Color formation due to non-enzymatic browning in amorphous, glassy, anhydrous, model systems

Polymeric matrix model systems (gelatinized starch, maltodextrin and polyvinylpyrrolidone (PVP) MW 40 000) containing a low concentration of added Maillardʹs reactants (glucose and l-lysine) were freeze dried, further desiccated (P2O5) to `zeroʹ % moisture, and heated for 48 h at 90°C. Under these conditions, all model systems were well below their measured glass transition temperature (Tg). Skim-milk powder samples (1.7 and 3.9% (dry basis) moisture) were also stored at 45 or 60°C, and browning was recorded. Browning was observed in the glassy polymeric matrices kept well below Tg and in the virtual absence of water. Browning developed in the milk powder samples stored at 60°C at a higher rate than at 45°C, even when both systems were in glassy conditions. This suggests that the Tg parameter should not be considered as an absolute threshold of stability with regard to non-enzymatic browning reactions. ©