EFFECT OF GLASS-TRANSITION ON RATES OF NONENZYMATIC BROWNING IN FOOD SYSTEMS

The effect of glass transition on nonenzymatic browning of dehydrated vegetables and of model systems (composed of amino acids and sugars reacting in matrices with different physical characteristics) was studied. Glass transition temperature (T(g)) was determined by differential scanning calorimetry. The rates of nonenzymatic browning were taken from the literature for vegetables and were determined for model systems by measuring absorbance at 280 and 420 nm. Rate constants were analyzed as a function of temperature (T) and of (T - T(g)). Browning below T(g) was very slow. Changes in activation energy (which were affected by structural changes) could be detected near the glass transition. A complete predictive model must include the variables T, (T - T(g)), m, and concentration of reactants.