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BackgroundThere is no fluorescence spectroscopic method for the determination of trigonelline and theobromine in green coffee beans. Therefore, the objective of this study was to develop a new fluorescence spectroscopic method to determine the alkaloids simultaneously in the aqueous extract of green coffee beans.ResultsThe calibration curves were linear in the range 2–6, 1–6, 1–5 mg/L for caffeine, theobromine and trigonelline, respectively, with R2 ≥ 0.9987. The limit of detection and limit of quantification were 2, 6 and 7 µg/L and 40, 20 and 20 µg/L for caffeine, theobromine and trigonelline, respectively. Caffeine and trigonelline exhibited well separated fluorescence excitation spectra and therefore the two alkaloids were selectively quantified in the aqueous extract of green coffee. While theobromine showed overlapping fluorescence excitation spectra with caffeine and hence theobromine could not be determined in the aqueous extract of green coffee beans. The amount of caffeine and trigonelline in the three samples of green coffee beans were found to be 0.95–1.10 and 1.00–1.10% (w/w), respectively. The relative standard deviations (RSD ≤ 4%) of the method for the three compounds of interest were of very good. The accuracy of the developed analytical method was evaluated by spiking standard caffeine and trigonelline to green coffee beans and the average recoveries were 99 ± 2% for both the alkaloids.ConclusionsA fast, sensitive and reliable fluorescence method for the simultaneous determination of caffeine and trigonelline in the aqueous extract of green coffee beans was developed and validated. The developed method reflected an effective performance to the direct determination of the two alkaloids in the aqueous extract of green coffee beans.

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This study was aimed to investigate volatile compounds of white and brown teff grain samples using the hydro-distillation and its extract in dichloromethane and n-hexane by gas chromatography-mass spectrometry. The optimized time for the hydro-distillation of the white and brown teff grain samples was nine hours. The dominant volatile compounds identified in the white and brown teff grain samples of the dichloromethane extract corresponding to peak area proportion were furfural (29.9%, 38.1%) and 5-methyl-2-furancarboxaldehyde (15.1%, 23.8%), respectively. The relative amount of dominant volatile compounds determined in the white teff grain sample of the n-hexane extract were 10.2% and 7.27% for the 5-methyl-2-furancarboxaldehyde and 2-[(methylthio)methyl] furan, respectively, and 18.4%, 16.0%, 12.5% and 9.73%, for the furfural, 5-methyl-2-furancarboxaldehyde, 2-[(methylthio)methyl]furan and benzeneacetaldehyde, respectively, for the brown teff grain sample. This study revealed that dichloromethane was efficient to extract more volatile compounds in the white teff grain sample than in the brown teff grain sample, whereas n-hexane was efficient to extract almost equal number of volatiles in both white and brown teff samples. Besides, aldehydes were the major constituents of the white and brown teff grain samples in both dichloromethane and n-hexane extracts.

ABSTRACT. This study was aimed to determine the total phenolics contents and antioxidant capacity of white and brown teff grain samples. The free total polyphenolic content (TPPC), bound TPPC and total flavonoids content ranged from 62.1–129.9, 84.6–189.6 mg GAE/100 g and 84.4–195.1 mg QE/100 g, respectively, in white teff samples, and, 118.6–196.7, 141.1–195.1 mg GAE/100 g and 97.8–202.5 mg QE/100 g, respectively, in brown teff samples. Besides, the free 2,2-diphenyl-1-picrylhydrazyl (DPPH) and bound DPPH ranged from 74.8–98.3, 77.1–99.9 mg AAE/100 g, respectively, for white teff samples, and, 68.7–93.1 and 71.2–99.4 mg AAE/100 g, respectively, for brown teff samples. This study revealed that total phenolics content was higher in brown teff samples than white teff samples and is in agreement with other reports. However, their DPPH scavenging activities were nearly equal, indicating that both varieties of teff are relevant for human nutrition and health. Furthermore, the dendrogram has shown sharp separation of the samples based on their origin and variety related to the total phenolics parameters. Hence, findings of this study can help consumers appreciate the nutritional value of white and brown teff grains; provide them guidance for teff purchase and production.   KEY WORDS: Teff, Phenolics, Gallic acid, Ascorbic acid, Anti-oxidant, DPPH   Bull. Chem. Soc. Ethiop. 2022, 36(4), 749-766.                                                              DOI: https://dx.doi.org/10.4314/bcse.v36i4.3