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

• Published in: Food chemistry Vol. 276; pp. 745 - 753
• Main Authors: Sommer, Thomas, Dlugash, Gelena, Hübner, Harald, Gmeiner, Peter, Pischetsrieder, Monika
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 15.03.2019
• Subjects: Animals; Beer; Beer - analysis; Brewing; CHO Cells; Chromatography, High Pressure Liquid; Cricetulus; Dopamine Agonists - analysis; Dopamine Agonists - metabolism; Dopamine D2 receptor agonist; Fermentation; Food Analysis - methods; Hordenine; Hordeum - metabolism; Humans; Mashing; N-Methyltyramine; Radioligand Assay; Receptors, Dopamine D2 - agonists; Receptors, Dopamine D2 - genetics; Receptors, Dopamine D2 - metabolism; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry; Tyramine - analogs & derivatives; Tyramine - analysis; Tyramine - metabolism; Hordenine; N-Methyltyramine; Mashing; Dopamine D2 receptor agonist; Brewing; Fermentation; Beer
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2018.10.067

•Both hordenine and NMT are functionally selective dopamine D2 receptor agonists.•During mashing, hordenine and NMT were released continuously from the malt.•Concentrations of hordenine and NMT remained stable during fermentation and conditioning.•In 24 beer samples, ranges of hordenine and NMT were 1.1–6.3 mg/mL and 0.6–4.6 mg/mL, respectively. 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.