Unknown Foods:
Macromolecule Lab
Chapter 2:
Carbohydrates, Lipids, and Proteins
Objectives
• Use chemical indicators and other tests
to determine the presence of
macromolecules in foods
• Identify the presence of organic
macromolecules in foods found in the
diet
Procedure
• Perform four tests on food samples to determine the
presence of
– Lipids
– Sugar
– Protein
– Starch
• Record the results of each test in the data table
• Clean all glassware before changing stations
How to test for lipids
• Fold a piece of paper into small squares
• Label each square with the name of the food sample
• Rub a small amount of each food on the paper
• Let the paper dry
• Hold the paper up to the light
Positive Lipid Test
• Lipids will cause the paper to become
translucent
– Light will pass through the paper
• Wet paper is not a positive test
• If paper stays opaque – the test is negative
– Opaque means light does not pass through
Test for Starch
• Place a small amount of each food in a petri
dish
• Add 2 drops of iodine to the sample
• Observe the color of the iodine and record in
the data table
Positive Starch Test
• If starch is present,
iodine will turn a
purple/black
• If there is no starch, the
iodine stays red
Test for Sugar
• Pour 5 mL Benedict’s solution into
numbered test tubes with a small
amount of each food sample
• Place the test tubes in a boiling
water bath, heat for 1 minute and
observe color changes
• Record results in data table
Positive Sugar Test
• Benedicts
Solution will
change from blue
to orange or green
in the presence of
sugar
Test for Protein
• Place a small amount of each food in a petri
dish
• Add 3 drops of Biuret to each food
• Observe any color change and record results
in data table
Positive test for Protein
• Biuret solution will
change from blue to
pink or purple in the
presence of protein