Physicochemical Studies and Origin Authentication of Coffee Bean from Ethiopia

Abstract

The first chapter deals with phytochemical screening of Ethiopian coffee beans. A total of 67 samples collected from different major coffee growing regions all over Ethiopia were examined for the presence of alkaloids, carbohydrates and cardiac glycosides, flavonoids, phenolic compounds, Phlobatannins, amino acids and proteins, saponins, Sterols, tannins, terpenoids, quinones and oxalates. Extraction solvents having different polarity; water, methanol, acetone, n-butanol and n-hexane were used for extracting the analytes. And out of the thirteen phytochemicals screened for, ten were found present in various solvent extracts. The degree of results obtained for each of the test varies based on the provinces from which the coffee beans were originated and that showed the concentration variation of biochemicals being present depending on the coffee bean origin. The second chapter deals with the determination of three isomers of chlorogenic acid (3, 4 and 5-caffeyolquinic acids), caffeine and trigonelline in a total of 48 samples processed by dry and wet post harvest processing methods. After extraction of the samples with 40 % methanol, the chlorogenic acid isomers were analyzed by HPLC with a gradient elution of 10 mM citric acid solution and methanol. While Caffeine and trigonelline were extracted with the help of 95 0C hot water and analyzed by HPLC using methanol:water:acetic acid (30:70:1) mixtures as a mobile phase. The results of the present study were compared with similar studies conducted elsewhere in the world. 3 and 4-caffeyolquinic acids exhibited a significant increase in concentration in the dry processed coffee bean samples compared with the wet processed one, whereas 5-caffeyolquinic acids did not show any variation of concentration between dry and wet methods. A slightly higher concentration was noted in trigonelline by dry processed samples over the wet ones, but the variation was not statistically significant. Caffeine contents in both dry and wet processed green coffee beans were similar. The third chapter focused on analysis of nutritional as well as toxic metals found in coffee beans originated from different coffee growing regions throughout Ethiopia. A total of 190 samples of dry and wet post harvest processed green coffee beans were analysed to find out the levels of major, minor, trace and toxic metals using ICP-MS, ICP-OES, and DMA instruments. A comparison of concentration between dry and wet processed coffee beans of the same region was made. For sample mineralization, all samples were made to go through microwave assisted digestion. The results were examined against international food safety and requirement standards. In general terms it was noted that the dry processed coffee beans contained higher nutritional metals than the wet processed coffee beans. It was also found that the coffee beans samples analyzed contained the required nutritional metals in a safe level. And there was no toxic metals found beyond the limits set by WHO and the American Food and Nutrition Board standards. On the fourth chapter an attempt on establishing the provenance of Ethiopian coffee beans based on multi-element analysis were made. One hundred twenty nine coffee bean samples collected from eleven different coffee growing provinces namely: Illubabor and Nekemeti from west; Jimma, Limu, Tepi and Bebeka from south west; Sidamo & Yirgacheffee from south; Bale from south east; Harar from east and Zage & Kossober (Gojjam) from North ethiopia. The concentration of 44 elements were analyzed using ICP-MS and ICP-OES. The results of the elements analysed were treated with different statistical tools; Principal Component Analysis (PCA) and Lnear Discriminant Anlysis (LDA), to help establishe the origion of green coffee beans. It was found that the LDA anaysis successfully discriminate the coffee samples in to their respective provinces. And therefore, using the database created by this study any regulatory outhority can authenticate the origin of coffee beans which are calimed to be from those regions included under this study.