Effect of Water Activity and Temperature in Color and Chlorophylls Changes in Yerba Mate Leaves

The kinetics of chlorophylls (a and b) degradation were studied in yerba mate leaves at different temperatures (50 to 808C) and water activities (0.1 to 0.8). Chlorophyll changes followed a first order-kinetic reaction in all cases. Rate constant values were fitted to different models to describe temperature and water activity dependence. When an Arrhenius model was used, the activation energy was found to be dependant on water activity for chlorophyll a (80.4–99.7 kJ/mol), while for chlorophyll b activation energy showed only a little variation (88.1–89.5 kJ/mol). Color parameter a* underwent a great decrease while parameters L* and b* had only a little variation.