LEVELS OF SELECTED ESSENTIAL AND NONESSENTIAL METALS IN ROASTED HARARGHE COFFEE BEAN VARIETIES

Abstract

The present study was conducted to determine the levels of essential and non-essential metals present in Hararghe coffee bean varieties. Three samples of Hararghe coffee bean (HCB) (Harar A, Harar B and Harar C) were obtained from the Ethiopian commodity exchange (ECX) Dire Dawa branch. The determination of the levels of selected metals in roasted coffee bean (K, Mg, Ca, Mn, Zn, Cd, and Pb) was conducted using Flame Atomic Absorption Spectrophotometer (FAAS). The digestion procedure was optimized and it was validated using spiking experiments. Recoveries of the spiked samples varied from 94% to 112% for the roasted coffee samples. Then the digestion process was carried out using an open vessel system with 3 mL HNO3 (70 %), 1 mL HClO4 (70%), 1 mL H2SO4 (98%) and 1 mL H2O2 (30 %) reagents. Generally, the levels of metals in all roasted coffee bean varieties were: K > Mg > Ca > Zn > Cd, but the metals Mn and Pb were found to be below the method detection limit. The concentrations of metals in Hararghe coffee bean varieties were comparable to the values reported in the literature. The mean concentration of each metal in the three coffee samples of Hararghe coffee bean varieties were: K (13.6669 – 15.7859 mg/kg), Mg (7.1473 – 8.3676 mg/kg), Ca (3.6691 – 5.569 mg/kg) and Zn (0.3897 – 2.3367 mg/kg). The toxic metal Cd was not detected in Harar A and B coffee varieties while a concentration of (0.2282 ± 0.02 mg/kg) was found in Harar C coffee variety. However, Mn and Pb were not detected in all coffee samples. The concentrations of the metals were in the recommended maximum permissible limits indicating no risk of health by drinking the coffee made from Hararghe coffee bean with respect to the metals considered in the present study.