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Scope: Coffee is a complex mixture of over 1000 compounds, including diverse heteroaromatic compounds such as alkylpyrazines. Little is known about the intake, metabolism, and bodily distribution of these compounds. Therefore, a human intervention study is conducted to investigate the excretion of alkylpyrazine metabolites in urine after the ingestion of brewed coffee containing alkylpyrazines. Methods and results: After consuming a diet without heat-processed food, ten volunteers consumed 500 mL of freshly brewed coffee prepared from coffee pads, providing intakes of 2-methylpyrazine (2-MeP), 2,5-dimethylpyrazine (2,5-DMeP), and 2,6-dimethylpyrazine (2,6-DMeP) amounting to 17.2, 4.4, and 4.9 µmol, respectively. These alkylpyrazines are metabolized into the corresponding pyrazine carboxylic acids, namely pyrazine-2-carboxylic acid (PA), 5-hydroxypyrazine-2-carboxylic acid (5-OHPA), 5-methylpyrazine-2-carboxylic acid (5-MePA), and 6-methylpyrazine-2-carboxylic acid (6-MePA). In total, 64% of the ingested 2-MeP is excreted as PA, as well as 26% as 5-OHPA, while 91% and 97% of the ingested 2,5-DMeP and 2,6-DMeP are recovered as 5-MePA and 6-MePA, respectively, in urine samples collected after coffee consumption. Conclusion: This study provides evidence that alkylpyrazines are rapidly metabolized into the corresponding carboxylic acids and excreted via urine by humans, which is consistent with earlier rodent studies.

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Up to now, knowledge of enzymes capable of degrading various contaminants of emerging concern (CEC) is limited, which is especially due to the lack of rapid screening methods. Thus, a miniaturized high-throughput setup using a chip-based robotic nanoelectrospray ionization system coupled to mass spectrometry has been developed to rapidly screen enzymatic reactions with environmentally relevant CECs. Three laccases, two tyrosinases, and two peroxidases were studied for their ability to transform ten pharmaceuticals and benzotriazole. Acetaminophen was most susceptible to enzymatic conversion by horseradish peroxidase (HRP), laccase from Trametes versicolor (LccTV), and a tyrosinase from Agaricus bisporus (TyrAB). Diclofenac and mefenamic acid were converted by HRP and LccTV, whereas sotalol was solely amenable to HRP conversion. Benzotriazole, carbamazepine, gabapentin, metoprolol, primidone, sulfamethoxazole, and venlafaxine remained persistent in this study. The results obtained here emphasize that enzymes are highly selective catalysts and more effort is required in the use of fast monitoring technologies to find suitable enzyme systems. Despite the methodological limitations discussed in detail, the automated tool provides a routine on-line screening of various enzymatic reactions to identify potential enzymes that degrade CECs. Graphical abstract A chip-based robotic nano-ESI-MS tool to rapidly monitor enzymatic degradation of environmentally relevant emerging contaminants.

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