Nonenzymatic Browning in Liquid Model Systems of High Water Activity: Kinetics of Color Changes due to Maillard's Reaction Between Different Single Sugars and Glycine and Comparison with Caramelization Browning

Sugar‐ (fructose, xylose, glucose, lactose, maltose, sucrose) glycine solutions of water activity adjusted to 0.90 (by adding NaCI) were heated at 45–65°C. The behavior of fructose‐glycine solutions was well described by a zero‐order reaction model, but for the other sugars a fractional‐order (∼ 0.5) kinetic model was necessary. Activation energies for glucose, fructose and sucrose systems were 25.7, 29.3 and 36.6 kcah/mole, respectively. At pH 6 the descending order for color development was xylose > glucose > fructose > lactose > maltose > sucrose; at pH lower than 6 fructose browned faster than glucose. The role of hydrolysis of sucrose as related to Maillard's browning of heated sucrose‐glycine solutions was studied. Caramelization browning seemed to contribute noticeably to total color development only in fructose‐glycine solutions.