Kinetics of colour change of raspberry, sweet (Prunus avium) and sour (Prunus cerasus) cherries preserves packed in glass containers: light and room temperature effects Original Research Article

This work studied the kinetics of colour change in preserves of raspberries, sweet and sour cherries exposed to different lighting conditions (light and darkness), at constant temperature, as well as stored at several temperatures. In all the preserves and treatments, the colour diminished noticeably during the first 90 days of storage to remain constant from then on. The kinetics of colour change was evaluated using the concept of fractional conversion, and a first-order kinetics was found in relation to both the effect of lighting conditions and temperature. The corresponding reaction rate constants were determined by regression analysis of the experimental data. For samples stored at different lighting conditions, the resulting constants of the different preserves were not alike: constants were higher in samples kept in the presence of light than the corresponding samples stored in the dark. However, the statistical analysis of the results indicated those not significant differences among the different light treatments. The statistical analysis of reaction rate constants obtained for the samples stored at constant temperatures, of 4°C, 20°C and 40°C, did indicate significant differences between treatments. In this case, applying one (A. Arabshai, D.B. Lund, Journal of Food Process Engineering 7 (1985) 239) and two-step (Arrhenius model) methods, the corresponding values of the pre-exponential factor (lnk0) and the energy of activation (Ea) were obtained and compared for the three preserves analysed.