Quantitative analysis of partial acylglycerols and free fatty acids in palm oil by C-13 nuclear magnetic resonance spectroscopy

The chemical shifts, spin-lattice relaxation times (T-1), and one-bond C-H coupling constants of the glycerol carbons of mono-, di-, and triacylglycer ols in CDCl3 solution are presented and discussed. The glycerol carbons hav e low T-1 values (<1.0 s) and full nuclear Overhauser effect and also exhib it broader linewidths than the aliphatic carbons, suggesting that the glyce rol carbons are at or near the T-1 minimum for the dipole-dipole relaxation mechanism. Therefore, for quantitative measurement of the composition of p artial acylglycerols (relative to the triacylglycerols) in palm oil, the nu clear magnetic resonance (NMR) spectrum of the beta-carbons, which lie excl usively in the region delta 68.3-72.1 ppm, should preferably be acquired at medium or low magnetic fields and at an elevated temperature in order to e nsure that the condition for extremely narrow spectral lines is satisfied. The chemical shifts and spin-lattice relaxation times of the aliphatic C-2 and C-3 carbons and of the carbonyl carbons (C-1) of acyl groups present in palm oil are also presented and discussed. The presence of free fatty acid in the palm oil is easily detected and quantified in the spectrum of the a liphatic carbons. The presence of partial acylglycerols in palm oil can als o be detected and/or quantified in the NMR spectra of the C-2 and the carbo nyl carbons. The quantitative analysis of the glycerol carbons of a known m ixture of acylglycerols obtained by using this method is presented.