J. Cosmet. Sci., 56, 227-251 Guly/August 2005) Hemp-seed and olive oils: Their stability against oxidation and use in 0/W emulsions S. SAPINO, M. E. CARLOTTI, E. PEIRA, and M. GALLARATE, Dipartimento di Scienza e Tecnologia def Farmaco, Universita degli Studi di Torino, via Pietro Giuria No. 9, 10125 Turin, Italy. Accepted for publication April 4, 2005. Synopsis Hemp-seed oil has several positive effects on the skin: thanks to its unsaturated fatty acid (PUPA) content it alleviates skin problems such as dryness and those related to the aging process. We present a comparative study of hemp-seed and olive oils, determining some physicochemical indices and evaluating their stability against oxidation. The peroxide value of hemp-seed oil was below 20, the threshold limit for edible oils. Hemp-seed oil was less stable against peroxidation than olive oil, but MDA and MONO assays showed its stability to be above expectations. The chlorophyll contained in extra virgin olive oil had a higher photo­ stability than that contained in hemp-seed oil, possibly due to the larger amount of antioxidant in the olive oil. A certain amount of Vitamin E was found in hemp-seed oil. Since quality analyses indicated that hemp-seed oil is relatively stable, emulsions were prepared with the two oils, and their stability and rheological characteristics were tested. Some of the resulting gel-emulsions were suitable for spraying on the skin. INTRODUCTION Hemp (Cannabis sativa 1.) is one of the oldest and most versatile plants (1-3). Docu­ mentation of its use dates back as far as the 28th century B.C., and it likely to have been used even earlier the fiber was used for textiles and the seeds for food. The existence of its botanical relative, marijuana (cannabis varieties containing psychoactive substances) did not enhance the status of the plant. Since the late 1930s many Western countries have prohibited its cultivation due to the presence of the phytochemical drug component 0-9-tetrahydrocannabinol (THC). Then, in the late 1980s and early 1990s, hemp was rediscovered today only varieties containing less than 0.3% THC in their flower por­ tions can legally be farmed in Canada and the European Union, whereas marijuana flowers typically contain between 3% and 20%. In addition to its nutritional value, hemp-seed has other health benefits, including lowering cholesterol and high blood pressure. Hemp seeds are a rich source of essential Address all correspondence to M. E. Carloni. 227

228 JOURNAL OF COSMETIC SCIENCE fatty and amino acids and contain other essential nutrients, such as the antioxidant vitamin E, minerals, and lecithin. Essential oil is one of the many products that may be obtained from hemp: it contains many volatile compounds, mainly monoterpenes, ses­ quiterpenes, and other terpenoid-like compounds that can be isolated by steam distil­ lation. Several factors influence the yield and quality of hemp essential oil, including weather and harvesting techniques (4). The fatty-acid spectrum of hemp-seed oil is the cause of its nutritional value: compared to other unrefined edible oils, hemp-seed oil contains a very high percentage of essential fatty acids (EFA). More importantly, a high proportion (15% to 25%) is omega-3 alpha-linolenic acid, only found in significant quantities in a few other commonly used cooking oils, such as soybean and canola oils. In hemp-seed oil, the monounsaturated oleic acid contributes 10% to 15 % , and total saturated fatty acids account for 9% to 11 % of the total fatty acids. It also contains small percentages of several other polyunsaturated fatty acids (PUFAs) that play important roles in human metabolism most notable are gamma-linolenic acid (GLA, 18:3 omega- 6) and stearidonic acid (18:4 omega-3), whose content varies considerably with variety and growing conditions. The fat-soluble compounds of the vitamin E complex, tocoph­ erols and tocotrienols, are other important constituents of hemp-seed oil compared to other cold-pressed and unrefined vegetable oils-olive, sunflower, canola-it has a moderate to high content of vitamin E compounds. Typical levels are 100 to 150 milligrams per 100 grams of oil, predominantly gamma-tocopherol. This makes hemp­ seed oil a valuable source of vitamin E, one to two tablespoons meeting daily require­ ments. Finally, unrefined hemp-seed oil also contains moderate amounts of several other beneficial or even essential constituents, such as phytosterols, phospholipids, carotenes, and several minerals including calcium, magnesium, and potassium. Besides its nutritional benefits, hemp-seed oil has a number of positive effects on the skin: clinical studies have shown that PUFAs can alleviate or even resolve some skin problems, such as dry skin (5). Moreover, clinical trials with GLA supplementation have demonstrated a gradual improvement in the symptoms of a topical eczema and acne. The rediscovery of hemp-seed oil has been accompanied by advertising campaigns for body-care products containing it, by the American and European companies that have developed and promoted related products since the early 1990s. Hemp-seed oil in body-care products protects the skin by reducing dryness and may slow the skin's aging process. Hemp is an eco-friendly crop requiring no biocides and little fertilizer in comparison with cotton, for which it is an excellent substitute. Industrial hemp products can also be substituted for products derived from fossil fuels, such as synthetic fibers (textile and rope), plastics and fuel, and wood-based products including paper and particle board (6). Hemp-seed oil's high PUFA content and its high omega-3: omega-6 ratio are the main reasons for its health benefits however, the same factors cause instability and mean that the product requires careful quality control throughout the production process since unsaturated fatty acids react with free radicals and oxygen to create numerous oxidation products. This gradual oxidation of fatty acids is called rancidification: oils turn rancid faster if exposed to oxygen, heat, and especially light. However, it has also been shown by differential scanning calorimetry (DSC) that hemp-seed oil has high kinetic stability during heating and cooling (7). Microwave treatment shifts the melting range of oils to