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 Zn2+ 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 Zn2+. 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.