Definition:
Carbohydrates are hydrates of carbon, which on hydrolysis produce polyhydroxy aldehydes or polyhydroxy ketones.
Introduction:
Carbohydrates are products of plant origin and are a part of an extremely large group of naturally occurring organic compounds.
e.g. Sugar Cane, Starch
Carbohydrates are a good source of energy.
Carbohydrates are also known as saccharides, the word saccharide comes from the Greek word saccharon which means sugar.
Classification of Carbohydrates:
Carbohydrates can be classified by following ways,
Depending on the product of hydrolysis.
Depending on Physical properties.
On the basis of test with chemical reagents
On the basis of Hydrolysis:
Monosaccharides:
The simple form of carbohydrates.
A carbohydrate that can be hydrolyzed only once to break down into simpler units of polyhydroxy aldehyde or ketone is called monosaccharide.
e.g. glucose, fructose, mannose, etc.
Oligosaccharides:
Sugars that on hydrolysis yield two or nine molecules of monosaccharides are called oligosaccharides.
These are further classified as di-, tri- or tetrasaccharides, etc.
(a) Disaccharides: These are sugars that produce two molecules of the same or different monosaccharides on hydrolysis. Examples are sucrose, maltose, and lactose.
(b) Trisaccharides: Sugars that yield three molecules of the same or different monosaccharides on hydrolysis are called trisaccharides. An example of trisaccharides is Raffinose.
Polysaccharides:
On hydrolysis, polysaccharides yield a large number of monosaccharides.
If monosaccharides are the same then they are called Homopolysaccharides.
If monosaccharides are different, then they are called Heterpolysaccharides
Examples of polysaccharide are starch, glycogen, Dextrin, Cellulose etc.
On the basis of Physical Characteristics:
On the basis of Physical Characteristics carbohydrates are classified as,
Sugars.
Non Sugars.
Sugars:
Sugars are crystalline substances, taste sweet and readily water soluble.
Because of their fixed molecular weight, sugars have sharp melting points.
e.g. glucose, fructose, sucrose, lactose, etc.
Non Sugars:
Characteristics of non-sugars are Amorphous, Tasteless, water-insoluble substances with variable melting points.
E.g. Starch, Glycogen.
C) On the basis of testing with chemical reagents:
Depending on chemical reactions with certain chemical reagents the carbohydrates are classified as ,
Reducing Sugars.
Non reducing sugars.
Reducing Sugars:
These have a free aldehyde (-CHO) or ketone (C=O) group.
These have the ability to reduce the cupric ions (Cu++; blue) in Fehling’s or Benedict’s Solution to cuprous ions (Cu+; reddish) that separate out as cuprous oxide (Cu2O) from the solution.
e.g. Glucose, lactose, melibiose, gentiobiose, cellobiose, mannotriose.
Non-reducing sugars:
A free aldehyde or ketone group is absent.
No cuprous oxide (Cu2O) producing chemical reaction takes place.
Examples are sucrose, trehalose, raffinose, gentianose, melezitose.
Commonly Asked Questions.
Define and classify Carbohydrates.