The kinetics of browning measured during the storage of onion and strawberry

The kinetics of non-enzymatic browning of onion and strawberry during stora ge at different temperature (5, 15, 25, 35, 45 degrees C) and equilibrium r elative humidities (33%, 44%, 53%) was measured. Colour formation in onion was observed by measuring absorbance versus time in aqueous extract solutio ns. 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 kin etics, while anthocyanin degradation in strawberry followed a second order kinetics. Rate coefficients obtained in both cases showed an increase in th e rate of the reactions with both temperature and water activity. With rega rd to temperature dependence of rate coefficients, statistical evidence sug gest that in the case of colour formation in onion, the Williams-Landel-Fer ry model is a better representation than Arrhenius. In the case of strawber ry it was not possible to reach such conclusion in spite of a lower summati on of residuals obtained with the WLF model.