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  • For the Urhobo cuisine dish known as starch see usi

  • Starch or amylum is a carbohydrate consisting of a large number of glucose units joined

  • by glycosidic bonds. This polysaccharide is produced by most green plants as an energy

  • store. It is the most common carbohydrate in human diets and is contained in large amounts

  • in such staple foods as potatoes, wheat, maize, rice, 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 branched

  • version of amylopectin. Starch is processed to produce many of the

  • sugars in processed foods. Dissolving starch in warm water gives wheatpaste, which can

  • be used as a thickening, stiffening or gluing agent. The biggest industrial non-food use

  • of starch is as adhesive in the papermaking process. Starch can be applied to parts of

  • some garments before ironing, to stiffen them.

  • Etymology The word "starch" is from sterchen, meaning

  • to stiffen. "amylum" is for starch, from the Greek αμυλον, "amylon" which means "not

  • ground at a mill". The root amyl is used in biochemistry for several compounds related

  • to starch. History

  • Starch grains from the rhizomes of Typha as flour have been identified from grinding stones

  • in Europe dating back to 30,000 years ago. Starch grains from sorghum were found on grind

  • stones in caves in Ngalue, Mozambique dating up to 100,000 years ago.

  • Pure extracted wheat starch paste was used in Ancient Egypt possibly to glue papyrus.

  • The extraction of starch is first described in the Natural History of Pliny the Elder

  • around AD 77-79. Romans used it also in cosmetic creams, to powder the hair and to thicken

  • sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. Rice

  • starch as surface treatment of paper has been used in paper production in China, from 700

  • AD onwards. In addition to starchy plants consumed directly,

  • 66 million tonnes of starch were being produced per year world-wide by 2008. In the EU this

  • was around 8.5 million tonnes, with around 40% being used for industrial applications

  • and 60% for food uses, most of the latter as glucose syrups.

  • Energy store of plants Most green plants use starch as their energy

  • store. An exception is the family Asteraceae, where starch is replaced by the fructan inulin.

  • In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The

  • glucose is stored mainly in the form of starch granules, in plastids such as chloroplasts

  • and especially amyloplasts. Toward the end of the growing season, starch accumulates

  • in twigs of trees near the buds. Fruit, seeds, rhizomes, and tubers store starch to prepare

  • for the next growing season. Glucose is soluble in water, hydrophilic,

  • binds with water and then takes up much space and is osmotically active; glucose in the

  • form of starch, on the other hand, is not soluble, therefore osmotically inactive and

  • can be stored much more compactly. Glucose molecules are bound in starch by the

  • easily hydrolyzed alpha bonds. The same type of bond is found in the animal reserve polysaccharide

  • glycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose

  • and peptidoglycan, which are bound by beta bonds and are much more resistant to hydrolysis.

  • Biosynthesis Plants produce starch by first converting

  • glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase.

  • This step requires energy in the form of ATP. The enzyme starch synthase then adds the ADP-glucose

  • via a 1,4-alpha glycosidic bond to a growing chain of glucose residues, liberating ADP

  • and creating amylose. Starch branching enzyme introduces 1,6-alpha glycosidic bonds between

  • these chains, creating the branched amylopectin. The starch debranching enzyme isoamylase removes

  • some of these branches. Several isoforms of these enzymes exist, leading to a highly complex

  • synthesis process. Glycogen and amylopectin have the same structure,

  • but the former has about one branch point per ten 1,4-alpha bonds, compared to about

  • one branch point per thirty 1,4-alpha bonds in amylopectin. Amylopectin is synthesized

  • from ADP-glucose while mammals and fungi synthesize glycogen from UDP-glucose; for most cases,

  • bacteria synthesize glycogen from ADP-glucose. In addition to starch synthesis in plants,

  • starch can be synthesized from non-food starch mediated by an enzyme cocktail. In this cell-free

  • biosystem, beta-1,4-glycosidic bond-linked cellulose is partially hydrolyzed to cellobioase.

  • Cellobiose phosphorylase cleaves to glucose 1-phosphate and glucose; the other enzymepotato

  • alpha-glucan phosphorylase can add glucose unit from glucose 1-phosphorylase to the non-ruducing

  • ends of starch. In it, phosphate is internally recycled. The other productglucosecan

  • be assimilated by a yeast. This cell-free bioprocessing does not need any costly chemical

  • and energy input, can be conducted in aqueous solution, and does not have sugar losses.

  • As a result, cellulosic starch could be used to feed the world because cellulose resource

  • is about 50 times of starch resource. Degradation

  • Starch is synthesized in plant leaves during the day, in order to serve as an energy source

  • at night. Starch is stored as granulates. These insoluble highly branched chains have

  • to be phosphorylated in order to be accessible for degrading enzymes. The enzyme glucan,

  • water dikinase phosphorylates at the C-6 position of a glucose molecule, close to the chains

  • 1,6-alpha branching bonds. A second enzyme, phosphoglucan, water dikinase phosphorylates

  • the glucose molecule at the C-3 position. A loss of these enzymes, for example a loss

  • of the GWD, leads to a starch excess phenotype. Because starch cannot be phosphorylated, it

  • accumulates in the plastid. After the phosphorylation, the first degrading

  • enzyme, beta-amylase is able to attack the glucose chain at its non-reducing end. Maltose

  • is released as the main product of starch degradation. If the glucose chain consists

  • of three or less molecules, BAM cannot release maltose. A second enzyme, disproportionating

  • enzyme-1, combines two maltotriose molecules. From this chain, a glucose molecule is released.

