ZINC COMPLEX-FORMATION IN HEATED VEGETABLE PUREES

Zinc complex formation with pyropheophytin a was studied on vegetable purees in order to further understand metallo complex formation during thermal processing. Zinc pyropheophytin a formation was dependent on added Zn2+ion, pigment concentration, and pH. Pea puree heated 60 min at 121 ° with 150 and 300 ppm added Zn2+ion contained 3 and 9 times more zinc pyropheophytin a than puree containing 75 ppm Zn2+ion. Spinach puree with 75 ppm Zn2+ion added, with 12 times the pigment concentration compared to pea puree, contained approximately 40 times more zinc complex than similar pea puree heated at 121 ° for 60 min. Increasing the pH value of the spinach puree from 4.0 to 8.5 resulted in an 11-fold increase in zinc pyropheophytin a formed after heating at 121 ° for 90 min. Green color of the puree, as measured by Hunter color value (-a), followed zinc complex formation. © 1990, American Chemical Society. All rights reserved.