This study evaluated the physicochemical qualities of washed specialty Bourbon Arabica from major producing areas of Rwanda in comparison with two world renowned Arabica coffees: natural/dry Bourbon from Brazil and washed Typica from Ethiopia. Significant differences in most physicochemical properties were observed between coffee growing areas within Rwanda as well as among the three countries. Washed Bourbon from Rwanda and washed Typica from Ethiopia were denser than the natural Bourbon from Brazil. Natural Bourbon from Brazil was found to be 20% more caffeinated whereas roasted washed Typica from Ethiopia contained about 21% higher caffeoylquinic acid (CQA) than the washed Bourbon from Rwandan. Generally, roasted washed Bourbon coffees from Rwanda showed higher acidity properties than Brazilian and Ethiopian coffees. This study indicated that coffee quality may vary even within the same variety from different origins which is due to conditions applied in different coffee growing areas.

Bourbon is the major coffee variety grown in Rwanda. Fully washed bourbon produced in Rwanda is a nascent specialty coffee and no investigation of its quality characteristics has been reported. Thus, this study aimed at providing information about intrinsic flavor characteristics and identifying the most discriminating aroma compounds of this coffee from the major growing areas in four provinces (considered by this study as geographical sub-regions) in comparison with Arabica coffee from Ethiopia and Brazil using electronic nose and electronic tongue. Samples were discriminated and characterized by performing a principal component analysis (PCA). A discriminant factorial analysis (DFA) model was also used to predict the geographic origin of coffee samples based on their flavor characteristics. A similarity was observed between flavor characteristics of coffee samples from western and southern sub-regions as well as between northern and eastern sub-regions of Rwanda. Twenty one most discriminating aroma compounds were found but the identified and confirmed ones are: Butan-2-one, Acetic acid, n-Butanol, 2, 3- Pentanedione, Ethyl-2-methybutyrate, Dimethylsulfide, 2-Prpanol, 2-Methylfuran, Ethylacetate, Ethyl propionate and Heptanal. A DFA model using e-nose was successful in predicting the geographic origin of coffee samples but not with e-tongue. This means that aroma can reliably be used to predict the geographic origin of coffee samples than their taste characteristics. Further investigation is required to test the possibility of origin recognition based on taste characteristics.

This study evaluated the physicochemical quality characteristics of raw and roasted beans of fully washed specialty Bourbon cultivar ofCoffea Arabica“BM 139" from seven of the major coffee growing areas in Rwanda in comparison with a wet processed Typica cultivar from Yirgacheffe, Ethiopia and a dry processed red Bourbon cultivar from Cerrado, Brazil. Tested samples had moisture content between 7.7 and10.2%. Raw coffee from Brazil had the lowest density and darker than samples from other regions. Other samples showed no significant differences in true density. Raw coffee from Kayumbu coffee washing station (CWS), Kamonyi district showed the lowest total phenolic content of 38.4 mg/g solid whereas raw coffee from Nyamyumba CWS, Rubavu district had the highest content of 46.8 mg/g solid. DPPH radical scavenging activity (RSA) ranged from 89.9 to 91.8% and varied little between samples. Raw coffee from Yirgacheffe, Ethiopia showed the highest total titratable acidity of 1.48% as citric acid and totalcaffeoylquinic acidof 82.62 mg/g solid whereas that from Brazil had the highest caffeine content of 18.5 mg/g solid. Raw coffee from Karenge CWS, Rwamagana district was characterized by having the lowest caffeine and trigonelline content (13.4 and 10.3 mg/g solid, respectively). After roasting, there was a drop in most physicochemical characteristics. Raw and roasted coffee samples from Rulindo and Kirorero CWS indicated higher bulk densities which might be due to higher altitudes of these two areas. Caffeine and RSA were not affected by the roasting process. The Brazilian coffee was characterized by higher caffeine content in raw as well as roasted forms. After roasting, coffees from Rwanda were more acidic than Brazilian and Ethiopian coffees. This study revealed that the physicochemical characteristics of the Bourbon cultivar may vary depending on the geographical sub-regions which is due to environmental conditions, processing and agricultural practices.