Assessment of metals in roasted indigenous coffee varieties of Ethiopia

The metals content (Ca, Cd, Cr, Co, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn) of roasted coffee varieties grown in five different regions of Ethiopia was determined by flame atomic absorption spectrometry. Representative samples were collected from Coffee Quality Inspection and Liquoring Center in the capital city, Addis Ababa, Ethiopia and the metals were extracted by wet digestion. The optimal digestion required 4 hours refluxing at 270 oC on Kjeldhal hot plate with a mixture of 5 mL HNO3 (70%) and 1.5 mL HClO4 (70%) to completely digest 0.5 g of roasted coffee samples. Recoveries of metals in the spiked samples varied from 90 to 110%. Analysis of variance revealed significant differences in the concentrations of Ca, Co, Cu, Mn, Cr, Ni and Zn with the variation of coffee beans geographic origin. Pearson correlation coefficients indicated high positive correlation among some metals and high negative correlation among others. The amounts of metals that a person can get from two cups of coffee are well below the daily recommended values and drinking two cups of coffee is safe for an adult person and free from the risks of Cd and Pb toxicity.