SNC4M
Nutritional Science Unit
Food Digestion and Macromolecule Lab
PART I: Digestion of Proteins and Carbohydrates
A: Digestion of Proteins
Proteins are the functional macromolecules in our cells. They carry out most of the work that is done
inside a cell. In fact, all enzymes are proteins. Proteins are composed of long chains of small chemical
structures called amino acids, which are linked in a specific order by a strong type of covalent bond,
called a peptide bond. You can think of proteins as a necklace of beads, where each bead is an amino
acid and the beads are connected together through peptide bonds. Our cells manufacture proteins
from amino acids that are present inside each cell, and this manufacturing happens continuously, as
new proteins are needed to replace old ones. Our cells can make some amino acids, but they need to
obtain the eight that we cannot make – the so-called “essential amino acids” from our food. So, in
order for us to make our own proteins we need to eat certain types of proteins to obtain essential
amino acids. When we eat proteins the proteins are digested into amino acids for our cells to easily
absorb them.
Protein digestion begins in the stomach. Here the HCl denatures the protein and it stimulates the
conversion of pepsinogen to pepsin, which is the enzyme that break proteins into shorter chains of
polypeptides. Further digestion happens in the duodenum of the small intestine, when the
polypeptides are broken down into individual “beads” or amino acids. These are then absorbed by the
villi and travel throughout the body using the circulatory system. Once the amino acids arrive in your
cells, your cells’ machinery will put them in the correct sequence depending on the type of protein
needed by the cell.
Materials
1 spot plate
4 pH strips
3 mL Albumin or peptone(protein)
3 mL Hydrochloric acid
3 mL Pepsin
3 mL Biuret’s solution
3 plastic droppers
5 Stirring sticks
Procedure
1. Label the wells on your spot plate 1-10.
2. Place 4 drops of albumin in wells 1-4 of the spot plate.
3. Add 4 drops of hydrochloric acid to well 2. Add 4 drops of pepsin to well 3 and 4. Add 4
drops of hydrochloric acid to well 4. Add 3 drops of hydrochloric acid to well 5.
4. Stir the mixture in each well using a clean stirring stick. Allow the mixture in each well to
remain undisturbed for 8 minutes.
5. Determine the pH in each of the wells. Record your results in Data Table 1 below.
6. Test for the presence of protein by adding 2 drops of Biuret’s reagent to each well.
Carefully observe any color changes in each of the wells. A positive test for protein is
indicated by a pinkish color. A negative test will show a blue color that indicates the
protein has been digested and broken down into amino acids.
SNC4M
Nutritional Science Unit
B: Digestion of Carbohydrates
Carbohydrates, commonly known as sugars, are the body’s main source of energy. The digestion of
some carbohydrates begins in the mouth. The enzyme salivary amylase starts the chemical breakdown
of complex polysaccharides (complex sugars) into simpler disaccharides. Digestion of carbohydrates
continues in the duodenum, the first part of the small intestine, where pancreatic amylase further
breaks down carbohydrates into simple monosaccharides. Once broken down, the sugar molecules are
absorbed and carried through the bloodstream to every cell in your body. Inside the cell they
combine with oxygen in cellular respiration, to produce usable energy.
Materials:
2 test tubes, 5 ml of starch sol’n, 5 ml of pancreatin (has amylase in it), 2 stirring rods, Lugol’s sol’n
In the presence of starch, the mixture will change color to blue-black. If the starch has been
digested the solution will remain yellow-brown.
Table 1: Digestion of macromolecules
Protein digestion
well
#
1
contents
2
albumin + HCl
3
albumin +
pepsin
albumin +
pepsin + HCl
HCl
4
5
pH
protein
test
observations
albumin
Starch digestion
Test contents
tube
#
1
starch
2
starch +
amylase
starch test
observations
SNC4M
Nutritional Science Unit
PART II: Food macromolecules
Purpose
1. To identify macromolecules
2. To determine the type of nutrients present in different foods
MATERIALS
test tubes, 8, test tube rack, Lugol’s iodine, starch solution
Benedict’s solution, glucose solution, fructose solution
Biuret Reagent, egg albumen
Sudan IV indicator, vegetable oil
10-mL graduated cylinders
brown paper (8 cm by 14 cm), 5 pieces
droppers
Miscellaneous food
PROCEDURE
Section A: Monosaccharides
1. Label two clean, dry test tubes A-1 and A-2
2. To test tube A-1 add 5 mL of glucose or fructose solution. Add two drops of
Benedict’s solution and then record your observations for colour changes in the space
provided on the Student Worksheet.
3. To test tube A-2 add 5 mL of distilled water. Add two drops of Benedict’s solution,
and make observations for colour changes.
Section B: Carbohydrates
1. Label two clean, dry test tubes B-1 and B-2
2. To test tube B-1 add 5 mL of starch solution. Add two drops of Lugol’s iodine and then
record your observations for colour changes in the space provided on the Student
Worksheet.
3. To test tube B-2 add 5 mL of distilled water. Add two drops of Lugol’s iodine, and
make observations for colour changes.
Section C: Proteins
1. Label two clean, dry test tubes C-1 and C-2.
2. Add 2 mL of egg albumen or peptone to test tube C-1. Add 2 mL of Biuret reagent and
gently agitate before making any observations on the Student Worksheet.
3. Add 2 mL of distilled water to test tube C-2. Add 2 mL of Biuret reagent and gently
agitate before making observations.
SNC4M
Nutritional Science Unit
Section D: Lipids
1. Place a drop of vegetable oil on a square piece of brown paper. Use a pencil to label
the spot “oil”.
2. Using another clean dropper, place a drop of distilled water about 4 cm away from the
drop of oil. Label this spot “water”.
3. Once the water drop has totally evaporated, examine the two spots. Hold both spots
up to the light. Record your observations.
Section F Testing Foods for Nutrients
1. Perform the carbohydrate, protein, fat and lipid tests just studied on the different
food samples.
2. The fat test should be done first.
3. Once each food item is tested with brown paper, it can be prepared for the other
nutrient tests. Chop and crush these foods into tiny pieces before you place them in
the test tubes.
4. The moisture content of each test tube should be equal. Be sure to add distilled water
to the food samples that have lower moisture content.
5. Record your observations on the charts provided.
SNC4M
Nutritional Science Unit
Part I: Food Macromolecules/Testing for Food Types: Data tables
Section A
Sample
Monosaccharides
Solution
A-1
Glucose
A-2
Distilled
Water
Section B
Sample
Solution
Starch
B-2
Distilled
Water
Sample
Before Benedict’s
Test Results
After Benedict’s
Carbohydrates
B-1
Section C
Colour
Colour
Before Lugol’s
Test Results
After Lugol’s
Proteins
Solution
Colour
Before Biuret
C-1
Egg
Albumin
C-2
Distilled
Water
Section D
Fats
Sample
Appearance Under Light
Test Results
After Biuret
Conclusion
Oil
Water
Section F
Nutrient Tested
Monosaccharide
Carbohydrate
Protein
Lipid
Nutrient Test of Various Foods
Test Result
Food A:
Test Result
Food B:
Test Result
Food C: