Factors Affecting Quality And Biochemical Attributes Of Arabica Coffee (Coffea Arabica L.) In Kafa Biosphere Reserve, Southwest Ethiopia

Abstract

Ethiopian coffee has a distinctive quality that is gifted by nature. Though improving yield and quality is a challenging process, identifying gaps in the natural quality of coffee produced in major coffee growing regions of the country appears to be a priority area, which should be addressed for traceability and sustainable supply to the world market. Regarding this, lack of comprehensive assessment of the quality of coffee produced generally in Southwest Ethiopia and specifically in the Kafa Biosphere Reserve is one of the research agendas at the national level. This study, therefore, aimed at creating better understanding of the production practices and factors associated with coffee quality and improving the livelihood of producers in Kafa Biosphere Reserve. Specifically, it was designed to identify socioeconomic factors, production constraints, processing, and handling practices related to coffee quality. In addition, attempt was made to identify the effect of location, production system, elevation, and processing method on coffee quality and the relationship of soil physiochemical attributes with physical characteristics, organoleptic qualities, and biochemical compounds of coffee bean produced in the Kafa zone, particularly in the Kafa Biosphere Reserve. Accordingly, a survey and three individual experiments were conducted in the study area. A three-stage nested design was used for the experiments. Locations (Gimbio, Gawata, and Decha districts) and coffee production systems (forest, semi-forest, and garden) or elevation gradient (low-<1600, mid-1600-1800, and high >1800 m a.s.l.) were considered as factors. Then processing methods (wet, semi-wet, and dry) were applied to the collected samples of the above two experiments. For the third one, fifty-four (54) coffee cherry samples were collected from individual coffee trees for physical and biochemical analysis. A preliminary coffee quality, soil attributes, and coffee biochemical analysis were done. The collected data was analyzed using standard procedures, including descriptive statistics, analysis of variance, multiple-factor analysis, principal component analysis, and Pearson's correlation coefficient analysis. The survey results revealed that coffee producers in the area are aged and experienced in coffee production, and most of them were enrolled in formal education. Since coffee production is conducted on less than one hectare of land, alternative food crop production helps farmers fulfill household food requirements. Insufficient pruning and coffee diseases pose significant reduction in both production and quality of the crop. Most farmers use only weed management options to control weeds. Farmers use polypropylene bags for dried coffee cherries' storage. Lack of fair coffee prices is discouraging farmers not to make a better livelihood from their well-prepared coffees as well as from proper coffee handling practices. Results of the first experiment revealed a significant (P < 0.05) effect of location and production system on bean moisture content and acidity, respectively. Processing method showed a significant (P < 0.05) effect on bean moisture content (P < 0.01), odor (P < 0.001), raw (P < 0.01), and preliminary grade (P < 0.05). Better coffee quality was obtained from the dry processing method within the recommended moisture content. Odor and overall raw coffee quality showed relatively lower value when forest and semi-forest coffees were treated with wet and semi-wet processing methods. According to the results of a multiple-factor and Pearson’s correlation analysis, the Gimbo and Decha coffees were found to be substantially different from the Gawata coffees in terms of quality. Screen retention (14) was significantly and positively correlated with soil iron content (0.21) but negatively correlated with boron (-0.20) and sodium (-0.19) content of the soil. A significant and positive relationship was also observed between green coffee bean moisture content and soil potassium (0.33), calcium (0.26), magnesium (0.26), boron (0.24), sodium (0.25), organic carbon (0.25), and silicon (0.20) contents, and soil pH (0.20). A positive and significant relationship was observed for soil molybdenum content and overall raw quality of coffee. Whereas the content of most soil micronutrients, such as zinc, sulfur, and manganese, was significantly and negatively correlated to organoleptic quality attributes of coffees. In the second experiment, it was observed that the effect of location was only significant (P < 0.05) for bean moisture content. Elevation gradient had a significant (P < 0.05) effect on above 14 screen retention and most of the cup quality variables. The effect of coffee processing method was significant (P < 0.05) for coffee bean moisture content, odor, and overall raw scores. Screen retention/green bean size decreased with increasing elevation gradient, but xv with better quality. High-elevation coffees processed with the dry method gave better raw (38.5–40%) and cup (48.0–51.75%) quality scores. Except for molybdenum content and clay percentages of soil, lower amounts of most soil nutrients, soil pH, and silt percentage were found to be important for better forest coffee quality. Results of the third experiment revealed that the effect of location was not significant (P > 0.05) on the bean physical quality variables and biochemical contents, whereas a significant effect of location was observed for fruit physical qualities. The physical characteristics and biochemical (caffeine, chlorogenic acids and nicotinic acid) composition of the samples were not significantly affected by forest zonation; however, plotting had a significant impact on the levels of chlorogenic acid, fruit width, and seed length. On the other hand, the result revealed significant variations of biochemical constituents of coffee beans across sampling locations. Principal component analysis revealed that 61.97% variation was retained in the first two dimensions and no negative relationship between physical and biochemical variables. It was also observed that forest coffee biochemical and physical attributes were primarily influenced by variables such as chlorogenic acid content and fruit and seed width. Results of multiple factor analysis indicated both positive and negative effects of elevation on the nicotinic acid and physical characteristics of coffee fruit and seed samples. Cluster analysis categorized the samples into three major clusters. Gimbo district coffees have higher nicotinic acid contents and smaller physical characteristics, while Gawata and Decha districts have more physical attributes and lower nicotinic acid content. Generally, land holding, the productive age of garden coffee, livestock production, the presence of cooperatives, extension support, and availability of training are good opportunities for quality coffee production. Proper harvesting, post-harvest handling, and farmers' understanding of quality maintenance would enhance coffee production and supply. A large family-sized coffee producers and a wealth of coffee production skill are necessary for effective coffee development. Stakeholders should provide improved technologies, strengthen intensive coffee production practices, and assist producers with extension services. Policymakers should also support resource-poor producers by formulating some regulations that ensure fair coffee prices. Consider appropriate processing techniques, like dry processing, to enhance the quality of hand-picked forest coffees that are collected at elevation gradients. It was observed that soil molybdenum is beneficial for coffee quality, so nutrient identification and utilization should be prioritized across locations, systems, and elevation gradients. Using systematic sampling techniques, different physical characteristics of coffee could be obtained by classifying the location. Variations observed in the biochemical contents of coffees suggested that there is a need for more research in the biosphere resources for the development of superior coffee varieties. Future studies should focus on improving the livelihoods of coffee-growing farmers by developing technologies that increase coffee production, identifying critical gaps in the coffee marketing chain and maintaining quality at every elevation gradient and production system. Forests exhibit diverse shade types and densities; future studies should also include shade components as a quality determining factor to assess the quality of Kafa Biosphere Reserve coffees. Additional research is required to fully understand the effect of factors on the physical characteristics and biochemical composition of coffees grown in the Kafa Biosphere Reserve Forest.