Espectrofotometria de cafe

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Food Chemistry
Food Chemistry 108 (2008) 310–315 www.elsevier.com/locate/foodchem

Analytical Methods

Measurement of caffeine in coffee beans with UV/vis spectrometer
Abebe Belay a,*, Kassahun Ture a, Mesfin Redi b, Araya Asfaw a
b a Physics Department, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia Chemistry Department, AddisAbaba University, P.O. Box 1176, Addis Ababa, Ethiopia

Received 31 December 2006; received in revised form 2 May 2007; accepted 4 October 2007

Abstract In this research work using UV/vis spectrophotometer the molar decadic absorption coefficients and transitional dipole moment of pure caffeine in water and dichloromethane were obtained at 272 and 274.7 nm. The molar decadic absorptioncoefficients of caffeine in water and dichloromethane at these wavelengths are 1115 and 1010 m2 molÀ1, respectively. The calculated values for the transitional dipole moment of caffeine in water and in dichloromethane are 10.40 Â 10À30 and 10.80 Â 10À30 C m, respectively. After characterizing caffeine in water and dichloromethane, fast and simple methods were developed that enable to quantify the content ofcaffeine in coffee beans. The methods helped in extracting caffeine from coffee dissolved in water by dichloromethane, and Gaussian fit was applied to eliminate the possible interference with the caffeine spectra. Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Absorbance; Caffeine; Characterization; Extraction; UV/vis spectrophotometer

1. Introduction Caffeine is found in various kinds of foodsand drinks that we consume in daily life (Singh & Sahu, 2006). It causes various physiological effects such as relaxation of bronchial muscle, stimulation of the central nervous system, gastric acid secretion and dieresis Bolton and Null (1981). And their concentration in vivo is a key mark for various disorders including heart disease, carcinogenesis, kidney malfunction and asthma (Zhang, Lian,Wang, & Chen, 2005). On the other hand, chemical analysis of caffeine in coffee beans is also used as an additional tool for evaluating coffee quality. Higher caffeine contents associated with highest quality samples compared to other Arabic samples have been reported by Franca, Mendonca, and Oliveira (2005). Therefore, establishing a rapid and cheap analytical method for the determination ofcaffeine in coffee beans has an interest for a wide range of physiological effects on the human body and quality controls.

*

Corresponding author. Tel.: +251 911712766. E-mail address: abebealem2004@yahoo.com (A. Belay).

Several chemical and physical methods have been developed for the determination of caffeine in coffee and other beverages. The most widely used methods for the determination ofcaffeine in beverages include various analytical techniques such as derivative spectrophotometer (Alpdogan, Karbina, & Sungur, 2002) HPLC (Branstrom & Edenteg, 2002; Casal, Oliveira, & Ferreira, 2000; Minawlsawa, Yoshida, & Takali, 2004; Ortega-Burrales, Padilla-Weigand, & Molina-Diaz, 2002), Fourier Transform infrared (Bousain, Garriques, Garriges, & Guardia, 1999; Najafi, Hamid, & Afshin, 2003;Paradkar & Irudayaraj, 2002), NIR reflectance spectrometry (Chen, Zhao, Huang, Zhang, & Liu, 2006), Raman spectroscopy (Edawards, Munish, & Anstis, 2005) and capillary electrophoresis (Zhang et al., 2005), which have been reported. Although Spectrophotometer is a fast and simple method it is not possible to determine caffeine directly in coffee beans by conventional UV absorption measurement due tothe spectral overlap (Zhang et al., 2005). On the other hand, the derivative spectrophotometer is relatively easy; however, it is not reliable for the determination of small concentration of caffeine in samples. With HPLC methods the use of expensive equipments and the demand for more operator attention prevent

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