Biochemist __________________________
Date _______________
Biology Lab: Testing Food For Nutrients
There are four types of organic compounds: proteins; carbohydrates; lipids and nucleic acids. In
this lab we will be looking at various food items to see which of these types of organic compounds are
present.
In order to tell what type of compounds are present we will be using chemical indicators. Chemical
indicators are substances that will undergo some sort of color change in the presence of a certain type
of chemicals. Lack of a color change indicates that either that type of substance is not present or is
present in very small quantities. As you test your samples remember it is possible for a substance to
contain more than one of the types of organic compounds.
Each of these procedures will involve using two controls. There will be one sample that should have
a positive result and one that should have a negative result. These samples will show you what a positive
and negative test will look like.
Lipids:
The presence of lipids can be detected by using WARD’S lipid test strips. In the presence of lipids it will
change from a pink color to red color.
1) Vegetable oil is a lipid. Label the test strip #1 and add a drop of oil to the strip. Record the color
change at the end of your lab. This is the positive control.
2) Albumin is a protein. Label the test strip #2 and add a drop of albumin to the strip. Record the color
change at the end of your lab. This is the negative control.
3) Label the rest of the five strips as follows: food sample #1, food sample #2, food sample #3, potato,
and milk. If a liquid, dip the strip into the liquid. If a solid press the strip into the solid. Record the
color changes at the end of the lab.
Carbohydrates: There are two different indicators that can be used on carbohydrates. Benedicts
solution will turn either a yellow of red color in the presence of monosaccharides (Sugars) such as
glucose that are carbohydrate monomers. IKI solution will turn a dark blue or black color in the
presence of the complex carbohydrate (polysaccharide) starch that is a carbohydrate polymer.
Remember a negative test for Benedicts (sugar test) does not mean that the substance is a complex
carbohydrate. It means that the substance is not a monosaccharide. It could be a protein or some
other type of organic material. Likewise, a negative test for Iodine does not mean that the substance
contains monosaccharides. It means that it does not contain starch.
Benedicts test:
1) Number your test tubes from 1 to 7 using a sharpie. Also mark each test tube with your initials.
2) To test tube 1, add 10 drops of glucose solution and 10 drops of Benedicts solution. Mix. This is the
positive control and shows what a positive result looks like.
3) To test tube 2, add 10 drops of starch solution, and 10 drops of Benedicts solution. Mix.
the negative control and shows what a negative results looks like.
This is
4) To test tube 3, add food sample #1 and 10 drops of Benedicts solution. Mix.
5) To test tube 4, add a small piece of potato, 10 drops of water and 10 drops of Benedicts solution.
Mix.
6) To test tube 5, add a food sample #2 and 10 drops of Benedicts solution. Mix.
7) To test tube 6, add 10 drops of milk and 10 drops of Benedicts solution. Mix.
8) To test tube 7, add food sample # 3 and 10 drops of Benedicts solution.
9) Place the test tubes into the hot water bath. Leave the test tube in the water for 5 minutes.
10) Remove the test tubes and place them in the test tube rack. When the tubes cool a red or orange
color will be present if large quantities of glucose are present. If smaller quantities of glucose are
present a yellow or green color will be present. Record your results in your data table.
11) Clean your test tubes out using soap and put them on the drying rack.
Iodine Test:
Notice: Iodine solution is light sensitive therefore it is in a brown bottle. Because of this you can not
see that the solution is a brownish color. Obviously when you add a brown solution to each of your
samples there will be a color change. This is not a positive result unless it turns dark blue or black.
1) Add 10 drops of starch solution and 5 drops of Iodine solution to well 1. In the presence of starch
Iodine will turn a dark blue or black color. This is the positive control. Record your observations in
your data table.
2) To well 2, add 10 drops of glucose solution and 5 drops of Iodine solution. This is your negative
control. Record your observations.
3) To well 3, add food sample #1 and 5 drops of Iodine solution. Record your observations.
4) To well 4, add a small piece of potato and 5 drops of Iodine solution. Record your observations.
5) To well 5, add food sample #2 and 5 drops of Iodine solution. Record your observations.
6) To well 6, add 10 drops of milk and 5 drops of Iodine solution. Record your observations.
7) To well 7, add food sample #3 and 5 drops of Iodine solution. Record your observations.
8) Clean out your well plate using soap to use in the next setup.
Proteins:
The presence of proteins can be detected using Biuret solution. In the presence of proteins the Biuret
solution will turn a purple color.
