Thermal degradation of chlorophylls and chlorophyllides in spinach puree was studied from 100 to 145°C (2-25 min) for chlorophylls and from 80 to 115°C (2.5-39 min) for chlorophyllides. The derivatives formed were: pheophorbides, pyropheophorbides, pheophytins and pyropheophytins. Degradation kinetics of chlorophylls and chlorophyllides followed a first-order kinetic model. Reaction rate data showed that the a form of both chlorophylls and chlorophyllides degraded more rapidly than the b form. Chlorophyllides were less stable than chlorophylls. Activation energies ranged from 15.0 to 22.8 Kcal/mol. A kinetic compensation effectwas observed for both chlorophylls and chloroohvllides with an isokinetic temnerature of 160.8"C. The relative stab&ty of these compounds suggests that methods to maximize chlorophyllides would not be effective for improving green color stability.

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Fresh and frozen green peas were blanched in zinc solution (50 to 500 mg/L) and thermally processed in a particle cell reactor, which simulates a continuous flow aseptic processing system. The thermal process temperatures ranged from 121 to 145 °C at holding times from 0 to 20 min. The degradation of chlorophyll and the resulting formation of Zn-pheophytin a and Zn-pyropheophytin a were monitored. Quantitative analysis of the metallo-chlorophyll complexes was performed by high-performance liquid chromatography. Complex formation increased during heat processing and was dependent on the zinc concentration absorbed within the peas during blanching. At 130 to 145 °C, the formation of Zn-pyropheophytin a increased and processing between 121 to 125 °C promoted the formation of Znpheophytin a. Improvements in color relative to control samples suggested that the process might be applicable to two-phase continuous aseptic processing of vegetables.

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