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

Abstract

Though Arabica coffee has evolved in Ethiopian forest areas, it is being produced without shade in many countries at varying altitudes. Systematically establishing a relationship between geographic origin of coffee and its quality leading to the generation of reliable data is a priority area in Ethiopia. Thus, the objective of this study was to determine the composition, fingerprinting and association of isotopes and biochemical composition as a function of altitude, shade and processing methods. The study included washed and unwashed coffee samples from 1150, 1545 and 1802 m a.s.l. to determine carbon, nitrogen and oxygen isotopes and %N and %C using a continuous flow (CF) EA-IRMS; caffeine and chlorogenic acids using HPLC/THERMO; sucrose using Gas Chromatography. Univariate Analysis of Variance, Automatic regression modelling, and Stepwise canonical discriminant function were conducted. Shading disfavoured the composition of δ¹⁸O as the altitude increased. The highest mean value of 5-caffeoylquinic acid (5-CQA) was obtained from unwashed-shaded coffee at 1545 m a.s.l. while unwashed- shaded coffee at 1802 was the lowest. The δ¹⁵N, higher δ¹³C and δ¹⁸O values may be useful indicators of altitudinal coffee. The association of isotopes and biochemical composition of green coffee beans was found to be weak although for caffeine percent N contributed significant positive weight (b = 6.604, p≤0.002) and %C significant negative (b = -0.388, p≤0.004) weight, respectively) for the model. Lowland coffees were well discriminated (94.4% of variation) by 4,5-DCQA from those at midland and highland grown coffees. In conclusion, isotopes, their respective elements, and biochemical composition of green coffee beans could be certainly exploited for discriminating growing environment and profiling of coffee quality.

Keywords/phrases: Coffee quality profile, Coffee value chain, Fingerprinting, Growing environments