Effects of pH on caramelization and Maillard reaction kinetics in fructose-lysine model systems

The nonenzymatic browning reactions of fructose and fructose-lysine aqueous model systems were investigated at 100 degreesC between pH 4.0 and pH 12.0 by measuring the loss of reactants and monitoring the pattern of UV-absorbance and brown color development. At all the pH values tested, the loss of fructose was lower in the presence than in the absence of lysine. And, in lysine-containing fructose solution, the sugar disappeared more rapidly than the amino acid. Lysine was moderately lost below pH 8.0. Caramelization of fructose, which accounted for more than 40% of total UV-absorbance and 10 to 36% of brown color development, may therefore lead to overestimating the Maillard reaction in foods.