Benchtop NMR spectroscopy

Hi. My name’s Will Jakes. And I’m a former MChem student from the University of East Anglia. I carried out my final year research project at the Institute of Food Research using benchtop NMR spectrometer. Unlike their high field cousins, benchtop NMR spectrometers are small, robust, and much lower cost. They are based on a permanent magnet, and work without needing any cryogens. Edible oils are ideal samples to study using benchtop NMR, as good quality spectra are obtained quickly and easily from substances that are mainly composed of triglycerides. Composition values such as the amounts of mono or polyunsaturated fatty acids in the sample can be calculated directly from the spectra in a quick and accurate analysis.

My research project was also concerned with measuring triglycerides, but extracted from samples of meat. The project was conceived following a news story which broke early in 2013, would soon come to dominate the headlines – the discovery of horse meat in beef burgers sold in the UK and Ireland. In the days that followed, undeclared horse meat was detected in a range of other processed meat products. This led to millions of pounds worth of food being recalled from supermarket shelves across Europe, and substantial brand damage to the companies involved.

The crisis exposed the potential vulnerability of the meat supply chain to fraud and highlighted gaps in testing regimes which could potentially be filled by new, fast, and low-cost analytical methods to screen meats and verify their species. With this in mind, the Institute of Food Research carried out some exploratory experiments using benchtop NMR. The fat components in a range of ground meat samples were isolated using a simple extraction in chloroform. Over the course of my project, this method was refined and repeated on hundreds of meat samples from different animal species, including horse meat. NMR spectra were acquired using the 16-megahertz benchtop instrument called Pulsar, manufactured by Oxford Instruments. Collecting data is quick and simple.

The triglyceride solution in a thin glass NMR tube is inserted into the cavity in the centre of the spectrometer’s permanent magnet, which also houses the electronics that generate a radio frequency pulse, and record a free induction decay. The results obtained were both striking and convincing. Each of the different meats examined exhibited clearly different spectra. In the case of beef and horse, the spectral profiles were found to be entirely distinct. Even with natural variation, no overlap between the two types was found. And the test was 100% accurate in determining whether an extract originated from a piece of horse or a piece of beef.

Easy-to-use software to carry out mathematical analysis of the spectral data was developed at IFR to give a complete system in which to authenticate beef. From start to finish, the test takes a total of 10 minutes. This makes it an ideal and affordable approach for high throughput screening, or for pre-screening ahead of a more time-consuming DNA testing. So how is it that this NMR approach is so effective? Well, we know from everyday experience that beef and pork fat, say, are physically quite different from one another. This is mostly due to differences in their fatty acid compositions, which arise in turn from differences in their diets, digestive systems, and metabolism.

Benchtop NMR is a really effective way of measuring these fatty acid compositions. In it’s current form, the test is suitable for key points in the supply chain. For example, at meat wholesalers and processors, where incoming raw materials are in the form of frozen blocks of trimmings. And in fact, trials of the system have recently been carried out in the industrial setting of this kind, and with the results now undergoing evaluation.