Abstract
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.
Highlights
There is no fluorescence spectroscopic method for the determination of trigonelline and theobromine in green coffee beans
Spectral characteristics of coffee alkaloid standards Caffeine, theobromine and trigonelline standard solutions were scanned by UV–VIS and fluorescence spectroscopic methods to determine their maximum excitation and emission wavelength
The maximum UV–VIS excitation bands were obtained at 272.89 nm, 272.73 nm and 264.59 nm
Summary
There is no fluorescence spectroscopic method for the determination of trigonelline and theobromine in green coffee beans. 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. Coffee is one of the most widely consumable beverages around the globe nowadays [1,2,3]. The arabica variety which is higher in cost than robusta variety due to its lower bitterness, better aroma and flavor is more prized by consumers [6]. The two types of alkaloids are derived from nucleotides. These are purine alkaloids like caffeine (1,3,7-trimethylxanthine) and theobromine (3,7-dimethylxanthine) as well as pyridine alkaloid, trigonelline (1-methylnicotinic acid) [7]
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