Carbohydrates are one of the most important nutrients needed for the development of the body. It is a nutrient which directly helps in the production of energy which is vital for the functioning of the organs of the body. Carbohydrates are the organic compounds of carbon (C), hydrogen (H) and oxygen (O), where the hydrogen and oxygen are present in the ratio of 2:1, as in water. They act as sources of energy for the cells. The carbohydrates can simply be classified into three categories which are monosaccharides, disaccharides and polysaccharides. They are also called ‘saccharides’. In Greek language, the word ‘sakcharon’ means sugar.
1. Monosaccharides: Monosaccharides are the simplest form of carbohydrates with only one simple sugar. Based on the number of carbon atoms, the members of monosaccharide are known as trioses, tetroses, pentoses, hexoses and heptoses. Glucose, fructose and galactose are the most common types of hexoses. They are highly soluble in water and sweet to taste.
They are also designated as aldoses and ketoses depending on whether they contain aldehyde of ketone groups. All sugars contain the C = O group. This is called a carbonyl group.. When carbonyl group is terminal in position and is jointed to at least one hydrogen atom, it is designated as aldehyde. But when it is sub-terminal in position or it is present between carbon atoms, it is designated as ketones.
2. Disaccharides: These are formed by two molecules of the monosaccharides with release of a water molecule. The most common disaccharides are maltose, sucrose and lactose. They are soluble in water and sweet in taste.
Sucrose is found in the juice of plants such as sugarcane, sugar beet, pineapple and carrot roots. Lactose or milk sugar occurs to about 5% in cow’s milk and 7% in human milk.
3. Polysaccharides: Polysaccharides are the condensation product of a large number of monosaccharides. Shorter polysaccharides with 2-10 monomers are called oligosaccharides. Polysaccharides are mostly insoluble in water and not sweet in taste. The most common polysaccharides found in living organisms are glycogen, starch and cellulose. Starch is the storage food of plant. Glycogen is the storage food of animal and also found in blue green algae, fungi and bacteria. Cellulose is an important constituent of plant cell wall.
Cellulose is the main constituent of paper and cloth. It is also the basis for the manufacture of several synthetic fibres like rayon.