BEFORE YOU LEAVE.
Identifying Organic Compounds: Carbohydrates, Proteins, Lipids
The most common organic compounds found in living organisms are lipids, carbohydrates, proteins and nucleic acids. A combination
of most of these is found in the every day foods that you eat. Simple chemical tests with substances called indicators can be conducted to
determine the presence of organic compounds. A color change of an indicator is usually a good positive test for the presence of an organic
In this investigation, you will use several indicators to test for the presence of lipids, carbohydrates and proteins in particular foods.
Purpose: To see what organic compounds (proteins, lipids and carbohydrates) are in each of the food substances..
Hypothesis: If I test vegetable oil then it will be positive for (lipids/proteins/both/neither). If I test milk then it will be positive for
(lipids/proteins/both/neither). If I test apple juice, then it will be positive for (lipids/proteins/both/neither).
CAUTION: SUDAN III CONTAINS ALCOHOL AND IS EXTREMELY DANGEROUS IF YOU GET IT INTO YOUR EYES. USE
THE SAFETY GOGGLES LOCATED IN THE DRAWERS OF YOUR LAB STATION.
3 Test Tubes
1 Large beaker to hold test tubes
3 small beakers of food substance.
Sudan III red stain to test for lipids
Biurets stain to test for protiens
Procedure: (EVEN # GROUPS START WITH #1 IN PROCEDURE, ODD # GROUPS START WITH # 9 IN PROCEDURE AND
THEN WORK YOUR WAY BACK TO THE BEGINNING OF PROCEDURE).
1. Gather your materials.
2. Put a small amount of each food substance into separate test tubes (1 substance per test tube).
3. Add 5 ml of water to the food substance. (This helps separate the lipids from the rest of the food).
4. Add 4 drops of Sudan III to each tube. Do not shake.
5. Look for one of two things:
a. A thin layer of red at the top of the substance.
b. Small red dots forming throughout the substance.
c. If it is simply a pink color, no lipids.
6. Was the test tubes out and fill them up again with the food.
7. Add 4 drops of Biurets to each substance. This time shake the test tube.
8. Look for a purple/pink color to form.
9. Record results into data table.
10. Wash test tubes and answer questions that follow.
Food tested Stain used Color change
Oil Sudan III
Milk Sudan III
Apple Juice Sudan III
Apple Juice Biurets
What you are looking for:
Sudan III: Test for Lipids: Will turn food red if lipids are present.
Benedicts: test for sugar (heated). Look for solids to form.
Yellow- a little sugar
Orange – medium sugar
Red – a lot of sugar
Iodine – Test for starch. Turns food deep blue/black if there is starch
Biuret – Test for protein. Turns from light blue to purple.
1. Why was water added to each test tube when testing for lipids?
2. Which is less dense, oil or water? How do you know?
3. Fats, oils, waxes and steroids are all examples of which macromolecule?
4. Amino acids are the building blocks of which macromolecule?
5. Enzymes and antibodies belong to which macromolecule group?
6. Explain how carbohydrates (from yesterday) are different than lipids in terms of the energy
7. Glucose is an example of a _______saccharide while starch is an example of a
1. Which indicator would be used to test a persons urine to see if it had high amounts of glucose in
it? Use yesterdays lab sheet for help.
2. Celiacs disease is a digestive disorder where a person cannot digest gluten, a protein found in
wheat. Which indicator would we use to test for gluten?
3. Why do lipids, such as fats, seem to collect around the midsection of the human body?