Detection and quantification of adulterated corn and soybean in ground coffee

Bui TP Thao, Truong TB Lieu, Tuan Q Dang


Adulteration in commercial ground coffee has been a regular concern all over the world, especially when it is difficult to percept adulterations with the naked eyes. This study was performed in order to set up a simple and quick procedure to detect and quantify adulteration of corn and soybean in commercial roasted ground coffee products. The floatation, spot check and microscopic methods were applied to detect adulterants in ground coffee, while caffeine was used as a chemical maker to quantify the level of adulteration. Ground coffee samples were taken from national brands, local brands and street vendor shops. The flotation test using distilled water at room temperature appeared to be a simple, quick and easy method to detect the presence of corn and soybean: corn and soybean particles started to sink within 5 seconds, while pure coffee particles can float for more than 2 min. Additionally, microscopic examination using both compound and stereo-microscope appeared to be effective tools for detection of corn and soybean while examination by a spot check could confirm the presence of starch containing materials such as corn. Using corn as a model of the adulterant, then the caffeine content in ground coffee was well correlated with the amount of corn added, which allowed estimation of the adulteration quantity possible. The results from qualitative tests revealed that 88.9±10.5% of the commercial ground coffee samples were adulterated, either with corn, soybean or some non-coffee materials. Projection from the caffeine content regression showed that the level of adulteration in the surveyed samples was in a range from 10.0 up to 47.0%.

Keywords— adulteration, caffeine, coffee, spot check, flotation test, microscopic test


Belay, A., Ture, K., Redi, M., & Asfaw, A. 2008. Measurement of caffeine in coffee beans with UV/vis spectrometer. Food Chemistry 108: 310-315.

Clarke, A. N., & Wilson, D. J. 1978. Separation by flotation. Separation and Purification Methods 7(1): 55-98.

Fontes, A. S., Bento, A. C., Baesso, M. L., & Miranda, L. C. M. 2006. Thermal lens and pH measurements in pure and adulterated brewed coffee. Instrumentation Science and Technology, 163-181.

Franca, A. S., Oliveira, L. S., Oliveira, R. C. S., Mancha Agresti, P. C., & Augusti, R. 2009. A preliminary evaluation of the effect of processing temperature on coffee roasting degree assessment. Journal of Food Engineering 92: 345-352.

Jham, G. N., Winkler, J. K., Berhow, M. A., & Vaughn, S. F. 2007. γ-Tocopherol as a marker of Brazilian coffee (Coffea arabica L.) adulteration by corn. Journal of agricultural and food chemistry 55(15): 5995-5999.

Khajarern, J. and Khajarern, S. 1999. Manual of feed microscopy and quality control. Khorn Kaen University Press, Thailand. 3rd Edition.

Mussatto, S. I., Machado, E. M., Martins, S., & Teixeira, J. A. 2011. Production, composition, and application of coffee and its industrial residues. Food and Bioprocess Technology 4(5): 661-672.

Phan, T. T. D., Kuban, V., & Kráčmar, S. 2012. Determination of caffeine contents of coffee brands in the Vietnamese market. Journal of Microbiology, Biotechnology and Food Sciences 1: 995-1002.

Reis, N., Franca, A. S., & Oliveira, L. S. 2013. Quantitative evaluation of multiple adulterants in roasted coffee by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and chemometrics. Talanta 115: 563-568.

Sano, E. E., Assad, E. D., Cunha, S. A., Correa, T., & Rodrigues, H. R. 2003. Quantifying adulteration in roast coffee powders by digital image processing. Journal of food quality, 123-134.

Smith, S. D. 2001. Coffee, microscopy, and The Lancet's analytical sanitary commission. Social history of medicine, 171-197.

Spiller, G. A. 1997. Chapter 6: The chemical components of Coffee. In G. A. Spiller, Caffeine (p. 97). CRC Press.

Full Text: PDF


  • There are currently no refbacks.

Publisher by Asia Pacific Network for Sustainable Agriculture, Food and Energy Network (SAFE Network).