1H NMR multisuppression approach for rapid detection and quantification of acyl groups and fatty acids supporting cyclopropane structures, either natural or generated during severe heating

This study has demonstrated the usefulness of ¹H Nuclear Magnetic Resonance (¹H NMR) multisuppression to investigate the potential occurrence of acyl groups/fatty acids supporting cyclopropane structures (AG/FA-3C) in commercial edible oils. An array of virgin and refined oils from 13 botanical origins was acquired and their ¹H NMR spectra, particularly the upfield region, studied. Although not previously described in edible oil spectra, several highly shielded signals corresponding to AG/FA-3C could be easily detected and quantified. Some of them were associated with cyclopropane-containing saturated AG/FA of natural origin resulting from plant metabolism. This was the case of lactobacillate or dihydrosterculate, whose characteristic quadruplet at -0.33 ppm was only found in rapeseed and cottonseed oil samples, being thus potential useful markers of their botanical origin. By contrast, other highly shielded proton signals were related with modified polyunsaturated AG/FA generated during severe heating. Indeed, these latter were only visible in the spectrum of the edible oils rich in polyunsaturated acyl groups if refined. Moreover, the profile of signals appearing between -0.4 and 0.5 ppm differed in the case of linoleic or linolenic-rich oil thermodegradation. The employed ¹H NMR approach enabled to gain insight into the composition of commonly consumed edible oils, providing information about these rare lipid components in a simple and fast way, without any chemical modification of the sample prior analysis. Additionally, in the case of polyunsaturated oils, the study of the upfield region of the ¹H NMR spectrum may be useful for a rapid discrimination between virgin and refined samples.