# Raman Spectroscopy and 2 DCOS Analysis of Unsaturated Fatty Acid in Edible Vegetable Oils
## 3 Results and Discussion  
Figure 1 presents the Raman scattering spectra of the seven vegetable oil samples A-G. For each sample, the spectrum was obtained from the average of five random spots. All these samples show characteristic vibrational bands at 1080 cm\({}^{-1}\), 1265 cm\({}^{-1}\), 1300 cm\({}^{-1}\), 1440 cm\({}^{-1}\), 1655 cm\({}^{-1}\), and 1750 cm\({}^{-1}\). The band at 1080 cm\({}^{-1}\) can be assigned to (C-C) stretching of the (CH\({}_{2}\))\({}_{n}\) group; the band at 1265 cm\({}^{-1}\) can be assigned to (=C-H) deformation of _cis_(R-HC=CH-R); the band at 1300 cm\({}^{-1}\) can be assigned to (C-H) bending twist of the CH\({}_{2}\) group; the band at 1440 cm\({}^{-1}\) can be assigned to (C-H) scissoring of CH\({}_{2}\); the band at 1655 cm\({}^{-1}\) can be assigned to (C=C) of _cis_(RHC=CHR); and the band at 1750 cm\({}^{-1}\) can be assigned to (C=O) stretching of RC=OOR [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. These peaks are the common characteristic vibrational bands of almost all edible vegetable oils. Among the common vibrational bands of vegetable oils observed in Figure 1, the bands at 1265 cm\({}^{-1}\) and 1655 cm\({}^{-1}\) are correlated with vibration of the carbon-carbon double bond within the acid chain. Thus, comparing the intensity ratios of these two characteristic vibrational bands with other bands which are not correlated with vibration of the double bond could be helpful to investigate the UFA content in vegetable oils. In our analyses, the relative intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) are investigated. For comparison, the relative intensity ratio  
Figure 1: Raman spectra of the seven vegetable oil samples: (**A**) Golden Dragon Fish sunflower seed oil; (**B**) Fortune corn oil; (**C**) Golden Dragon Fish corn oil; (**D**) Luhua peanut oil; (**E**) Huilerie Loued olive oil; (**F**) Olivoila olive oil; (**G**) Luhua olive oil. Each spectrum is \(y\)-shifted for clarity. of 1440 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) is also studied, these two bands are correlated with vibration of single carbon-carbon bond. Figure 2 shows the relative intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\), 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\), and 1440 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) as a function of total UFA content in the seven vegetable oil samples. These relative intensity ratios were calculated from the averaged spectra presented in Figure 1. At first thought, it would be expected that with increasing the UFA content in vegetable oils, the intensity increase of the bands at 1265 cm\({}^{-1}\) and 1655 cm\({}^{-1}\) would be more significant than that of the bands at 1300 cm\({}^{-1}\) and 1440 cm\({}^{-1}\). Thus, when the UFA content increases, the relative intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) would also increase, while the relative intensity ratio of 1440 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) would not change. As can be seen in Figure 2, the relative intensity ratio of 1440 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) indeed does not depend on the UFA content. However, the correlation of intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) with the UFA content is contradictory to the expectation. Even with the same UFA content, the intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) in one sample could be about twice that of those in another sample. This suggests that the relative intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) are not proportional to the UFA content. In Figure 3a, b, the intensity ratios of 1655 cm\({}^{-1}\) to 1440 cm\({}^{-1}\) and 1265 cm\({}^{-1}\) to 1300 cm\({}^{-1}\) as a function of the content of PUFA and MUFA are plotted, respectively.