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Laboratory Test for Protein Using Quicklime and Litmus
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#1
Big Grin 
Materials Required:

*Calcium oxide (sold as quicklime in building supply stores)
* Red litmus paper (or another method
to test pH)
* Water
* Candle, burner, or another heat source
* Eye-dropper
* Test tube
* Milk or other foods to test

Procedure:

Because milk contains casein and other
proteins, it's a good food to start your
testing with. Once you understand what to
expect from testing milk, you can examine
other foods.
Notes About the Protein Test
Calcium oxide (sold as quicklime in
building supply stores)
Red litmus paper (or another method
to test pH)
Water
Candle, burner, or another heat
source
Eye-dropper
Test tube
Milk or other foods to test
Add a small amount of calcium
oxide and five drops of milk to a
test tube. 1.
Add three drops of water. 2.
Dampen the litmus paper with
water. Water has a neutral pH, so it
should not change the color of the
paper. If the paper does change
color, start again using distilled
water rather than tap water.
3.
Carefully heat the test tube over a
flame. Hold the damp litmus paper
over the mouth of the test tube and
observe any color change. 4.
If protein is present in a food, the
litmus paper will change color from
red to blue. Also, smell the test tube:
If protein is present, you should be
able to detect the odor of ammonia.
Both of these indicate a positive
test for protein. If protein is not
present in the test sample (or is in
insufficient concentration to
produce adequate ammonia during
testing), the litmus paper will not
turn blue, resulting in a negative
test for protein.

Note:

Calcium oxide reacts with protein to
break it down into ammonia. The
ammonia changes the acidity of the
sample, causing a pH change. If your
food is already very alkaline, you
won't be able to use this test to
detect protein. Test the pH of food to
see if it changes the litmus paper
prior to performing the protein test.
Milk is an easy food to test because
it's a liquid. To test solids, such as
meat, cheese, or vegetables, you must
first grind the food by hand or by
using a blender. You may need to mix
the food with some water to make a
sample you can test.
The test registers a change in pH,
which is the concentration of
hydrogen ions in an aqueous or
water-based solution. Most foods
contain water, so they work fine for
the test. However, oily foods may not
work as well. You can't test pure
vegetable oil, for example, because it
doesn't contain any water. If you test
greasy foods, such as french fries or
potato chips, you'll need to mash
them up and mix them with a bit of
water first.
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