Oils and Fats

13C-NMR spectra of seed oils and of processed fats provide useful information about their fatty acid compositions. In a study of 15 fats, Gunstone showed that it was possible to demonstrate the presence or absence of milk fats from signals associated with butyric acid, lauric oils (containing octanoic acid), partially hydrogenated fats (olefinic and allylic signals), and of linoleic and linolenic acid (1993a). He also reported a more detailed study of hydrogenated fats (1993b). These points have been discussed more fully in the 1992 review cited in the contents page. Lie Ken Jie et al. (1996) and Sacchi et al. (1995) have also used 13C nuclear magnetic resonance to study a range of domestic fats.

NMR spectra have been used to detect adulteration of vegetable oils with castor oils based on characteristic signals of ricinoleic acid at 132.4 [C10], 125.6 [C9], 71.3 [C12], 36.8 [C13], and 35.4 [C11]. As part of a study of olive oil cultivars Vlahov et al. (1999) have given a full description of the spectrum of soybean oil. It has 43 signals related to saturated, oleic, linoleic, and linolenic acids in the α and β chains (see Table 1). Miyake et al. (1998) analysed 17 oils in terms of saturated, oleic, linoleic, and linolenic acids. More information on chemical shifts of some vegetable oils is given in the web page on Regiospecific Analysis.

Table 1. Chemical shifts (ppm) of saturated, oleic, linoleic, and linolenic glycerol esters from a study of soybean oil (Vlahov et al., 1999)
 SaturatedOleicLinoleicLinolenic
 αβαβαβαβ
2 34.00   33.98 34.14 33.98 34.14 33.98 34.14
3 24.82   24.82 24.85 24.82 24.85 24.82 24.85
4     29.06 29.03 29.06 29.03 29.06 29.03
5 29.27   29.16 29.18 29.16 29.18 29.16 29.18
6 29.47              
7                
8     27.17 27.17 27.17 27.17 27.17 27.17
9     129.65 129.62 129.90 129.88 130.13 130.10
10     129.94 129.95 128.04 128.06 127.73 127.74
11     27.17 27.17 25.56 25.56 25.56 25.56
12     29.76 29.76 127.88 127.87 128.18 128.17
13     29.32 29.32 130.10 130.10 128.22 128.22
14     29.53 29.53 27.17 27.17 25.51 25.51
15 29.37   29.32 29.32 29.34 29.34 127.10 127.10
16 31.93   31.91 31.91 31.52 31.52 131.84 131.84
17 22.68   22.67 22.67 22.57 22.57 20.54 20.54
18 14.08   14.08 14.08 14.04 14.04 14.25 14.25
                 
C1 signals are not reported; saturated acids were not identified in the β position; unresolved peaks appear at 29.68, 29.66, 29.61, and 29.10; many signals overlap and the same shifts occur several times in this table.

References

  • Gunstone, F.D. Information on the composition of fats from their high-resolution 13C nuclear magnetic resonance spectra. J. Am. Oil Chem. Soc., 70, 361-366 (1993a).
  • Gunstone, F.D. The composition of hydrogenated fats by high resolution 13C nuclear magnetic resonance spectra. J. Am. Oil Chem. Soc., 70, 965-970 (1993b).
  • Husain, S., Kifayatullah, M., Sastry, G.S.R. and Raju, N.P. Quantitative determination of castor oil in edible and heat-abused oils by 13C nuclear magnetic resonance spectroscopy. J. Am. Oil Chem. Soc., 70, 1251-1254 (1993).
  • Lie Ken Jie, M.S.F., Lam, C.C., Pasha, M.K., Stefanov, K.L. and Marekov, I. 13C Nuclear magnetic resonance spectroscopic analysis of the triacylglycerol composition of some margarines. J. Am. Oil Chem. Soc., 73, 1011-1017 (1996).
  • Mannina, L., Luchinat, C., Emanuele, M.C. and Segre, A. Acyl positional distribution of glycerol tri-esters in vegetable oils: a 13C-NMR study. Chem. Phys. Lipids, 103, 47-55 (1999).
  • Miyake, Y., Yokomizo, K. and Matsuzaki, N. Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy. J. Am. Oil Chem. Soc., 75, 1091-1094 (1998).
  • Sacchi, R., Addeo, F., Musso, S.S., Paolillo, L. and Giudicianni, I. A high resolution 13C-NMR study of vegetable margarine. Ital. J. Food Sci., 7, 27-36 (1995).
  • Vlahov, G., Shaw, A.D. and Kell, D.B. Use of 13C nuclear magnetic resonance distortionless enhancement by polarization transfer pulse sequence and multivariate analysis to discriminate olive oil cultivars. J. Am. Oil Chem. Soc., 76, 1223-1231 (1999).