Food and Beverage
by Susanne D. Riegel
Determination of Olive Oil Adulteration With 60-MHz Benchtop NMR Spectrometry
W
hile the health benefits of extra virgin olive oil (EVOO) are well documented, the purity of any specific batch remains highly debatable. The great demand for EVOO, paired with the rela- tively high production costs, has incentivized unlawful adulteration, rendering EVOO one of the most fraudulent foods. Although EVOO is typically diluted with cheaper oils, includ- ing soybean and corn, the addition of more deleterious diluents (e.g., yellow aniline) have also been reported. Centralized regulatory agencies and analytical methods have looked for reliable protocols with which to identify and even quantify instances of economic adul- teration. This has included the use of GC and/ or hyphenated mass spectrometry techniques (e.g., LC-MS).
a
Proton nuclear magnetic resonance spectros- copy (1
H NMR) offers an attractive alternative to
these more cumbersome analytical methods. Benefits include facile and repeatable sample preparation, simplified data analysis and versa- tile multicomponent screening. 1
H NMR is not
limited to a specific temperature, solvent or flow protocol. Instead, each spectrum contains resonances of every hydrogen-containing com- ponent within a sample, and every component has an equal response factor. This means that the relative concentration of each component can be assessed directly without the need for elaborate calibration methods.
Despite the potential benefits of introducing 1 H
NMR into a regulatory environment, the large physical size of traditional NMR spectrometers
b
paired with the capital required to purchase and maintain these instruments has made incorporation of this technique into food sci- ence largely unrealistic. Recent advances in permanent rare earth magnet technology and the development of a new class of benchtop NMR spectrometers have begun to alleviate these barriers. Benchtop NMR spectrometers are typically easier to use and more affordable than their high-field counterparts. They are compact enough to be introduced into any standard laboratory environment. Although the resolution they offer is lower, benchtop spectrometers have sufficiently homogeneous magnetic fields to accurately speciate and quantitate. This paper highlights the efficacy of benchtop NMR technology for the quantifica- tion of soybean oil content in EVOO.
Figure 1 – Stacked 60-MHz 1
the appropriate resonance. The peak integral regions are defined as: carboxylic acid (COOH) (δ 10.50–12.00), olefin (CH=CH) (δ 4.92–5.67), bis-allylic (=CH-CH2
-CH=) (δ 2.50–3.05), allylic/alpha-C (=CH-CH2
H NMR spectra for: a) saturated and b) unsaturated fatty acids. The corresponding functional groups are labeled above -alkyl or O=C-CH2
) (δ 1.75–2.50) and alkyl (-CH2 /-CH3 ) (δ 0.46–1.75 ppm). (Reproduced with
permission from Chemical & Engineering News;
http://www.heterobetainas.uah.es/intranet/REVISTA%20CHEM&ENG%20NEWS/cen20140602- EUR-dl.pdf)
AMERICAN LABORATORY • 16 • MARCH 2015
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