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-T-g), where T-g is the glass transition temperature. Nonenzymic browning rates at low and intermediate moisture contents in a polymeric matrix above its glass transition were shown to be closely related to (T-T-g). The initially porous matrices underwent a time-dependent shrinkage (collapse) above T-g and this shrinkage increased the rate of browning, presumably by minimizing diffusion paths for reactants. When the 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.