Acyl positional distribution of glycerol tri-esters in vegetable oils: a 13C NMR study

A novel approach to the rapid assignment of 13C NMR spectra of major components of vegetable oils such as avocado, mango kernel and macadamia nut oils

“…GC analysis of the oils indicated that apricot kernel, avocado pear, grapeseed, macadamia nut, mango kernel and marula oils contained the same major fatty acid components, namely oleic acid, palmitic acid, linoleic acid and stearic acid found in olive oil, although palmitoleic acid not detected in any olive oil samples was observed to be present in macadamia nut and avocado pear oil in significant amounts. With the exception of tripalmitolein, the 13 C NMR spectra of the other triacylglycerols present in the six vegetable oils have previously been assigned by Mannina et al [10] The full assignment of the 13 C NMR spectrum of a sample of pure tripalmitolein (Fig. 2) was carried out by methodologies given by Mannina et al [10] for other triacylglycerols, and comparison of chemical shift trends observed for mainly triolein (Table 1).…”

“…With the exception of tripalmitolein, the 13 C NMR spectra of the other triacylglycerols present in the six vegetable oils have previously been assigned by Mannina et al [10] The full assignment of the 13 C NMR spectrum of a sample of pure tripalmitolein (Fig. 2) was carried out by methodologies given by Mannina et al [10] for other triacylglycerols, and comparison of chemical shift trends observed for mainly triolein (Table 1). With the aim of developing a rapid method with which to determine the major triacylglycerols present in apricot kernel, avocado pear, grapeseed, macadamia nut, mango kernel and marula oils using 13 C{ 1 H} NMR spectroscopy we initially investigated the use of the procedure developed for mainly olive oils [10] which involves the addition of standard triacylglycerols Table 2.…”

“…2) was carried out by methodologies given by Mannina et al [10] for other triacylglycerols, and comparison of chemical shift trends observed for mainly triolein (Table 1). With the aim of developing a rapid method with which to determine the major triacylglycerols present in apricot kernel, avocado pear, grapeseed, macadamia nut, mango kernel and marula oils using 13 C{ 1 H} NMR spectroscopy we initially investigated the use of the procedure developed for mainly olive oils [10] which involves the addition of standard triacylglycerols Table 2. Assignment of 13 C NMR resonances of the major fatty acid residues in olive oil Chemical shift (ppm) Literature assignments [3,4,13] Section Assignment Position on glycerol backbone Chemical shift (ppm) measured Vlahov et al [3] Sacchi et al [4] Shaw et al [13] Chemical shift (ppm) Literature assignments [3,4,13] Section Assignment Position on glycerol backbone Chemical shift (ppm) measured Vlahov et al [3] Sacchi et al [4] Shaw et al [13] (triolein, tristearin, etc.)…”

“…Approximately 100 µl of each oil in 700 µl of CDCl 3 with TMS as reference was used for NMR analysis at 25 • C. 13 C NMR spectra were run on a 400 MHz Varian Unity Inova NMR spectrometer operating at 100 MHz for 13 C. Acquisition parameters similar to those recommended by Mannina et al [10] were used for collecting the 13 C NMR spectra: number of points 256 K; spectral width 195 ppm; relaxation delay: 7 s; acquisition time 4.5 s. When processing, a line-broadening of −0.092 and Gaussian enhancement of 0.7 was used to optimize the resolution of the spectra. The precision of the procedure is estimated by the average half height of the resonances in the crowded region which is at most 0.7 Hz (0.007 ppm).…”

“…The conventionally used method for the full assignment of 13 oils is by means of standard addition (spiking) of the vegetable oil with a standard triacylglycerol. [10] Comparison of the resulting 13 C NMR spectra of the unspiked and spiked vegetable oil leads to the assignment of the 13 C resonances in the NMR spectrum of the different fatty acid components present in the vegetable oil. Besides this method having some practical disadvantages, we found that it was not possible to achieve a full, unambiguous assignment of the 13 C NMR spectra of the desired oils using this technique.…”