1) Albumin is a protein. Add 10 drops of albumin solution and 4 drops of Biuret solution to well 1.
Shake gently. The solution should turn a purple color. This is the positive control. Record your
results.
2) To well 2, add 10 drops of amino acid solution and 4 drops of Biuret's solution. Shake gently and
record your observations. This is the negative control.
3) To well 3, add food sample #1 and 4 drops of Biuret's solution. Shake gently and record your
observations.
4) To well 4, add a small piece of potato and 4 drops of Biuret's solution. Shake gently and record your
observations.
5) To well 5, add food sample #2, 10 drops of water and 4 drops of Biuret's solution. Shake gently and
record your observations.
6) To well 6, add 10 drops of milk and 4 drops of Biuret's solution. Shake gently and record your
observations.
7) To well 7, add food sample #3 and 4 drops of Biuret's solution. Shake gently and record your
observations.
8) Clean out the well plate with soap. Place on the drying rack above the sink.
Biology Lab: Testing Food For Nutrients
Data Table:
Lipid Test:
Sample
+
contro
l
contro
l
Strip 3
Strip 4
Strip 5
Strip 6
Strip 7
Benedicts Test:
Color
Conclusion
Lipid: Yes
or No?
Sample
+
contro
l
contro
l
Well 3
+
contro
l
contro
l
Test
tube 3
Test
tube 4
Test
tube 5
Test
tube 6
+
Test
contro
tube 7
l
contro
l
Well 3
Well 4
Well 4
Well 5
Well 5
Well 6
Well 6
Well 7
Well 7
Iodine Test:
Biurets Test:
Sample
Color
Conclusion
Starch: Yes
or No?
Sample
Color
Conclusion
Monosaccharides
: Yes or No?
Color
Conclusion
Protein:
Yes or No?
Testing Food For Nutrients - Lab Write Up (INCLUDE TITLE)
Due Date _________________
INTRODUCTION
You should include a list of the 4 types of macromolecules.
For each macromolecule list the monomer(s), elements and functions.
List the types of macromolecules (remember there were 2 for carbohydrates)
you tested for and the specific indicator used in that test.
PURPOSE
 Write the purpose of this lab. YOU NEED TO CREATE THIS, IT IS
NOT FOUND DIRECTLY IN YOUR LAB. So in a statement explain
WHY we completed the lab.
MATERIALS
The materials used in this lab include…(LIST ALL MATERIALS USED. THIS
LIST IS NOT FOUND IN YOUR LAB IN ONE LOCATION. YOU WILL
NEED TO SERACH THE LAB AND CREATE YOUR OWN LIST)
PROCEDURE
1. Describe the lipid test in summary form.
2. Describe the Benedict’s test in summary form.
3. Describe the Iodine test in summary form.
4. Describe the Biuret’s test in summary form.
RESULTS
Re-draw the data tables for your lab OR just attach your data sheet (But
reference to “See Attached”.)
ERROR
Include any error you may have encountered in lab both human and otherwise.
CONCLUSION
Include these things in this order in at least TWO PARAGRAPHS:
 Restate the purpose of the lab.
 Explain why each of the control substances were chosen (both POSTIVE
and NEGATIVE).
 For each of the 5 foods you tested state what type(s) of macromolecules
make up that material AND explain how you drew that conclusion (USE
SPECIFIC DATA FROM THE LAB).
The presence of lipids can be detected by using WARD’S lipid test strips. In the presence of lipids
Sudan III will change from a red color to an orange or pink color.
4) Vegetable oil is a lipid. Add 10 drops of oil and 10 drops of Sudan III to test tube 1. Shake gently.
After a couple of minutes the Sudan III should turn an orange color. This is the positive control.
5) To test tube 2, add 10 drops of albumin and 10 drops of Sudan III. Shake gently. Let sit for a couple
minutes and observe. This is the negative control.
6) To test tube 3, add 10 drops of food sample #1 and 10 drops of Sudan III. Shake gently. Let sit for a
couple minutes and observe.
7) To test tube 4, add a small piece of potato 10 drops of Sudan III. Shake gently. Let sit for a couple
minutes and observe.
8) To test tube 5, add a small piece of food sample #2 and 10 drops of Sudan III. Shake gently. Let sit
for a couple minutes and observe.
9) To test tube 6, add 10 drops of milk and 10 drops of Sudan III. Shake gently. Let sit for a couple
minutes and observe.
10) To test tube 7, add 10 drops of Food sample # 3 and 10 drops of Sudan III. Shake gently. Let sit for
a couple minutes and observe.