Nonenzymatic browning kinetics of a carbohydrate-based low-moisture food system at temperatures applicable to spray drying.

Effects of water contents on nonenzymatic browning (NEB) rates of amorphous, carbohydrate-based food model systems containing L-lysine and D-xylose as reactants were studied at different temperatures (40, 50, 60, 70, 80, and 90 degrees C) applicable to spray drying conditions. Water sorption was determined gravimetrically, and data were modeled using the Brunauer-Emmett-Teller and Guggenheim-Anderson-deBoer equations. Glass transition, Tg was measured by DSC. NEB was followed spectrophotometrically. The rate of browning increased with water content and temperature, but a lower T-Tg was needed for browning at decreasing water content. Water content seemed to affect the activation energy of NEB, and higher water contents decreased the temperature dependence of the NEB. At higher temperatures, the NEB became less water content dependent and enhanced browning in spray-drying. The temperature dependence of nonenzymatic browning could also be modeled using the Williams-Landel-Ferry (WLF) equation, but the WLF constants were dependent on the water content.