Effect of Altitude, Shade, and Processing Methods on Isotope and Biochemical Composition of Green Coffee Beans in Ethiopia

Abstract

Though Arabica coffee has evolved in Ethiopian natural forests, it is being produced without shade in many countries at varying altitudes. 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. Carbon, nitrogen and oxygen Isotopes as well as %N and %C of the beans were determined using a continuous flow (CF) EA-IRMS, while caffeine, trigonelline and chlorogenic acid content were determined using HPLC/THERMO. Sucrose content was determined using Gas Chromatography. The study included washed and unwashed coffee samples from altitudes of 1150, 1545 and 1802 meters above sea level. For the determination of the aforementioned components of the bean, univariate analysis of variance, automatic regression modelling, and stepwise canonical discriminant functions were used. Percent N, δ¹⁵N, δ¹³C and %C did not show significant result by altitude. For δ¹⁸O and δ¹³C, unshaded coffee showed higher mean value than the shaded counterpart. Shading disfavoured the composition of isotopic oxygen (δ¹⁸O) as the altitude increases. Shaded coffee at 1150 meters above sea level (m a.s.l.) showed the highest mean value while at 1802 m a.s.l. the lowest for both sucrose and trigonelline composition of green coffee beans. Washed coffee at 1802 m a.s.l. for 5-CQA, unwashed coffee at 1150 m a.s.l. for CFQA, unwashed coffee at 1545 m a.s.l. for TCGA, unwashed coffee at 1150 m a.s.l. for both sucrose and trigonelline showed the highest mean value while unwashed coffee at 1802 m a.s.l. for 5-CQA, TCGA, sucrose and trigonelline, and washed coffee at 1545 m a.s.l. for CFQA showed the least value. The highest mean value was obtained from unwashed- shaded coffee at 1545 m a.s.l. while unwashed- shaded coffee at 1802 was the lowest. The association of isotopes and biochemical composition of green coffee beans was found to be weak although for caffeine and percent N contributed a significant positive weight (b = 6.604, P ≤ 0.002) and %C contributed a significant negative (b = - 0.388, P ≤ 0.004) weight for the model. Lowland coffees were well discriminated (94.4% of variation) by 4,5-Dicaffeoylquinic acids (4,5-DCQA) compared to coffees from midlands and highlands.