WORKSHEET 1
FOOD TESTING
The nutrients in the food you eat supply your body with energy for growth and repair.
These nutrients include carbohydrates, proteins, fats, minerals and vitamins. Carbohydrates
make up a group of organic compounds that include sugars and starches, which are important
in supplying the body with energy. Proteins are important for growth and repair. Lipids (e.g.
fats) can supply as much as four times the amount of energy as carbohydrates or proteins.
The presence of these nutrients in food can be tested by using chemical reagents that
react in predictable ways. Benedict's solution is used to test for simple sugars, Fehling’s
solution for reducing sugar, iodine solution for starch, Biuret’s solution for protein, and
Sudan III for lipids in fluid.
Objectives

To test the presence of carbohydrates, proteins, and fats in the food samples
Materials needed:




Food samples: rice, sugar, milk,
margarine, banana, four other selected
foods
Chemicals: Benedict’s solution,
Fehling’s solution, iodine solution,
Biuret solution, Sudan III stain
Test tubes with stand
Test tube clamps






Beaker glass
Droppers
Mortar and pestle
Burner
White paper
Glass marking pen
Procedures
Food Test 1: Sugar – Benedict's solution
Benedict's solution is a clear blue solution that in the presence of simple sugars will
change color to green, yellow, and brick-red, depending on the amount of sugar.
1. For solid food samples: mix small amount of crushed food samples with water to
make a liquid.
2. To a test tube, add 10 drops of liquid to be tested.
3. If testing more than one liquid, label each test tube with a marker.
4. Add 10 drops of Benedict's solution to each test tube.
5. Carefully heat the test tubes by suspending in a hot water bath for five minutes.
6. Note any color change.
SBI SMAN 2 Kota Bengkulu
1
Food Test 2: Reducing sugar – Fehling’s solution
Fehling’s solution is used to test for reducing sugar. When equal quantities of Fehling’s
solution A and B are mixed with an aqueous solution of a reducing sugar and the mixture
is heated on a boiling water bath, a reddish precipitate of cuprous oxide is formed.
1. Take small amount of crushed food sample or 10 drops of aqueous solution of the
sample in a test tube.
2. Add 10 drops of each of Fehling’s solution A and Fehling’s solution B.
3. Keep the test tube in a boiling water bath.
4. Note any change.
Food Test 3: Starch – Iodine solution
Starch gives a purple-blue color when treated with iodine or
1. Take small amount of crushed food sample or 10 drops of aqueous solution of the
sample in a test tube.
2. Add 3-4 drops of iodine solution.
3. Note any color change.
Food Test 4: Protein – Biuret solution
Biuret solution is used to identify the presence of protein. Biuret reagent is a blue solution
that, when it reacts with protein, will change color to pink-purple.
1. Take small amount of crushed food sample or 10 drops of aqueous solution of the
sample in a test tube.
2. If testing more than one liquid, label each test tube with a marker.
3. Add 3 drops of Biuret reagent solution to each test tube. Shake gently to mix.
4. Note any color change.
Food Test 3: Fat - Sudan III stain
Sudan III is used to identify the presence of lipids in liquids. It will stain fat cells red.
1.
2.
3.
4.
To a test tube, add equal parts of test liquid and water to fill about half full.
If testing more than one liquid, label each test tube with a marker.
Add 3 drops of Sudan III stain to each test tube. Shake gently to mix.
A red-stained oil layer will separate out and float on the water surface if fat is present.
Food Test 5: Fat – Spot test using a white paper
When a sample containing fats is pressed or rubbed on a clean white sheet of paper, a
greasy spot (translucent spot) appears
1. Take a food sample to be tested and press or rub it on a clean white sheet of paper.
2. Hold it against light to see if the paper become transparent or not.
SBI SMAN 2 Kota Bengkulu
2
Observation Result
Food Sample
Benedict’s Test
Food Testing
Fehling’s Test
Iodine Test
Biuret’s Test
Spot Test
Note:
+ for positive result
- for negative result
Conclusion
What nutrients presence in each food sample?
.......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
.......................................................................................................................................................
......................................................................................................................................................
......................................................................................................................................................
.......................................................................................................................................................
......................................................................................................................................................
SBI SMAN 2 Kota Bengkulu
3
SBI SMAN 2 Kota Bengkulu
4