Browning and pigmentation in food through the Maillard reaction.

The Maillard reaction was discovered in 1912 by Louis C. Maillard when he observed the browning phenomena with aroma formation in a heated solution containing a sugar and an amino acid. The Maillard reaction starts from the reactions between carbonyl groups of various sugars and amino groups of amino acids/ proteins, following the formation of intermediate compounds or poly-carbonyl compounds, which further react with each other and amino acids/proteins. Through various chemical reactions such as condensation, polymerization, degradation, cyclization etc., color and aroma are formed. The imparting of brown color is mainly attributed to melanoidins. However, the chemical structure of melanoidins remains unclear because melanoidins are complex and heterogeneous polymers. On the other hand, various kinds of low-molecular-weight pigments formed through the Maillard reaction have been isolated and their structures have been identified. Even though the contribution of each pigment is small, the recognition of color is cumulative. In some case, these pigments form brown polymers or significantly contribute to the total color of a model solution. These chemically clear information gives us a novel aspect for an overview of browning or pigmentation through the Maillard reaction. Graphical abstract.