ELEMENTAL AND POLYPHENOL CONTENTS OF GREEN COFFEE BEANS FROM CENTRAL GONDAR ZONE, ETHIOPIA

Abstract

The total polyphenol and some essential metal contents of twenty three green coffee bean samples, collected from four coffee growing districts (Gondar Zuria, Takusa, Tach Armachiho and Chilga) in Central Gondar Zone, Ethiopia, were quantified using UV/Vis-spectrometer and flame atomic absorption spectrometry, respectively. A previously reported procedure was employed for the extraction of total polyphenols using 80% aqueous methanol and maceration for 24 h. 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. The recovery of the stated parameters ranged from 85 to 116.3%. The levels of metals determined in the green coffee beans were relatively higher than those reported in the literature.the average metal concentration of green coffee from Central Gondar Zone was show the following trend mg/kg: Ca (3,163.5 ±65.8), Mg (853.5 ±2.65), Cu (46 ± 11.1), Zn (11.8 ± 1.4), Fe (91.75 ± 33.6) and Mn (22.2 ±1.5) .The polyphenol contents of the coffee beans ranged from 43.1 to 46.73 mgGAE/g. Analysis of variance (p < 0.05) noted that there was no significant difference in the concentrations of all the metals, except for copper, as well as the total polyphenols among the four sampling districts. In general, this study revealed that the coffee bean samples from the Central Gondar Zone contained substantial amounts of total polyphenols and essential elements like calcium