Signs and symptoms.

Early symptoms are malaise and lethargy. After one to three months, patients develop shortness of breath and bone pain. Myalgias may occur because of reduced carnitine production. Other symptoms include skin changes with roughness, easy bruising and petechiae, gum disease, loosening of teeth, poor wound healing, and emotional changes (which may appear before any physical changes). Dry mouth and dry eyes similar to Sjögren's syndrome may occur. In the late stages, jaundice, generalised edema, oliguria, neuropathy, fever, convulsions, and eventual death are frequently seen.

Cause.

Scurvy, including subclinical scurvy, is caused by a deficiency of dietary vitamin C since humans are unable to metabolically synthesize vitamin C. Provided the diet contains sufficient vitamin C, the lack of working L-gulonolactone oxidase (GULO) enzyme has no significance, and in modern Western societies, scurvy is rarely present in adults, although infants and elderly people are affected. Virtually all commercially available baby formulas contain added vitamin C, preventing infantile scurvy. Human breast milk contains sufficient vitamin C, if the mother has an adequate intake. Commercial milk is pasteurized, a heating process that destroys the natural vitamin C content of the milk.  Scurvy is one of the accompanying diseases of malnutrition (other such micronutrient deficiencies are beriberi and pellagra) and thus is still widespread in areas of the world depending on external food aid. Although rare, there are also documented cases of scurvy due to poor dietary choices by people living in industrialized nations.

Pathogenesis.

Vitamins are essential to the production and use of enzymes that are involved in ongoing processes throughout the human body. Ascorbic acid is needed for a variety of biosynthetic pathways, by accelerating hydroxylation and amidation reactions. In the synthesis of collagen, ascorbic acid is required as a cofactor for prolyl hydroxylase and lysyl hydroxylase. These two enzymes are responsible for the hydroxylation of the proline and lysine amino acids in collagen. Hydroxyproline and hydroxylysine are important for stabilizing collagen by cross-linking the propeptides in collagen.  Collagen is a primary structural protein in the human body, necessary for healthy blood vessels, muscle, skin, bone, cartilage, and other connective tissues. Defective connective tissue leads to fragile capillaries, resulting in abnormal bleeding, bruising, and internal hemorrhaging. Collagen is an important part of bone, so bone formation is also affected. Teeth loosen, bones break more easily, and once-healed breaks may recur. Defective collagen fibrillogenesis impairs wound healing. Untreated scurvy is invariably fatal.

Diagnosis.

Differential diagnosis.

Various childhood onset disorders can mimic the clinical and X-ray picture of scurvy such as:

Prevention.

Scurvy can be prevented by a diet that includes vitamin C-rich foods such as amla, bell peppers (sweet peppers), blackcurrants, broccoli, chili peppers, guava, kiwifruit, and parsley. Other sources rich in vitamin C are fruits such as lemons, limes, oranges, papaya, and strawberries. It is also found in vegetables, such as brussels sprouts, cabbage, potatoes, and spinach. Some fruits and vegetables not high in vitamin C may be pickled in lemon juice, which is high in vitamin C. Though redundant in the presence of a balanced diet, various nutritional supplements are available, which provide ascorbic acid well in excess of that required to prevent scurvy.  Some animal products, including liver, muktuk (whale skin), oysters, and parts of the central nervous system, including the adrenal medulla, brain, and spinal cord, contain large amounts of vitamin C, and can even be used to treat scurvy. Fresh meat from animals which make their own vitamin C (which most animals do) contains enough vitamin C to prevent scurvy, and even partly treat it. In some cases (notably French soldiers eating fresh horse meat), it was discovered that meat alone, even partly cooked meat, could alleviate scurvy. Conversely, in other cases, a meat-only diet could cause scurvy.  Scott's 1902 Antarctic expedition used lightly fried seal meat and liver, whereby complete recovery from incipient scurvy was reported to have taken less than two weeks.

Treatment.

Scurvy will improve with doses of vitamin C as low as 10 mg per day though doses of around 100 mg per day are typically recommended. Most people make a full recovery within 2 weeks.

History.

Hippocrates documented scurvy as a disease, and Egyptians have recorded its symptoms as early as 1550 BCE. The knowledge that consuming foods containing vitamin C is a cure for scurvy has been repeatedly forgotten and rediscovered into the early 20th century.

Early modern era.

