Identifying Nutrients Lab
In this activity, you will use laboratory tests to identify single sugars (monosaccharides),starches, proteins, and lipids. You will then use these tests to identifythe nutrients present in an unknown sample.
Question
What nutrients are present in the unknown sample?
Materials
Goggles
lab apron
test tubes
test tube racks
test tube brushes
hot plate
thermometer
400-mL beaker
10-mL graduated cylinder
test-tube holder
medicine droppers
depression spot plate
rubber stoppers
For monosaccharide test:
Benedict’s reagent
5% glucose solution
5% sucrose solution
5% starch suspension
unknown solution
water
For starch test:
Lugol’s solution
5% glucose solution
5% sucrose solution
5% starch suspension
unknown solution
water
For lipid test:
Sudan IV solution
unknown solution
vegetable oil
skim milk
whipping cream
water
For protein test:
Biuret reagent
gelatin
egg albumin
skim milk
unknown solution
water
Procedure
Before you begin
• make sure that all the glassware is clean and well rinsed;
• note the location of the eyewash station;
• put on your apron and goggles.
Part 1: Monosaccharide Test
Benedict’s reagent is an indicator for monosaccharides and some disaccharides, such as maltose.
1.Prepare a water bath by heating 300 mL of tap water in a 400-mL beaker on a hot plate. Heat the water until it reaches approximately 80°C. (Use the thermometer to monitor the temperature.)
2.Using a 10-mL graduated cylinder, measure 3 mL each of water, glucose, sucrose, starch, and the unknown solution. Pour each solution into a separate test tube. Clean and rinse the graduated cylinder after pouring each solution. Label each test tube. Record the code for your unknown sample. Add 1 mL of Benedict’s reagent to each of the test tubes.
3.Using a test tube holder, place each of the test tubes in the hot water bath. Observe for 6 min. Record any colour changes in a chart.
Part 2: Starch Test
Lugol’s solution contains iodine and is an indicator for starch. Iodine turns blue-black in the presence of starch.
4.Using a medicine dropper, place a drop of water on a depression spot plate and add a drop of Lugol’s solution. Record the colour of the solution.
5.Repeat the procedure, this time using drops of starch, glucose, sucrose, water, and your unknown solution. Record the colour of the solutions in a chart. Which solutions indicate a positive test?
Part 3: Sudan IV Lipid Test
Lipids can be detected using Sudan IV solution. Sudan IV is non-polar, so it does not mix with water and it does mix with lipids. In the presence of lipids, sudan IV appears dark pink in a bubbly layer above the water. The taller this layer is, the more lipids are present.
6.Place 3 mL of vegetable oil, skim milk, whipping cream, water, and unknown solution, each inside its own test tube.
7.Add 1 mL Sudan IV solution to each test tube. Stopper the test tube and shake vigorously.
8.Allow the solution to settle for 3 minutes, then record your observations in a chart.
Part 4: Protein Test
Proteins can be detected by means of the Biuret reagent test. Biuret reagent reacts
with the peptide bonds that join amino acids together, producing colour changes
from blue, indicating no protein, to pink (+), violet (++), and purple (+++). The
+ sign indicates the relative amounts of peptide bonds.
9.Measure 2 mL of water, gelatin, albumin, skim milk, and the unknown solution into separate labelled test tubes.
10.Add 2 mL of Biuret reagent to each of the test tubes, then tap the test tubes with your fingers to mix the contents. Record any colour changes in a chart.
Analysis
(a)Which test tube or depression plate served as a negative control in the test for monosaccharides, starches, lipids, and proteins? Explain what purpose the negative control served.
(b)Do some research to find out which nutrients the unknown should have had (hint: Google nutrition label ______(food)).
(c)Summarize your group’s findings about the nutrients present in your unknown solution. Be sure to include the identifying code.
(d)Were there any discrepancies between your answers to b and c? Explain.