NONENZYMATIC BROWNING KINETICS IN AN INTERMEDIATE MOISTURE MODEL SYSTEM: EFFECT OF GLUCOSE TO LYSINE RATIO

An intermediate moisture model food system containing casein, glucose, glycerol, oil, microcrystalline cellulose and water, was used to study nonenzymatic browning. The initial molar ratio of glucose to available lysine was varied from one‐half to five. The model food system samples were prepared to 0.52 water activity and were stored in sealed cans at 45°C and analyzed periodically. The browning was followed by determining pigment accumulation, glucose utilization, and loss in FDNB‐available lysine. The rate of pigment formation followed zero order kinetics after an initial short induction period. This rate increased linearly as the initial molar ratio of glucose to available lysine increased from one‐half to three. Above this ratio the rate did not change. The initial rate of glucose utilization and available lysine loss obeyed first order kinetics, and increased as the initial molar ratio of glucose to available lysine increased from one‐half to five. This work shows that in the presence of glycerol, the initial condensation reaction is not the rate controlling step for pigment production.