Kinetics of formation of acrylamide and Schiff base intermediates from asparagine and glucose

From the concentration of glucose and asparagine as reactants and of acrylamide as product each determined by LC–MS during reaction in an acetonitrile/water (68:32) model system at pH 7.6 (0.04 M phosphate buffer) and from the relative concentration of the Schiff base intermediate, the decarboxylated Schiff base intermediate, the Amadori product and aminopropionamide determined in the same reaction mixtures at 120 °C, 140 °C, 160 °C and 180 °C for up to 16 min, the energy of activation for formation of the Schiff base intermediate was found to have the value 50 ± 2 kJ mol−1, while the apparent activation energy for formation of acrylamide was 64.4 ± 0.6 kJ mol−1, for formation of the decarboxylated Schiff base intermediate 92 ± 2 kJ mol−1, and for formation of the Amadori compound 59 ± 4 kJ mol−1, respectively. At high temperature conditions, formation of the Schiff base is accordingly rate determining, while at lower temperatures, decarboxylation becomes rate determining. Aminopropionamide was only detected at reaction times at which acrylamide formation already is significant in favor of, a reaction path including direct formation of acrylamide from the decarboxylated Schiff base, rather than including dissociation of ammonia from aminopropionamide.