Analogy Type:
1. Starch test: Iodine solution :: Sugar test:
Answers
Answer:
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.