Detection and quantification of adulterated corn and soybean in ground coffee

Abstract

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