KS_3 Nutrients
1.2 Food tests
Scientists use food tests to find out which nutrients are in a food product.
1.2.0 How can you test foods?
To prepare a food solution:
1. Crush the food using a pestle and mortar
2. Add a few drops of distilled water, and mix well.
1.2.1 Testing for starch
Chemical used
: Iodine solution
Procedure
: 1. Add a few drops of iodine solution to the food
solution/food that contain moisture.
2. Orange-yellow liquid turns to blue-black colour when the
food contains starch.
Orange-yellow liquid
Result
drops iodine solution onto the food
:
Positive test
Negative test
Iodine solution remains Iodine solution turns to
orange-yellow
blue-black
KS_3 Nutrients
1.2.2 Testing for lipids
Method 1
: Spot test
Material used
: A piece of filter paper
Procedure
: 1. Rub some of the food onto a
piece of filter paper.
2. Hold the paper up to the light.
3.
If
the
paper
has
gone
translucent, the food contains lipids.
Result
:
Positive test
Translucent spot occurs
Negative test
No translucent spot
Method 2
: Emulsion test
Chemical used
: Ethanol
Procedure
: 1. Add a few drops of ethanol to
the food solution.
2. Shake the test tube and leave
for one minute.
3. Pour the ethanol into a test tube of water. If the solution
turns cloudy, the food contains lipids.
Result
:
Positive test
A layer of cloudy white
suspension forms
Negative test
Solution remains colourless
KS_3 Nutrients
1.2.3 Testing for sugar
Chemical used
: Benedict’s solution (blue liquid)
Procedure
: 1. Add a few drops of Benedict’s solution to the food solution.
2. Heat the test tube in a water bath. If the solution turns
orange-red, the food contains sugar.
Result
:
Positive test
Benedict’s solution turns
to brick red colour
Negative test
Benedict’s solution remains
in blue colour
KS_3 Nutrients
1.2.4 Testing for protein (Biuret test)
Chemical used
: Copper sulfate and sodium hydroxide solutions
Procedure
: 1. Add a few drops of copper sulfate solution to the food
solution.
2. Add a few drops of sodium hydroxide solution. If the
solution turns purple, the food contains protein.
Pale-blue liquid
Colourless liquid
Result
:
Positive test
The solution turns from
blue to purple
Negative test
The solution remains in
blue colour