OXIDATION OF CAFFEINE AND RELATED METHYLXANTHINES IN ASCORBATE AND POLYPHENOL-DRIVEN FENTON-TYPE OXIDATIONS

Caffeine and related methylxanthines were subjected to free radical me diated oxidation by incubation with Fe3+-EDTA/ascorbate and Fe3+-EDTA- polyphenolics. The reaction mixtures were analysed by reverse-phase HP LC, revealing the corresponding C-8 hydroxylated analogues as the majo r products of hydroxyl radical mediated attack. Further oxidation prod ucts of caffeine, analysed by liquid chromatography - mass spectrometr y (LC-MS), were the N1-, N3- and N7-demethylated methylxanthine analog ues theobromine, paraxanthine and theophylline, respectively. Isolable amounts of the imidazole ring opened amino-5-(N-formylmethyl-amino)-1 ,3-dimethyl-uracil (1,3,7-DAU) derivative were also detected, which wa s characterised by H-1 NMR and mass spectroscopy. The identified produ cts indicate that the pertinent chemical reactions, i.e. C-8 hydroxyla tion, demethylations, and C8-N9 bond scission, are comparable to the p rimary metabolic pathways of caffeine in humans. The influence of pH, transition metals, hydrogen peroxide, free radical scavengers and meta l chelators on caffeine oxidation was studied. This report illustrates that natural food-borne reactants can aid in identifying specific che mical markers of free radical induced damage. Furthermore, potentially anti- and pro-oxidative reactions can be elucidated which may be impo rtant in assessing the impact of nutrient additives and supplements on the shelf life and stability of foods and beverages.