PROTEIN, CARBOHYDRATE AND LIPID TESTING PRACTICAL
SAFETY
For today’s practical you will be testing several different items to check for the presence of
carbohydrate, protein and lipids. This practical requires the use of some chemicals which can
be either skin or eye irritants. This means that lab coats, gloves and glasses are required at
all times during the practical. I will give you instructions on proper disposal. Also if a spillage
occurs do not attempt to soak it up or clean it, alert me straight away.
INTRODUCTION
Biomacromolecules are large organic molecules critical to the structure and function of all
living organisms. There are 4 biomacromolecules: Lipids, Proteins, Carbohydrates and
Nucleic Acids. Today’s practical will involve you testing a variety of different products to
check for the presence or absence of proteins, carbs or lipids. There will be 3 stations set up
on for each biomacromolecule. Do not move anything from the station it is on! You should
visit each station and will need to complete a table for each station with your results.
MATERIALS AND METHODS
Protein Station
1. In the table provided fill in your prediction for each of the items. + for present –for
absent.
2. Once made your predictions you can now go to the protein station. Place a small
sample (no more than a matchhead amount) of each item into wells of a sample tile. If
something is a solid you will need to mash it with a little bit of water and stir with a
toothpick.
Do not mix up toothpicks.
3. Once it is mashed add 2-3 drops of copper sulfate solution and then add 1-2 drops
of sodium hydroxide solution. You will need to stir the mixture for about 1 minute
or more. A positive reaction will give a colour change from blue to violet. Warming
may be necessary. You can warm it by placing it on a hot plate for a short time don’t
overheat. Use a leather glove and metal tongs to remove the tray and place it on a
heatproof mat
4. Record your observations in the table.
PROTEIN TEST
ITEM
PREDICTION
OBSERVATION
Milk
Yogurt
Meat
Tofu
Apple
Potato
Yeast
Boiled Egg
Carbohydrate Station
At this station you will be conducting 2 types of test a glucose test and a starch test.
To conduct the glucose test you will use Benedict’s solution and to test for starch you will
use iodine solution.
1. Fill in your predictions in the tables provided below.
2. Once you have made your predictions you can now go to the carbohydrate station.
Once you are there you will need to collect a small amount of each item.
3. For the GLUCOSE test. Once you have each item, chop them up finely and add water
to make it mushy, then place them into separate test tubes or in wells of a sample
tile and add 1ml of Benedict’s solution to each. Stir with a toothpick for about a
minute. Then place the sample tray on a hot plate for a short time. You may need
to stir some more until the liquid boils. Observe the colour changes. If glucose is
present the solution will change from blue to orange-red precipitate.
4. For the STARCH test. Place labelled samples on a large plate or sample tile. Again
chop finely and mix with water each item, then place a couple of drops of iodine
solution on each item and observe the colour changes. A bluish black colour
indicates a positive result.
5. Record your observations in the tables.
GLUCOSE TEST
ITEM
PREDICTION
OBSERVATION
PREDICTION
OBSERVATION
Sweet Potato
Apple
Potato cubes
Bread
Crackers
Corn Chips
Corn starch
Cooked pasta
STARCH TEST
ITEM
Sweet Potato
Apple
Potato cubes
Bread
Crackers
Corn Chips
Corn starch
Cooked pasta
Lipid Station
For Lipids a Grease spot test and a Sudan Red test will be conducted. (Please note the Sudan
red test is only to be used on the milk)
1. Fill in your predictions into the tables provided below.
2. Once you have made your predictions you can now go to the Lipid station.
3. For Sudan Red testing. In a test tube or in a sample tile place 2ml of the liquid
you are testing and add 2ml of water. Place 2-5 drops of Sudan Red to the mix
and stir. A positive result will be seen when Sudan red stains fat particles within
the solution.
4. For Grease Spot testing: Collect some brown paper squares and draw 4 squares
onto each paper. Place a little (1 small drop or no more matchhead amount ) of
each item onto a portion of the square. Smear the samples around until there is
no excess. Allow the paper to dry. Label each of the samples. Once dry, lipids or
fats will stain the paper translucent.
5. Record your observations in the table.
LIPID TEST
ITEM
Olive oil
Grapeseed oil
Sesame oil
Butter
Lard
Skim milk
Full cream milk
No fat milk
PREDICTION
OBSERVATION
STEP BY STEP GUIDE TO WRITING YOUR REPORT
Introduction
-
Include your aim and background to the study
What are biomacromolecules?
Why are they important?
What tests are we conducting?
What is your hypothesis for each station?
Materials and Methods
-
You can refer to this practical sheet, but must state any changes to procedure.
Result
-
Include here your table of results
You must include a table or graph with the results of your findings but do not include
your prediction at this point.
Discussion
-
-
Discuss your results here. So why did certain items react? What does it mean?
(Example: A positive test for starch means that the iodine has reacted with the
starch and caused the colour to change to blue-brown) How does this relate to your
hypothesis?
You may include diagrams that explain your results etc
Include here your conclusion.
Discuss improvements and errors.
What other experiments could you conduct to further explore this area in the
future?
References or Bibliography
-
Make sure you list all the resources you used and that they are all in the same
format.
If you collected an image from a website you must say where it has come from (cite)
underneath it.
EXTRA THINGS TO REMEMBER




Reports are always written in 3rd person, so there should be no I, We or Me
All tables and diagrams must have an explanatory caption and be numbered.
All reports should be typed up neatly and include clear titles for each section.
All work should be your own. Do not copy and paste from any website (I will find
out!!!). Put everything into your own words.
POSSIBLE DEMONSTRATION
ETHANOL EMULSION TEST FOR FATS AND OILS
The Ethanol Emulsion Test is a food test which determines the presence of a broad group of naturally
occurring compounds known as lipids. Lipids consist of fats and oils. Other lipid tests include the Grease Spot
Test and the Sudan Stain Test. The Grease spot test is performed on fats – lipids which are solid at room
temperature. Sudan stain colours lipids red, but is a less common bench reagent than ethanol. The Ethanol
Emulsion Test is the most common test amongst the three.
Procedure:
Solid sample :
1.
2.
3.
4.
5.
6.
Crush the food sample and place in a dry test tube.
Add ethanol to about 2 cm3 above the level of the sample and shake thoroughly.
Allow the solid to settle (about 3 min) to allow the lipid to be extracted.
Decant the ethanol into another test tube.
Add 2 cm3 of deionized water to the second test tube
Make observations.
Liquid sample:
1.
2.
3.
4.
Add a few drops of the liquid food sample to a dry test tube.
Add 2 cm3 ethanol and shake it thoroughly
Add 2 cm3 of deionized water.
Make observations.
OBSERVATIONS & INTERPRETATION
The above image shows the presence of lipids.