Investigation of Metals in Raw and Roasted Indigenous Coffee Varieties in Ethiopia
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Date
2006-07
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Addis Ababa University
Abstract
The metal contents of raw and roasted coffee varieties that are grown in five different parts of
Ethiopia; (Wollega, Sidamo, Harar, Benchi Maji and Kafa zones) have been analyzed. The
representative samples of these coffee varieties were collected from Coffee Quality Inspection
and Liquoring Center, Addis Ababa, Ethiopia. Different digestion procedures were tested by
varying reagent volumes, time of digestion, temperature of digestion, types of reagents and
amount of the sample to develop a procedure that consume less reagent volume, short digestion
time, low temperature of digestion and smaller mass of the sample. The optimal procedure
required 4 hours and consumes 5 mL HNO 3 (70 %) and 1.5 mL HClO 4 (70 %) to completely
digest 0.5 g of both raw and roasted coffee samples. The accuracy of the optimized procedure
was evaluated by analyzing the digest of the spiked samples. Recoveries of the spiked samples
varired from 85 to 115 % and 84 to 120 % for raw and roasted coffees, respectively.
Concentrations of metals; (Ca, Cd, Cr, Co, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn) were analyzed by
fame atomic absorption spectrometer employing a four point external calibration curve. The
observed metal concentrations in roasted coffee varieties are relatively higher than their
corresponding raw varieties. The metals levels observed in both raw and roasted coffee varieties
are comparable with their corresponding world wide reported values with the exception of Cr, Cd
and Pb that are differing from the reported values. Indeed, the study has revealed the existence ofvariation of metal composition of coffee beans with the geographical origin in which coffee
plants grow.
Key words: Indigenous coffee, Coffee beans, Roasted coffee, Major metals, Trace
metals, Toxic metals
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Keywords
Indigenous coffee; Coffee beans; Roasted coffee; Major metals; Trace metals; Toxic metals