Melanoidins Formed by Heterocyclic Maillard Reaction Intermediates via Aldol Reaction and Michael Addition

Thermal treatment of food leads to the formation of melanoidins by reactions of carbohydrates with free amino acids or proteins in the late stage of Maillard reaction. The aim of this study was the identification of reaction mechanisms responsible for the formation of melanoidins involving active methylenes with the heterocyclic structure and the structural characterization of the resulting products. For this purpose, norfuraneol was incubated with the aldehydes pyrrole-2-aldehyde or furfural at 125 degrees C. With the help of high-resolution mass spectrometry, the structural composition of oligomers of up to fifteen C-5-units could be described for the first time. Aldol and Michael reactions could be identified as crucial steps for the formation of new C-C-bonds. With increasing heating time, the elimination of water from the products was facilitated, and oxidation reactions of integrated reductone structures lead to the expansion of conjugated double -bond systems responsible for the color formation of the samples.