MODEL REACTIONS ON ROAST AROMA FORMATION .15. INVESTIGATIONS ON THE FORMATION OF PYRIDO[3,4-D]IMIDAZOLES DURING THE MAILLARD REACTION

When aqueous solutions of histidine and glucose were heated to 100, 120, 150, or 180 degrees C or when this mixture was roasted at 220 degrees C, a total of 231 volatile compounds were identified. Among them 2-acetyl- and 2-propionylpyrido[3,4-d]imidazole were found. Their formation pathway via a reaction of pyruvic aldehyde or 2-oxobutyraldehyde with, respectively, histidine or histamine is discussed. Experiments with C-13 isotope labeled glucose point out that the terminal methyl groups of both aldehydes can arise from C-1 as well as C-6 of glucose. While pyruvic aldehyde can be formed by retro aldol scission of intermediate diacetylformoin, 2-oxobutyraldehyde was obviously formed from 2,5-dimethyl-4-hydroxy-3(2H)-furanone, By reaction of 1-, 2-, or 3-methylhistidine with glucose seven more pyrido[3,4-d]imidazoles were identified, the structures of which, like the structures of the above-mentioned compounds, were unknown up to now.