Tests of Carbohydrates, Fats and Proteins in Given Food Stuffs

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What are Carbohydrate, Protein, and Fat?

Carbohydrates are naturally occurring sugars, starches and fibre in food. These are the main source of energy. Carbohydrates are subdivided into several categories on the basis of the number of sugar units and how the sugar units are chemically bonded to each other. Proteins are the biomolecule made up of amino acids. It is essential to building muscle mass. It is commonly found in animal products, though is also present in other sources, such as nuts and legumes. Fats are a class of lipids containing two kinds of monomers, fatty acids and glycerol. It is a subgroup of lipids. Here we’ll discuss tests for carbohydrates proteins and fats.


Tests for Carbohydrates Proteins and Fats

Test for carbohydrates and proteins in any foodstuff is done with the extract of the foodstuff. These tests do not restrict each other. Test for carbohydrates and proteins confirm the presence of these molecules in the food.


Food Test for Carbohydrates

Carbohydrate can be tested by using the following methods:

1. Tollen’s Test

Take the given food sample, prepare the extract of the given food sample. Then add the Tollen’s reagent to the prepared food extract. A silver mirror formed on the wall of the test tube confirms the presence of carbohydrate in the foodstuff. 

AgNO₃  +  NH₄OH  →  NH₄NO₃  +  AgOH

2AgOH  →  Ag₂O  +  H₂O

Ag₂O  + 2NH₄OH  →  2[Ag(NH₃)₂]OH  +  3H₂O

                                       (Soluble)

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2. Molisch’s Test

Take the given food sample, prepare the extract of the given food sample. Then add the Molisch’s reagent to the prepared food extract. A purple-violet ring formed in the test tube confirms the presence of carbohydrate in the foodstuff. 

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3. Benedict’s Test 

Take the given food sample, prepare the extract of the given food sample. Then add Benedict’s reagent to the prepared food extract. A red precipitate formed in the test tube confirms the presence of carbohydrate in the foodstuff.

CuSO₄  →  Cu²⁺ + SO₄²⁻

Cu²⁺  +  Reducing sugar  →  Cu⁺

Cu⁺  →  Cu₂O


4. Fehling’s Test

Take the given food sample, prepare the extract of the given food sample. Then add Fehling’s A and Fehling’s B reagent to the prepared food extract. A red precipitate formed in the test tube confirms the presence of carbohydrate in the foodstuff.

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5. Iodine Test

This test is used to identify starch. Starch is a type of carbohydrate. Take the given food sample, prepare the extract of the given food sample. Then add an iodine solution to the prepared food extract. A solution will turn blue in colour to confirm the presence of starch (carbohydrate) in the foodstuff.


Food Test for Proteins

Proteins can be tested by using the following methods

1. Biuret Test

Take the given food sample, prepare the extract of the given food sample. Then add the aqueous copper sulphate to the prepared food extract. A solution turns violet in colour confirms the presence of protein in the foodstuff.

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2. Ninhydrin Test

Take the given food sample, prepare the extract of the given food sample. Then add the pyridine ninhydrin solution to the prepared food extract. A solution turns violet in colour confirms the presence of protein in the foodstuff.

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3. Xanthoproteic Test

Take the given food sample, prepare the extract of the given food sample. Then add the nitric acid solution to the prepared food extract. A solution turns yellow in colour confirms the presence of protein in the foodstuff.

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4. Millions Test

Take the given food sample, prepare the extract of the given food sample. Then add sodium nitrite and sulfuric acid to the above extract followed by Mercuric sulfate. A solution will turn brick-red in colour. This confirms the presence of protein in the food.

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Food Test For Fats


1. Acrolein Test

Take the given food sample, prepare the extract of the given food sample. Then add potassium bisulphite to the above extract. A Pungent irritating odour evolves to form the solution confirms the presence of Fats in the food.

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2. Translucent Spot Test 

Take the food sample and place it between the folds of filter paper and rub it lightly. Presence of translucent spots on the filter paper confirms the presence of fats in foodstuff. 

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3. Solubility Test

Take the given food sample, prepare the extract of the given food sample. Then add the above extract to the chloroform solution or alcohol solution. If the extract gets dissolved into the solution it confirms the presence of Fats in the food.


Did You Know?

  • Zero food contains zero carbohydrates.

  • Carbohydrate is also known as brain food. 

  • Occasional carbohydrate cutting can beat cancer.

  • High protein diet aids fat loss. 

FAQ (Frequently Asked Questions)

Question: Name Three Tests that Can be Used for the Identification of Carbohydrates.

Answer: Three tests that can be used for the identification of carbohydrate are: 

  1. Fehling’s Test

  2. Molisch’s Test

  3. Tollen’s Test

Question: Explain the Biuret Test.

Answer: Biuret Test is used for the identification of protein in the food. In this test, we take the given food sample, prepare the extract of the given food sample. Then add the aqueous copper sulphate to the prepared food extract. A solution turns violet in colour confirms the presence of protein in the foodstuff.