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Carbohydrates were originally thought of as the hydrates of carbon, but they are more adequately defined as polyhydroxy- Aldehydes and Ketones and their derivatives. They normally conform to the general structure Cx(H2O)y. The term carbohydrates includes all the sugars, starches, celluloses, and a wide variety of Gums, and Biological Polymers. This broad class of compounds is further subdivided into monosaccharides, disaccharides,
and polysaccharides.
Monosaccharides or simple sugars are represented by the formula: CH2OH(CHOH)nCHO if the compound is an aldehyde derivative, i.e., an aldose; or CH2OH(CHOH)nCOCH2OH if the compound is a ketone, i.e., a ketose. The major 6-carbon monosaccharides are Glucose (an aldose in which n equals 4), Fructose (a ketose in which n equals 3), and Galactose, which is chemically similar to Glucose but possesses a different steric
configuration.
Disaccharides are Ethers, formed from two monosaccharides. The most common disaccharides are Maltose (two glucose units), Sucrose (one glucose and one fructose unit), and Lactose (one glucose and one galactose unit).
Polysaccharides are the polyethers of monosaccharides which generally occur in nature. They may be polymers of the same monosaccharide, in which case they are known as homopolysaccharides; or may include differing and occasionally carboxyl-substituted monosaccharides, in which case they are known as heteropolysaccharides. Starch is a homopolysaccharide derived from Glucose; Cellulose is also built up from glucose units but differs from starch in the configuration around the ether oxygen bonds. Heteropolysaccharides found in terrestrial and oceanic plants are important gums and natural polymers. Polysaccharides found in the animal kingdom include Chitin and a large group of complex polysaccharides which are chemically bound to proteins, e.g., glycosaminoglycans (mucopolysaccharides), Hyaluronic Acid and Chondroitin Sulfate.
All types of carbohydrates are used in cosmetics to impart viscosity or other textural characteristics. |