## 2 Materials and Methods
### Methods
#### 2.2.2 Determination of the Fatty Acid Composition of Oils by Gas Chromatography  
In order to determine the fatty acid composition by gas chromatography, fatty acids were converted to volatile methyl esters in accordance with PN-EN ISO 5509:2001 [18]. The gas chromatography apparatus YL6100 GC equipped with a flame ionization detector (FID) and a BPX 79 capillary column (filled with stationary phase, length 30 m, internal diameter 0.22 mm, film thickness 0.25 um) was used. Nitrogen was applied as the carrier gas. The following conditions were used: starting temperature 70 \({}^{\circ}\)C/0.5 min; then increasing the temperature from 70 \({}^{\circ}\)C to 160 \({}^{\circ}\)C at a rate of 15 \({}^{\circ}\)C/min; temperature rise from 160 \({}^{\circ}\)C to 200 \({}^{\circ}\)C at a rate of 1.1 \({}^{\circ}\)C/min; 200 \({}^{\circ}\)C/12 min; temperature rise from 200 \({}^{\circ}\)C to 225 \({}^{\circ}\)C at a rate of 30 \({}^{\circ}\)C/1 min; end temperature 225 \({}^{\circ}\)C/1 min. The detector temperature was 250 \({}^{\circ}\)C and the injector temperature was 225 \({}^{\circ}\)C. The fatty acids were then identified by comparing the retention times with FAME standard (Supelco 37 Component FAME Mix). For the quantitative analysis of fatty acids, the peak area in the chromatogram was determined and the percentage of a given acid was calculated [19]. The determinations were conducted in 3 replications. 2.3 Determination of the Distribution of Fatty Acids between the sn-2 and sn-1,3 Positions of Triacylglycerlycerols by Enzymatic Hydrolysis  
In order to determine the structure of triacylglycerlycerols, the method of partial hydrolysis of triacylglycerols with pancreatic lipase was used. For this purpose, 0.1 g of the tested oil was weighed, and then the following were added: 8 cm\({}^{3}\) of TRIS-HCl solution with concentration of 1 mol/dm\({}^{3}\), pH = 8; 0.5 cm\({}^{3}\) of 2.2% CaCl\({}_{2}\) solution; 0.2 cm\({}^{3}\) of 1% aqueous solution of bile salts. The sample was shaken for 30 s, 20 mg of pancreatic lipase was added and it was shaken again for 30 s. The sample was then incubated in a water bath at 40 \({}^{\circ}\)C for 10 min. In order to stop the reaction, 15 cm\({}^{3}\) of ethyl alcohol and 5 cm\({}^{3}\) of 6 mol/dm\({}^{3}\) hydrochloric acid were added. The sample was placed in the centrifuge for 5 min. The top organic layer was then removed. The obtained products were separated by preparative thin layer chromatography (TLC) using silica gel plates, and the chromatogram was developed in a chromatographic chamber. The composition of fatty acids in the sn-2 position of monoacylglycerolglycerols was determined by gas chromatography [19]. The comparison of the obtained data and the known initial profile of triacylglycerlycerols allowed determination of the percentage of fatty acids in the sn-1,3 position and fatty acids in the sn-2 position. The following formulas were used:  
\[\text{sn-1},3= \frac{3\times\left(\text{FA in TAGi}\right)-\left(\text{FA in sn-2 MAG}\right)}{2}\]  
\[\text{sn-2}= \frac{\left(\text{FA in sn-2 MAG}\right)\times 100\%}{3\times\left(\text{FA in TAGi}\right)}\]  
where:  
sn-1,3--content of a given fatty acid in sn-1 and sn-3 positions [%];  
sn-2--content of a given fatty acid in the sn-2 position [%];FA in TAGi--content of a given fatty acid in the initial TAG [%];  
FA in sn-2 MAG--content of a given fatty acid in sn-2 MAG [%]. 2.4 Assessment of Oxidative Stability of Oils by Means of Pressure Differential Scanning Calorimetry  
The time of induction of the oil oxidation reaction was determined by pressure differential scanning calorimetry with a TA Instruments DSC Q20 apparatus. For this purpose, 3-4 mg of the tested oil was weighed into an aluminum pan. The pan was placed in the pressure chamber with the reference sample, i.e., an identical empty pan. Measurements were carried out in an oxygen atmosphere at a pressure of approx. 1350 kPa. The samples were oxidized at 100 \({}^{\circ}\)C and 120 \({}^{\circ}\)C [20].