Effect of physical changes on the rates of nonenzymic browning and related reactions

Nonenzymic browning (NEB) due to reaction of d-xylose and l-lysine was studied in a dehydrated matrix based on poly(vinylpyrrolidone) (PVP) of different average molecular weights. Physical changes (collapse) and NEB were studied temperatures (T) and moisture contents resulting in different values of (T − Tg), where Tg is the glass transition temperature. ymic browning rates at low and intermediate moisture contents in a polymeric matrix above its glass transition were shown to be closely related to (T − Tg). The initially porous matrices underwent a time-dependent shrinkage (collapse) above Tg and this shrinkage increased the rate of browning, presumably by minimizing diffusion paths for reactants. he reactants (xylose and lysine in PVP) were separated by a reactant-free layer of PVP, the reaction rate decreased as the thickness of the empty layer increased. A lag time was observed, which was directly related to the thickness of this layer.