Tests of Carbohydrates, Fats and Proteins in Given Food Stuffs

Objective:

The aim of this experiment is to identify the presence of carbohydrates, fats and proteins in various food items.

Background:

The identification of carbohydrates, fats and proteins in a food item is achieved by conducting specific tests for each of these components using an extract from the food item. The benefit of these tests is that they do not interfere with each other.

Further Reading: Viva Questions on Tests of Carbohydrates, Fats and Proteins in Food Items

Carbohydrate Test:

1. Molisch’s test – Food sample + Molisch’s reagent → Purple or violet ring indicates the presence of carbohydrate.
2. Fehling’s test – Food sample + Fehling’s reagent → Red precipitate indicates the presence of carbohydrates
3. Benedict’s test – Food sample + Benedict’s reagent → Red precipitate indicates the presence of carbohydrates.
4. Tollen’s test – Food sample + Tollen’s reagent → Silver mirror indicates the presence of carbohydrates.
5. Iodine test – Food sample + Iodine solution → Blue colour solution indicates the presence of starch.

Protein Test:

1. Biuret test – Food sample + Aqueous copper sulfate → Violet colouration indicates the presence of Proteins
2. Xanthoproteic test – Food sample + Nitric acid → Yellow colour solution indicates the presence of proteins.
3. Millions test – Food sample + Mercuric sulfate in the presence of sodium nitrite and sulfuric acid → Brick red colour solution indicates the presence of proteins.
4. Ninhydrin test – Food sample + Pyridine solution of ninhydrin → Violet colour solution indicates the presence of proteins.

Test for Fats and Oils:

1. Solubility test – Food sample + Chloroform or alcohol → Miscibility with chloroform and immiscibility with water confirms the presence of fat.
2. Translucent spot test – Food sample rubbed between the folds of filter paper → If a translucent spot is present, then the presence of fats is confirmed.
3. Acrolein test – Food sample + Potassium bisulfite KHSO ₄ → If a pungent irritating odor is present, then the presence of fats or oil is confirmed.

Required Materials:

1. Molisch’s reagent
2. Fehling’s reagent
3. Benedict’s reagent
4. Tollen’s reagent
5. Iodine solution
6. Copper sulfate solution
7. Sodium hydroxide
8. Nitric acid
9. Mercuric sulfate
10. Sodium nitrite
11. Alcohol
12. Chloroform
13. Filter paper
14. Potassium bisulfate
15. Concentrated hydrochloric acid
16. Furfural solution
17. Test tubes
18. Test tube holder
19. Water bath
20. Dropper
21. Stirrer
22. Bunsen burner

Experimental Setup:

Experimental Procedure:

To test the presence of carbohydrates, proteins, fats and oils in the given food sample, first the extract of the given foodstuff should be prepared. Dry the given foodstuff in the mortar with a pestle or by boiling with minimum quantity of water extracting with a small quantity of an organic solvent after grinding the foodstuff.

Here are some examples of how to prepare the extract of food stuff:

1. For carrots – Chop into small pieces and boil with water.
2. For cheese – test directly
3. For oranges – Extract the juice.
4. For boiled chicken – take the white portion grind and shake with water.

Observations and Conclusion:

Food item	For carbohydrates				For proteins				For fats and oils
cheese
carrots
cheese
boiled chicken

Results and Analysis:

The tested food sample contains _________ (carbohydrates/ proteins/ fats).

Safety Measures:

1. Always use minimum quantity of reagents and ensure they are freshly prepared for the test.
2. Use droppers to take the reagents from the bottle.
3. Ensure to wear lab aprons and hand gloves during the experiment.

Also, Check ⇒ Properties of Maltose

Stay tuned for more practical chemistry experiments.