In the 13th century, the Crusaders frequently suffered from scurvy. In the 1497 expedition of Vasco da Gama, the curative effects of citrus fruit were already known and confirmed by Pedro Álvares Cabral and his crew in 1507.  The Portuguese planted fruit trees and vegetables in Saint Helena, a stopping point for homebound voyages from Asia, and left their sick, who had scurvy and other ailments, to be taken home by the next ship if they recovered.  In 1500, one of the pilots of Cabral's fleet bound for India noted that in Malindi, its king offered the expedition fresh supplies such as lambs, chickens, and ducks, along with lemons and oranges, due to which "some of our ill were cured of scurvy".  Unfortunately, these travel accounts did not stop further maritime tragedies caused by scurvy, first because of the lack of communication between travelers and those responsible for their health, and because fruits and vegetables could not be kept for long on ships.  In 1536, the French explorer Jacques Cartier, exploring the St. Lawrence River, used the local natives' knowledge to save his men who were dying of scurvy. He boiled the needles of the arbor vitae tree (eastern white cedar) to make a tea that was later shown to contain 50 mg of vitamin C per 100 grams. Such treatments were not available aboard ship, where the disease was most common. In February 1601, Captain James Lancaster, while sailing to Sumatra, landed on the northern coast to specifically obtain lemons and oranges for his crew to stop scurvy. Captain Lancaster conducted an experiment using four ships under his command. One ship's crew received routine doses of lemon juice while the other three ships did not receive any such treatment. As a result, members of the non-treated ships started to contract scurvy, with many dying as a result.  During the Age of Exploration (between 1500 and 1800), it has been estimated that scurvy killed at least two million sailors. Jonathan Lamb wrote: "In 1499, Vasco da Gama lost 116 of his crew of 170; In 1520, Magellan lost 208 out of 230;...all mainly to scurvy."  In 1579, the Spanish friar and physician Agustin Farfán published a book in which he recommended oranges and lemons for scurvy, a remedy that was already known in the Spanish Navy.  In 1593, Admiral Sir Richard Hawkins advocated drinking orange and lemon juice as a means of preventing scurvy.  In 1614, John Woodall, Surgeon General of the East India Company, published "The Surgion's Mate" as a handbook for apprentice surgeons aboard the company's ships. He repeated the experience of mariners that the cure for scurvy was fresh food or, if not available, oranges, lemons, limes, and tamarinds. He was, however, unable to explain the reason why, and his assertion had no impact on the opinions of the influential physicians who ran the medical establishment that scurvy was a digestive complaint.  Even on dry land, in Europe, until the late middle ages, scurvy was common in late winter, when few green vegetables, fruits and root vegetables were available. This gradually improved with the introduction from the Americas of potatoes; by 1800, scurvy was virtually unheard of in Scotland, where it had previously been endemic.

18th century.

