TESTING
BIOMOLECULES
LEARNING OBJECTIVES
At the end of the discussion, the learners
should be able to:
a. identify which tests are conducted in
detecting different types of biomolecules on
food;
b. use a simulation to detect biomolecules on
foods; and
c. cite the significance of conducting tests on
food to detect the presence of biomolecules.
TESTS FOR
CARBOHYDRATES
BENEDICT'S TEST
Benedict’s Test is used to test for simple
carbohydrates.
Benedict’s chemical test can be used to check
for reducing sugars in a given analyte.
When exposed to reducing sugars, the
reactions undergone by Benedict’s reagent
result in the formation of a brick-red
precipitate, which indicates a positive
Benedict’s test.
PROCEDURE
a) Using a dropper, take a small quantity of Benedict’s
reagent.
b) Add the reagent to the test tube containing banana
extract.
c) Boil the sample over a burner for 2 minutes holding the
test tube firmly with a test tube holder.
d) Keep shaking the test tube as it is being heated.
e) A brick-red precipitate appears, indicating the
presence of glucose in the banana extract.
INTERPRETATION OF BENEDICT'S
TEST RESULTS
If the color upon boiling is changed into green, then
there would be 0.1 to 0.5 percent sugar in the solution.
If it changes color to yellow, then 0.5 to 1 percent sugar
is present.
If it changes to orange, then it means that 1 to 1.5 percent
sugar is present.
If the color changes to red, then 1.5 to 2.0 percent sugar
is present.
And if the color changes to brick red, it means that more
than 2 percent sugar is present in the solution.
IODINE TEST
A test used to determine the presence
of starch in materials.
A positive result for the iodine test
(starch test) was a color change
ranging from violet to black; a negative
result (no starch) was the yellow (no
change) of the iodine solution.
PROCEDURE
a)Using a dropper, take a small quantity
of iodine solution.
b)Add 5 drops of iodine solution to the
test tube containing potato extract.
c)Blue-black color indicates the
presence of starch in potato extract.
TESTS FOR
LIPIDS
ETHANOL EMULSION TEST
is a method to detect the
presence of lipids in a food
sample.
PROCEDURE
a)Add the food sample to 2 cm^3 of
ethanol, shake well.
b)Allow to settle in a test tube rack for 2
minutes for food to dissolve in ethanol.
c)Empty any clear liquid into a test tube
containing 2 cm^3 of distilled H2O.
INTERPRETATION OF ETHANOL
EMULSION TEST RESULTS
Lipids are not present if the
substance remains colorless
and no emulsion is formed.
Lipids are present in the
substance if a layer of cloudy
suspension forms above the
solution.
TESTS FOR
PROTEINS
BIURET TEST
A chemical test used to
determine the presence of
a peptide bond (chemical
bond between amino acids)
in a substance.
PROCEDURE
a)Using a dropper, take a small quantity of 40% NaOH
solution.
b)Add a few drops of NaOH solution to the test tube
containing egg albumin.
c)Using a dropper, take a small quantity of 1% CuSO4 solution.
d)Add 2-3 drops of CuSO4 solution to the test tube containing
egg albumin.
e)Shake the solution to mix it well.
f)A violet color appears in the test tube, which indicates the
presence of proteins.
INTERPRETATION OF BIURET TEST
RESULTS
·The test yields a negative
result if the Biuret reagent
remains blue.
·The test yields a positive result
if the reagent changes from
blue to violet.
INTERPRETATION OF BIURET TEST
RESULTS
SEATWORK
1. Which of the following tests detect starch in
food?
a.Benedict’s Test
b.Biuret Test
c.Ethanol Emulsion Test
d.Iodine Test
SEATWORK
2. Which of the following tests detect proteins in
food?
a.Benedict’s Test
b.Biuret Test
c.Ethanol Emulsion Test
d.Iodine Test
SEATWORK
3. What does it mean when a cloudy suspension
forms on the solution during the Ethanol Emulsion
Test?
a.There are lipids present in the substance.
b.There are proteins present in the substance.
c.There are no lipids present in the substance.
d.There are no proteins present in the substance.
SEATWORK
4. What color of Benedict’s test describes that there
are more than 2 percent sugar is present in the
solution?
a. blue
b. green
c. orange
d. brick red
SEATWORK
5. Why do you think determining the presence of
biomolecules in foods is important for our health?
a.It is not important in our health.
b.It ensures the balance of nutrients in our body.
c.It helps us make an ignorant decision on our diet.
d.It helps us have confusion about the contents of
food.
