Kinetics of chlorophyll degradation and color loss in heated broccoli juice

Degradation of chlorophyll in broccoli juice occurred at temperatures excee ding 60 degrees C. Chemical analysis revealed that degradation of chlorophy ll a and b to pheophytin a and b, respectively, followed first-order kineti cs and that chlorophyll:a was more heat sensitive than chlorophyll b. Tempe rature dependencies of chlorophyll a and b degradation rate constants could be described by Arrhenius equations with activation energies (E-a) of 71.0 4 +/- 4.89 and 67.11 +/- 6.82 kJ/mol, respectively. Objective greenness mea surements, using the -a value as the physical property, together with a fra ctional conversion kinetic analysis, indicated that green color degradation followed a; two-step process. Kinetic parameters for the first degradation step were in accordance with the kinetic parameters for pheophytinization of the total chlorophyll content, as determined by chemical analysis (E-a a pproximate to 69 kJ/mol). The second degradation step, that is, the subsequ ent decomposition of pheophytins, was characterized by an activation energy of 105.49 +/- 4.74 kJ/mol.