Full of beans: NMR spectroscopy confirms coffee

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  • Published: Jan 15, 2015
  • Channels: NMR Knowledge Base
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The daily grind

NMR spectroscopy has been used for some time to allow food regulators to distinguish between coffee beans by country of origin. Now an international team from Colombia and Germany has demonstrated that they can also use NMR spectroscopy to drill down to the specific region of origin within a country.

Next time you're whipping the froth off your skinny frappa mocha double-shot coffee, how can you be sure that the beans used to make it are the beans the packaging claims them to be? Well, nuclear magnetic resonance spectroscopy has been used for some time to allow food regulators to spot food fraud in various food and drink products. An international team from Colombia and Germany has demonstrated how to use NMR spectroscopy to identify adulteration or contamination of coffee beans based on country of origin, a useful tool in the fight against food fraud in a high-value market.

V.A. Arana, J. Medina and J Wist in the Chemistry Department at the Universidad del Valle, in Cali, Colombia, R. Alarcon and E. Moreno of Almacafé S.A., in Bogotá D.C., Colombia, and L. Heintz and H. Schäfer of of Bruker Biospin, in Rheinstetten, Germany, explain how food monitoring is vital in a global marketplace. Ensuring food quality standards are high and food fraud low can only be achieved on this scale through the development of rapid, efficient and straightforward analytical tools. One aspect of food assurance is to corroborate the country or region of origin of any given product label. Fingerprinting a sample with NMR is one way that this might be done with relative ease as adulterants or changes to samples will become immediately apparent from differences in the spectra of a verified sample and one that has been contaminated.

Arabica

The team has focused on one particular food product to ascertain whether or not NMR spectroscopy can be used to home in on country and region of origin: Arabica coffee beans (Coffea arabica). Small (less than three hectares) family farms in Colombia support half a million families through manual harvesting of these coffee beans and their eventual trade in the international marketplace. Half a century ago, the "100% Café de Colombia" program was initiated in an effort to, primarily, improve the quality of coffee bean production by guiding farmers to improved practices but also to promote the image of Colombian coffee abroad. Of course, products purportedly sourced in Colombia but contaminated with other types of, perhaps inferior, coffee, would do nothing for the farmers nor for the international image of the product.

The researchers point out that isotope ratio mass spectrometry (IRMS), electron spray ionization mass spectrometry (ESI-MS), gas chromatography–mass spectrometry (GC-MS), Raman spectroscopy and near-infrared spectroscopy (NIRS) have all been used with varying degrees of success and ease in the quality control of coffee beans and the detection of food fraud. NMR spectroscopy has also found application in testing honey, olive oil, wine, fruit juice and, indeed, coffee, specifically for the determination of the ratio of Arabica to Robusta (Coffea canephora var. Robusta) in samples) as well as to determine the country of origin of Arabica coffee.

Fingerprinting coffee stains

Now, the team has used proton NMR spectroscopy and a trained expert system for analysing the spectra to demonstrate how it can differentiate with 100% precision between Arabica coffees from different South American and Central American countries. The high-quality fingerprinting technique does not rely on deuterated solvents like the techniques developed by others, moreover, the process can be readily automated; a first in coffee extract analysis, the team reports in the journal Food Chemistry.

The team concedes that although their results are very promising, their current methodology is carried out in a very controlled manner that might not be achievable on a larger scale given budgetary and technical limitations. They add that they also need to assess the effects of different types of schemes on the NMR fingerprint as well as the effects of post-harvest yeast fermentation of coffee beans, which is increasingly common for high profile coffees, they add.

Related Links

Food Chem 2015, 175, 500-506: "Coffee’s country of origin determined by NMR: The Colombian case"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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