kinetics of browning measured during the storage of onion and strawberry

The kinetics of non-enzymatic browning of onion and strawberry during storage at different temperature (5, 15, 25, 35, 45 degrees C) and equilibrium relative humidities (33%, 44%, 53%) was measured. Colour formation in onion was observed by measuring absorbance versus time in aqueous extract solutions. Experimental results of colour formation of onion as a function of time for each level of water activity were best represented by a zero order kinetics, while anthocyanin degradation in strawberry followed a second order kinetics. Rate coefficients obtained in both cases showed an increase in the rate of the reactions with both temperature and water activity. With regard to temperature dependence of rate coefficients, statistical evidence suggest that in the case of colour formation in onion, the Williams-Landel-Ferry model is a better representation than Arrhenius. In the case of strawberry it was not possible to reach such conclusion in spite of a lower summation of residuals obtained with the WLF model.