Correlation between caffeine contents of green coffee beans and altitudes of the coffee plants grown in southwest Ethiopia

Caffeine contents of 45 green coffee bean samples collected from coffee plants grown at different altitudes in Southwest Ethiopia was determined by UV-Vis spectrophotometry. The caffeine contents were found in the range of 0.62 - 1.2% (w/w). A moderate negative correlation (R = 0.5463) was found between the caffeine contents of green coffee beans and the altitudes at which the coffee plants were grown. The caffeine contents of 9 of the green coffee bean samples analyzed by high performance liquid chromatography (HPLC) provided comparable results in the range of 0.60−1.1% (w/w). Statistical analysis of data (t-test) indicated absence of significant differences between the caffeine contents obtained by the two methods. Nonetheless, HPLC method is precise, accurate and reliable in determining caffeine content in green coffee bean samples while the UV-Vis spectrophotometry is simple, rapid, precise and more economical. KEY WORDS: Green coffee beans, Caffeine, Correlation between caffeine content and altitude of coffee plant, UV-Vis spectrophotometry, High performance liquid chromatography, Ethiopia Bull. Chem. Soc. Ethiop. 2018, 32(1), 13-25DOI: https://dx.doi.org/10.4314/bcse.v32i1.

Volatile profile of green coffee beans from Coffea arabica L. plants grown at different altitudes in Ethiopia

ABSTRACT. This study was aimed to identify volatile compounds of 31 green coffee bean samples and evalute their correlation with altitude of the coffee plants grown in two zones (Gedeo and Jimma) in Ethiopia. A total of 81 different compounds were detected. The contents of dominant volatile compounds in green coffee beans were in the range: trans-linalooloxide (3.24⎯19.13%), linalool (1.56⎯21.76%), 2-methoxy-4-vinylphenol (2.34⎯15.08%) and cis-linalooloxide (1.03⎯13.27%). In addition, benzene acetaldehyde (0.45⎯10.97%), 2-heptanol (0.67⎯8.49%), ⍺-terpineol (0.64⎯6.52%), phenylethyl alcohol (0.44⎯4.98%) and furfural (0.92⎯5.3%) were the next dominant compounds. The volatile compounds identified in the green coffee beans are groups of alcohols, aldehydes, ketones, pyrazines, pyridines, and furans. The volatile compounds in green coffee beans showed either weak positive or weak negative correlation with the altitude of coffee plants indicating that variation in altitude of the coffee plants does not significantly influence the volative compounds of green coffee beans.               KEY WORDS: Coffea arabica L., Coffee plants, Green coffee beans, Volatile compounds, Effect of altitudes, Heterocyclic compounds Bull. Chem. Soc. Ethiop. 2019, 33(3), 401-413.   DOI: https://dx.doi.org/10.4314/bcse.v33i3.

Levels of selected metals in teff grain samples collected from three different areas of Ethiopia by microwave plasma-atomic emission spectroscopy

The levels of selected essential and non-essential metals in the white, red, and mixed teff grains collected from Bure, Debre Markos and Bahir Dar (Ethiopia) were determined by microwave plasma-atomic emission spectroscopy (MP-AES). After proper sample pretreatment, the powdered teff was wet digested with the acid mixture (5 mL HNO3:1 mL HClO4) at 240 oC for 2:30 h over Kjeldhal digestion block. The accuracy of the optimized procedure was evaluated by analyzing the digest of the spiked samples with a standard solution of metals, and the percentage recoveries varied from 92% to 104%. The mean concentrations of metals determined (mg/kg, dry weight) were in the ranges of Al (713-1513) > Fe (252-1195) > Ca (233-348) > Zn (69-102) > Mn (20-45) > Cu (13-15) > Pb (1.8-2.8) > Cd (0.8-1.8). In this study, Al and Cd were determined in the teff for the first time. Analysis of variance indicated no significant difference between the mean concentrations of Cu and Mn among the white teff samples, Mn among the red teff samples and Cd and Pb among the mixed teff samples, but there was a significant difference for the other studied metals among the corresponding teff samples at 95% confidence level.                     KEY WORDS: Teff grain, Eragrostistef (Zucc.) Trotter, Essential metals, Non-essential metals, Ethiopia   Bull. Chem. Soc. Ethiop. 2020, 34(3), 449-462. DOI: https://dx.doi.org/10.4314/bcse.v34i3.

