Carbohydrates are energy yielding substances which include starch, glucose,sugar, cane sugar,grain foods, roots and tubers.The carbohydrates derived from cereals are chief source of energy in the Indian diets. 1 gram of carbohydrates yield 4.0 calories in the body. Chemical composition : A carbohydrate is a chemical compound made up of carbon(C), hydrogen(H) and oxygen(O). Basic unit of a carbohydrate is a monosaccharide. It contains a series of carbon atoms linked together in a chain , attached with oxygen and hydrogen atoms. Glucose a monosaccharide , most common sugar, which is used to store and release energy.Its formula is C6H12O6 . Carbohydrates in the form of glucose molecules cannot be stored in nature on a large scale, so they form chain like complex polymeric molecules with the removal of water, such as,
- Starch in plants and
- Glycogen in animals.
Classification of carbohydrates:
- Monossacharides- (from Greek monos : single, sacchar: sugar ) are the simplest carbohydrates.Monosaccharides are classified by the number of carbon atoms they contain:
- Triose, 3 carbon atoms
- Tetrose, 4 carbon atoms
- Pentose, 5 carbon atoms
- Hexose,6 carbon atoms
- Heptose,7 carbon atoms
- Octose, 8 carbon atoms
- Nonose,9 carbon atoms
- Decose,10 carbon atoms
Examples of monosaccahrides are glucose, galactose, fructose and ribose. Glucose is the sugar which is neccesary for all body systems. it is abundantly found in nature. Biomedically glucose is the most important monosaccharide. Fructose is the fruit sugar found in honey and fruits. 2. Disaccharides- Two molecules of monosaccharides they join to form a disaccharide, with the removal of one molecule of water. Glucose+ Fructose -> Sucrose + water Sucrose or table sugar is one the dissacharides, found in almost all plants, sugarcane and beet and the others are:
- Glucose+Glucose-> Maltose(malt sugar, found in sprouted and malted products)
- Glucose+ Galactose-> Lactose(Milk sugar)
3.Oligosaccharides- are condensation products of two to ten monosaccharides; maltotriose (is not a true triose but a trisaccharide containing three a-glucose residues) is an example.
4.Polysaccharides- are complex compounds formed by the combination of more than two molecules of a monosaccharide .Their structural formula is (C6H10O5)n, where n>2. Polysaccharides are least sweet. Examples of polysaccharides is starch in plants and glycogen in animals.