J. Cosmet. Sci., 56, 175-182 (May/June 2005) Study of sensory properties of emollients used in cosmetics and their correlation with physicochemical properties MARIA EMMA PARENTE, ADRIANA GAMBARO, and GERARDO SOLANA, Cdtedra de Quimica Cosmetica (M.E.P., G.S.) and Secci6n Evaluaci6n Sensorial, Cdtedra de Ciencia y Tecnologia de Alimentos (A.G.), Facultad de Quimica, Universidad de la Republica, Montevideo, Uruguay. Accepted for publication February 28, 2005. Synopsis Eight liquid emollients (mineral oil, sunflower oil, squalane, decyl oleate, isopropyl myristate, octyldo- decanol, dimethicone, and cyclomethicone) were characterized by instrumental and sensory methods and evaluated to determine the relationship between sensory and instrumental measures. Sensory analysis was carried out by a panel of 14 assessors, who evaluated the following attributes: difficulty of spreading, gloss, residue, stickiness, slipperiness, softness, and oiliness. The physicochemical properties measured were spreadability (at one-half minute and at one minute), viscosity, and superficial tension. Data collected were statistically analyzed by analysis of variance (ANOVA), principal component analysis (PCA), and linear partial least squares regression analysis (PLS). In consideration of their physicochemical characteristics, the studied emollients were sorted into three groups, in which the silicones distinctly separate from the rest. Sensory characteristics enabled the discrimination of four groups of emollients where, besides the two silicones, isopropyl myristate was also differentiated. PLS revealed that emollient sensory attributes could be well predicted by instrumental measurements. INTRODUCTION The inclusion of emollients in cosmetic emulsions is a common practice, independent of the final use of the emulsion. In consideration of their action on the skin, emollients can be regarded as a replacement of natural lipids, as they contribute to water retention by the stratum corneum. They result in a smoother, more elastic, and lubricated skin, and impart a pleasant and comfortable skinfeel (1-3). Lipophyllic emollients offer a wide variety of sensations when applied to the skin (waxy, Address all correspondence to Marfa Emma Parente. 175

176 JOURNAL OF COSMETIC SCIENCE greasy, oily, dry, astringent, sticky, velvety, etc.) and may have great incidence on the sensory characteristics of the cosmetic emulsions in which they are included ( 4-6). Emollients also have major incidence on the physicochemical properties, such as con- sistency and spreadability, of the emulsions in which they are included. These charac- teristics are very important to achieve adequate efficacy and user acceptance of the products. In general, there are few bibliographical references about sensory evaluation of cosmetics and, particularly, of emollients. In 1971 Goldember and De la Rosa (4) found that it was possible to quantify the skinfeel of emollient cosmetics incorporated in a standard base by using a skinfeel index (SFI) (ratio of the initial slip of a product (scale of 1 to 5) to its total end feel (scale of 4 to 20). Perceived skinfeel attributes of creams and lotions (appearance, rub-in, absorption, appearance of skin, immediate and delayed afterfeel) have been evaluated by Aust et al. (7) using a trained descriptive panel. In 1991, Civille and Dus (8) used the skinfeel spectrum descriptive analysis (skinfeel SDA) method to characterize skin care products. They used strict protocols for manipu- lation and precisely defined terms to describe the qualitative properties and their relative intensities in each product. The evaluation process was divided into four categories: pick-up (firmness, stickiness, cohesiveness, peaking) rub-out (wetness, spreadability, thickness, absorbency) residual feel and appearance, immediate and after 20 minutes (glossy, sticky, slippery, oily, waxy, greasy). The aims of the present work were to: (a) characterize, from a sensory point of view, eight liquid emollients frequently used in cosmetic emulsions and (b) study the correlation between the sensory characteristics of the emollients and their physicochemical proper- ties. MATERIALS AND METHODS SAMPLES The following emollients were used: mineral oil (MO), sunflower oil (SO), squalane (SQ), decyl oleate (DO), isopropyl myristate (1PM), octyldodecanol (OD), dimethicone (DM), and cyclomethicone (CM). The selected emollients have different chemical structures, including silicones (linear and cyclical), hydrocarbons (saturated and unsaturated), esters, branched-chain fatty alcohols, and natural oils. Sunflower oil, a common oil in Uruguay, is a substance of cosmetic interest due to its high content of unsaturated fatty acids (9,10). SENSORY ANALYSIS Selection of attributes and training of judges. Initially the emollients were presented to a group of 14 sensory judges experienced in the evaluation of food, who lacked experience in cosmetic products. They were asked to describe the sensations experienced when emollients were spread on their skin and the sensations they perceived when they touched and observed the emollient film formed over the skin immediately after appli- cation. The descriptors to be employed in the evaluation of emollients were selected by