A 1707 handwritten book by Mrs. Ebot Mitchell, discovered in a house in Hasfield, Gloucestershire, contains a "Recp.t for the Scurvy" that consisted of extracts from various plants mixed with a plentiful supply of orange juice, white wine or beer.  In 1734, the Leiden-based physician Johann Bachstrom published a book on scurvy in which he stated, "scurvy is solely owing to a total abstinence from fresh vegetable food, and greens; which is alone the primary cause of the disease", and urged the use of fresh fruit and vegetables as a cure.  However, it was not until 1747 that James Lind formally demonstrated that scurvy could be treated by supplementing the diet with citrus fruit, in one of the first controlled clinical experiments reported in the history of medicine. As a naval surgeon on HMS "Salisbury", Lind had compared several suggested scurvy cures: hard cider, vitriol, vinegar, seawater, oranges, lemons, and a mixture of balsam of Peru, garlic, myrrh, mustard seed and radish root. In "A Treatise on the Scurvy" (1753) Lind explained the details of his clinical trial and concluded "the results of all my experiments was, that oranges and lemons were the most effectual remedies for this distemper at sea.”  Unfortunately, the experiment and its results occupied only a few paragraphs in a work that was long and complex and had little impact. Lind himself never actively promoted lemon juice as a single 'cure'. He shared medical opinion at the time that scurvy had multiple causes – notably hard work, bad water, and the consumption of salt meat in a damp atmosphere which inhibited healthful perspiration and normal excretion – and therefore required multiple solutions. Lind was also sidetracked by the possibilities of producing a concentrated 'rob' of lemon juice by boiling it. Unfortunately this process destroyed the vitamin C and was therefore unsuccessful.  During the 18th century, disease killed more British sailors than enemy action. It was mainly by scurvy that George Anson, in his celebrated voyage of 1740–1744, lost nearly two-thirds of his crew (1,300 out of 2,000) within the first 10 months of the voyage. The Royal Navy enlisted 184,899 sailors during the Seven Years' War; 133,708 of these were "missing" or died from disease, and scurvy was the leading cause.  Although throughout this period sailors and naval surgeons were increasingly convinced that citrus fruits could cure scurvy, the classically trained physicians who ran the medical establishment dismissed this evidence as mere anecdote which did not conform to current theories of disease. Literature championing the cause of citrus juice, therefore, had no practical impact. Medical theory was based on the assumption that scurvy was a disease of internal putrefaction brought on by faulty digestion caused by the hardships of life at sea and the naval diet. Although this basic idea was given different emphases by successive theorists, the remedies they advocated (and which the navy accepted) amounted to little more than the consumption of 'fizzy drinks' to activate the digestive system, the most extreme of which was the regular consumption of 'elixir of vitriol' – sulphuric acid taken with spirits and barley water, and laced with spices.  In 1764, a new variant appeared. Advocated by Dr David MacBride and Sir John Pringle, Surgeon General of the Army and later President of the Royal Society, this idea was that scurvy was the result of a lack of 'fixed air' in the tissues which could be prevented by drinking infusions of malt and wort whose fermentation within the body would stimulate digestion and restore the missing gases. These ideas received wide and influential backing, when James Cook set off to circumnavigate the world (1768–1771) in, malt and wort were top of the list of the remedies he was ordered to investigate. The others were beer, Sauerkraut and Lind's 'rob'. The list did not include lemons.  Cook did not lose a single man to scurvy, and his report came down in favour of malt and wort, although it is now clear that the reason for the health of his crews on this and other voyages was Cook's regime of shipboard cleanliness, enforced by strict discipline, as well as frequent replenishment of fresh food and greenstuffs. Another rule implemented by Cook was his prohibition of the consumption of salt fat skimmed from the ship's copper boiling pans, then a common practice in the Navy. In contact with air, the copper formed compounds that prevented the absorption of vitamins by the intestines.  The first major long distance expedition that experienced virtually no scurvy was that of the Spanish naval officer Alessandro Malaspina, 1789–1794. Malaspina's medical officer, Pedro González, was convinced that fresh oranges and lemons were essential for preventing scurvy. Only one outbreak occurred, during a 56-day trip across the open sea. Five sailors came down with symptoms, one seriously. After three days at Guam all five were healthy again. Spain's large empire and many ports of call made it easier to acquire fresh fruit.  Although towards the end of the century MacBride's theories were being challenged, the medical establishment in Britain remained wedded to the notion that scurvy was a disease of internal 'putrefaction' and the Sick and Hurt Board, run by administrators, felt obliged to follow its advice. Within the Royal Navy, however, opinion – strengthened by first-hand experience of the use of lemon juice at the siege of Gibraltar and during Admiral Rodney's expedition to the Caribbean – had become increasingly convinced of its efficacy. This was reinforced by the writings of experts like Gilbert Blane and Thomas Trotter and by the reports of up-and-coming naval commanders.  With the coming of war in 1793, the need to eliminate scurvy acquired a new urgency. But the first initiative came not from the medical establishment but from the admirals. Ordered to lead an expedition against Mauritius, Rear Admiral Gardner was uninterested in the wort, malt and elixir of vitriol which were still being issued to ships of the Royal Navy, and demanded that he be supplied with lemons, to counteract scurvy on the voyage. Members of the Sick and Hurt Board, recently augmented by two practical naval surgeons, supported the request, and the Admiralty ordered that it be done. There was, however, a last minute change of plan. The expedition against Mauritius was cancelled. On 2 May 1794, only and two sloops under Commodore Peter Rainier sailed for the east with an outward bound convoy, but the warships were fully supplied with lemon juice and the sugar with which it had to be mixed. Then in March 1795, came astonishing news. "Suffolk" had arrived in India after a four-month voyage without a trace of scurvy and with a crew that was healthier than when it set out. The effect was immediate. Fleet commanders clamoured also to be supplied with lemon juice, and by June the Admiralty acknowledged the groundswell of demand in the navy had agreed to a proposal from the Sick and Hurt Board that lemon juice and sugar should in future be issued as a daily ration to the crews of all warships.  It took a few years before the method of distribution to all ships in the fleet had been perfected and the supply of the huge quantities of lemon juice required to be secured, but by 1800, the system was in place and functioning. This led to a remarkable health improvement among the sailors and consequently played a critical role in gaining the advantage in naval battles against enemies who had yet to introduce the measures.

19th century.

