Food Chemistry Lab*
Living organisms are composed largely of water and organic macromolecules (large molecules
containing carbon). Most of these molecules can be found in living organisms and classified as:
carbohydrates (sugars and starches), proteins, lipids, and nucleic acids. Many of these can be
identified in solution by simple chemical tests with results based on a color change. In this lab
exercise, we will test solutions for the presence of STARCH, GLUCOSE (sugar), and LIPIDS.
Procedures:
For each test, we will look at color changes associated with a positive result (solution contained
the macromolecule in question) and color changes associated with a negative result (solution
did not contain the macromolecule in question) for each test. Once you have completed all
tests, you will then obtain an unknown solution and determine if it contains starch, glucose, or
lipids.
To test for starch:
Positive Result
1a. Add 2 ml (20 drops) of starch solution in a clean test tube.
1b. Add 1-2 drops of iodine solution.
1c. Shake the tube gently to mix.
1d. Record results in table below. This is a positive result for the presence of starch.
Negative Result
2a. Place 2 ml of water in a new, clean test tube.
2b. Add 1-2 drops of iodine.
2c. Shake the tube gently to mix.
2d. Record results in table below. This is a negative result for the presence of starch.
Solution
Corn Starch
Water
Color
Result (+/-)
Positive (+)
Negative (-)
*Modified from the Science of Biology Laboratory Manual: The University of
Arkansas at Little Rock, Little Rock, AR.
To test for glucose:
Positive Result
1a. Place 2ml of glucose solution (soda) in a clean test tube.
1b. Add 2ml of Benedict’s solution to the tube.
1c. Shake the tube gently to mix.
1d. Using a test tube clamp, hold the test tube over a hot water bath for 3-5 minutes.
1e. Record the results in the table below. This is a positive test for glucose.
Negative Result
2a. Place 2ml of water in a new, clean test tube.
2b. Add 2ml of Benedict’s solution to the tube.
2c. Shake the tube gently to mix.
2d. Using a test tube clamp, hold the test tube over a hot water bath for 3-5 minutes.
2e. Record the results in the table below. This is a negative test for glucose.
Solution
Color
Soda
Water
Result (+/-)
Positive (+)
Negative (-)
To test for lipids:
Positive Result
1a. Place 2ml of cooking oil in a test tube.
1b. Add 5 drops of Sudan IV suspension to the tube.
1c. Shake the tube gently to mix.
1d. Record the color changes in the table below. This is a positive test for lipids.
Negative Result
2a. Place 2ml of water in a new, clean test tube.
2b. Add 5 drops of Sudan IV suspension to a tube.
2c. Shake the tube gently to mix.
2d. Record the color changes in the table below. This is a negative test for lipids.
Solution
Cooking Oil
Water
Color
Result (+/-)
Positive (+)
Negative (-)
To test an unknown solution for starch, lipids, and glucose:
For Starch:
1a. Place 2ml of unknown solution into a test tube.
1b. Add 1-2 drops of iodine tube.
1c. Gently shake the tube to mix.
1d. Record results in table below. Does this solution contain starch?
For Glucose:
2a. Place 2ml of unknown solution into a clean test tube.
2b. Add 2ml of Benedict’s solution to the tube.
2c. Gently shake the tube to mix.
2d. Using a test tube clamp, place the test tube in a hot water bath for 3-5 minutes.
2e. Record results in table below. Does this solution contain glucose?
For Lipids:
3a. Place 2ml of unknown solution into a test tube.
3b. Add 5 drops of Sudan IV solution to the tube.
3c. Gently shake the tube to mix.
4c. Record results in table below. Does this solution contain lipids?
Solution
Lipids
Glucose
Starch
Color
Result (+/-)