Amino acids promote melanoidin formation through aldol reactions in the Maillard chemistry of methylglyoxal.

The browning reaction of the key Maillard reaction product methylglyoxal (MGO) was investigated in the presence of ten proteinogenic amino acids. Equimolar mixtures of the reactants were heated in water at 100 °C and pH 5 for up to 120 min. Each sample was analyzed for color formation, conversion of reactants, antioxidant activity, and molecular weight distribution of colorants. Direct-infusion high-resolution mass spectrometry was employed to determine molecular composition of reaction products, identify prevalent repeating units, and postulate formation mechanisms of colorants. It was found that most amino acids significantly promote the reaction, especially proline. Arginine acted as effective MGO scavenger, inhibiting browning. Lysine, on the other hand, formed amino acid modifications but accelerated color formation. Colorants were formed involving aldol and Michael reactions of MGO and its conversion products including formaldehyde, acetaldehyde, acetol, and glycolaldehyde.