60 MHz 1H NMR spectroscopy for the analysis of edible oils

T. Parker, E. Limer, A.D. Watson, M. Defernez, D. Williamson, E. Kate Kemsley

Abstract
We report the first results from a new 60 MHz 1H nuclear magnetic resonance (NMR) bench-top spectrometer, Pulsar, in a study simulating the adulteration of olive oil with hazelnut oil. There were qualitative differences between spectra from the two oil types. A single internal ratio of two isolated groups of peaks could detect hazelnut oil in olive oil at the level of ∼13%w/w, whereas a whole-spectrum chemometric approach brought the limit of detection down to 11.2%w/w for a set of independent test samples. The Pulsar’s performance was compared to that of Fourier transform infrared (FTIR) spectroscopy. The Pulsar delivered comparable sensitivity and improved specificity, making it a superior screening tool. We also mapped NMR onto FTIR spectra using a correlation-matrix approach. Interpretation of this heat-map combined with the established annotations of the NMR spectra suggested a hitherto undocumented feature in the IR spectrum at ∼1130 cm−1, attributable to a double-bond vibration.

To download the “open access” paper, follow the link: http://www.sciencedirect.com/science/article/pii/S0165993614000387

60 MHz 1H NMR Spectroscopy of Triglyceride Mixtures

A. Gerdova, M. Defernez, W. Jakes, E. Limer, C. McCallum, K. Nott, T. Parker, N. Rigby, A. Sagidullin, A. D. Watson, D. Williamson and E. K. Kemsley

Abstract
Edible oils and fats consist almost entirely of triglycerides, thus triglycerides are of great economic and nutritional importance. Triglycerides are esters of glycerol comprising a glyceride backbone with three fatty acids. These three acyl residues need not be the same, thus edible oils and fats naturally exhibit diverse triglyceride compositions. There are numerous ways of analysing the triglyceride content of oils and fats however the presence of hydrogens in the different environments allows for proton NMR. Here, the authors outline recent results on triglyceride mixtures obtained using a new, low-field 1H NMR spectrometer called Pulsar. The Pulsar is based on permanent magnets rather than the superconducting magnets standard in modern high-field instruments. Any technique capable of analysing triglyceride mixtures is therefore able to establish key compositional properties of pure oils and fats and may be able to detect the addition of one oil to another. Using these approaches, low-field 1H NMR offers a viable method for testing the authenticity of meat and the detecting the adulteration of edible oils with one another.

From the book: Magnetic Resonance in Food Science : Defining Food by Magnetic Resonance

To download the paper, follow the link: http://pubs.rsc.org/en/content/chapter/bk9781782620310-00017/978-1-78262-031-0#!divabstract

Evaluation of a Benchtop Cryogen-Free Low-Field 1H NMR Spectrometer for the Analysis of Sexual Enhancement and Weight Loss Dietary Supplements Adulterated with Pharmaceutical Substances

Guilhem Pagès, Anna Gerdova, David Williamson, Véronique Gilard, Robert Martino, and Myriam Malet-Martino

Abstract
Nuclear magnetic resonance (NMR) spectroscopy is a unique tool for detection, structural characterization, and quantification of compounds in complex mixtures. However, due to cost constraints, NMR is rarely used in routine quality control (QC) analysis. The recent release of benchtop cryogen-free low-field NMR spectrometers represents a technological break in the NMR field. In this paper, we evaluated the potential of a benchtop cryogen-free 60 MHz spectrometer for uncovering adulteration of “100% natural” sexual enhancement and weight loss dietary supplements. We demonstrated that the adulterant(s) can readily be detected in ≈20 min of recording after a very simple and rapid sample preparation. We also showed that the quantification by the internal standard method can be done on the low-field NMR spectrometer and leads to results similar to those obtained with high-field NMR. Considering the cost and space efficiency of these spectrometers, we anticipate their introduction in QC laboratories as well as in governmental agencies, especially in the field of fraud detection.

To download the “open access” paper, follow the link: http://pubs.acs.org/doi/abs/10.1021/ac503699u

Authentication of beef versus horse meat using 60 MHz 1H NMR spectroscopy

W. Jakesa, A. Gerdova, M. Defernez, A.D. Watson, C. McCallum, E. Limer, I.J. Colquhoun, D.C. Williamson, E.K. Kemsley

Abstract
This work reports a candidate screening protocol to distinguish beef from horse meat based upon comparison of triglyceride signatures obtained by 60 MHz 1H NMR spectroscopy. Using a simple chloroform-based extraction, we obtained classic low-field triglyceride spectra from typically a 10 min acquisition time. Peak integration was sufficient to differentiate samples of fresh beef (76 extractions) and horse (62 extractions) using Naïve Bayes classification. Principal component analysis gave a two-dimensional “authentic” beef region (p = 0.001) against which further spectra could be compared. This model was challenged using a subset of 23 freeze–thawed training samples. The outcomes indicated that storing samples by freezing does not adversely affect the analysis. Of a further collection of extractions from previously unseen samples, 90/91 beef spectra were classified as authentic, and 16/16 horse spectra as non-authentic. We conclude that 60 MHz 1H NMR represents a feasible high-throughput approach for screening raw meat.

To download the “open access” paper, follow the link: http://www.sciencedirect.com/science/article/pii/S0308814614018391