Chlorophyll Degradation and Zinc Complex Formation with Chlorophyll Derivatives in Heated Green Vegetables

Chlorophyll degradation and zinc complex formation with chlorophyll derivatives in processed green vegetables were studied using pea puree containing added Zn(2+) and heated at 121 degrees C for up to 150 min. Chlorophyll a decreased to trace levels after 20 min as zinc complexes of pheophytin a and pyropheophytin a were formed. Further heating decreased zinc pheophytin a and increased zinc pyropheophytin a concentrations. Zinc pyropheophytin may form by decarbomethoxylation of zinc pheophytin or by reaction of pyropheophytin with Zn(2+). pH effects were determined using pea puree adjusted to pH between 4.0 and 10.0 and heated at 121 degrees C for 30 min. Zinc complex formation increased in purees between pH 4.0 and 6.0 but decreased at pH values of 8.0 or greater. Chlorophyll a was retained at pH 8.0 or higher, suggesting that high pH processing may decrease zinc complex formation by reducing the amount of chlorophyll derivatives available for the reaction