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.