page_title: Starch
section_title: Structure
hierarchical_section_title: Starch / Properties / Structure
caption_attribution_description: Deutsch: Stärkemehl (Maisstärke) bei 800fach mit Polfilter. Ausschnitt ca: 200µm x 150µm. English: Cornstarch at 800x with polarizer filter. Excerpt size: 200µm x 150µm.
context_page_description: Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants as energy storage. It is the most common carbohydrate in human diets and is contained in large amounts in staple foods like potatoes, maize, rice, wheat and cassava.
  Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight. Glycogen, the glucose store of animals, is a more highly branched version of amylopectin.
  In industry, starch is converted into sugars, for example by malting, and fermented to produce ethanol in the manufacture of beer, whisky and biofuel. It is processed to produce many of the sugars used in processed foods. Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent. The biggest industrial non-food use of starch is as an adhesive in the papermaking process.
context_section_description: While amylose was thought to be completely unbranched, it is now known that some of its molecules contain a few branch points.
  Amylose is a much smaller molecule than amylopectin. About one quarter of the mass of starch granules in plants consist of amylose, although there are about 150 times more amylose than amylopectin molecules.
  Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size:  rice starch is relatively small (about 2 μm) while potato starches have larger granules (up to 100 μm).
  Starch becomes soluble in water when heated. The granules swell and burst, the semi-crystalline structure is lost and the smaller amylose molecules start leaching out of the granule, forming a network that holds water and increasing the mixture's viscosity. This process is called starch gelatinization. During cooking, the starch becomes a paste and increases further in viscosity. During cooling or prolonged storage of the paste, the semi-crystalline structure partially recovers and the starch paste thickens, expelling water. This is mainly caused by retrogradation of the amylose. This process is responsible for the hardening of bread or staling, and for the water layer on top of a starch gel (syneresis).
  Some cultivated plant varieties have pure amylopectin starch without amylose, known as waxy starches. The most used is waxy maize, others are glutinous rice and waxy potato starch. Waxy starches have less retrogradation, resulting in a more stable paste. High amylose starch, amylomaize, is cultivated for the use of its gel strength and for use as a resistant starch (a starch that resists digestion) in food products.
  Synthetic amylose made from cellulose has a well-controlled degree of polymerization. Therefore, it can be used as a potential drug deliver carrier.
  Certain starches, when mixed with water, will produce a non-newtonian fluid sometimes nicknamed "oobleck".
caption: Corn starch, 800x magnified, under polarized light, showing characteristic extinction cross
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