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