HEMP-SEED AND OLIVE OILS 231 dynamic viscosity (11, expressed in mPa s) was calculated from equation 2. The mea­ surements were repeated three times for each oil sample and were conducted at 25°C. v=Kt 11 = Kpt (1) (2) where K is the viscometer constant (0.01053), p is the oil density, and t is the oil flow time through the capillary. DETERMINATION OF REFRACTIVE INDEX (RI) The refractive index is an important parameter in terms of quality it can reveal adul­ teration if its value is outside the accepted range (1.4672-1.4679). The refractive index was determined with an Abbie refractometer: the oil was placed in the prism cell, whose refractive index was known. The index was determined directly by reading it from the scale. DETERMINATION OF ACIDITY INDEX The acidity index I A is the amount of KOH, in milligrams, required to neutralize the free fatty acids present in 1 gram of fat. It is considered an important analytic parameter, as it indicates the state of conservation of a fat and its quality. This is because the presence of free acids in a fat increases as triglycerides become hydrolyzed, and this process reduces quality. Acidity may also be expressed as the percentage content of oleic acid. The acidity index was determined as follows: 5 g (m 1 ) of oil was dissolved in 25 ml of a mixture of absolute ethyl alcohol and diethyl ether in equal volumes, previously neutralized with a solution of O. lM KOH, using 0.5 ml of phenolphthalein (R 1 ) as indicator. The dissolved oil was then titrated, adding n 1 ml of KOH 0.1 M until the pink color of phenolphthalein persisted for at least 15 seconds. The acidity index was calculated from equation 3. One milliliter of KOH N/10 corresponds to 0.0282 g of oleic acid thus the percentage of oleic acid was calculated from equation 4. 0.0282 X n Oleic acid%= 100 X ---- DETERMINATION OF PEROXIDE NUMBER (3) (4) Peroxides are the primary products of fat lipoperoxidation hence determination of the amount of peroxide present in an oil is another analytical method to evaluate its quality. Peroxides are not only oxidizing agents they also promote the release of iodine from

232 JOURNAL OF COSMETIC SCIENCE potassium iodide, and for this reason the peroxide number can be determined by io­ dometric titration. The peroxide number is the number of active oxygen milliequiva­ lents present in 1000 g of fat mass, which correspond to the milliequivalents of iodine released from potassium iodide titrated with sodium thiosulphate solution. Degraded oils may have peroxide numbers well below expectations, since the first step of lipoperoxidation, auto-oxidation, may already be completed, and all the hydroperox­ ides derived from this step may have been transformed into secondary volatile unpleas­ ant-smelling compounds. The peroxide number was determined as follows: Five grams (m2) of oil was placed in a 250-ml Erlenmeyer flask, and the flask was closed with an emery cap. Thirty milliliters of chloroform/acetic acid (2:3) mixture was then added to the oil sample under stirring. After complete dissolution, 0.5 ml of potassium iodide saturated solution (R2) was added. The solution was stirred for one minute, and 30 ml of distilled water was added. The mixture was then titrated with 0.01 M sodium thiosulphate solution, added slowly under continuous stirring until the yellow color disappeared. Five milliliters of starch indicator was then added and a dark blue color appeared. The titration continued during addition of sodium thiosulphate solution and vigorous stirring until the blue color disappeared (n2 ml of 0.0lM sodium thiosulphate solution). A control titration was carried out on a reference sample under the same conditions. The final volume (n 3 ml of 0.0lM sodium thiosulphate solution) employed for the control titration must be less than 0.1 ml. The peroxide number, expressed in milliequivalents of oxygen per 1000 grams of fat, is calculated from the following equation: 10(n2 - n 3 ) Peroxide number = --- ­- m2 DETERMINATION OF CONJUGATED DIENES AND TRIENES (5) Spectrophotometric examination can provide information on the quality of a fat, its state of conservation, and any changes produced in it by technological processes. Absorption at the wavelength 232 nm is due to the presence of conjugated diene systems, while trienes absorb at 262, 268, and 274 nm. The normal spectrum of a non-rancid virgin oil shows no absorption at these wavelengths. Oil was dissolved in 1-butanol, spectropho­ tometrically pure in the range of wavelengths considered. Extinctions at the various wavelengths were then detected with reference to pure solvent. The absorbence values were expressed as specific extinctions E 1 % 1cm ( the extinction of 1 % solution of the fat in the specified solvent, at a thickness of 1 cm), conventionally indicated by K, also referred to as the "extinction coefficient." In accordance with the official method in the EEC regulations, spectrophotometric analysis of oil involves determining the specific extinction at a wavelength of 232 nm and determining the variation in specific extinc­ tion, which is given by the following equation: (6)