## 3 Results and Discussion
### Concentration of Sterol Oxidation Products in Food Products
The highest content of 7-ketocholesterol was found in salami, containing 0.9 ug of this [PERSON] per 1 g of fat and the lowest in pork kabanos (0.21 ug/g fat), beef kabanos (0.16 ug/g fat), smoked bacon (0.05 ug/g fat) and poultry kabanos (0.03 ug/g fat) (Figure 3a,b). Summarizing, the total content of cholesterol oxidation products represented from 0.002 to 0.352% of oxidized cholesterol was found in analyzed samples. The highest percentage of oxidized cholesterol was found in pork kabanos--0.352%, then in smoked bacon--0.307%, and next in salami--0.119% of oxidized cholesterol. In canned pork, steamed bacon, and beef kabanos the percentage of oxidized cholesterol was as follows: 0.055%, 0.038%, and 0.035%, respectively[PERSON] A lower level of oxidized cholesterol was found in poultry kabanos--0.002%[PERSON] [PERSON] et al. stated that the ratio of cholesterol oxidation products to cholesterol was about 1% in meat products: fresh milk, yogurt, eggs (yolk), edam cheese, chicken breast meat, pork [PERSON], salmon, and cod [21][PERSON] The lower percentage of oxidized cholesterol observed in the current study could be due to preservatives added to the processed foods, e.g., antioxidants, or type of packaging, e.g., modified atmosphere, which is commonly used for sausages, e.g., kabanos, or other processed meat products, e.g., bacon, etc[PERSON]  
A statistically significantly higher content of total cholesterol oxidation products was found in products subjected to thermal processing; for example, raw beef contained 8.66 ug/g fat, while after thermal processing, this value increased to 30.06 ug/g fat [14]. In our previous research [16], in salami-type products, the following COPs were additionally determined, 58,6,6-epoxycholesterol, 5\(\alpha\),6\(\alpha\)-epoxycholesterol, and 25-hydroxycholesterol, and the total content of cholesterol oxidation products ranged from 6.9 to 7.9 ug/g of fat. The study also found an increase in the content of cholesterol oxidation products in meat after heat treatment in comparison to raw meat. Initially, the content of oxysterols in pork meat was 8.7 ug/g of fat, and after thermal treatment, it was 19.3 ug/g of fat. It was similar in beef meat: 6.4 ug/g of fat before thermal treatment and 25.9 ug/g of fat, after processing. [PERSON] et al. [14] describe the content of cholesterol oxidation products before and after thermal treatment in meat products, e.g., the total oxysterol content in a beef hamburger was 2.3 ug/g of fat, and after heating with microwaves, it was 12.3 ug/g of fat, and in a poultry hamburger, its content in raw meat was 4.0 ug/g of fat, and after frying with olive oil, it was 24.6 ug/g of fat. The study by [PERSON] and [PERSON] also presented the difference in the content of cholesterol oxidation products before and after the thermal process. In the pork and beef cutlets, the content of cholesterol oxidation products before thermal treatment was 8.7 and 6.4 ug/g of fat, respectively, and after thermal treatment, it was 19.3 and 25.9 ug/g of fat [16]. Only two cholesterol oxidation products were determined in the tested pastry products: 7\(\alpha\)-hydroxycholesterol and 7\(\beta\)-hydroxycholesterol. Phytosterol oxidation products were not determined in any of the tested products. The total content of cholesterol oxidation products was the highest in biscuits, and it amounted to 3.94 \(\upmu\)g/g fat (including 2.09 of 7\(\upalpha\)-hydroxycholesterol and 1.85 7\(\upbeta\)-hydroxycholesterol \(\upmu\)g/g fat), while the lowest in cereal cakes was 0.16 \(\upmu\)g/g fat, in which only 7\(\upalpha\)-hydroxycholesterol was determined (Figure 4). The content of oxysterols in the remaining cookies was 0.56 \(\upmu\)g/g in milk powder, 0.54 \(\upmu\)g/g in sweet dessert cakes (Figure 5), and 0.34 \(\upmu\)g/g fat in chocolate chip cookies.