Analytical methods to detect coffee adulteration reviewed

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Approaches to test the accuracy of claims for samples of roast ground coffee have been reviewed by researchers.

They suggest ways to deal with the key problems such as determining degree of dilution, specific adulterant, geographic origin of the beans and their species and any post growth treatment.

Ground coffee has been the target of adulteration because of its high market value and the amounts consumed. Arabica and Robusta are the most popular varieties.

Fraud includes adulteration of coffee with cheaper materials such as coffee husks, chicory, cereal grains, woody tissue, cocoa or soya beans, acai berries or exogenous sugars and substitution of the more expensive Arabica with cheaper beans.

Laura Tweed, Prof Duncan Thorburn Burns and Dr Michael Walker looked at methods to determine the most commonly found materials used to adulterate coffee as diluents and to establish geographic and genotypic origin of beans.

Adulterant detection and bean origin

The most recent common diluents, marker features and detection methodologies include rice and soybean as the diluents, 17 oligosaccharides as markers and UPLC-HRMS oligosaccharide profiling as the methodology and Acai palm seeds and wheat as diluents, five carbohydrates and HPLC-HPAEC-PAD & HPLC-UV-Vis with PCA as the methodology.

Adulteration by common diluents can be detected by BS ISO 24114 (BS 2011) and the specific materials determined by BS 5752-15 (BS 1997) with the help of chromatograms of authentic coffee/diluent mixtures.

Looking at DNA with Real-Time PCR is a viable alternative to chemistry-based methods.

Claims for specific coffee bean geographic origin can be checked by identification of discriminant molecular markers although these are not available for all coffee growing areas.

Analytical methods to characterise and quantify the most important bioactive compounds in coffee samples have been reviewed but definitive geographic or species markers have not been identified.

There is no internationally validated method to confirm the claim of a specific country of origin for a single sample.

Element-specific techniques such as inductively coupled plasma emission spectroscopy (ICP-OES), atomic adsorption (AAS) and neutron activation analysis (NAA) have been used to examine trace element composition of coffee samples.

Fourier transform infrared spectroscopy (FTIR) following solvent extraction, near-infrared spectroscopy (NIR), metabolomic analysis by nuclear magnetic resonance spectroscopy (NMR) and ultra-performance high pressure liquid chromatography coupled with mass spectrometry (UPLC-MS) have been used in different studies.

Price point

Due to the difference in price and potential for adulteration of Arabica coffee with Robusta, it is necessary to examine samples, labelled as pure Arabica, for authenticity.

Identification of Arabica and Robusta species in coffee samples is possible via marker compounds kahweol and 16-O-cafestol predominant in Robusta.

NMR has the advantage of being faster and simpler than the DIN HPLC method.

Kopi Luwak is made from coffee beans harvested from the faeces of the palm civet cat after being processed in its digestive tract.

Due to the cost of civet coffee interest in falsification by attempting to mimic the rich taste and smell by treating beans using microorganisms and enzymes has led to patent applications.

Discriminant markers identified by gas chromatography with mass spectrometry (GC-MS) has proved successful.

The paper is the third in a series linking historical adulteration with modern manifestations.

Source: Food Anal. Methods (2017)

DOI: 10.1007/s12161-016-0756-3

Ground Roast Coffee: Review of Analytical Strategies to Estimate Geographic Origin, Species Authenticity and Adulteration by Dilution

Authors: Thorburn Burns D, Tweed L & Walker MJ

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