Determination of selected secondary and tertiary amine alkaloids in barley malt

Graduation date: 1984The malt alkaloids N-methyltyramine, N,N-dimethyltyramine\ud (hordenine), N-methyl-3-aminomethylindole and N,N-dimethyl-3-aminomethylindole\ud (gramine) are known precursors for N-nitrosamines.\ud Analytical procedures were developed and applied to extract and\ud quantify these alkaloids from malt, green malt, malt roots, and\ud raw barley. A ground malt sample under nitrogen atmosphere was\ud extracted with 5 percent concentrated ammonium hydroxide in methanol\ud at room temperature for 24 hours. After purification, the\ud extracted alkaloids were quantitated by reverse phase high performance\ud liquid chromatography using both phosphate buffer and\ud ion-pairing solvent systems. The recoveries obtained for the alkaloids\ud listed were, respectively, 77.4, 92.0, 74.0 and 80.5 percent\ud with detection limit of 0.2, 0.2, 0.1 and 0.1 μg/gm. Conformation\ud of identity of each alkaloid was accomplished by TLC,\ud UV, and MS.\ud Twenty-three samples of kilned malts, five samples of green\ud malts, ten samples of kilned malt roots, five samples of green malt roots, and ten raw barley samples, from a total of 11 varieties\ud of Hordeum vulgare were analyzed for the alkaloids of interest.\ud N-Methyltyramine was found in every sample from all\ud sources with a mean and range, respectively, of 26.8 (15.7-48.5),\ud 21.4 (11.6-37.5), 1959.8 (1358.4-2798.4), 1532.5 (962.3-2091.1)\ud and 4.7 μg/gm (0.4-17.9 μg/gm) on a dry weight basis. The means\ud and ranges for hordenine were, respectively, 28.1 (8.9-42.4),\ud 21.2 (9.6-35.5), 4066.4 (2741.2-5180.1), 3363.3 (1956.2-4744.3)\ud and 0.7 μg/gm (0.5-1.0 μg/gm). Gramine was found in only two\ud barley malt varieties examined where kilned and green malts contained,\ud respectively, mean values and ranges of 7.4 (4.9-10.0)\ud and 6.0 μg/gm (4.7-7.3 μg/gm). N-Methyl-3-aminomethylindole was\ud not detected in any of the samples examined.\ud The results of this investigation indicated that the variety\ud of barley affected alkaloid production during malting. The results\ud also showed that the kilning step of the malting process increased\ud the total amount of each alkaloid produced.\ud Finally, room temperature nitrosation of five varieties of\ud kilned and green malts, in which the contents of hordenine and\ud gramine were known, was carried out with an excess of nitrite in\ud acetic acid at pH 3.2 for 18 hours. The amounts of N-nitrosodimethylamine\ud (NDMA) obtained from this nitrosation were far greater\ud than the expected yields for NDMA from the hordenine and gramine\ud present in the malts. The results strongly suggest that the alkaloids hordenine and gramine were not the only precursors for NDMA and that there must be additional precursors; dimethylamine was\ud suggested as a possibility