IDENTIFYING
MACROMOLECULES
IN FOOD
LAB
Introduction
Carbohydrates, proteins, and fats
are all essential nutrients.
We cannot manufacture these
nutrients, so we must obtain
them from our environment.
The presence of these
macromolecules can be
detected by chemical indicators
Introduction
In lab, with the use of indicators as
chemical detection tools, you will
analyze a variety of foods for the
presence of nutrients.
Detection is based upon observing a
chemical change that takes place
most often a change in color.
Objective
Identify the presence of major nutrients in
common foods
• simple carbohydrates (glucose)
• complex carbohydrates (starch)
• Protein
• Fat
What is an indicator?
• Indicators are chemical compounds used
to detect the presence of other
compounds.
LAB SAFETY and CLEAN UP
WEAR safety
goggles and
apron at all times
NO GOOFING
AROUND
Loose Hair
BACK
WORK at LAB
Automatic FailureBENCHES ONLY
of LAB
THOROUGHLY
CLEAN lab area
and equipment
with plenty of
water
NO EDIBLE
products
in lab
Test for Simple Carbohydrates
Benedict’s solution
• Benedict's solution is a chemical indicator for
simple sugars such as glucose: C6H12O6.
 yellow/green/brick red, etc.: positive test
Test for Simple Carbohydrates
Benedict’s solution
• Unlike some other indicators, Benedict’s
solution does not work at room
temperature - it must be heated first.
Procedure
Simple carbohydrate
1. Add 5ml of food sample to test
tube
2. Add 20 drops of Benedict solution
3. Place test tube in a hot
water bath for 10 minutes.
Test for Complex Carbohydrates
IKI solution
• Iodine solution is an indicator for a molecule
called starch.
• Starch is a huge molecule made up of hundreds
of simple sugar molecules (such as glucose)
connected to each other.
Test for Complex Carbohydrates
IKI solution
• IKI solution  (Iodine Potassium Iodine) color
change = blue to black
Procedure
Complex carbohydrate
1. Add 5ml of food sample to test
tube
2. Add 20 drops of IKI solution
Test for Protein (amino acids)
Biuret solution
• Biuret solution  dark violet blue to
pinkish purple is positive for protein
Procedure
Protein (amino acids)
1. Add 5ml of food sample to test
tube
2. Add 20 drops of Biuret solution
Test for Fats (lipids)
Sudan III
• Like lipids, the chemical Sudan
III is not soluble in water; it is,
however, soluble in lipids.
• In this test dark red Sudan III is
added to a solution.
• If lipids are present the Sudan III
will stain them reddish-orange
(positive test).
Procedure
Fats (lipids)
1. Add 5ml of food sample to test
tube
2. Add 20 drops of Sudan III
3. Stopper and gently shake (rock)
the test tube.
4. If the the Sudan III color mixes
with the solution it is a positive test
Additional Fat Test
• Fats will leave a glossy, oily residue when
wiped on paper.
Procedure:
1.Draw 6 squares on one side of your paper
bag (5 foods + water)
2.With a fresh cotton swab, wipe a sample
of the food to be tested in the square.
3.Let the paper dry.
4.Hold paper up to light and look for glossy,
oily residue (use water as comparison).
Identification of Macromolecules in Foods
FOOD
Apple
Juice
Potato
Egg
White
Veg Oil
Milk
INDICATOR
Benedict
IKI
(Sugar) (Starch)
Biuret
Sudan III
(Protein) (Lipids)
Color
Color
+/-
Color
+/-
+/-
Color
+/-
Brown
paper
(Lipids)
Color
+/-
Macromolecule Test Protocols Table
INDICATOR
Benedict’s
solution
IKI solution
Biuret
solution
Sudan III
Brown
paper
MACROMOLECULE
- TEST
+ TEST
PROTOCOL
Procedure for Today
1. Set up your notebook
2. Go to your assigned station
3. Write the PROCEDURE down in your
notebook
4. Make hypothesis which samples will test
positive.
5. Gather Samples
6. Run Test & Record Results
7. Conclusion
Macromolecule Test Protocols Table
INDICATOR
MACROMOLECULE
- TEST
+ TEST
PROTOCOL
Benedict’s
simple
solution carbohydrate
blue
IKI solution
complex
carbohydrate
gold
Biuret
solution
protein
blue
violet,
black
Sudan III
lipid
Light
pink
reddishorange
5 ml +
20 drops
5 ml +
20 drops + rock
Brown
paper
Lipid
No oily
residue
Oily
residue
Label & wipe on
paper, let dry
green,
orange,
Red
black
5 ml +
20 drops + 10
min. bath
5 ml +
20 drops
Exit Task:
Why does the Sudan III not mix with the
apple juice?