May 08

How do you give coffee authentication an extra shot?

With a high market value and commercial importance coffee is in the top 10 products most at risk of food fraud.

A recent paper by the Government Chemist team at LGC, and the Institute of Global Food Security in Queen’s University, Belfast (QUB), tackles the question of where and how to analytically check the coffee supply chain.

Analysing the results of several studies in the scientific literature Dr Michael Walker and a team from QUB have produced key instructions for probing the authenticity of coffee.

Michael Walker, Referee Analyst, Government Chemist Programme, LGC, said, “Coffee is one of the most widely traded tropical products and is produced in over 50 developing countries around the world. Because of its high market value and commercial importance it is increasingly the target of adulteration by dilution of cheaper materials. This fraud can take many forms, from swapping cheaper materials – e.g. coffee husks, chicory, cereal grains, woody tissue, cocoa or soya beans, acai berries or exogenous sugars – or substituting the more expensive Arabica species with cheaper beans.

M Cup Coffee IStock 000012881314Medium[1]“Adulteration of coffee has been around for a long time. Indeed, one of the first large scale samplings of foodstuff performed by the Laboratory of the Government Chemist, which was set up in 1842, was of coffee for adulteration and ceased in 1863. At that time adulterants included chicory, and, later, orange pips and iron oxide, burnt sugar or caramel, locust beans, ground acorns, and even date stones being found in 1878. (Weighed in the balance, PW Hammond and Harold Egan, HMSO, 1992, pp 40-43) But the food fraud episode of 2013 has reiterated that consumers need clear and accurate information so they can make informed choices about their diet and the foods they buy. This choice might reflect lifestyle, economic or health concerns but, in a multicultural society, it can also reflect religious practices.”

The full paper contains outline experimental details and references to the key studies so that any laboratory wishing to check coffee in the supply chain can make a good start.

Most of the common modern adulterants can be detected by chromatography of marker carbohydrates as detailed in standard methods (BS ISO 24114 and BS 5752-15) with the help of chromatograms of authentic coffee/ adulterant mixtures. Looking at DNA by Real Time PCR is a viable alternative to the chemical methods.

Claims for specific coffee bean geographic origin can be checked by discriminant molecular markers, although these are not as yet available for all coffee growing areas. Solvent extraction and Fourier Transform Infrared spectroscopy, FTIR, for the markers has the advantage that the FTIR spectra for authentic dichloromethane extracts are freely available online.

Discrimination between Arabica and Robusta species in coffee samples is possible via the marker compounds kahweol and 16-O-cafestol, predominant in Robusta. Determination of the latter by Nuclear magnetic Resonance, NMR, spectroscopy has the advantage of speed and relative simplicity.

Perhaps the most intriguing coffee authenticity problem is posed by Kopi Luwak, coffee beans harvested from the faeces of the palm civet cat. Processing in the digestive tract of this cat indigenous to Indonesia contributes to Kopi Luwak’s mystique and price. Although proof of identity of Kopi Luwak has been made more difficult by the possibility of mimicking the effect of the cat’s gut on beans by the use of microorganisms and enzymes, discriminant markers identified by Gas Chromatography – Mass Spectrometry, GC-MS, has proved successful. The question as to whether or not any residual civet cat DNA can be detected on ground roast coffee can be detected remains unanswered.

Thorburn Burns, D., Tweed, L. & Walker, M.J., 2017, Ground Roast Coffee: Review of Analytical Strategies to Estimate Geographic Origin, Species Authenticity and Adulteration by dilution,  Food Anal. Methods  doi:10.1007/s12161-016-0756-3

If you would like to find out how you could use our dPCR expertise to address your measurement challenges, please contact LGC’s Measurement Services.

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