Evaluation of the effect of various drying techniques on the composition of the psychoactive phenylpropylamino alkaloids of khat (<i>Catha edulis</i> Forsk) chewing leaves

The study demonstrated that by freezing or drying under different conditions, cathinone could be detected in the khat (<i>Catha edulis</i> Forsk) samples that have been harvested for more than four months. Freeze drying or freezing in the refrigerator (-20 ^oC) yielded more than 73% of cathinone. Air drying, sun drying or oven drying at 60 ^oC resulted in a cathinone composition of 57%, 42% and 36%, respectively. The study confirmed that, freshly harvested tender leaves of khat contained exclusively of cathinone but upon sun drying, part of it decomposes to cathine and norephedrine leaving cathinone as a major component. Thus it is wrong to assume that sun drying the leaves can result complete conversion of cathinone to cathine and norephedrine. Furthermore, the results of the study confirmed that it was possible to preserve khat samples for longer periods after freeze drying or deep freezing without significant loss of cathinone.DOI: http://dx.doi.org/10.4314/bcse.v27i3.

Experimental and computational studies on zeolite-Y encapsulated iron(III) and nickel(II) complexes containing mixed-ligands of 2,2′-bipyridine and 1,10-phenanthroline

Mixed ligand complexes of 2,2′-bipyridine and 1,10-phenanthroline with iron(III) and nickel(II) have been encapsulated into a zeolite cage by the reaction of zeolite exchanged metal ion with flexible ligands. The synthesized catalyst has been characterized by X-ray powder diffraction, scanning electron microscopy, BET surface area and pore volume analysis, FT-IR spectroscopy, thermo-gravimetric analysis and elemental analysis. Density functional theory calculations have been carried out on both neat complexes as well as metal complexes encapsulated into NaY zeolite to investigate changes in structural parameters, energies of the HOMO and LUMO, and global hardness and softness of the two metal complexes upon encapsulation into zeolite. Experimental results confirm successful formation of a mixed ligand complex of Fe(III) and Ni(II) inside the zeolite cage. Density functional theory calculations predict a higher reactivity of the zeolite encapsulated metal complexes compared to respective metal complexes. The zeolite encapsulated Fe(III) and Ni(II) complexes are found to be catalytically active toward the oxidation of 2-phenyl phenol (OPP).Solomon Legese Hailu sincerely thanks the Leather Industry Development Institute (LIDI), Government of Ethiopia, Addis Ababa, for full nancial support for his PhD studies under Twinning Program between Leather Industry Development Institute (LIDI), Addis Ababa University (AAU) and CSIR-Central Leather Research Institute (CLRI). ID acknowledges CSIC, Spain for the research leave at AAU.Peer Reviewe

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

The objective of this study was to find out the influence of altitude of coffee plant and soil pH and organic carbon on alkaloid contents of green coffee beans. The alkaloids content of 54 green coffee beans samples collected from coffee plants in Sidama, Illubabor, Jimma, Wellega and Gedeo in southern region of Ethiopia grown at different altitudes (1515-2220 masl)was determined by high performance liquid chromatography. The caffeine and trigonelline were found in the range of 0.68-1.74% (w/w) and 0.68-1.44% (w/w), respectively. Theobromine was detected in only 18 samples and ranged 0.0186-0.32% (w/w). It was not detected in 36 samples. Theophylline was not detected in any of the green coffee beans samples. A weak negative correlation (R = -0.222) was found between the caffeine contents and the altitude of the coffee plants while a very weak positive correlation (R = 0.072) was found between the trigonelline contents and the altitude of the coffee plants. A strong negative correlation (R = -0.775) was found between the trigonelline contents and the caffeine content. A weak negative correlation was found between the caffeine contents and the soil organic carbon (R = -0.279) and between the trigonelline contents and the soil organic carbon (R = -0.101) while a weak positive correlation was found between the caffeine contents and the soil pH (R = 0.173) and between the trigonelline contents and the soil pH (R = 0.358) at which the coffee plants were grown

Synthesis, characterization and catalytic application of zeolite based heterogeneous catalyst of iron(III), nickel(II) and copper(II) salen complexes for oxidation of organic pollutants

In this study heterogeneous catalysts have been synthesized based on encapsulation of iron(III), nickel(II) and copper(II) complex of N,N′-Ethylenebis(salicylimine) or salen ligand into zeolite Y cavities by ship in a bottle method. The catalysts have been characterized by X-ray powder diffraction, BET surface area and pore volume analysis, FT-IR spectroscopy, thermo-gravimetric analysis, elemental analysis and electron paramagnetic resonance. The results show that ship in a bottle method is an efficient and simple approach for encapsulation of metal complexes into zeolite Y supercage. The prepared catalysts have been found to be very effective in the removal of azo dye from wastewater. The extent of its reusability for the catalytic oxidation of azo dye and the possible deactivation mechanism after ten successive reuse of the catalyst has also been studied.Solomon Legese Hailu sincerely thanks the Leather Industry Development Institute (LIDI), Government of Ethiopia, Addis Ababa, for full financial support for his Ph.D. studies under Twinning Program between Leather Industry Development Institute (LIDI), Addis Ababa University (AAU) and CSIR-Central Leather Research Institute (CLRI). ID acknowledges CSIC, Spain for the research leave at AAU.Peer Reviewe