Starch or Amylum (C6H10O5)n) is a polysaccharide carbohydrate consisting of a huge number of glucose units joined with one another by glycosidic bonds. Starch is formed by all green plants as an energy store and is a main food source for humans.

Pure starch is a white, tasteless and odorless residue that is insoluble in cold water or alcohol. It is made up by two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the source plant, starch generally contains 20 to 25 percent amylose and 75 to 80 percent amylopectin.Glycogen, the glucose stockpile of animals, is a more branched form of amylopectin.

The word “starch” is derivative from Middle English sterchen, meaning to harden, which is appropriate since starch can be used as a thickening or glueing negotiator when dissolved in water and heated, giving wheatpaste.

In Textile it is used to decrease breaking of yarns during weaving, the warp yarns are sized. Starch is one of the main agents utilize for cotton sizing. Starch also is used as printing thickener.

Iodine solution is used to test for starch; a blue color points to the existence of starch. The details of this reaction are not yet completely known, but it is thought that the iodine (I3 and I5 ions) fits inside the twirl of amylose, the charge transfers between the iodine and the starch, and the energy plane spacing’s in the resulting complex match to the absorption spectrum in the visible light region. The strength of the resul
tant blue color depends on the amount of amylose present.

Starch indicator solution containing of water, starch and iodine is regularly used in redox titrations: in the existence of an oxidizing agent the solution turns blue, in the presence of reducing agent the blue color vanish because triiodide (I3) ions break up into three iodide ions, dis-assembling the starch-iodine complex. A 0.3% w/w solution is the typical concentration for a starch indicator. It is made by accumulation 4 grams of soluble starch to 1 litre of heated water; the solution is cooled prior to use keep in mind that starch-iodine compound becomes unstable at temperatures above 35 °C).

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