vitamin c indicator

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Science projects about nutrition & health
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Learn how to prepare award-winning science fair projects.

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1. Do different varieties of the same fruit have the same level of
vitamin C?

What about different brands of orange juice? Or fresh juice compared
to juice from frozen concentrate? Does the way a fruit is stored or
how long it is stored change the level of vitamin C?

Background Info: Most birds and animals make their own vitamin C. But
a few species, like people and guinea pigs, must get it from their
food. Good sources of vitamin C are citrus fruits like oranges and
grapefruit, strawberries, green peppers, broccoli and potatoes.
Vitamin C is required for the body to make and maintain collagen, a
protein. Collagen forms the base for all connective tissue in the
body. If you don't have enough vitamin C in your diet, you might get
the disease scurvy. Symptoms include loss of appetite, bleeding gums,
loose teeth, swollen ankles and tiny hemorrhages (bleeding spots) in
the skin.

Procedure to test for vitamin C content. (With this method, you can
compare relative vitamin C content and rank foods from highest to
lowest, but you won't be able to get exact concentrations.)

You'll need some 2% iodine solution (find it at your local pharmacy)
to prepare the vitamin C indicator solution described in steps 1 to 4.

1. Mix 1 tablespoon of cornstach into enough water to make paste.
2. To this paste, add 250 milliliters of water and boil for 5 minutes.
3. Add 10 drops of the starch solution to 75 milliliters of water (use
an eyedropper).
4. Add enough iodine to produce a dark purple-blue color. Now your
indicator solution is ready.
5. Put 5 milliliters of indicator solution (about 1 teaspoon) in a
15-milliliter test tube (one for each sample).
6. To the test tube, use a clean eyedropper to add 10 drops of juice
from the fruit or beverage (for solids, pulp them in a blender and
strain the juice). Re-clean the eyedropper for each sample.
7. Hold the test tube against a white background. Line up the tubes
from lightest to darkest purple. The lighter the solution, the higher
the vitamin C content. That's because vitamin C causes the purple
indicator solution to lose its color

2. Are there different amounts of iron in different breakfast cereals?

The iron in ready-to-eat breakfast cereals is in the form called
elemental, not in combination with any other chemical compound. Iron
is sprayed on the outside of cereal flakes. You can separate the iron
with a strong magnet.

Background Info: Iron is essential in a healthy diet to build blood.
Iron is easiest to absorb from meat, fish and poultry.

Procedure:
You'll need a fairly sensitive scale for this procedure. A bathroom
scale won't cut it!
1. Crush 1/2 cup of cereal in a baggie, until the flakes are half
their original size. Pour into a bowl.
2. Add 1 cup of hot water and mix with a wooden spoon.
3. Get a strong, 3-inch bar magnet that is not grey or black (so the
iron filings will show up). Don't use a horseshoe magnet.
4. Put the magnet into the cereal mix and stir gently in a circle for
a fixed amount of time, say 5 minutes. Try not to bump the bottom or
sides of the bowl.
5. Take out the magnet. Remove the iron filings that it pulled from
the cereal, and weigh them on a laboratory scale.

3. Are all apples equally sweet?

As apples ripen, the starch in the fruit changes to sugar, making the
fruit sweet. What kind of sweet differences are there between apple
varieties or individual apples of the same type?

Background Info: Starch levels in apples can be measured by dipping a
portion of the apple into an iodine solution. The starch reacts with
the iodine solution to produce a blue-black color in a pattern that is
characteristic for each variety of apple. For example, Red Delicious
apples lose starch in a fairly even ring, while Golden Delicious
apples have an uneven pattern.
Recipe for the Iodine Solution:
Always make up a fresh iodine solution. Keep this solution in a
dark-colored (or foil-wrapped) bottle and away from light. Since
iodine is poisonous, treated apples should also be considered
poisonous and should not be eaten by people or animals or used in
composting. Do not allow pets to lick the fruit after testing.
Dissolve 10 grams (about 1/3 ounce) of potassium iodide in 10 ml
(approximately 1/8 cup) of water. When it is dissolved, add 2.5 grams
(about 1/12 ounce) of iodine crystals. Shake the mixture until the
crystals are thoroughly dissolved. Dilute this mixture with water to
make 1.14 liters (1 quart).
Make sure the solution is completely mixed by shaking the bottle
everyday for several days.

Procedure:
1. It is best to test fresh apples that have not been stored, so this
experiment is best done in the fall. Another way to use this test is
to track apple ripening from a single tree over the harvest season to
pinpoint the best time to harvest that tree's apples.
2. Pour the iodine solution into a shallow glass container to a depth
of 5 to 7.5 mm (approx. 1/4 inch). Cut each apple in half horizontally
across the core and put the exposed surface of one of the halves in
the iodine solution. The apple stem can serve as a convenient handle,
if the top half is used.
3. Wait 1 minute before removing the apple half. Repeat with the next
test apple.
4. Compare the patterns of black spots, which indicate the presence of
starch.
5. When there is no reaction and no color change, all of the starch
has changed to sugar.
For comparison, you can find reference standards for starch iodine
patterns for Macintosh, Red Delicious, Empire & Spartan
(http://www.omafra.gov.on.ca/english/crops/facts/00-027.htm#pics), and
Gala (http://www.umass.edu/fruitadvisor/clements/articles/gala.jpg)
apple varieties on the Internet.

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