Structural characterization of polar melanoidins deriving from MAILLARD reaction intermediates - A model approach

Chemical conversions of reducing sugars and amino compounds induce the formation of heterogenous, highmolecular-weight colorants ('melanoidins') with widely unknown chemical structures. Model experiments of reactive intermediates have proven to be suitable for unravelling the formation mechanisms of colored reaction products. Here, the active methylene norfuraneol was selected and incubated individually as well as in combination with glyoxal, glycolaldehyde, and acetaldehyde at elevated temperatures. Photometric and chromatographic methods as well as mass spectrometry were used to analyze the colored reaction products and reveal the reactivity of different carbonyls regarding the formation of heterogenous oligomers. Aqueous solutions of norfuraneol and glyoxal exceeded the color formation of all other model reaction systems and it could be shown that the initial reactants as well as their degradation products were incorporated into the colorants. The colored oligomers described herein were composed of carbohydrate-based intermediates of the MAILLARD reaction and defined as melanoidin precursors or pre-melanoidins.

Automated summary

Chemical reactions of reducing sugars and amino compounds result in the formation of heterogeneous, high molecular weight colorants (melanoidins) with unknown structures. Model experiments using reactive intermediates were conducted to understand the formation mechanisms of colored reaction products. Norfuraneol, a reactive methylene compound, was incubated individually or combined with glyoxal, glycolaldehyde, and acetaldehyde at elevated temperatures. Photometric, chromatographic, and mass spectrometric methods were employed to analyze the colored reaction products and investigate the reactivity of different carbonyls. Aqueous solutions of norfuraneol and glyoxal showed the highest color formation among the model reaction systems, and it was observed that the initial reactants and their degradation products were incorporated into the colorants. The colored oligomers identified in this study were composed of carbohydrate-based intermediates of the Maillard reaction and termed as melanoidin precursors or pre-melanoidins.