Characterization of the Diversity of Coffee Genotypes in Kenya by Genetic, Biochemical and Beverage Quality Profiles

Abstract

Coffee has been one of the most important products for the Kenyan economy for decades, and a high proportion of the coffee produced in Kenya is considered as the best quality coffee in the world. The natural variation of coffee places it in a widening spectrum of differentiated food products which include wines, beers, and cheeses among others. The possibility of coffee producers capturing price differentials will depend on consumers recognizing valuable characteristics produced at the green coffee production level. This study was conducted to: assess the genetic diversity among coffee genotypes in Kenya using molecular markers, evaluate the sensory characteristics of different Coffea arabica genotypes grown in Kenya, characterize Coffea arabica genotypes grown in Kenya by determination of their biochemical components and assess the level of association between sensory and biochemical variables. Genetic diversity of coffee genotypes was assessed using RAPD primers and microsatellites. Coffee samples for sensory and biochemical characterizations were processed by the wet method. Seven sensory variables namely; fragrance/aroma, flavour, aftertaste, acidity, body, balance and overall were assessed and scored together with three process control variables (uniformity, clean cup and sweetness) by a panel of seven trained cuppers on a 10-point scale. All the sensory parameters (including the process control parameters) were added together to constitute the total score which was a reflection of the broad coffee quality performance. Caffeine, oil, trigonelline, total chlorogenic acids (CGA), and sucrose were analyzed in green coffee samples using specific methodologies and quantified on dry weight basis. The sensory and biochemical data obtained were subjected to xxiv analysis of variance and multivariate analysis using Costat, R-statistics, SPSS and XL-STAT statistical programs. This study confirmed the low genetic diversity in Arabica coffee genotypes evaluated with dissimilarity of less than 5%. The study also widened the information on genetic diversity of coffee germplasm available for breeding programmes in Kenya since previous work was biased to commercial cultivars and donors of resistance to diseases. The molecular diversity shown among the Hibrido de Timor (HDT) derivatives could be exploited in breeding programmes especially by subjecting more intensive molecular characterization and consequently selecting elite lines among them. Analysis of variance indicated significant differences among the forty (40) ex-situ conserved coffee genotypes evaluated alongside two commercial varieties for sensory characteristics. Cluster analysis grouped the forty two (42) coffee genotypes into two major groups. The first group comprised of twenty seven (27) coffee genotypes, most of which were characterized by low beverage quality. The second cluster comprised of the remaining fifteen (15) coffee genotypes, most of which were relatively better in beverage quality. Ninety two percent (92%) of the fourty ex-situ conserved genotypes scored 80 points and above in mean total score qualifying them as specialty coffee. In molecular analysis, Ennareta and Geisha 11 clustered with non-introgressed Arabica genotypes and also revealed high beverage quality. The kind of diversity presented could be exploited with the aim of recommending some accessions for commercial cultivation. Sensory characteristics of the five advanced breeding lines Cr8, Cr22, Cr23, Cr27 and Cr30 together with the check cultivars SL28 and Ruiru 11 showed considerable xxv variations. Diversity was observed in some of the genotypes due to seasons and sites where they were grown. However, their sensory characteristics were similar to those of the check cultivars SL28 and Ruiru 11. In all the genotypes evaluated in this study, the levels of caffeine, trigonelline, oil, total chlorogenic acids (CGA) and sucrose agreed with documented values in Arabica coffee. Ex situ conserved coffee genotypes were most diverse in green bean caffeine, chlorogenic acids and sucrose contents compared to the commercial varieties. HDT had the highest amount of caffeine (1.68%) while Dilla Alghae had the lowest amount (0.77%). Moka Cramer had the lowest level of total chlorogenic acids (6.13%) while Barbuk Sudan had the lowest amount of sucrose (5.11%). Correlation of the cup quality and biochemical attributes showed that trigonelline significantly correlated to body, flavour, aftertaste and overall. Total chlorogenic acids negatively correlated with all sensory parameters while sucrose positively correlated significantly with all the sensory parameters. Higher green bean trigonelline and sucrose content can be improved together with desirable cup quality. Similarly, desirable cup quality traits and low green bean caffeine content can be selected simultaneously. Incorporating biochemical components analysis as a complementary method of evaluating coffee genotypes would generate additional information on the coffee genotypes and may reveal further diversity and potential for eventual exploitation.