Effect of altitude, shade, and processing methods on the quality and biochemical composition of green coffee beans in Ethiopia

Abstract

There are growing demands for high quality coffee in the international market today. This has given coffee producing countries an impetus to increase the quality as well as the quantity of coffee they produce. For improving coffee quality and meet market demands, attention has been given to exploring genetic and environmental factors as well as agronomic and other coffee management practices. However, little information is available in Ethiopia regarding effect of environmental factors such as altitude and coffee management practices such as shading and processing methods on the quality and biochemical composition of green coffee beans. This problem has constrained efforts being made in the country to further exploit the growing demands for quality coffees in the international market. Therefore, a study was conducted during the 2010/11 main cropping season to determine coffee quality attributes as a function of altitude, shade, and processing methods. Red ripe coffee cherries were handpicked from three coffee farms in south-western Ethiopia located at altitudes of 1150, 1545 and 1802 meters above sea level, which represented lowland, midland, and highland coffee growing areas, respectively. The coffee cherries were obtained from both shaded and unshaded farms in each of the aforementioned coffee growing areas. The green coffee beans were subjected to both wet and dry coffee processing methods. A total of 36 coded samples (18 washed and 18 unwashed green coffee beans) with a moisture content of about 10.5% were subjected to cup and laboratory tests. Coffee cup test was done according to the procedure of Ethiopian Commodity Exchange (ECX) using 36 green coffee bean samples. Contents of caffeine, trigonelline, and chlorogenic acids were determined using HPLC/THERMO. Sucrose was determined using GC VARIAN 3800. Univariate analysis of variance and stepwise multiple regression analyses were conducted using SPSS 16 v2. The results revealed that coffee beans originating from the high altitude had significantly higher first grade and Q1 grade points than coffee beans originating from the low and middle altitudes. Unshaded and unwashed coffee grade was better than the washed and shaded coffee grade. Caffeine content of the beans was affected neither by altitude, shading, nor by the processing method. Shading affected only the content of bean caffeoylferuloylquinic acids (CFQA), which was found to be significantly higher for the unshaded coffee bean samples than the shaded coffee bean samples. Contents of 4,5-dicaffeoylquinic acid (4,5-DCQA), feruloylquinic acids (FQA), and total chlorogenic acid (TCGA) were significantly higher for coffee beans originating from the low and middle altitudes than those originating from the high altitude. Similarly, coffee beans that originated from the low altitude had significantly higher contents of 3,4- dicaffeoylquinic acid (3,4-DCQA), caffeoylferuloylquinic acids (CFQA), and trigonelline than coffee beans that originated from the high altitude. However, coffee beans that originated from the high and middle altitudes had significantly higher contents of chlorogenic acids, i.e., 3-caffeoylquinic (3-CQA) and 5-caffeoylquinic acid (5-CQA) than coffee beans that originated from the low altitude. The sucrose content of coffee beans that originated from the low latitude was significantly higher than the sucrose content of coffee beans that originated from middle and high altitudes. Washed coffee beans contained significantly higher amounts of dicaffeoylquinic acid (4,5-DCQA), caffeoylquinic acid (5-CQA), chlorogenic acid (TCGA), and trigonelline than unwashed coffee beans. However, unwashed coffee beans had significantly higher 3-caffeoylquinic (3-CQA) and caffeoylferuloylquinic acids (CFQA) contents than washed coffee beans. Unwashed coffee beans had higher values for primary defect, secondary defect, odour, total-point and preliminary grade whilst washed coffee beans had better scores for acidity, body, and flavour attributes, which distinctly influence the ultimate taste profile of coffee origins. It is concluded that coffee bean quality attributes and contents of the associated chlorogenic acids improved in response to increased altitude under both shaded and unshaded conditions regardless of the type of processing method used. The results imply that growing coffee plants in the highlands and midlands rather than in the lowlands as well as washing the beans results in the production of coffee beans with high quality attributes and chlorogenic acid contents that could meet the rising international market demands for high cup quality.

Keywords: Chlorogenic acid; Final grade; High altitude; Low altitude; Mid altitude