QUANTIFICATION OF COLOR-CHANGE RESULTING FROM PHEOPHYTINIZATION AND NONENZYMATIC BROWNING REACTIONS IN THERMALLY PROCESSED GREEN PEAS

The visual green color degradation, as represented by the change of th e -a value measured by a tristimulus colorimeter, was found to be caus ed by not only pheophytinization but also by nonenzymatic browning rea ctions in green peas at 100, 110, and 120 degrees C. Mathematical mode ls were developed for predicting the change in the -a value as a funct ion of time and temperature by knowing the kinetic parameters (rate co nstant and activation energy) of each mechanism. The rate of disappear ance of greenness via pheophytinization followed a first-order kinetic model, while the rate of color loss due to nonenzymatic browning reac tions followed a zeroth-order kinetic model after an initial lag perio d. The activation energies for pheophytinization and nonenzymatic brow ning were 20.4 and 22.3 kcal/mol, respectively.