Influence of altitudes of coffee plants on the alkaloids contents of green coffee beans

Abstract

ISSN: 2410-9649 Gebrekidan et al / Chemistry International 5(4) (2019) 247-257 iscientic.org. 248 www.bosaljournals/chemint/ [email protected] Coffee grows at various altitudes, ranging from 550 to 2750 meters above sea level (Hagos et al., 2018). However, Arabica coffee best thrives and is produced between altitudes of 1300 and 1800 meters, with annual rainfall amount ranging from 1500 to 2500 mm with an ideal minimum and maximum air temperatures of 15 and 25 oC, respectively. This prevails in most of the country’s coffee growing areas (Mekonen, 2009). The recognition and worldwide demand of coffee, which stems from its distinctive flavor, made it currently one of the most desirable and commonly consumed beverages. Furthermore, it has a strong historical, cultural, social and economic value in each and every society in Ethiopia (Shiferaw et al., 2018, Yisak et at., 2018a; Yisak et al., 2018b). It also plays the leading role in the national economy being the primary source of foreign exchange earnings (Mehari et al., 2016a; Mehari et al., 2016b; Shiferaw et al., 2018; Hagos et al., 2018). It is also a source of revenue of millions of Ethiopians. The major and most known coffee producing regions in the country are Oromiya and Southern Nations Nationalities and Peoples Region (Mehari et al., 2016a; Mehari et al., 2016b; Shiferaw et al., 2018). Coffee is a rich source of alkaloids such as caffeine, trigonelline, theobromine and theophylline (Fig. 1) (Mehari et al., 2016c; Yasak et al., 2018a, Yisak et al., 2018b) and their profile in the green coffee beans is important and helpful to know the quality of coffee brew. The content of alkaloids (caffeine, theobromine and trigonelline) in green coffee beans is influenced by numerous factors such as coffee variety, genetic properties of the cultivars, environmental factors (soil, altitude, sun exposure), climatic parameters (rainfall, temperature), maturity of the beans at harvest, harvesting method and agricultural practices (shade, pruning, fertilization) (Alonso et al., 2009, Mehari et al., 2016c, Hagos et al., 2018). The altitude and soil characteristic at which coffee plant is grown plays a major role in determining the quality of the green coffee beans. Coffee cherries from plants grown at higher altitudes take longer time to mature than plants grown at lower altitudes because there is less oxygen. High altitude grown coffee beans usually have a higher density than low altitude grown beans. Longer maturation times and increased bean sizes are usually observed for plants grown at high altitude (Sridevi and Giridhar, 2014). The different types of coffee have diverse tastes depending on their geographical origins (Mehari et al., 2016c, Mehari et al., 2019). Due to the immense variety of genetic properties, soil types, climate change and altitude of the coffee growing areas, there is an extensive ranges of variability in the quality of green coffee beans. These factors are supposed to influence coffee characteristics (flavor, aroma and chemical content) (Hagos et al., 2018). Altitude and the parameter of the soil, such as pH value and organic carbon are very important factors. High altitudes are critical for the successful production of high quality Arabica coffee in equatorial region. The amount of alkaloids (caffeine, theobromine, trigonelline and theophylline) in green coffee bean samples is determined by various analytical methods. Quantitative determination of alkaloids in large number of samples needs an accurate and rapid method. The complete extraction of alkaloids from test samples and removal of interfering substances varies from method to method. Therefore, choosing the right analytical method is essential for the accurate simultaneous determination of alkaloids (caffeine, theobromine, trigonelline, theophylline) in test samples (Gopinandhan et al., 2014, Mehari et al., 2016c; Hagos et al., 2018). Many analytical methods have been reported for the determination of alkaloids in green coffee beans such as ultraviolet visible spectroscopy (Belay et al., 2008; Zewdu et al., 2016; Demissie et al., 2016), fluorescence spectroscopy (Yisak et al., 2018a), FT-IR-ATR (Weldegebreal et al., 2016; Yisak et al., 2018b), high performance liquid chromatography (Belitz et al., 2009; Gopinandhan et al., 2014; Mehari et al., 2016c; Hagos et al., 2018), gas chromatography (McCusker et al., 2003; McCusker et al., 2006; Sereshti and Samadi, 2014). However, the literature survey also revealed that there is limited reports available on study of the simultaneous determination of alkaloids in green coffee beans for a given set of samples and effect of altitude and soil composite (Belitz et al., 2009; Mehari et al., 2016c; Hagos et al., 2018). N