## Results
### ATR-FTIR-MIR Spectra Fingerprints  
Edible oils contain mainly triacylglycerlycerols, including three long chain fatty acids attached via ester links. The IR regions of 2956-2853, 1740 cm\({}^{-1}\) are attributed to the fatty acid chain length and the absorption of free fatty acids (FFAs) occurring within the range of 1720-1700 cm\({}^{-1}\), which is used to estimate the hydrolysis of triglycerides to FFAs [22]. At higher wave numbers (3535 cm\({}^{-1}\)), but also at approx. 723 cm\({}^{-1}\), the increased absorption intensity indicates the oxidation to alcohols or secondary oxidized products [6, 8]. The fingerprint region from 1500-900 cm\({}^{-1}\) is generally used to identify their authenticity: the out-of-plane bending vibrations of isolated trans double bonds ranges between 967-969 cm\({}^{-1}\), while those of cis double bonds occur at approximately 914 cm\({}^{-1}\). The degree of unsaturation of  
Figure 1: Typical spectral fingerprints of six authentic oils absorbing in the Vis region (360–700 nm): (a)—Pumpkin oil; (b)—Hempesed oil; (c)—Linseed oil; (d)—Soybean oil; (e)—Sea buckthorn oil; (f)—Olive oil. oils can be detected through characteristics of cis and trans peaks at 3006 and 968 cm\({}^{-1}\), respectively, while a second band at 975 cm\({}^{-1}\), is associated also to secondary oxidation products (aldehydes and ketones with trans-double bonds). The ratio of absorptions at 3006/2925 cm\({}^{-1}\) was used to evaluate the extra virgin olive oil (EVOO) adulteration [51]. Fresh oils show a weak band at 1645 cm\({}^{-1}\), which is associated with stretching vibrations of C=C _cis_-olefins, which decreases after oxidation, concomitant with the appearance of a new band at 1627 cm\({}^{-1}\) due to the presence of unsaturated aldehydes and ketones. Concomitantly, an increase in absorption at 1746 cm\({}^{-1}\) is associated with the carboxyl group of FFAs and with a new peak at 1721 cm\({}^{-1}\), associated with the carbonyl group of aldehydes [52]. The ATR-FTIR-MIR spectra specific to each oil from each group (I to VIII) were recorded on the whole domain (650-3600 cm\({}^{-1}\)) as well as in the fingerprint region (1800-650 cm\({}^{-1}\)). Figure 2 represents comparatively the spectra registered for sea buckthorn oils (SBO1-SB4) at both regions). Figure S1 (Supplementary Materials) shows comparatively, for all oils, the spectra corresponding to the fingerprint region (1800-650 cm\({}^{-1}\)), which is considered more relevant for the authenticity confirmation [51]. The dominant peak in the spectra of all eight oil groups were located at 1743 cm\({}^{-1}\), corresponding to C=O stretching of fatty acids and esters (whose absorption intensity was normalized at value 1) followed by peaks which were allocated to 19 different subdomains, as presented in Table 3. The most intense peaks (considering the mean intensity values) were located at 2922-2924 cm\({}^{-1}\), 1159-1161 cm\({}^{-1}\), 2852 cm\({}^{-1}\), 719-721 cm\({}^{-1}\), 1097 cm\({}^{-1}\), 1234-1236 cm\({}^{-1}\) and 1460-1462 cm\({}^{-1}\). Significant differences between peak intensities were noticed at 2925 and at 2854 cm\({}^{-1}\), corresponding to antisymmetric and symmetric stretching vibration of methylene and methyl groups, while the band at 723 cm\({}^{-1}\) was assigned to both CH\({}_{2}\) rocking and bending vibrations of cis-disubstituted olefins. Specific absorption intensities were noticed at 3008-3009 cm\({}^{-1}\), especially in hempseed oils, corresponding to the stretching vibration of olefinic double bonds and explained by its highest degree of unsaturation. In the fingerprint region, the stretching vibrations of aliphatic and olefinic functional groups were observed.