New method detects coffee adulteration

Are you sure the coffee you’re drinking is the one it says on the label? High-quality, expensive arabica coffee may be adulterated with cheaper robusta coffee for financial gain, which is why researchers from the Quadram Institute have developed a new technique to detect contamination.

The price difference between arabica coffee and robusta coffee is not only down to taste, but also because robusta plants are higher yielding and easier to grow. However, once they have been roasted and ground, it is difficult to distinguish between the two types.

Identifying undeclared blends relies on detecting the chemical 16-O-methylcafestol, or 16-OMC, which is found in robusta but not in arabica. But this method is expensive and can take up to three days, making large-scale surveillance impractical.

Instead, researchers from the Analytical Sciences Unit used a benchtop NMR spectrometer from Oxford Instruments to detect 16-OMC, which uses radio waves and strong magnets to get detailed information about the molecular composition of a sample. This method reduced the time taken to process samples to 30 min, and is sensitive enough to detect just 1% robusta in an arabica/robusta blend.

“This is an important milestone for detecting fraud in coffee, as 1% is the generally accepted cut-off between trace contamination, which might be accidental, and more deliberate adulteration for economic gain,” said Dr Kate Kemsley from the Quadram Institute, who led the research.

The new sensitivity revealed that arabica does in fact contain low levels of 16-OMC, so rather than testing for its presence, they devised software to assess whether the level was above a certain threshold.

After testing 60 retail samples of ‘100% arabica’ coffees sourced worldwide, they found six of them were suggestive of adulteration with another coffee.

“It was immediately obvious using our test that there were several suspicious samples, producing results that were consistent with the presence of substantial amounts of robusta — far more than would be expected through unavoidable contamination,” explained Dr Kemsley.

The researchers estimated there is a 5–20% prevalence of fraud for ground roast coffee products claiming to be 100% arabica.

Therefore, consumers may be paying premium prices for a product they are not receiving. Better surveillance techniques, such as the NMR detection method, will help reassure consumers about the authenticity of their products and ensure farmers receive a fair price for their produce.

Giles Chapman, Head of Intelligence at the Food Standard Agency’s National Food Crime Unit, said: “We’re always keen to understand how scientific advances expand the range of tools which can be used to validate the authenticity of food products sold to UK consumers. This piece of work has generated some interesting insights which we will be looking to explore further.”

The research was funded by the Biotechnology and Biological Sciences Research Council and published in the journal Food Chemistry.

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