Here we will learn about Biochemical Tests. The food we eat is rich in a variety of nutrients. These nutrients are essential for the growth, development and proper functioning of our organ and organ system, therefore keeping us healthy. The three main nutrients that are required in our daily diet are carbohydrates, fats, and proteins. These nutrients can be obtained from different types of food products obtained from plants and animals.

We all know that pulses are rich in proteins. Likewise, potatoes and rice are the sources of carbohydrates, and Oily substances such as butter, ghee, etc., fulfil the requirements of fats in our body. Have you ever thought about how we get to know which food product is rich in what particular nutrient? This can be ensured by performing biochemical tests on the given sample of the food product. Let’s study the different biochemical tests performed to ensure the presence of carbohydrates, fats, and proteins in various food products. Continue reading to know more.

What are Nutrients?

Definition: The chemical substances present in the food that provide the metabolic energy for the growth, development, repair of damaged tissues and therefore help to maintain a healthy life are called nutrients. Nutriology is the science that deals with the study of foods and their use in diet and therapy.

Types of Nutrients – Nutritional Requirements of Humans

The following types of nutrients are required in our daily diet:
1. Carbohydrates: Energy-giving foods.
2. Fats: Energy-giving foods that can be stored in the body.
3. Proteins: Body-building foods.
4. Vitamins and minerals: Protective foods that mainly protect us from diseases and are required for growth and good health.
5. Water and Roughages are also an important part of our daily meal.

Learn Everything About Carbohydrates Here

Why are Different Nutrients Consumed?

1. Our body requires energy for several living activities that can be obtained from food.
2. Growth is one of the characteristic features of living organisms that can be obtained by consuming protein-rich food products.
3. Several minerals constitute the essential components of our body, such as calcium is required for strengthening bones, iron is needed for haemoglobin (a blood pigment).
4. Water is the basis of our life that is required to transport the substances to the target organs in our body.
5. Several fat-containing foods serve as a food reservoir and provide energy during illness and help to overcome body discomfort.

Some nutrients, their sources and functions can be tabulated as follows:

Carbohydrates

Carbohydrates are energy giving food. All carbohydrates can be represented by a common empirical formula (CH₂O_n). Carbohydrates are commonly called sugar. These can be classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on the number of sugar units. Glucose is a monosaccharide and serves as an instant source of energy.

Test for the Presence of Carbohydrates (Starch)

The most common complex carbohydrate in our food is Starch. An iodine test is performed to detect the presence of Starch in the given sample. The stepwise explanation can be discussed as follows:
1. Material required: Iodine solution, potato extract or rice flour, test tube, dropper.
2. Procedure:
a. A small quantity of potato extract or rice flour is taken into the test tube.
b. Further, 2-3 drops of dilute iodine solution are added to the sample.
c. The test tube is left undisturbed for a few minutes.
3. Observation & Result: It has been observed that the solution turns into a blue-black colour, indicating the presence of Starch in the given sample. This ensures that potatoes and rice are rich sources of complex carbohydrates.

Fig: Iodine Test for Starch

Proteins

Proteins are complex organic compounds that consist of amino acids joined by peptide bonds. Proteins are known as body-building food as they are required for growth and repair.

Test for the Presence of Proteins

Proteins are the building blocks of plants and animals. All proteins contain carbon, hydrogen, oxygen, nitrogen and, with a few exceptions, sulphur also. The following test can be performed to test the presence of proteins in a given food sample:

1. Material required: Copper sulphate (CuSO₄), Sodium hydroxide or Caustic soda (NaOH), egg albumin, test tube, test tube holder.
2. Procedure:
a. The solid food sample is firstly crushed and mixed with water to convert into a semi-solid paste.
b. A sample of foodstuff is taken into the test tube, and a few drops (2-3 drops) of copper sulphate is added to the sample.
c. The process is further followed by the addition of sodium hydroxide (8-10 drops) into the solution.
d. The test tube content is mixed well by stirring.
e. Afterwards, the test tube is kept at rest for about 5 minutes.
3. Observation & result: The solution in the test tube appears violet and therefore ensures the presence of protein in the given foodstuff sample.

Fig: Test for the Presence of Protein

Fats

These are also energy-giving foods. They provide more energy compared to carbohydrates. When we are short of carbohydrates, our body uses the fat stored under the skin of our body to maintain the supply of energy.

Test for the Presence of Fat

Fats and oils are found abundantly in plants and animals, forming distinct foodstuffs. Fats have double caloric value than carbohydrates. The following test is  widely performed for the presence of Fat in the given sample:

Paper Drop Test
1. Materials required: Peanut seeds (fat sample), a piece of paper, light source.
2. Procedure:
a. Fresh peanut seed is placed on the paper and crushed so that the oil comes on the paper.
b. The crushed seed is then removed, and the paper is placed in front of the light source.
3. Observations & Results: A bright greasy translucent patch is observed on the paper. The translucent spot ensures the presence of fats in the given seed.

Fig: Paper Spot Test for Fat

Food Products and their Nutrients Value

We consume a variety of food items in our daily meals. Since all types of nutrients cannot be obtained from a single food item, therefore It is necessary to take a balanced diet to fulfil the requirement of different types of nutrients on a regular basis. Some of the food products and their nutrient values can be tabulated as follows:

Food Items	Test for the presence of Starch	Test for the presence of Proteins	Test for the presence of Fats
Rice	Present	–	–
Eggs	–	Present	–
Bread	Present
Meat	–	Present	–
Beans	–	Present	–
Potato	Present	–	–
Nuts	–	–	Present
Bacon	–	–	Present
Curd	–	Present	–
Soya bean	–	Present	–
Ghee	–	–	Present

Summary

Food is the source of energy for all the living beings on the earth. Humans and other animals are heterotrophs that cannot prepare their food and hence consume a variety of food products to obtain different nutrients required for the growth and development of an organism. Carbohydrates, proteins, fats, vitamins, minerals are the main nutrients that are taken by consuming different types of food products.

Since all the nutrients are not present in adequate amounts in all types of food items, therefore it is necessary to have a complete diet with all nutrients. Biochemical tests are performed to know about the nutrients present in a specific food item. Iodine test, Biuret test, Paper spot tests are performed to test the presence of carbohydrates, proteins, and fats, respectively. Besides these, some other alternative tests are also performed for the presence of nutrients in the food.

Frequently Asked Questions

Q.1. How can you test the presence of starch in food?
Ans: The carbohydrate can be tested by putting the drops of iodine solution in the given sample. The violet colour of the solution confirms the presence of carbohydrate (starch) in the sample.

Q.2. What kinds of food are rich in fats?
Ans: Dairy products such as milk, ghee, butter, cheese, and nuts (groundnut, cashew, almonds) are rich in fats.

Q.3. Which colour indicates the presence of protein in the food sample?
Ans: Purple colour indicates the presence of protein in the food sample.

Q.4. Which test is done for fats?
Ans: A paper spot test is done for testing the presence of fat in the sample.

Q.5. What foods test positive for proteins?
Ans: Eggs, meat, pulses, soybean, etc., are tested for the presence of proteins.