## 3 Results and Discussion
### FTIR Spectra Interpretation of Edible Fixed Oils  
The analyzed infrared spectra contain fundamental and characteristic bands whose frequencies and intensities can clearly determine the relevant functional groups in the investigated oils. The assignment of the absorption bands of ATR-FTIR spectra of edible fixed oils at the spectral range of 3300-500 cm\({}^{-1}\) (Figure 1) was performed on the basis of data given in the literature. The bands at 3640-3530 and 3300-3400 cm\({}^{-1}\) are associated with the nonbonded and bonded O-H stretching vibrations, respectively [40]. The bands at 2954, 2924, and 2954 cm\({}^{-1}\) are ascribed to the asymmetric and symmetrical C(sp\({}^{3}\))-H stretching vibrations of methyl- and methylene groups of lipids, whereas the bands at 1462 and 1377 cm\({}^{-1}\) are related to their bending vibrations [20; 41; 42]. The strong band at 1743 cm\({}^{-1}\) has been assigned to the C=O stretching vibration of ester groups in triglycerides [20; 43]. The bands at 3008 and 1654 cm\({}^{-1}\) are attributed to the C(sp\({}^{2}\))-H and C=C(cis) stretching vibrations, respectively, while the bands at 1417 and 1396 cm\({}^{-1}\) are attributed to the C-H bending vibrations of cis-ofelnic groups [20; 43]. The band at 966 cm\({}^{-1}\) is assigned to the -HC=CH- (trans) out-of-plane bending vibrations, whereas the bands at 914, 866, and 721 are attributed to the -HC=CH- (cis) out-of-plane bending vibrations [44; 45; 46]. The band at 846 cm\({}^{-1}\) corresponds to C-H bending vibrations of para-substituted aromatic rings [40]. The bands at 1238, 1159, and 1118 cm\({}^{-1}\) are associated with the asymmetric and symmetrical stretching vibrations of the C-O bond of the ester group [13; 20; 43; 45], whereas the bands at 1099 and 1027 cm\({}^{-1}\) are attributed to the C-O stretching vibrations in secondary and primary alcohols, respectively [40].  
Although the FTIR spectra of most of the edible fixed oils appear similar, minor differences exist in the specific band intensities at characteristic wavenumbers of edible oils spectra (Table S4) due to the variation in their composition. More specifically, the relative intensity of the band at 3008 cm\({}^{-1}\) depends on the oil composition, as oils with a high proportion of polyunsaturated fatty acids show higher values in this band than those with a high proportion of monounsaturated fatty acids. This finding was clearly evidenced by [PERSON] et al. [45], who implemented the changes in the absorbance at 3006 cm\({}^{-1}\) (A3006) and in the ratio of the maximum heights of the bands at 3006 and 2925 cm\({}^{-1}\) (A3006/A2925) in order to detect the adulteration of extra virgin olive oil by the addition of soybean oil.  
Intensity variations at wavenumbers associated with monounsaturated bonds (3008 cm\({}^{-1}\), 1654 cm\({}^{-1}\), 1417 cm\({}^{-1}\), and 721 cm\({}^{-1}\)) are related to the fatty acid composition of the oils. Oils rich in monounsaturated fatty acids (MUFA), such as hazelnut, almond, avocado, plum, pomeranate, mustard seed, and apricot oils, exhibit lower intensities at these wavenumbers, reflecting their higher percentage of oleic acid, a predominant MUFA. On the other hand, oils rich in polyunsaturated fatty acids (PUFAs), such as evening primrose, chia seed, walnut, pine cone, and linseed oils, exhibited higher intensities, reflecting their higher concentrations of linoleic acid or \(\alpha\)-linolenic acid.