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Carbohydrates - Classification of Carbohydrates and Its Importance

Carbohydrates - Classification of Carbohydrates and Its Importance

A group of compounds composed of Carbon, Hydrogen, Oxygen, Nitrogen normally expressed by the standard formula (CH2O) N i.e. hydrates of carbon are known as carbohydrates.


Carbohydrates are normally present in almost all the plants and are also called Poly-hydroxy-aldehydes or Polyketones or compounds which on hydrolysis produce aldehydes and ketones.


These are normally classified into two major categories, named as:
1. Simple sugars
2. Polysaccharides


Those carbohydrates which consist of simplified basic sugars or saccharides as their chemical moiety are termed as simple sugars. These are generally grouped according to the fact depending on the no. of carbon atoms present in them.

Properties of Simple sugars:

1. Simple sugars are sweet in taste.
2. Simple sugars are crystalline in nature.
3. Simple sugars are soluble in water.
4. Simple sugars contain low molecular weight.

Classification of Simple Sugars:

These are further classified into the following saccharides depending upon the no. of sugar entities present inside
their main chemical structures.


Those sugars which cannot be further hydrolysed and simplified are known as monosaccharides. Depending on the no. of carbon atoms present these may be termed as following:
1. Biose: these contain 2-carbon atom and normally occur free in nature.
2. Triose: these contain 3-carbon atoms but in the form of phosophodiesteric esters
Example: glyceraldehydes.
1. Tetrose: these contain 4-carbon atoms in their structure.
Examples: erythrose
1. Pentose: these contain 5-carbon atoms and are very common in plants and are a product of hydrolysis of polysaccharides like gums, mucilage.
Examples: arabinose, ribose.
1. Hexose: these contain 6-carbon atoms and are further subdivided into following types depending upon the functional groups attached to the structural basic nucleus,
2. Aldose (glucose, galactose, mannose)
3. Ketose (fructose, sucrose)


Those sugars that yield 2 monosaccharides when hydrolysed are termed as disaccharides.
Examples: Sucrose ——>(Presence of H2O) 1 Glucose + 1 Glucose
Maltose ——>(Presence of H2O) 1 Glucose + 1 Fructose


Those sugars which yield 3 molecules of monosaccharides on hydrolysis are termed as trisaccharides.
Examples: Raffinose ——>(Presence of H2O) 1 Glucose + 1 Galactose + 1 Fructose


Those sugars that yield 4 monosaccharides when hydrolysed are termed as tetrasaccharides.
Example: staychose.


Those carbohydrates which yield indefinite number of monosaccharides when subjected to hydrolysis are termed as Polysaccharides.

Properties of Polysaccharides

1. Polysaccharides are amorphous in nature.
2. Polysaccharides are tasteless compounds.
3. Polysaccharides are less soluble in water.
4. Polysaccharides contain high molecular weight.

Classification of Polysaccharides

These are further classified depending on the product of hydrolysis as follows:
1. Hexaxon
2. Pentazon
3. Mucilages: these are normal or physiological products of plants, they are generally plant exudates which are already present in the plant.
Examples: some types of tubers and leaves such as pectin.
1. Gums: these polysaccharides are abnormal or pathological products of plants
Examples: acacia, tragacanth, isapgol, ghatti gum, guar gum.