Quantitative13C NMR method using the DEPT pulse sequence for the detection of olive oil adulteration with soybean oil

The polarization transfer method DEPT (distortionless enhancement by polarization transfer) was employed to set up a quantitative method to detect olive oil adulteration by seed oils, in particular soybean oil. The DEPT pulse sequence promotes the transfer of polarization from ‘concentrate spins =1H’ to ‘dilute spins =13C’ via scalar coupling interaction. This improves the signal-to-noise ratios in the 13C NMR spectra which would have to be acquired for quantitative purposes, under conditions of NOE suppression that reduce dramatically the carbon-13 resonance intensities. The resonance intensities of unsaturated carbons, C-9 for oleyl and C-10 for linoleyl and linolenyl chains, were used to detect olive oil adulteration by addition of soya oil at different levels. Calibration graphs based on a linear relationship between resonance intensities and soybean oil concentration were obtained. The limits of detection of the method were determined for each acyl chain.