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,

OXIDATIVE STABILITY OF COSMETIC ARGAN OIL 83 whereas the other half was in brown glass bottles and stored in a cupboard. Head-space volume for each bottle was 3.5 ml. Analyses were performed just after pressing, then after 1 month of storage, and then every 2 months over 1 year. ANALYSIS OF OILS Physicochemical parameters were determined using procedures that we have already re- peatedly described (7,8,18,19). In brief, acid and peroxide values were determined using International Standard Organization methods ISO-660 (20) and ISO-3960 (21), respec- tively. Results are expressed in mg KOH/g and meq O2/kg, respectively. Iodine index was determined using the International Standard Organization method ISO 3961 (22) or calculated using Carreras’ method (23). Results are expressed in gI2/g. Ultraviolet ab- sorption was determined at l 232 and 270 nm using the International Standard Organiza- tion method ISO 3656 (24). Fatty acid (FA) composition was determined using the International Standard Organization method ISO 5508 (25). A gas chromatograph (Var- ian CP-3800, Varian Inc., Middelburg, The Netherlands) equipped with a FID and a CP- Wax 52CB column (30 m × 0.25 mm i.d. Varian Inc.) were used. The carrier gas was helium, and the total gas fl ow rate was 1 ml/min. The initial and fi nal column tempera- ture was 170° and 230°C, respectively. Temperature was increased by steps of 4°C/min. The injector and detector temperature was 230°C. Data were processed using Varian Star Workstation v 6.30 (Varian Inc., Walnut Creek, CA). Results are expressed as the relative percentage of each individual FA present in the sample. Sterol composition was deter- mined using the International Standard Organization method ISO 6799 (26) using a Varian 3800 instrument equipped with a VF-1 ms column (30 m and 0.25 mm i.d.) and using helium (fl ow rate 1.6 ml/min) as carrier gas. Column temperature was isothermal at 270°C, and injector and detector temperature was 300°C. Injected quantity was 1 μL for each analysis. Data were processed using Varian Star Workstation v 6.30 (Varian Inc.). STATISTICAL ANALYSIS Values reported in tables and fi gures are the means ± S.E. of three replications. The sig- nifi cance level was set at p = 0.05. Separation of means was performed by Tukey’s test at the 0.05 signifi cance level. RESULTS AND DISCUSSION CHANGES IN ACID AND PEROXIDE VALUES AS A FUNCTION OF TIME AND STORAGE CONDITION Variations in acid and peroxide value as a function of time for the three evaluated storage conditions are presented in Figure 1. Cosmetic industry requires an acid value below 4 mg KOH/g (16). Such value corresponds to the “extra virgin” or “fi ne virgin” labels of argan oil and excludes the “ordinary virgin” and “lampant” quality according to the of- fi cial norm (15). Cosmetic argan oil presented an initial acid value of 0.5 mg KOH/g, a low value fully in accordance with our previous results (18). Acid value of cosmetic argan oil stored at 25°C did not signifi cantly change over 12 months whether or not protected