The repeatability of the measurement is depicted in Figure 4a by overlay- ing the acquired spectra. The zoom on the bis-allylic region shows good agreement between the three trials. The bis-allylic absolute integration mean and median are reported along with standard deviation for the three trials (Figure 4b). Once prepared, this linear calibration curve can be used within unknown samples of EVOO to determine how much, if any, soybean oil was added to the sample within a few percent.
a b
Summary Benchtop NMR spectroscopy has been demonstrated to be an effective tool for identifying and quantifying soybean adulteration in EVOO samples. Although benchtop NMR affords less resolution than traditional NMR spectrometers, there is still sufficient resolution to ac- curately and repeatedly identify differences in fatty acid composition. Additionally, these spectra can be used to easily assess the presence of other contaminants. For example, the aromatic peaks of yellow aniline would be very apparent in the range of 6.0–8.0 ppm. We are now looking to: 1) expand this method to other EVOO adulterants, 2) examine a wider range of EVOO samples, 3) better understand the accuracy and utility of NMR for comprehending the origin and purity of samples and 4) expand benchtop NMR techniques to support quality assurance in other areas of food science.
Reference 1. Knothe, G. and Kenar, J.A. Determination of fatty acid profile by 1 NMR spectroscopy. Eur. J. Lip. Sci. and Tech. 2004, 106(2), 88–96.
Figure 4 – a) Overlaid 1 H NMR spectra of three trials of EVOO doped at
35% soybean oil. b) Mean, median and standard deviation (STD) for the average for the trial samples.
H
Susanne D. Riegel is manager of application chemistry, Nanalysis Corp., Bay 4 4500 5 St. NE, Calgary, Alb., Canada, T2E 7C3; tel.: 1.855.667.3239; e-mail:
susie.riegel@nanalysis.com;
www.nanalysis.com
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