## 4 Discussion
The lower values of oil oxidative stability may be explained by differences in terms of the adopted measurement parameters. Based on the available literature, differences in terms of surfactant ingredients and oil composition lead to varied responses to water content and the formation of various physical surfactant structures in vegetable oil [58]. The resulting effects may be positive, but, in most cases, the presence of phospholipids in vegetable oils triggers oxidation, negatively affecting the smell and taste of the product [58]. In the course of refining vegetable oil, phosphorus, as well as other active ingredients such as fatty acids, monoglycerides, and diglycerides, are removed in the so-called degumming process [59]. However, in cold-pressed oil, the presence of phosphorus affectsoxidation and contributes to the formation of colloidal aggregates and sediments [60]. The eventual content of phosphorus in vegetable oil depends on the type of seeds, conditions of their storage, moisture content, and processing method. As follows from numerous publications, seeds of, e.g., rape or soya contain considerably more phosphorus than the oils analysed in this study. As posited by [PERSON] and [PERSON] [61], the level of this element can range from 132 to 224 mg\(\cdot\)kg\({}^{-1}\) depending on the initial moisture content in the seeds. In his research, [PERSON] [62] demonstrated that the content of phosphorus in soybean oil can be within the range of 448-1286 mg\(\cdot\)kg\({}^{-1}\). The iodine number indicates the degree of fatty acids' saturation and the oil's oxidative stability, which in turn influences the economic viability of such products [63]. The rancidification of oils poses potential health risks, including an increased risk of cancer and inflammation, due to the formation of toxic and reactive oxidation products [64]. The iodine number measured for the analysed oil samples was within the range of typical values for commercially available seed oil products--118-123 g l\(\cdot\)100 g\({}^{-1}\)[65]. In the fuel industry, it is accepted that the desirable level of FFA and water content as well as the acid number should be below, respectively, 0.06% wt., 0.5% wt., and 1 mg KOH\(\cdot\)g\({}^{-1}\) oil [66]. As posited by [PERSON] and [PERSON] [67], the presence of water in raw oil material can reduce the FAME conversion ratio and cause saponification during transesterification reactions. Depending on the particular biological, meteorological, agricultural, and handling factors, the content of fatty acids (FFA) can vary considerably. As observed by [PERSON] et al. [51], the content of FFA in borage oil can correspond to any value between 2.7 and 10.5% depending on the method of obtaining the oil. One should aim to minimise the presence of free fatty acids in the oil as they reduce the product's commercial value. The purification of raw borage or milk thistle oil is important not only due to customer preferences but also due to its indisputable impact on the economic viability of production [23; 68]. As follows from our results, the analysed oil samples were within the commercial ranges. Specifically, the content of free fatty acids in milk thistle and borage oils was, respectively, 5.2 and 1.9%. Another parameter analysed in our study pertained to a group of compounds described as antioxidants. They increase the durability of fats by preventing rancidification resulting from the oxidation of unsaturated fatty acids. One group of primary natural antioxidants is composed of octopherols. Due to their high bioactivity, tocopherols and toctorienols are usually generally described as vitamin E and associated with the effects of dilating blood vessels and inhibiting blood coagulation. The antioxidative properties of oils are inherited from their chemical components, such as polyunsaturated fatty acids, sterols, tocopherols, and polyphenols [69]. The content of sterols may be influenced by the geographical location of cultivation, differences between cultivars, and the maturity of fruit [70].