Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds.

Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol.

Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent.

Starch grains from the rhizomes of Typha (cattails, bullrushes) as flour have been identified from grinding stones in Europe dating back to 30,000 years ago.

[7] Pure extracted wheat starch paste was used in Ancient Egypt, possibly to glue papyrus.

The glucose is used to generate the chemical energy required for general metabolism as well as a precursor to myriad organic building blocks such as nucleic acids, lipids, proteins, and structural polysaccharides such as cellulose.

Green algae and land-plants store their starch in the plastids, whereas red algae, glaucophytes, cryptomonads, dinoflagellates and the parasitic apicomplexa store a similar type of polysaccharide called floridean starch in their cytosol or periplast.

The semicrystalline granules generally consist of concentric layers of amylose and amylopectin which can be made bioavailable upon cellular demand in the plant.

By contrast, many structural polysaccharides such as chitin, cellulose, and peptidoglycan are linked by β-glycosidic bonds, which are more resistant to hydrolysis.

The second type is green tissue, for example, leaves, where many plant species synthesize transitory starch on a daily basis.

A number of starch synthases available in plastids then adds the ADP-glucose via α-1,4-glycosidic bond to a growing chain of glucose residues, liberating ADP.

[23][24][25] Furthermore, two proteins named ESV and LESV play a role in the aqueous-to-crystalline phase transition of glucan chains.

[28] The starch that is synthesized in plant leaves during the day is transitory: it serves as an energy source at night.

The insoluble, highly branched starch chains require phosphorylation in order to be accessible for degrading enzymes.

The enzyme glucan, water dikinase (GWD) installs a phosphate at the C-6 position of glucose, close to the chain's 1,6-alpha branching bonds.

[39] If starch is subjected to dry heat, it breaks down to form dextrins, also called "pyrodextrins" in this context.

The major sources of starch intake worldwide are the cereals (rice, wheat, and maize) and the root vegetables (potatoes and cassava).

[41] Many other starchy foods are grown, some only in specific climates, including acorns, arrowroot, arracacha, bananas, barley, breadfruit, buckwheat, canna, colocasia, cuckoo-pint, 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.

Upon cooking, starch is transformed from an insoluble, difficult-to-digest granule into readily accessible glucose chains with very different nutritional and functional properties.

It is thought that this shift in energy delivery (as a result of eating more processed foods) may be one of the contributing factors to the development of metabolic disorders of modern life, including obesity and diabetes.

[44] In addition, cooking and food processing significantly impacts starch digestibility and energy release.

[47] Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta, porridge and tortilla.

During cooking with high heat, sugars released from starch can react with amino acids via the Maillard reaction, forming advanced glycation end-products (AGEs), contributing aromas, flavors and texture to foods.

Recent evidence suggests that the intestinal fermentation of dietary AGEs may be associated with insulin resistance, atherosclerosis, diabetes and other inflammatory diseases.

The extent of conversion is typically quantified by dextrose equivalent (DE), which is roughly the fraction of the glycosidic bonds in starch that have been broken.

[64][65] Papermaking is the largest non-food application for starches globally, consuming many millions of metric tons annually.

These starch derivatives associate with the anionic or negatively charged paper fibers / cellulose and inorganic fillers.

In the dry end of the papermaking process, the paper web is rewetted with a starch based solution.

Top and bottom heavyweight sheets of paper are applied to the formulation, and the process is allowed to heat and cure to form the eventual rigid wall board.

The starches act as a glue for the cured gypsum rock with the paper covering, and also provide rigidity to the board.