Test For The Presence Of Sugar, Starch, Proteins, And Fats - Detection In Suitable Plant And Animal Materials

Aim

To carry out appropriate tests to detect the presence of sugar(sucrose), starch, proteins, and fats in suitable animal and plant materials.

Theory

Nutrition is a source through which living entities obtain food for the body to get fueled with energy. Therefore the food we eat must be well-balanced with all the substances that are required by our body to perform daily activities, these substances are known as nutrients.

Nutrients nourish the body by releasing the energy required for the body’s growth. Some of the nutrients found in food are:

  • Proteins
  • Carbohydrates
  • Fats
  • Vitamins
  • Minerals
  • Dietary fibers

What are proteins?

They are body-building nutrients which aid in the repair of damaged body parts and also in the growth of the body

What are vitamins and minerals?

These nutrients are reflected to be protective food. They protect us from diseases by providing resistance against germs that are known to cause diseases.

What are carbohydrates?

Carbohydrates are nutrients that provide energy to the body instantly. Fats are also energy-giving foods and store energy.

Carbohydrates contain starch, sugars, and fibres which consist of sugar molecules containing hydrogen, carbon, and oxygen. Carbohydrates can be categorized into:

  • Simple carbohydrates – They are composed of 1 or 2 units of sugar, hence can be broken down and be absorbed easily. Simple carbohydrates are subdivided into:
  • Monosaccharides – Composed of one sugar unit
  • Disaccharides – Consists of 2 chemically-associated monosaccharide units. Example – Lactose, Maltose, Sucrose, etc.
  • Complex carbohydrates – consists of long chains of simple carbohydrate units. Since they are large in size they can be broken down into simple carbohydrates. They are further subdivided into
  • Oligosaccharides – Composed of less than 10 monosaccharides parts
  • Polysaccharides – composed of a large number of polysaccharides. Example – Glycogen, starch, and cellulose

Test For Sucrose

The presence of sucrose can be tested in a sample using Benedict’s test.

Material Required

  • Benedict’s Reagent
  • Sugar cane extract
  • Concentrated HCl
  • NaOH solution
  • Burner
  • Dropper
  • Test-tube
  • Test tube holder

Procedure

  • Take a clean and dried test-tube and add sugar cane extract into it.
  • Now carefully add a few drops of concentrated HCl using a dropper to the test tube.
  • Hold the test tube securely with the help of a test tube holder.
  • Place the test tube near the Bunsen burner and allow the solution to boil for two minutes.
  • While boiling, the hydrolysis of sucrose occurs and the fructose converts to glucose.
  • With the help of a dropper, add a few drops of NaOH solution to the test tube so as the solution turns alkaline.
  • Now add a few drops of Benedict’s reagent with the help of a dropper into the test tube.
  • With the help of a test tube holder, place the test tube near the Bunsen burner and allow the solution to boil for a few minutes.
  • Observe the changes.

Observation

The colour of the solution colour from blur colour to green colour. From green colour, it finally changes to brick red or orange colour. This indicates that the solution contains glucose.

Test For Starch

Material Required

  • Potato extract
  • Iodine solution
  • Test tube
  • Dropper

Procedure

  • Take a clean and dried test-tube and add potato extract into it.
  • Add five to six drops of iodine solution with the help of a dropper into the test tube.
  • Keep the test tube undisturbed and allow the mixtures to stand for a few seconds.
  • Observe the changes.

Observation

The presence of starch in the potato extract is indicated when the colour changes to a blue-black colour.

Test For Proteins

The presence of proteins in a sample can be detected by the following tests:

  • Biuret Test
  • Xanthoproteic Test
  • Million’s Test

1. Biuret Test

Material Required

  • 1% CuSO4
  • 40% NaOH solution
  • Dropper
  • Egg Albumin
  • Test tube
  • Test tube holder

Procedure

  • Take a clean and dried test-tube and add egg albumin into it.
  • Now add a few drops of 40% NaOH solution with the help of a dropper into the test tube containing the egg albumin.
  • With the help of a dropper, add 2 to 3 drops of 1% CuSO4 solution into the same test tube contained in the egg albumin.
  • Now shake the test tube slowly in order to mix the solution present in it completely.
  • Keep the test tube undisturbed and allow the mixtures to stand for 5 minutes. After a few minutes, observe the changes.

