J. Cosmet. Sci., 65, 81–87 (March/April 2014) 81 Oxidative stability of cosmetic argan oil: a one-year study SAID GHARBY, HICHAM HARHAR, BADR KARTAH, DOMINIQUE GUILLAUME, IMANE CHAFCHAOUNI-MOUSSAOUI, ZAKIA BOUZOUBAA, and ZOUBIDA CHARROUF, University Mohammed V-Agdal, Rabat, Morocco (S.G., H.H., B.K., Z.C.), University of Reims Champagne Ardenne, Reims, France (D. G.), Universiapolis, Agadir, Morocco (I. C.-M.), and INRA-CRRA Agadir, Morocco (Z.B.). Accepted for publication February 23, 2014. Synopsis The objective of this work is to determine the chemical stability of cosmetic argan oil (INCI: Argania spinosa kernel oil). The methodology involves the repeated measurement over a 1-year period of the quality metrics used in the cosmetic industry: acid and peroxide value and specifi c absorbance. During this year, storage is performed at 40° or 25°C to assess the importance of temperature. In this latter case, oil samples have been either protected or exposed to sunlight. In addition, sterol and fatty acid composition is determined to attest argan oil chemical integrity over 1 year. Storage of argan oil at 40°C results in a rapid loss of quality. Stored at 25°C and protected from sunlight, argan oil quality is still satisfactory after 12 months according to the offi cial Moroccan norm, but storage should not be longer than 6 months to fulfi ll industrial standards. INTRODUCTION The recent worldwide success of edible argan oil is only challenged by the concomitant global success of cosmetic argan oil (INCI: Argania spinosa kernel oil, CAS: 223747-87-3) (1). Whereas edible argan oil, which constitutes the basic ingredient of the Amazigh diet (2), is mainly prized for its hypocholesterolemiant properties (3), so far, cosmetic argan oil is sought for its skin antiaging moisturizing and conditioning, and hair-protecting capac- ity, not to mention its nail strengthening or emollient properties (4). Consequently, cos- metic argan oil is included in various cosmetic formulations as shampoo, lotion, skin-care cream, ointment, and facial makeup. Because of its limited supply and unprecedented success, argan oil has become the most expensive oil in the world in 2011 (1). Edible and cosmetic argan oils are prepared by cold-pressing argan kernels (5). Pressing roasted ker- nels affords edible argan oil while unroasted kernels are used to prepare cosmetic argan oil that is very pale gold-colored and whose taste is slightly bitter. Edible argan oil is copper- colored and presents a hazelnut taste mostly resulting from the presence of volatile Address all correspondence to D. Guillaume at dominique.guillaume@univ-reims.fr and Z. Charrouf at zcharrouf@menara.ma.

JOURNAL OF COSMETIC SCIENCE 82 compounds formed during kernel roasting (6). Those volatile compounds, produced via oxidation and/or Maillard reaction, are present in very minute amounts but actively par- ticipate in the good preservation of edible argan oil (7) whose shelf life is estimated to about 2 years (8). Cosmetic argan oil whose moisture content is slightly higher than that of edible argan oil necessarily lacks these volatile compounds it presents a much shorter shelf life (7). For a while, cosmetic argan oil suffered with trust issues due to major adulteration mat- ters, making the cosmetic industry reluctant to use it. A large number of solutions are now available to solve adulteration problems (9–14). Even though food and cosmetic industries have fundamentally different requirements, the Moroccan Institute of Normalization only recognizes a single norm applicable to both argan oil types (15). In other words, offi cial specifi cations regarding cosmetic and edible argan oil are strictly similar. Consequently, when purchasing argan oil, cosmetic laboratories gener- ally use requirements that are more severe than those depicted in the offi cial norm (16). These are not only microbiological or hazardous fl ask-released chemical restrictions but re- sult from the absolute necessity for cosmetic formulations to respect the skin physiological parameters as well as the integrity of the other ingredients. Accordingly, the cosmetic in- dustry is particularly cautious concerning the presence of any source of free radicals or over- oxidation products (17) which requires argan oil peroxide value and E270 absorption below 10 meq O2/kg and 0.2 (16), respectively. Whereas the Moroccan norm stipulates a value below 20 meq O2/kg and 0.45 (15), respectively, for regular virgin argan oil. To identify the oxidative phenomena occurring in cosmetic argan oil during its storage, their kinetics, and to understand some of the cosmetic argan oil oxidation processes, we have periodically determined several physicochemical parameters of the same initial batch of cosmetic argan oil placed in different storage conditions. In light of our previous study on edible argan oil (8), one-third of the batch was kept at 25°C and exposed to sunlight, and two-thirds were kept at 25° and 40°C, respectively, and protected from sunlight. MATERIALS AND METHODS MATERIALS AND CHEMICALS Argan oil was prepared by women of the cooperative of Tiout (Taroudant county, Mo- rocco) using their current technology as previously described (18). Kernels were cold- pressed using a Komet DD 85 G press (IBG Monforts Oekotec GmbH & Co. KG, Mönchengladbach, Germany). All reagents used were of analytical or HPLC grade. 2,2,4-Trimethylpentane, heptane, and isopropanol used for chromatography, and cyclo- hexane used for extinction coeffi cient determination were purchased from Professional Labo (Casablanca, Morocco). Clear and brown glass bottles were purchased from Cfi mu sarl (Casablanca, Morocco). SAMPLE PREPARATION AND DISTRIBUTION Immediately after fresh-kernel pressing, cosmetic argan oil was distributed in 60-ml glass bottles. Samples were stored either at 5 ± 1°, 25 ± 2°, or in an oven at 40 ± 1°C. One half of the samples stored at 25°C were in clear glass bottles exposed to daylight,