Belete, Adefris (2008) Determination of Caffeine Level in Coffee. Masters thesis, Addis Ababa University.
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Abstract
Coffee is an important commodity culturally, commercially and economically in the world. Because of its consumption in most countries in the world, it is important to investigate the exact amounts of its chemical constituents. Caffeine is one of the main components of coffee that affect the quality of coffee, both before and after processing. In this project, rapid, simple and sensitive quantitative thin-layer chromatography and proton nuclear magnetic resonance spectroscopy methods for the quantification of caffeine in coffee, tea and soft drinks were developed and validated. The methods involved extracting samples with chloroform by sonication, and analysis by Camag TLC scanner 3 and quantitative proton NMR (qHNMR). In the first method, Camag TLC scanner 3 was used for densitometric scanning and analysis in absorbance mode at 276 nm. The system was found to give a sharp peak for caffeine at Rf value of 0.64. The linear regression analysis data for calibration plots showed good linear relationship with r2 = 0.999 in the concentration range of 200-1600 ng spot-1 with respect to peak area. The method was validated for accuracy, precision and recovery. In the qHNMR analysis, the method was based on 400 MHz proton NMR spectra of caffeine and theophylline (internal standard). Quantitative analyses were based on the integral ratio of selected signal belonging to the analyte with respect to that of an internal standard. The linear regression analysis data for calibration plots showed good relationship with r2 = 0.999 in the concentration range of 0.4-2.0 mg/mL with respect to peak area (integration). The recovery studies performed on pre-analyzed samples ranged between 97-108%. The caffeine values in coffee, tea and soft drink samples, quantified by both methods, were found to be in agreement with those reported in the literature. Caffeine contents were found to be: in green and roasted coffees (0.8 - 1.1%), tea (1.9 - 2.1%), soft drinks (5 - 7 mg per 100 mL), machine-brewed coffees (80 - 103 mg per 150 mL) and home-brewed coffees (Ethiopian traditional style) 12 – 39 mg per 150 mL. Both methods can be recommended for routine analysis.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | Q Science > Q Science (General) Q Science > QD Chemistry |
| Divisions: | Africana |
| Depositing User: | Selom Ghislain |
| Date Deposited: | 12 Sep 2018 07:32 |
| Last Modified: | 12 Sep 2018 07:32 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/5212 |
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