Abstract
Caffeine (1,3,7-trimethylxanthine) is the most consumed psychoactive substance in the world, acting by means of antagonism to adenosine receptors, mainly A1 and A2A. Coffee is the main natural source of the alkaloid which is quite soluble and well extracted during the brew’s preparation. After consumption, caffeine is almost completely absorbed and extensively metabolized in the liver by phase I (cytochrome P450) enzymes, mainly CYP1A2, which appears to be polymorphically distributed in human populations. Paraxanthine is the major caffeine metabolite in plasma, while methylated xanthines and methyluric acids are the main metabolites excreted in urine. In addition to stimulating the central nervous system, caffeine exerts positive effects in the body, often in association with other substances, contributing to prevention of several chronic diseases. The potential adverse effects of caffeine have also been extensively studied in animal species and in humans. These aspects will be approached in the present review.
Highlights
There are reports on the use of coffee at least since the 9th century, caffeine was only understood as a substance and component of food matrices in the middle of the 19th century
High-performance liquid chromatography (HPLC) technique was used in caffeine analysis for the first time in the early 1970s [22]
In coffee matrix, due to the very low amount of other methylxanthines, HPLC and ultra-high-performance liquid chromatography (UPLC) isocratic systems have been often applied for determination and quantification of these compounds, using a reverse-phase column and a mixture of methanol and water as the mobile phase [24,25,26]
Summary
Caffeine is colorless at room temperature, odorless, and bitter [13]. It dissolves well in boiling water, and its solubility is increased by the addition of acids and formation of complexes, such as benzoate, citrate, and salicylate, at high temperatures (1%, w/v, at 15 ◦C and 10% at 60 ◦C) [14]. In coffee matrix, due to the very low amount of other methylxanthines, HPLC and ultra-high-performance liquid chromatography (UPLC) isocratic systems have been often applied for determination and quantification of these compounds, using a reverse-phase column and a mixture of methanol and water as the mobile phase [24,25,26]. Spectroscopy in the infra-red region has been introduced as a promising alternative technique to wet chemical methods [18,32], especially the Fourier transform infra-red spectroscopy (FTIR) [33] Methods using this technique dissolve the active principles in chloroform, followed by filtration of the solution to remove the excipients [18]. Bare carbon electrodes have been proposed as simple and efficient sensors for the quantification of caffeine in commercial beverages, presenting similar values when compared to results from UPLC analyses [30]
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