Food Substances And Food Tests: Classification And Tests Of Food Substances

Topic: Food Substances And Food Tests
Table Of Contents

  • Classification of Food Substances
  • Meaning Of Carbohydrates
  • Meaning Of Proteins
  • Meaning Of Fat And Oils
  • Meaning Of Mineral Salts
  • Meaning Of Vitamins
  • Meaning Of Water
  • Meaning Of Roughages.

Food Substances All living organisms need food for their survival and daily activities. Plants can manufacture their food through the process of photosynthesis, hence they are called autotrophs. On the other hand, animals cannot manufacture their food as they depend on plants directly or indirectly for their food, hence they are called heterotrophs.
Animals sometimes are classified according to the type of food they eat. On this basis, they are classified into three groups, namely:
1. Carnivorous animals: These animals feed only on flesh or other animals, e.g. Dog, lion, lizard, snake , cat etc.
2. Herbivorous animals: These animals feed on plants, e.g. Goat, cattle, sheep, rabbit etc.
3. Omnivorous animals: These animals feed on both plants and animals, e.g. Man, pig etc.
Classification of Food Substances
All the food eaten or taken in by an animal can be classified or divided into seven groups of food substances. These food substances are:
(i) Carbohydrates
(ii) Proteins
(iii) Fats and oils
(iv) Mineral salts
(v) Vitamins
(vi) Water
(vii) Roughages.
The composition, sources and functions of these food substances are explained as follows:
Composition: Carbohydrate is made up of carbon, hydrogen and oxygen. The ratio of hydrogen to oxygen is 2:1 as in the case with water. The main sources of carbohydrate include yam, rice, maize, millet, guinea corn, potatoes, bread, garri etc.
Types of Carbohydrates
There are three major types of carbohydrate. These are:
a. Monosaccharides (Simple sugars): They are the simplest sugar and have only one unit of simple sugar. Examples are glucose, fructose and galactose.
b. Disaccharides (Reducing sugars): These contain two units of simple sugars, examples are sucrose, maltose and lactose.
c. Polysaccharides (Complex sugars): These consists of more than two simple sugars or several simple sugars joined together. Examples are starch, cellulose, chitin and glycogen (animal fat).
Importance of Carbohydrates
1. Carbohydrate provides energy required by animals for their daily activities.
2. It also provides heat, during its oxidation, used in maintaining the body temperature.
3. Carbohydrates are also used to build certain body parts, e.g. Exoskeleton of arthropods.
4. Mucus, an important lubricant in our bodies, is composed of carbohydrates.
2. Proteins
Proteins are complex molecules and are made of smaller units called amino acids. Proteins have to be digested to amino acids before they are absorbed in the bodies of amino animals.
Composition of protein: Protein is composed of carbon, hydrogen, oxygen, nitrogen and sometimes phosphorus and sulphur.
Sources of proteins: Animal sources of proteins are milk, egg, fish, cheese, meat and chicken while plant sources are beans (cowpea), groundnut, soyabeans etc.
Importance of Protein
1. Protein is used for the growth of young ones.
2. It is used for the repair of worn-out tissues or cells.
3. It aids reproduction.
4. It is used for the production of enzymes.
5. It is used for tissue and cell formation (body building).
3. Fats and Oils
Fats and oils are also called lipids. Fats are solid lipids at room temperature while oils are liquid lipids at room temperature. They are hydrolysed during digestion to fatty acids and glycerol which can be absorbed into the lymphatic system.
Composition of fats and oils: Fats and oils are composed of carbon, hydrogen and little oxygen.
Sources of fats and oils: Sources of fats and oils include palm oil, groundnut, soyabean oil, melon oil, butter, fish, cheese, margarine, lard etc.
Importance of Fats And Oils
1. Fats and oils provide more energy to animals than carbohydrates.
2. Fats supply essential fatty acids to animals.
3. Fats and oils also provide fat soluble vitamins.
4. They help in the maintenance of body temperature.
4. Mineral Salts
Animals require various mineral salts for metabolic activities within the body. Lack of mineral salts will result to nutritional deficiency.
Classes of Mineral Salts: These include calcium, phosphorus, magnesium, potassium, sulphur, sodium, chlorine, iron, iodine, manganese, flourine, copper and cobalt.
5. Vitamins
Vitamins are organic food substances required by man and other animals only in small amount for normal growth and healthy development. Inadequate or lack of these vitamins do lead to nutritional deficiency in animals generally.
Groups of Vitamins
Vitamins are grouped into two main classes. These are:
i. Fat soluble vitamins: These are vitamins that are soluble only in fats, e.g. Vitamins A, D, E and K.
ii. Water Soluble Vitamins: These are vitamins that are soluble only in water, e.g. Vitamin B-complex and Vitamin C.
6. Water
Composition Of Water: Water is composed of two elements- hydrogen and oxygen.
Sources of Water: Sources of water available to animals include metabolic water from food, drinking water from rivers, taps, rain, pond etc.
Importance of Water
Water is very important to animals in the following ways:
1. Water is required for metabolic activities in the body.
2. It is necessary for the digestion of food.
3. It can be used for the maintenance of body temperature.
4. Water is the main component of plants and animals, e.g. It forms about 75% of man’s body.
5. It is the basis of body secretion from endocrine glands.
6. It constitutes a greater part of blood.
7. Roughages
Roughages consists of indigestible fibrous materials derived from vegetables, fruits, carbohydrates and proteins. Roughages provide bulk to the intestinal content thereby stimulating the movement of bowel. Lack of roughages in the diet can cause constipation. Roughages are easily digested by micro-organisms in the intestinal tract.
8. Balanced Diet
Balanced diet is a diet containing the correct proportion or the right amount of all the six substances required by an organism or man. The balanced diet must contain the six food substances such as carbohydrates, proteins, fats and oils, minerals, vitamins and water.
Importance Of Balanced Diet
Balanced diet is important to the body in the following ways:
1. Balanced diet makes us healthy and by so doing makes us to be resistant to diseases.
2. It encourages growth and normal development of the body.
3. It also provides energy required for normal activities.
4. Balanced diet prevents malnutrition deficiency or diseases.
Food Test
1. Test For Proteins
Test: Biuret’s Test
i. Take a small quantity of fresh milk or egg white solution.
ii. Add 1cm of protein and sodium hydroxide and 1% of copper (ii) solution in drops.
iii. Shake the mixture after each drop. Do not heat.
Observation: Mixture will turn to purple or violet colour.
Inference: Protein is present.
2. Test for starch
i. Collect any starch material like bread or yam;
ii. Add few drops of dilute iodine solution.
Observation: The colour will change to blue-black.
Inference: Starch is present.
3. Test for simple sugars, glucose and fructose
i. Put a small quantity of glucose solution in a test tube;
ii. Add 2% Benedict solution;
iii. Boil the mixture for 4-6 minutes.
Observation: A brick-red or orange precipitate is seen.
Inference: Glucose is present.
4. Test for water
i. Dip a blue, dey cobalt chloride paper in a food item.
Observation: The colour of the paper changes from blue to pink.
Inference: Water is present.

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