Fourier transform Raman spectroscopy was employed for structural analysis of triacylglycerols and edible oils. Raman spectra sensitively reflected structural changes in oils. Even slight structural fluctuation between triacylglycerols and free fatty acids led to obvious differences in Raman bands as shown by C-O-C stretching from 800 to 1000 cm-1 and the band at 1742 cm-1. Structural difference in geometric isomers was easily distinguished as proved by C=C stretching at 1655 cm-1 (cis) shifting to 1668 cm-1 (trans) and by =C-H in-plane bending at 1266 cm-1 in cis disappearing in the trans isomer. Raman intensity at 1266, 1302, and 1655 cm-1 changed concomitantly with the change of double-bond content in oils. It showed that FT-Raman was capable of precisly reflecting the content of double bonds in oils. A linear correlation with high consistency between the Raman intensity ratio (ν1655/ν1444) and the iodine value was obtained for commercial oils. Based on the results, FT-Raman spectroscopy proved itself a simple and rapid technique for oil analysis since each measurement could be directly completed in 3 min without any sample modifications.
Yih-Ming Weng, Ru-Hui Weng, Chin-Yin Tzeng, and Wenlung Chen, "Structural Analysis of Triacylglycerols and Edible Oils by Near-Infrared Fourier Transform Raman Spectroscopy," Appl. Spectrosc. 57, 413-418 (2003)