GLASS-TRANSITION AND REACTION-RATES - NONENZYMATIC BROWNING IN GLASSYAND LIQUID-SYSTEMS

Effects of physical state and glass transition on nonenzymatic brownin g rate in water, glycerol, poly(vinylpyrrolidone) (PVP), and maltodext rin (MD) systems were studied. All systems had the same concentration of reactants, glucose and lysine, in the water phase. The systems, exc ept water, had also comparable water activities (0.33). Sorption isoth erms and glass transition temperatures (T-g) at various water contents for the freeze-dried PVP and MD systems were determined. Nonenzymatic browning rate was determined at several temperatures from optical den sity at 280 and 420 nm. The PVP and MD systems contained 12.9 and 8.2 g of H2O/100 g dry matter and had T-g values of 67 and 62 degrees C at 33% relative humidity and 24 degrees C, respectively. The liquids exh ibited significantly higher browning rates than the concentrated syste ms, especially below the T-g values. The browning rate was higher in t he PVP than in the MD system, suggesting that a possible phase separat ion may affect nonenzymatic browning in foods.