## 3 Results
At the same time, the bands corresponding to saturated esters, i.e., C-C(=O)-O are also found between 1240 and 1160 cm\({}^{-1}\)--in our case, at approximately 1230 cm\({}^{-1}\). Meanwhile, vibrations of this type corresponding to unsaturated esters tend to be located at considerably lower frequencies. The characteristic O-C-O band associated with primary alcohols tends to appear within the range from 1090 to 1020 cm\({}^{-1}\), and was present in our case at 1093 cm\({}^{-1}\). For secondary alcohols, the band is typically found with the maximum at \(\sim\)1100 cm\({}^{-1}\); in the described case, it was present as an enhancement in  
Figure 1: FTIR spectra for the analysed samples of borage oil (black line) and milk thistle oil (red line), measured in the spectral range from 800 to 3200 cm\({}^{-1}\). The spectra were measured at room temperature. the band with the light maximum at 1137 cm\({}^{-1}\). Both mentioned ester types are present in triglyceride molecules. In turn, the band with the maximum at approximately 1230 cm\({}^{-1}\) is often associated exclusively with the out-of-plane deformation vibrations originating from the methylene group. Further regions represented in Table 9 and Figure 1 correspond to other vibrations characteristic of food ingredients. Firstly, there is the region with the maximum at ~1458 cm\({}^{-1}\), and, secondly, at ~1315 cm\({}^{-1}\) (as band widening, Figure 1). The former vibrations (~1458 cm\({}^{-1}\)) originate from the methyl groups in the aliphatic chains of the analysed oils. The band with the maximum at ~905 cm\({}^{-1}\) present in both oil samples can be attributed to the stretching vibrations of _cis_-substituted olefin groups, which may be additionally enhanced by the vibrations of the vinyl group. The infrared spectra of the analysed oil samples were fairly similar, albeit not without certain discrepancies that seem fairly characteristic and therefore analytically useful. Another characteristic area of vibrations corresponds to the band maximum at ~1741 cm\({}^{-1}\) and originates from the stretching vibrations of the C=O group. On the shorter wavelength side, this band is enhanced with the maximum at ~1703 cm\({}^{-1}\) corresponding to the vibrations of another carbonyl group, this one present primarily in acid groups. In turn, the band with the maximum at ~1646 cm\({}^{-1}\) represents the stretching vibrations of the -C=C-group (_cis_-transformation). A very characteristic region is also found in the band with the maximum at 1458 cm\({}^{-1}\) (already mentioned above), originating from the deformation vibrations of -C-H groupings in -CH\({}_{2}\) and -CH\({}_{3}\) groups (scissor vibrations). Moving on to longer-wavelength regions, one should also mention the =C-H stretching vibrations (_trans_-transformation) with the maximum at ~3066 cm\({}^{-1}\) (Table 9), originating from the vibrations of triglyceride fractions. In turn, for the stretching vibrations of =C-H in the _cis_-configuration, characteristic vibrations are observed with the maximum at ~3005 cm\({}^{-1}\) (Figure 1 and Table 9). The bands with the maxima at 2951 and 2852 cm\({}^{-1}\) correspond to the stretching vibrations of -C-H in -CH\({}_{3}\), CH\({}_{2}\), present in the aliphatic groups in triglycerides.