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Monitoring of the dopamine D2 receptor agonists hordenine and N-methyltyramine during the brewing process and in commercial beer samples

Sommer, Thomas, Dlugash, Gelena, Hübner, Harald, Gmeiner, Peter, Pischetsrieder, Monika
Food chemistry 2019 v.276 pp. 745-753
agonists, alkaloids, barley, beers, brewing, dopamine receptors, drinking, fermentation, hordenine, humans, malt, malting barley, mashing, monitoring, phenethylamine, tandem mass spectrometry
The phenethylamine alkaloid hordenine, present in germinated barley, was identified recently as a functionally selective dopamine D2 receptor agonist contributing potentially to the rewarding effects of drinking beer. Here, it was shown that the hordenine precursor N-methyltyramine binds with a similar affinity to the dopamine D2 receptor as hordenine (Ki 31.3 µM) showing also selectivity towards the G protein-mediated pathway over the β-arrestin pathway. Using a newly developed UHPLC–ESI–MS/MS method to monitor beer production, we demonstrated that hordenine and N-methyltyramine were released continuously from barley malt during mashing and were stable during fermentation and conditioning. The amounts released from different base malt types were in a similar range but tended to be higher from caramel malts. Hordenine and N-methyltyramine concentrations in 24 types of beer varied between 1.05–6.32 and 0.59–4.61 mg/L, respectively. Thus, the human uptake of the alkaloids during beer consumption is in the low milligram range.