FOOD TESTS FOR DETECTING GLUCOSE, SUCROSE,
STARCH, PROTEIN, AND LIPID MOLECULES
INTRODUCTION
In this lab session, we will perform biochemical assessments to find
glucose, sucrose, starch, protein, and lipids in various food items like
bread, pasta, and chicken. For each assessment, a certain reagent will
react with the specific molecules, resulting in visible color changes.
MATERIALS NEEDED
• Test tubes (10 cm³)
• Measuring cylinder (50 ml)
• Pipettes (1 ml and 5 ml)
• Benedict’s solution (for glucose detection)
• Hydrochloric acid and sodium hydroxide (for sucrose testing)
• Iodine solution (to identify starch)
• Biuret reagent (for protein detection)
• Ethanol and water (for lipid analysis)
• Water bath (set at 80°C)
• Food samples (bread, pasta, chicken)
• Mortar and pestle
• Filter paper
TEST FOR GLUCOSE (BENEDICT’S TEST)
1. Crush 2 g of bread in a mortar and combine with 10 ml of distilled
water. Mix well and filter to get a solution.
2. Transfer 2 ml of the filtered solution into a test tube and mix in 2 ml of
Benedict’s solution.
3. Put the test tube in a water bath set to 80°C for 5 minutes.
4. Watch for any color change.
Observation: The solution may shift from blue to green, yellow, or brick
red, reflecting the amount of glucose present.
TEST FOR SUCROSE (HYDROLYSIS & BENEDICT’S TEST)
1. In a test tube, mix 2 ml of hydrochloric acid with 2 ml of pasta
solution.
2. Place it in a water bath at 80°C for 5 minutes to break down sucrose
into glucose and fructose.
3. Neutralize it using 2 ml of sodium hydroxide
solution.
4. Add 2 ml of Benedict’s solution and heat it again for 5 minutes.
5. Observe the resulting color change.
Observation: If sucrose is in the solution, a green, yellow, or red change
after heating suggests that glucose has formed.
TEST FOR STARCH (IODINE TEST)
1. Put 2 ml of pasta solution in a test tube.
2. Add 3 drops of iodine solution.
3. Look for any color change.
Observation: A blueblack color indicates starch's presence, while a
brown color suggests it is not present.
TEST FOR PROTEIN (BIURET TEST)
1. Pour 2 ml of chicken solution into a test tube.
2. Add 2 ml of Biuret reagent and mix it carefully.
3. Watch for a color change.
Observation: The solution turns violet if proteins are detected; if not, it
remains light blue.
TEST FOR LIPIDS (EMULSION TEST)
1. Crush 2 g of bread and place it into a dry test tube.
2. Add 5 ml of ethanol and shake it for 1 minute to dissolve any lipids.
3. Pour this solution into another test tube that
contains 5 ml of water.
4. Observe any changes.
Observation: A milkywhite emulsion is evidence of lipid presence.
CONCLUSION
These experiments offer dependable ways to detect macromolecules in
food. Bread is known to have glucose, starch, protein, and lipids. Pasta
comprises starch and sucrose, whereas chicken is rich in proteins and
lipids.
Substance
Name of Brief Description of Observation Result of Test
Being Tested
Test Test After the Test (Positive/Negative)
For
Heat bread solution
with Benedict’s Solution changed
Benedict’s
Glucose solution in a water color to brick Positive
Test
bath at 80°C for 5 red.
minutes.
Hydrolyze pasta
Hydrolysis & solution with HCl, Color changed to
Sucrose Benedict’s neutralize with NaOH, green/yellow Positive
Test then heat with after heating.
Benedict’s solution.
Add iodine solution to
Solution turned
Starch Iodine Test pasta solution and Positive
blue-black.
observe color change.
Add Biuret reagent to
Solution turned
Protein Biuret Test chicken solution and Positive
violet.
observe color change.
Mix bread solution Milky-white
Emulsion
Lipids with ethanol, shake, emulsion Positive
Test
then pour into water. appeared.
