## 1 Introduction  
Fax (_Linum usitatissimum_ L.) is an annual plant from the family Linaceae. There is no exact information on the origin of flax, since there are many wild species in many areas of the globe. Cultivated species are widely distributed almost everywhere with suitable conditions for their cultivation. The flax crop is grown under different conditions on various continents. In Europe, it is distributed in broad areas, but in the Alps, it reaches a height equal to that of rye. The leading producers are located in Northern and Southern Europe, Eastern Asia, Egypt, Algeria, Morocco, and Brazil. Fax seeds are a good source of a dietary fibers (about 28 g/100 g), soluble polysaccharides, lignans, phenolic compounds, vitamins (A, C, F, and E), and different mineral elements (phosphorus, magnesium, potassium, iron, copper, manganese, zinc, etc.). They are rich in proteins (about 20-30 g/100 g), lipids (about 40 g/100 g), and carbohydrates (about 29 g/100 g). According to some reports, the amount of vegetable oil in flaxseeds has been found to be (25-45%), respectively [1; 2; 3; 4]. The composition and quantities of fatty acids can vary and depend on growing conditions. \(\alpha\)-Linolenic acid predominates (34-65%), followed by oleic (16-24%) and linoleic (12.5-17%), while the quantities of saturated palmitic (3.0-6.0%) and stearic acid (3.0-7.1%) are lower [1; 2; 3; 4; 5; 6; 7; 8]. Flaxseed oil is rich in biologically active substances--sterols and tocopherols. They are present in the unsaponifiable fraction, which contains terpenic (sterols, tocopherols, tocopherols, tocopherols, carotenoids, carotenoids, etc.) and aliphatic (fatty alcohols, saturated and unsaturated hydrocarbons) compounds. They are significant for determining the nutritional value of the oil. According to [PERSON] [9] and [PERSON] [10], the amount of phytosterols in oils is low (0.2-0.4%). \(\beta\)-sitosterol is a main component of the sterol fraction (more than 50.0%), followed by campesterol, stigmasterol, and \(\Delta^{5}\)-avenasterol [11; 12; 13]. The reported amount of tocopherols is between 300 mg/kg and 700 mg/kg as \(\gamma\)-tocopherol predominates, and \(\alpha\)-tocopherol in minimal quantity can also be detected in the oil [9; 12; 14]. In turn, the extracted flaxseed oil is one of the most popular vegetable oils due to its multiple uses in medicine; in the industrial production of various products, such as paints, linoleum, varnishes, inks, and cosmetics, in the past [15; 16; 17]; and for nutritional purposes regarding the human diet. Flaxseed oil is a rich source of the essential fatty acids (EFAs) linoleic acid (\(\omega\)-6) and \(\alpha\)-linolenic acid (\(\omega\)-3), which regulate prostaglandandins synthesis, and hence, induce the wound healing process. Deficiency in EFAs results in phrynoderma or road skin, horny eruptions on the limbs, poor wound healing, etc. [1; 4; 8; 18; 19]. During the heat treatment of vegetable oils, undesirable processes such as oxidation, polymerization, etc., occur, which leads to the deterioration of their taste and nutritional qualities. Because flaxseed oil's unsaturated fatty acid composition is easily oxidized, it should be stabilized with different antioxidants, for example, butylhydroxytoluene or other synthetic products or plant extracts [8], or encapsulated [20]. The oil is rich in polyunsaturated fatty acids--the most important being linolenic (\(\omega\)-3) and linoleic (\(\omega\)-6) as the main ones. They have a good effect on health as food supplements and for preventing coronary heart disease [5; 21; 22; 23; 24; 25; 26]. Liquid components, including vegetable oils, are characterized by various physico-chemical parameters, such as pH, solubility, density, viscosity, surface tension, etc., and their determination is essential for the oil's application, storage and transportation. They are influenced by various factors--oil composition, temperature, pressure, etc. The saturated-to-unsaturated fatty acid ratio determines vegetable oils' viscosity.