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

Author:
Sommer, Thomas, Dlugash, Gelena, Hübner, Harald, Gmeiner, Peter, Pischetsrieder, Monika
Source:
Food chemistry 2019 v.276 pp. 745-753
ISSN:
0308-8146
Subject:
agonists, alkaloids, barley, beers, brewing, dopamine receptors, drinking, fermentation, hordenine, humans, malt, malting barley, mashing, monitoring, phenethylamine, tandem mass spectrometry
Abstract:
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.