## 1 Introduction  
Fats are one of the main sources of nutrients essential to human nutrition and proper functioning of the body. They supply energy, constituents of cell membranes, fat-soluble vitamins, antioxidants, and other biologically active substances [1]. Nonetheless, they are often associated with the risk of civilization diseases such as obesity, _diabetes mellitus_, and cardiovascular diseases. These problems, however, are not the result of the properties of fats themselves, but are rather caused by their excessive consumption, unbalanced intake of fatty acids, or inappropriate culinary processing (especially usage of cold-pressed oils for hot kitchen processes [2]. Complete exclusion of fat from diets can lead to deficits of fat-soluble vitamins, fluctuations in the level of hormones, or weakening of overall immunity. Edible fats and oils are the carriers of essential fatty acids, and vegetable oils are the primary source of these acids [3]. Fatty acids present in these oils are known to absorb sunlight. With absorption, their ability to react with oxygen improves so they become unstable and very active chemically. Therefore, the greatest enemy of these acids is light, which causes the destruction of their vital biological properties, which manifests in altered organoleptic properties, including bitter taste [4]. Flax seed oil is known as the richest source of the essential omega-3 acid \(\alpha\)-linolenic, which amounts to 50 to 62% of the total fatty acid content [3]. Positive effects of this fatty acid in the prevention and improvement of cardiovascular diseases, selected cancer types, rheumatoid arthritis, and autoimmune diseases have been reported [5]. Poppy seed oil is used in human nutrition and cosmetics, but it is also a raw material for the technical industry. The nutritional value of oil is based on the quantitative ratio of mono- and polyunsaturated fatty acids to saturated fatty acids. The dominant fatty acids in poppy seed oil are linoleic, oleic, and palmitic acids [4]. Steraric, palmitoleic, and \(\alpha\)-linolenic acids are less abundant. Grape seed oil has a high content of essential omega-6 acids, important for the synthesis of prostaglandin, which has an impact on the aggregation of blood platelets and inflammatory processes [6]. It has a strong antioxidant effect, due to the high content of vitamin E, which helps reduce the risk of arteriosclerosis. It has a positive effect on the reduction of low-density cholesterol and, on the contrary, increases the level of high-density cholesterol, thereby reducing the risk of developing cardiovascular diseases. It is also rich in \(\beta\)-sitosterol and \(\gamma\)-tocopherol [7]. Grape seed oil has proven to have great potential for use in the pharmaceutical and food industries [8]. The predominant fatty acids in walnut oil are linoleic, oleic, and linoleic acids. The proportions of these acids determine the nutritional and economic value of the oil, e.g., a lower amount of linoleic and linolenic acid in the oil will ensure a longer shelf life, while a higher amount of polyunsaturated fatty acids is desirable for their potential health benefits [9]. The optimal ratio between n-6 and n-3 polyunsaturated fatty acids is 4:1. Together with antioxidant substances such as tocopherols and phytosterols, unsaturated fatty acids help prevent diseases and maintain health [10]. The content of oil in milk thistle seeds is approximately 22% [9]. This crop is also used to produce edible oil that has a positive impact on human health. It was found that the oil is rich in unsaturated fatty acids, which make up 75.1% of the total amount of fatty acids [11]. Among the tocopherols contained in milk thistle seed oil, \(\alpha\)-tocopherol is the most abundant at 84.5%, while \(\beta\)-, \(\gamma\)- and \(\delta\)-tocopherol constitute 9.9%, 5.4%, and 0.2%, respectively [12].