A compound of carbon, hydrogen, and oxygen that contains the saccharose unit or its first reaction product and in which the ratio
of hydrogen to oxygen is the same as in water. Carbohydrates are the most abundant class of organic compounds, constituting three-fourths of the dry weight of all vegetation. They are also widely distributed in animals and lower forms of life. They comprise: (1) monosaccharides, simple sugars such as fructose (levulose) and its isomer glucose (dextrose), both having the formula C6H12O6; (2) disaccharides, sucrose (C12H22O11), maltose, cellobiose, and lactose; and (3) polysaccharides (high polymeric substances). The last group includes all starch and cellulose families, as well as pectin, the seaweed products agar and carrageenan, and natural gums. The simple sugars are crystalline and water soluble, with a sweet taste; starches are water soluble, tasteless, and amorphous; cellulose is insoluble in water and organic solvents and is only partially crystalline. Galactose, sorbose, xylose, arabinose, and mannose are constituents of more complex sugars. The natural gums are water soluble plant products composed of monosaccharide units joined by glycosidic bonds (arabic, tragacanth).
Carbohydrates are an important natural source of ethanol now in extensive use in gasohol and other energy applications.See Energy Sources; Gasohol; Fermentation.
