j. Cosmet. Sd., 50, 15-22 (January/February 1999) A study of I-cyclodextrin-stabilized paraffin oil/water emulsions SERGE LAURENT, MICHEL SERPELLONI, and DANIEL PIOCH, UR Chimie-Technologie Laboratoire de Lipotechnie, Centre de Coopgration Internationale en Recherche Agronomiq/•e pour le Dgveloppement, B.P. 5035, F 34032 Montpellier (S.L., D.P.), and Roqz/ettes Fr•res, F 62136 Lestrein (M.S.), France. Accepted for publication December 15, 1998. Synopsis This paper reports a study of the liquid paraffin emulsions stabilized only by I3-cyclodextrin (IBCD), a starch derivative well known for its ability to form inclusion compounds with a wide range of molecules. The effects of IBCD, which is not a surfactant, on emulsions' stability under heat and centrifugation, was checked. From a rheological standpoint, the IBCD emulsions are characterized by a very high flow threshold. The formation of an inclusion compound in the emulsion is likely to occur because a precipitate is always observed, even at low IBCD concentrations in the aqueous phase. The low particle size of tinis precipitate might play a role in the stabilization of these emulsions. INTRODUCTION Since the late 1980s changing consumer habits and environmental awareness have induced an evolution of the marketing strategies for cosmetics and toiletries. [3-cyclo- dextrin ([3CD), an oligosaccharide synthesized through a biotechnological process (1) from starch, was proposed intensively in the patent literature as an alternative emulsifier for food and cosmetics (2-6). Unfortunately, the properties of the emulsions that have always contained several emulsifers were not developed in the patent and only a few scientific papers deal with this subject (7,8). Because of the complexity of such systems, there still remains a doubt about the type of activity of [3CD. However, due to important scientific work in the last twenty years about [3CD, it is well known for its remarkable ability to form inclusion compounds with a wide range of molecules (9). This interesting property is due to the cylindrical cavity in its toroidal structure, which can provide a hydrophobic environment for guest molecules (9). At the opposite pole, the external surface of [3CD toroid is hydrophilic. As a result of these interesting properties, the use of this starch derivative was proposed for protection and solubilization of active compounds such as flavors or pharmaceuticals (11,12). 15

16 JOURNAL OF COSMETIC SCIENCE Therefore, [3CD should be used in the composition of some emulsions in the near future. Shimada et al. assume that [3CD, which has no effect on the surface tension at the air/water interface, stabilizes the emulsions through the formation of a layer of complexes at the oil/water interface (12). The purpose of this paper is to investigate paraffin oil/water emulsions stabilized by [3CD in order to promote the use of this new emulsifier in cosmetics. MATERIALS AND METHODS MATERIALS AND EMULSION PREPARATION Each batch (300 g) of emulsion was prepared as follows. The hydrated [3CD (Kleptose from Roquettes FrSres) and deionized water are stirred for 15 min with a propeller in a 600-ml stainless steel beaker thermostated at the temperature of emulsification through a water bath. The paraffin oil (Primol 352 from ESSO), warm at the same temperature, is poured into the beaker at a rate of 100 ml/min. Then, the speed of the blender is increased, taking care not to introduce air bubbles into the dispersion. The emulsion is homogenized for 15 min. The temperature of emulsification is usually 20øC, except when otherwise stated. STABILITY TESTS ON EMULSIONS A greasy layer appears at the top of the oil/aqueous phase mixture after stopping the homogenization when the experimental conditions are unfavorable to emulsification. In the other cases, three samples of emulsion are poured into a 3-ml glass tube and sealed. In order to investigate emulsion stability, the samples are submitted to various stresses: storage for a week at 25øC followed by centrifugation at 4200 g for 30 min storage for a month at 25øC storage for a week at 60øC. Then the emulsion breakdown (formation of a greasy layer) is checked visually. The nature of the continuous phase is investigated by a conductimetric method. DROPLET SIZE Before measurement, the emulsion is diluted in deionized water and the dispersion is slowly stirred in order to separate flocculated droplets. The average droplet diameter is measured using a Malvern Mastersizer light-scattering sizer. MEASUREMENT OF [3CD CONCENTRATION OF THE AQUEOUS PHASE The aqueous phase, separated by centrifugation (4200 g for 30 min), is filtered with a Merck Dynaguard-ME (0.2 lam) filter. The measure of the [3CD concentration in the clear aqueous phase is performed by Roquette Frbres, the [3CD supplier, by an HPLC method. RHEOLOGICAL PROPERTIES OF THE EMULSIONS A Carrimed CS 550-Rheo rheometer (cone diameter: 2 cm cone-plane angle: 1 ø) is used for measuring the flow threshold at 20øC, with a linear strain rise speed of 200 N/m2/