Did you ever notice when vegetables are cooked they brighten up? Spinach becomes a bight green, then if it's cooked too long it seems to turn grey. What is behind this color change? How can we keep the color? Why does the color change occur?

About Vegetables with Color:

Fruits and Vegetables owe their colors to various plant pigments. Spinach is green because it contains the pigment chlorophyll.Chlorophyll is a chlorin pigment, which is structurally similar to the iron-containing porphyrin compound known as heme. At the center of the chlorin ring is a magnesium ion. The sidechains vary somewhat between the different forms of chlorophyll found in different organisms. Chlorophyll a is present in all green plants, but chlorophylls b and c also occur in various groups. They also contain carotenoids, determining the color of the plant All green plants contains chlorophyll a, and most vegetables that we eat contain both chlorophyll a and chlorophyll b, some vegetables contain particularly high amounts of total chlorophyll. Best studied of all the vegetables is spinach (Spinacia oleracea in the Latin scientific name), with this vegetable containing about 300-600 milligrams per ounce.

What happens when chlorophyll is heated?

Chlorophyll has a chemical structure (containing a porphyrin ring) that is quite similar to a chemical structure found within our red blood cells. Chlorophyll however contains a magnesium atom in its center while heme contains an iron atom. When plants are heated and/or exposed to acid (and when green vegetables are cooked and/or exposed to acid), the magnesium gets removed from the center of this ring structure and replaced by an atom of hydrogen. This results in a change from chlorophyll to pheophytin. Chlorophyll a gets turned into a molecule called pheophytin a, and the chlorophyll b gets turned into pheophytin b. The color of the vegetable changes from bright green to olive-gray. (The pheophytin provides a green-gray color, and the pheophytin b provides an olive-green color).

Questons to Consider:

What can be used to slow the change in color?

What effect do acids and bases have on the color of different vegetables?

What effect do different cooking methods have on changes in color?

What effect does Vitamin C have on changes in color?

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Use chromatography during different stages of cooking. This will identify the changes of pigments.

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