Concentration levels of metals in commercially available Ethiopian roasted coffee powders and their infusions

The concentrations of nine essential metals (K, Mg, Ca, Na, Mn, Fe, Cu, Zn, Co) and two non-essential (Pb, Cd) metals were determined in three brands of commercially available roasted Ethiopian coffee powders (Abyssinia, Alem and Pride) obtained from local markets and their infusions using flame atomic absorption spectrometry (FAAS). An optimized digestion procedure was developed using 5 mL of HNO3 and 1 mL of HClO4 with 4 hours total time at temperature around 350 oC for digestion of 0.5 g of powder sample while 4 mL of HNO3 and 1 mL of HClO4 with 4 hours total time for 25 mL infusion evaporated to dryness. The validity of the optimized procedure was evaluated by the analysis of spiked samples whose recovery of analytes was in the range of 97-103 % for the coffee powder and 95-102 % for the infusion samples. The mean concentration of each metal in the three brands of coffee powder samples was (μg element/g): K (14488±467), Mg (1964±78), Ca (945±65), Na (484±12), Fe (52.0±4.0), Mn (23.0±0.9), Cu (14.0±0.6), Zn (15.0±0.8), Co (1.60±0.05) while that in their infusions (mg element/100 mL): K (37205±1501), Mg (2829±105), Ca (1619±102), Na (591±20), Fe (18.3±1.5), Mn (23.7±1.2), Cu (3.0±0.3), Zn (24.0±1.1), Co (1.8±0.1), respectively. The metal concentrations of the coffee powders were higher than those of coffee infusions, when expressed in the same units. The extraction was highest for K (85.6%), intermediate for Zn (57.5%), Ca (56.6%), Mg (48.0%), Na (40.7%), Co (39.8%), and Mn (33.5%) and lowest for Fe (11.6%) and Cu (6.8%). The concentrations of metals in the Ethiopian coffees were comparable to the values reported in other parts of the world. KEY WORDS: Coffee, Roasted coffee powder, Coffee infusion, Essential metals, Non-essential metals, FAAS Bull. Chem. Soc. Ethiop. 2011, 25(1), 11-24.