Elemental and Polyphenol Contents of Green Coffee Beans from Central Gondar Zone, Ethiopia

Abstract

Variations in the major (Ca and Mg) and trace (Cu, Zn, Fe and Mn) essential metals as well as in the total polyphenol contents of green coffee beans with the major growing districts of Central Gondar Zone, Ethiopia, (Gondar Zuria, Takusa, Tach Armachiho and Chilga) were assessed using flame atomic absorption spectroscopy and UV/Vis spectroscopy, respectively. A total of 23 samples were used for analysis. For the analysis of metals, a wet digestion procedure was optimized. Accordingly, a 0.5 g of green coffee bean powder was digested on a hot plate with HNO3:HClO4 (4:4 v/v) at 240 °C for 3.5 h. The accuracy of the optimized procedure was evaluated from recoveries of spiked samples, which varied in the range 85‒116%. The coffee beans were found to contain considerable amounts of the essential elements, particularly Ca, and total polyphenols. The average concentration (mg/kg) of the elements were in the range of 2876‒3515 Ca, 839‒877 Mg, 71.8‒140 Fe, 31.6‒100 Cu, 21‒24.2 Mn and 10.0‒13.3 Zn. Significantly higher concentrations of Fe and Ca was found for green coffee beans from Takusa than the other districts. The polyphenol content of the coffee beans ranged from 31.5‒52.5 mgGAE/g, across samples. Analysis of variance (p < 0.05) revealed that there were no significant differences in the concentrations of total polyphenols among coffee beans from the four districts.