J. Cosmet. Sci., 68, 159–172 (March/April 2017) 159 A comparative study of the rheological and sensory properties of a petroleum-free and a petroleum-based cosmetic cream FAN C. WANG and ALEJANDRO G. MARANGONI, Department of Food Science, University of Guelph, Guelph, ON, Canada, N1G 2W1. Accepted for publication July 21, 2016. Synopsis A petroleum-free skin cream was developed using food-grade ingredients. The rheological and sensorial properties of this petroleum-free skin cream were compared to a commercially available petroleum-based skin cream. Specifi cally, large-amplitude oscillatory shear (LAOS) characterization of the two skin creams was performed. The petroleum-free skin cream showed similar linear and nonlinear viscoelastic rheological properties, comparable skin hydration functions, and consumer acceptance as the commercially available skin cream. A schematic diagram aiming to correlate the physical and sensorial properties of skin cream was also proposed at the end of the work. Results of this work could provide the cosmetic industry necessary information for the development of alternatives for petroleum-based skin creams. INTRODUCTION A growing consumer preference toward sustainable and natural cosmetic products nowa- days has been driving the cosmetic industry to look for naturally derived replacements for petroleum-based products. Petrolatum and mineral oil have been widely used in skin creams and lotions because of their excellent moisture barrier function to prevent the skin from drying out (1). However, petrolatum and mineral oil can contain carcinogenic con- taminants such as polycyclic aromatic compounds if improperly refi ned. Thus, in Europe, these materials are classifi ed as carcinogenic if the full refi ning history is unknown (2). Additionally, petrolatum and mineral oil do not meet the standard of “natural” in cosmetics because they undergo chemical treatment during the refi ning process (1). Many attempts have been made to develop petroleum-free cosmetics, and our group has developed an oleo- gel using ethyl cellulose, food emulsifi ers, and plant oils, which has desirable properties in cosmetic applications and is effi cient in reducing water vapor transmission rate (3). In addition to this oleogel, a monoglyceride (MG)-structured emulsion, which was origi- nally developed as a low-fat shortening in baked goods (4,5), also showed desirable Address all correspondence to Alejandro G. Marangoni at amarango@uoguelph.ca.

JOURNAL OF COSMETIC SCIENCE 160 cosmetic properties when its water content was increased. This MG-structured emulsion contains approximately 5% (w/w) saturated MGs, 0.25% (w/w) coemulsifi er, 20% (w/w) oil, and 70% (w/w) water. Potassium sorbate is also added at 0.1% (w/w) as an antifungal agent. The structure of this MG-structured oil-in-water (o/w) emulsion has been well characterized by our group (6,7). It has a unique architecture where oil droplets are sur- rounded fi rstly by an MG monolayer and then alternating water and MG bilayers (4,6). Such onion-like structure allows this emulsion to entrap large amount of water within, thus providing desirable cosmetics properties such as semisolid spreadable texture and a skin moisturizing effect. MGs have polymorphic and mesomorphic properties (8–12). The hydrated lamellar phase of MGs is the desirable phase for this emulsion, because it provides the emulsion with desirable texture (6,13,14) and could signifi cantly increase the water content of the stra- tum corneum compared with nonlamellar MG structures (15). Additionally, the physical properties of this MG-structured emulsion are not largely affected by the type of oils therefore, a large variety of oil and oil-soluble active ingredients can be encapsulated within its structure (5,16,17). The stability of this MG-structured emulsion has also been examined and it is stable for up to 8 weeks at 45°C (14). Higher stability could be achieved with the use of higher content of coemulsifi er sodium stearoyl lactylate (SSL) and the addition of texture modifi ers such as xanthan gum (14). Previous work done on the characterization and evaluation of this MG-structured emul- sion only focused on its application in food systems. This work, therefore, is an interdis- ciplinary study and will evaluate cosmetic properties and consumer acceptance of the MG-structured emulsion, by comparing it with a commercially available petroleum- based cosmetic skin cream. In the development of cosmetic products, sensory evaluation is one of the most important methods used to evaluate skin feel and consumer acceptance. Properties of cosmetic lo- tions are affected by complex factors such as emulsifi er (18), emollient (19), thickener (texture modifi er) (20–23), water and oil content, and emulsion structure. Parameters in the sensory evaluation of skin lotions have been well established, where some common attributes include appearance, pickup, and rubout (24,25). The major drawback of sen- sory evaluation is that it is time consuming and expensive. In order to be more cost and time effi cient, alternative methods have recently been employed in the characterization of the behavior of skin care products. Rheology and texture analysis are two of the common physical measures in the characterization of physical properties of food products, and they have been applied in cosmetic science to help predict the sensory properties of cosmetic creams and lotions (21,24,26–28). Previous work has built up the relationship between some of the rheological param- eters and sensory properties in cosmetic creams, with emphasis on the viscosity and viscoelastic properties (23,27). In these works, the skin feel after the application of a skin cream was divided into two parts, primary skin feel and secondary skin feel, in order to correlate various rheological parameters with the sensorial properties (27). Primary skin feel describes how the product feels when removed from the container, and how hard to spread the product when rubbing onto the skin while secondary skin feel describes the sensation at the end of the application such as the oiliness, greasi- ness, and softness. Primary skin feel is correlated with the onset of fl ow and dynamic viscosity of a product, whereas secondary skin feel is correlated with its steady-state