OXIDATIVE STABILITY OF COSMETIC ARGAN OIL 85 stored at 25°C and sunlight protected, peroxide value reached a plateau after 10 months of storage. Such an event has as a consequence the 15 meq O2/kg limit value was never reached. It is also evidenced that after some months, the kinetic of FA peroxidation and of secondary oxidation product formation were similar. The peroxide value of sunlight- protected edible argan oil stored at 25°C has been shown to reach 10 meq O2/kg after 2 years (8). Therefore, our combined results clearly indicate cosmetic argan oil is much more sensitive to peroxide formation than edible argan oil. This not only emphasizes the critical importance of the Maillard’s compounds formed during roasting in argan oil overoxidation preservation but also demonstrates that to be introduced in cosmetics, cos- metic laboratories should not store argan oil more than 7 months at room temperature. In addition to a peroxide value determination, we also monitored primary oxidation product formation from extinction coeffi cient at 232 nm (E232) even though the cosmetic industry does not impose any rules regarding this analysis (Figure 2, full line). E232 under- went a particularly fast increase for cosmetic argan oil stored at 40°C, confi rming an impor- tant peroxide formation over a 1-year period. At 25°C, sunlight exposure favored primary oxidation product formation, although not as rapidly as at 40°C. Sunlight protection al- lowed to reduce the rate of formation of primary oxidation product, resulted in a plateau being reached after 8 months. We also determined the extinction coeffi cient at 270 nm (E270) to evaluate secondary peroxidation product formation (Figure 2, dot line). Because these oxidation products encompass highly chemically reactive compounds such as alde- hyde or ketones, a drastic limit of 0.2 is imposed by the cosmetic industry, whereas the limit of the Moroccan norm is 0.35. The 0.2 limit was reached after only 1 month for argan oil stored at 40°C. It was reached between April and June for samples stored at 25°C whether protected or not from sunlight. These measurements indicate that after 6 months of storage at 25°C, cosmetic argan oil is not suitable anymore to be introduced in cosmetic formula- tion according to industrial requirements, even though, in terms of Moroccan norm, the limit value is not reached after 1 year of storage at 25°C and using sunlight protection. Cosmetic argan oil properties result from its physicochemical properties and from its specifi c chemical composition (4). Main components, as unsaturated FA, and minor Figure 2. Extinction coeffi cient at 232 nm (full line, left axis) and 270 nm (dot line, right axis) of cosmetic argan oil stored at various temperatures as a function of time.

JOURNAL OF COSMETIC SCIENCE 86 components, as sterols, participate in argan oil cosmetic activity (4). In our physico- chemical analyses indicating a 6-month-limit for argan oil stored at 25°C, we compared the FA and sterol composition of argan oil just after pressing and after 6 months. No signifi cant difference was observed for sterol or FA composition after this period (Table I). Such chemical stability suggests that the dermocosmetic properties of argan oil are fully preserved during the fi rst 6 months of its storage when performed at 25°C. SUMMARY Cosmetic argan oil is often presented as possessing low preservation properties. Storage at various temperatures demonstrate that when argan oil is stored at temperatures up to 25°C its quality can be easily ascertained for 12 months according to the Moroccan norm, and for 6 months according to the cosmetic industry norm. Formation of oxidative spe- cies is the main reason for argan oil instability, far ahead from triglyceride hydrolysis or sterol loss. Storage of argan oil under inert atmosphere or/and at low temperature should increase argan oil shelf life if necessary. To increase argan oil shelf life, the addition of antioxidants could also be considered, but the resulting product would not satisfy the “extra virgin argan oil” labeling anymore. REFERENCES (1) T. J. Lybbert, A. Aboudrare, D. Chaloud, N. Magnan, and M. Nash, Booming markets for Moroccan argan oil appear to benefi t some rural households while threatening the endemic argan forest. Proc. Natl. Acad. Sci. USA, 108, 13907–13912 (2011). (2) Z, Charrouf and D. Guillaume, Should the Amazigh diet (regular and moderate argan-oil consumption) have a benefi cial impact on human health? Crit. Rev. Food Sci. Nutr., 50, 473–477 (2010). Table I Sterol and Fatty Acid Composition of Cosmetic Argan Oil Immediately after Cold-Pressing and after 6 Months (1 Year) of Storage Sunlight-Exposed or -Protected Initial 25°C Exposed Protected Sterol (%) Schottenol 46.6 ± 2.5 46.5 ± 3.9 (47.8 ± 4.1) 47.5 ± 3.5 (46.2 ± 2.5) Spinasterol 39 ± 2 36 ± 4 (38.1 ± 6.2) 37 ± 3 (40 ± 4) Stigma-7a 4.2 ± 0.8 5 ± 2 (4.1 ± 1.5) 5 ± 1 (4.3 ± 2.1) Stigma-8a 3.9 ± 0.6 4.1 ± 0.9 (3.8 ± 1.1) 3.8 ± 0.7 (4 ± 1) Campesterol 0.2 ± 0.1 0.1 ± 0.1 (0.2 ± 0.1) 0.2 ± 0.1 (0.2 ± 0.1) Fatty acid (%) Palmitic 13.2 ± 1.5 13.2 ± 1.8 (13.1 ± 2.1) 13.1 ± 2.5 (13.2 ± 1.8) Stearic 5.3 ± 0.4 5.6 ± 0.9 (5.5 ± 1.1) 5.2 ± 0.7 (5.7 ± 1.5) Oleic 48 ± 3 48 ± 4 (48 ± 6) 47 ± 4 (48 ± 4) Linoleic 33 ± 2 33 ± 2 (33 ± 4) 32 ± 2 (33 ± 4) Linolenic 0.1 ± 0.1 0.1 ± 0.1 (0.1 ± 0.1) 0.1 ± 0.1 (0.1 ± 0.1) a Stigma-7: Stigma-7,24-dien-3-ol, Stigma-8: Stigma-8,22-dien-3β-ol.