  • Now, BAM can release another maltose molecule from the remaining chain. This cycle repeats

  • until starch is degraded completely. If BAM comes close to the phosphorylated branching

  • point of the glucose chain, it can no longer release maltose. In order for the phosphorylated

  • chain to be degraded, the enzyme isoamylase is required.

  • The products of starch degradation are to the major part maltose and to a less extensive

  • part glucose. These molecules are now exported from the plastid to the cytosol. Maltose is

  • exported via the maltose transporter. If this transporter is mutated, maltose accumulates

  • in the plastid. Glucose is exported via the plastidic glucose translocator. Now, these

  • two sugars act as a precursor for sucrose synthesis. Sucrose can the be used in the

  • oxidative pentose phosphate pathway in the mitochondria, in order to generate ATP at

  • night. Properties

  • Structure

  • While amylose was traditionally thought to be completely unbranched, it is now known

  • that some of its molecules contain a few branch points. Although in absolute mass only about

  • one quarter of the starch granules in plants consist of amylose, there are about 150 times

  • more amylose molecules than amylopectin molecules. Amylose is a much smaller molecule than amylopectin.

  • 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 while potato

  • starches have larger granules. 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. 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 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.

  • Hydrolysis The enzymes that break down or hydrolyze starch

  • into the constituent sugars are known as amylases. Alpha-amylases are found in plants and in

  • animals. Human saliva is rich in amylase, and the pancreas also secretes the enzyme.

  • Individuals from populations with a high-starch diet tend to have more amylase genes than

  • those with low-starch diets; chimpanzees have very few amylase genes. It is possible that

  • turning to a high-starch diet was a significant event in human evolution.

  • Beta-amylase cuts starch into maltose units. This process is important in the digestion

  • of starch and is also used in brewing, where amylase from the skin of seed grains is responsible

  • for converting starch to maltose. Dextrinization

  • If starch is subjected to dry heat, it breaks down to form dextrins, also called "pyrodextrins"

  • in this context. This break down process is known as dextrinization.dextrins are mainly

  • yellow to brown in color and dextrinization is partially responsible for the browning

  • of toasted bread. Chemical tests

  • Iodine solution is used to test for starch; a dark blue color indicates the presence of

  • starch. The details of this reaction are not yet fully known, but it is thought that the

  • iodine fit inside the coils of amylose, the charge transfers between the iodine and the

  • starch, and the energy level spacings in the resulting complex correspond to the absorption

  • spectrum in the visible light region. The strength of the resulting blue color depends

  • on the amount of amylose present. Waxy starches with little or no amylose present will color

  • red. Starch indicator solution consisting of water,

  • starch and iodine is often used in redox titrations: in the presence of an oxidizing agent the

  • solution turns blue, in the presence of reducing agent the blue color disappears because triiodide

  • ions break up into three iodide ions, disassembling the starch-iodine complex. A 0.3% w/w solution

  • is the standard concentration for a starch indicator. It is made by addinggrams of

  • soluble starch to 1 liter of heated water; the solution is cooled before use.

  • Each species of plant has a unique type of starch granules in granular size, shape and

  • crystallization pattern. Under the microscope, starch grains stained with iodine illuminated

  • from behind with polarized light show a distinctive Maltese cross effect.

  • Food Starch is the most common carbohydrate in

  • the human diet and is contained in many staple foods. The major sources of starch intake

  • worldwide are the cereals and the root vegetables. Many other starchy foods are grown, some only

  • in specific climates, including acorns, arrowroot, arracacha, bananas, barley, breadfruit, buckwheat,

  • canna, colacasia, katakuri, kudzu, malanga, millet, oats, oca, polynesian arrowroot, sago,

  • sorghum, sweet potatoes, rye, taro, chestnuts, water chestnuts and yams, and many kinds of

  • beans, such as favas, lentils, mung beans, peas, and chickpeas.

  • Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta,

  • porridge and tortilla. Digestive enzymes have problems digesting

  • crystalline structures. Raw starch will digest poorly in the duodenum and small intestine,

  • while bacterial degradation will take place mainly in the colon. When starch is cooked,

  • the digestibility is increased. Hence, before humans started using fire, eating grains was

  • not a very useful way to get energy. Starch gelatinization during cake baking can

  • be impaired by sugar competing for water, preventing gelatinization and improving texture.

  • Starch industry The starch industry extracts and refines starches

  • from seeds, roots and tubers, by wet grinding, washing, sieving and drying. Today, the main

  • commercial refined starches are cornstarch, tapioca, wheat, rice and potato starch. To

  • a lesser extent, sources include rice, sweet potato, sago and mung bean. Historically,

  • Florida arrowroot was also commercialized. To this day, starch is extracted from more

  • than 50 types of plants. Untreated starch requires heat to thicken

  • or gelatinize. When a starch is pre-cooked, it can then be used to thicken instantly in

  • cold water. This is referred to as a pregelatinized starch.

  • Starch sugars Starch can be hydrolyzed into simpler carbohydrates

  • by acids, various enzymes, or a combination of the two. The resulting fragments are known