Starch
The starch (of Latin amylum , not ground) is a complex Glucide of reserve, for the vegetable higher. The starch is one of the principal heating resources for the Mankind, because it is the constituent main thing of the Céréale S (Riz, Maïs, Blé, Sorgho.) or of the Potato.
For the plant, the starch is a reserve of energy and nutrient, necessary to survive the bad season (dry or cold). It makes it possible to store glucidic Nutriment S in the cells, without dissolving them in water. Indeed the presence of simple glucids increases the osmotic potential intern of the cells what requires a great quantity of water. The starch is a form of the glucid reserve which makes it possible to save the Eau. In the cells, it is presented in the form of grains visible with the Microscope: the Amyloplaste S.
At the plants of the family of the Astéracées (in the past Made up S) the molecule of reserve is not the starch, but the Inuline and at the animal , it is the Glycogène.
Properties
It is a Polysaccharide of chemical formula (C6H10O5) n. It is composed of molecules of Glucose bound by connections α (1 4), in general characteristic of the polyosides of reserve (exception: Inulin). It is composed of two polysaccharidic fractions:
- the Amylose (approximately 25% of the starch constitute), Molécule made of envion 600 to 1000 molecules of glucose in linear chains. The amylose is synthesized by the insoluble starch synthase.
- the Amylopectin (approximately 75% of the starch constitute), ramified molecule all the 25 residues glucoses approximately (connection alpha 1-6). The total chain can make between 10000 and 100000 residues glucoses. The amylopectin is synthesized by the soluble starch synthase.
The starch grain protéiniquement genetic is presented in the form of granules semicrystalline: the amylopectin is organized in layers, the amylose forms an amorphous zone less better organized between the various layers.
The amylose is organized in a right propeller with six glucoses per turn. It dissociates in assimilable glucose under the action of Enzyme S, the Amylase S, all the more easily if it is in the form of amylopectin. Indeed, the helicoid formation does not support the accessibility of the starch to the enzymes.
The starch is insoluble in the cold Eau. By treating it by warm water, one obtains the Empois. It is exploited in industry for its thickener properties and of gelling.
Origin
One finds it in the Organe S of reserves of many plants:
- the Seed S (in particular the Cereal S (Corn, wheat) and Leguminous S),
- the root S,
- Tuber S and rhizome S (Potato, Sweet potato, Manioc, etc).
- Fruit (Banana), where the starch has as a function to stimulate the dispersion of the seeds (when it there of a) by animals.
Digestion
The Amylase is the Enzyme which allows Hydrolyze R the starch in Glucose. This enzyme is present in the Salive, like in the pancreatic Suc.
Chemical properties
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the starch is insoluble in water and organic solvents. In suspension in water one obtains starch milk, unstable suspension but which heated with 70°C becomes viscous and translucent.
- In contact with a iodo-iodized solution, the starch takes a color violet (reaction between amylose and iodine).
- the starch cannot oxidize the Fehling's solution, because its function alcohol (- OH) reducing is " perdue" in the face of the molecule.
- During the heating, the starch grains inflate and form the starch paste (to rigidify the collars of shirt) which can be used to produce paste and adhesives. The disadvantage is that this freezing can retrogress (to become again liquid) what is problematic for industries.
Uses
Under the economic angle , the starch is of double interest:- for the Alimentation human and animal, in which he plays a crucial role, it is in particular the main component of the Farine;
- for the Industry, which transforms it by physical processes, chemical or biological out of particular starches (modified starch, cation starch, anion starch…) and in a certain number of by-products, such as Glucose, Fructose, Dextrin, Maltodextrine, Mannitol, ethanol, Sorbitol.
- a a little obsolete use: the manufacture of Starch paste, for the empesage of the Clothing S (collars of shirts…).
Related articles
See too
Simple: Starch
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