Kinetics of interaction of vanillin with amino acids and peptides in modelsystems

Model systems were used to study the reaction kinetics of vanillin and pent alysine, lysine, glutathione, cysteine, aspartame, or phenylalanine (molar ratio 1:1) in phosphate buffer. The buffer pH was adjusted to the pK(a2) of the available ol-amino group of each amino acid or peptide. Reductions of vanillin followed first-order kinetics at 55, 65, and 75 degrees C in the p resence of each of the amino acids or peptides used. The reaction rates wer e accelerated as the temperature increased. The rate constants were highest for pentalysine followed by lysine, phenylalanine, glutathione/cysteine, a nd aspartame. The reduction of phenylalanine followed first-order kinetics, whereas the formation of its reaction product followed zero-order kinetics . The activation energy (E-a) for the reaction ranged from 5.6 to 14.5 kcal /mol.