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?
Vegetables with Color:
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.
happens when chlorophyll is heated?
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).
can be used to slow the change in color?
effect do acids and bases have on the color of different vegetables?
effect do different cooking methods have on changes in color?
effect does Vitamin C have on changes in color?
on this project!
chromatography during different stages of cooking. This will identify
the changes of pigments.
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