'etude a montre que les mesures rheologiques pourraient etre correlees a certains attributs sensoriels et utilisees pour le developpement rapide d'emulsions SWOP a l'avenir. Enfin, des emulsions SWOP devraient etre considerees pour des complement d'enquete comme vehicules appropries dans les produits cosmetiques en raison de leur physico-chimique favorable et des caracteristiques sensorielles qui pourrait etre partiellement predites avec la caracterisation instrumentale.