Contribution of Hydroxycinnamic Acids to Color Formation in Nonenzymatic Browning Reactions with Key Maillard Reaction Intermediates

The Maillard reaction is a vital part of food processing, involving a vast number of complex reaction pathways, resulting in high-molecular-weight colorants. So far, studies have been focused on the conversion of carbohydrates and amino compounds, but the literature elaborating the contribution of phenolic compounds to the formation of the colored end-products is still rare. The aim of this study was to characterize early reactions, underlying the formation of phenol-containing melanoidins. For this purpose, binary model systems of the prominent phenolic compounds caffeic acid and ferulic acid combined with α-dicarbonyl compounds typically formed in the Maillard reaction such as glyoxal, methylglyoxal, and diacetyl were analyzed after heat treatment. High-resolution mass spectrometry revealed that decarboxylation, aromatic electrophilic substitution, and nucleophilic addition are important reaction steps that lead to colored heterogeneous oligomers. Polymerization was favored for phenolic compounds with a high electron density in the aromatic system and for α-dicarbonyl compounds carrying aldehyde functions.