Observation

The solution in the test tube appears to be violet in colour. This indicates that the sample that is tested contains proteins.

2. Xanthoproteic Test

Material Required

  • Ammonia solution
  • Concentrated HNO3
  • Dropper
  • Test tube
  • Egg albumin
  • Test tube holder

Procedure

  • Take a clean and dried test-tube and add egg albumin into it.
  • Add five drops of concentrated HNO3 with the help of a dropper into the test tube containing the egg albumin.
  • Holding the test tube securely with a test tube holder, bring the sample to a boil over a burner.
  • As the solution starts to boil, a yellow precipitate is formed.
  • Now add a few drops of ammonia solution into the test tube slowly.
  • Stir the test-tube continuously in order to mix the solution completely. After a few minutes, observe the changes.

Observation

The sample contained in the test tube, which appeared to have yellow precipitate changes its colour to orange. This indicates that the sample contains proteins.

3. Million’s Test

Materials Required

  • Million’s Reagent
  • Egg albumin
  • Test tube
  • Dropper

Procedure

  • Take a clean and dried test-tube and add egg albumin into it.
  • With the help of a dropper, add a few drops of the Million’s reagent into the test tube containing the egg albumin.
  • Keep the test tube undisturbed and allow the mixtures to stand for 5 minutes.
  • After a few minutes, observe the changes.

Observation

The sample indicates the presence of proteins when the colour changes to pink.

Test For Fats

The presence of fats in a sample can be detected by the following tests:

  • Sudan III Test
  • Paper Spot Test

1. Sudan III Test

Materials Required

  • Sudan III Solution
  • Oil
  • Test tube
  • Dropper
  • Egg Albumin

Procedure

  • Take a clean and dried test-tube and add a few drops of oil into it.
  • Now into the same test tube, add five to six drops of the Sudan III reagent with the help of a dropper.
  • Stir the test tube continuously and allow the solution to stand for a while.
  •  After a few seconds, observe the changes.

Observation

The presence of fat in the sample is indicated when pink colour droplets appear on the test tube.

2. Paper Spot Test

Materials Required

  • A piece of white paper
  • Peanut seeds
  • Watch glass

Procedure

  • On the piece of white paper, place the fresh peanut seeds.
  • Crush and rub the peanut seeds in the white paper.
  • Remove the peanut seed remaining on the watch glass.
  • Observe the changes on the piece of white paper.

Observation

The spot where the peanut seeds are rubbed turns translucent. This indicates the presence of fats in the sample.

Viva Questions

Q.1. List examples of simple carbohydrates.

A.1. Simple carbohydrates are present in the form of fructose in fruits, in the form of lactose in milk and in the form of sucrose in table sugar.

Q.2. What are stachyose and raffinose?

A.2. They are examples of oligosaccharides and are categorized under complex carbohydrates.

Q.3. What are peptide linkages?

A.3. Proteins are made up of a large number of amino acids that are linked together by specific linkages known as peptide linkages. The amino acids comprise of both carboxylic acids and an amino group.

Q.4. What is the xanthoproteic test?

A.4. It is used to detect the presence of proteins that contain aromatic amino acid units.

The benzene ring present in the amino acid, upon heating, is nitrated to form a yellow nitro-compound. It switches to orange colour with the presence of an alkali.

Q.5. What do fats contain?

A.5. They are complex molecules. Fats contain glycerol and fatty acids.

Q.6. What is a Fehling’s Test used for?

A.6. It is used to detect the presence of aldehydes and reducing sugars. The Fehling’s solution is a deep blue coloured solution. This test is performed with glucose, fructose, sucrose, and maltose.

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