Nonenzymatic browning reaction of essential amino acids: Effect of pH on caramelization and Maillard reaction kinetics

The interaction between glucose and essential amino acids at 100 degrees C at pH values ranging from 4.0 to 12.0 was investigated by monitoring the di sappearance of glucose and amino acids as well as the appearance of brown c olor. Lysine was the most strongly destroyed amino acid, followed by threon ine which induced very little additional browning as compared with that und ergone by glucose. Around neutrality, the nonenzymatic browning followed ps eudo-zero-order kinetics after a lag time, while the glucose and amino acid losses did not follow first-order kinetics at any of the pH values tested. Glucose was more strongly destroyed than all of the essential amino acids, the losses of which are really small at pH values lower than 9.0. However, glucose was less susceptible to thermal degradation in the presence of ami no acids, especially at pH 8.0 with threonine and at pH 10.0 with lysine. T he contribution of the caramelization reaction to the overall nonenzymatic browning above neutrality should lead to an overestimation of the Maillard reaction in foods.