The surgeon-in-chief of Napoleon's army at the Siege of Alexandria (1801), Baron Dominique-Jean Larrey, wrote in his memoirs that the consumption of horse meat helped the French to curb an epidemic of scurvy. The meat was cooked but was freshly obtained from young horses bought from Arabs, and was nevertheless effective. This helped to start the 19th-century tradition of horse meat consumption in France.  Lauchlin Rose patented a method used to preserve citrus juice without alcohol in 1867, creating a concentrated drink known as Rose's lime juice. The Merchant Shipping Act of 1867 required all ships of the Royal Navy and Merchant Navy to provide a daily lime ration of one pound to sailors to prevent scurvy. The product became nearly ubiquitous, hence the term "limey", first for British sailors, then for English immigrants within the former British colonies (particularly America, New Zealand and South Africa), and finally, in old American slang, all British people.  The plant "Cochlearia officinalis", also known as "common scurvygrass", acquired its common name from the observation that it cured scurvy, and it was taken on board ships in dried bundles or distilled extracts. Its very bitter taste was usually disguised with herbs and spices; however, this did not prevent scurvygrass drinks and sandwiches from becoming a popular fad in the UK until the middle of the nineteenth century, when citrus fruits became more readily available.  West Indian limes began to supplement lemons, when Spain's alliance with France against Britain in the Napoleonic Wars made the supply of Mediterranean lemons problematic, and because they were more easily obtained from Britain's Caribbean colonies and were believed to be more effective because they were more acidic. It was the acid, not the (then-unknown) Vitamin C that was believed to cure scurvy. In fact, the West Indian limes were significantly lower in Vitamin C than the previous lemons and further were not served fresh but rather as lime juice, which had been exposed to light and air, and piped through copper tubing, all of which significantly reduced the Vitamin C. Indeed, a 1918 animal experiment using representative samples of the Navy and Merchant Marine's lime juice showed that it had virtually no antiscorbutic power at all.  The belief that scurvy was fundamentally a nutritional deficiency, best treated by consumption of fresh food, particularly fresh citrus or fresh meat, was not universal in the 19th and early 20th centuries, and thus sailors and explorers continued to suffer from scurvy into the 20th century. For example, the Belgian Antarctic Expedition of 1897–1899 became seriously affected by scurvy when its leader, Adrien de Gerlache, initially discouraged his men from eating penguin and seal meat.  In the Royal Navy's Arctic expeditions in the 19th century it was widely believed that scurvy was prevented by good hygiene on board ship, regular exercise, and maintaining the morale of the crew, rather than by a diet of fresh food. Navy expeditions continued to be plagued by scurvy even while fresh (not jerked or tinned) meat was well known as a practical antiscorbutic among civilian whalers and explorers in the Arctic. Even cooking fresh meat did not entirely destroy its antiscorbutic properties, especially as many cooking methods failed to bring all the meat to high temperature.  The confusion is attributed to a number of factors: In the resulting confusion, a new hypothesis was proposed, following the new germ theory of disease – that scurvy was caused by ptomaine, a waste product of bacteria, particularly in tainted tinned meat.  Infantile scurvy emerged in the late 19th century because children were being fed pasteurized cow's milk, particularly in the urban upper class. While pasteurization killed bacteria, it also destroyed vitamin C. This was eventually resolved by supplementing with onion juice or cooked potatoes. Native Americans helped save some newcomers from scurvy by directing them to eat wild onions.

20th century.

By the early 20th century, when Robert Falcon Scott made his first expedition to the Antarctic (1901–1904), the prevailing theory was that scurvy was caused by "ptomaine poisoning", particularly in tinned meat. However, Scott discovered that a diet of fresh meat from Antarctic seals cured scurvy before any fatalities occurred.  In 1907, an animal model which would eventually help to isolate and identify the "antiscorbutic factor" was discovered. Axel Holst and Theodor Frølich, two Norwegian physicians studying shipboard beriberi contracted by ship's crews in the Norwegian Fishing Fleet, wanted a small test mammal to substitute for the pigeons then used in beriberi research. They fed guinea pigs their test diet of grains and flour, which had earlier produced beriberi in their pigeons, and were surprised when classic scurvy resulted instead. This was a serendipitous choice of animal. Until that time, scurvy had not been observed in any organism apart from humans and had been considered an exclusively human disease. Certain birds, mammals, and fish are susceptible to scurvy, but pigeons are unaffected, since they can synthesize ascorbic acid internally. Holst and Frølich found they could cure scurvy in guinea pigs with the addition of various fresh foods and extracts. This discovery of an animal experimental model for scurvy, which was made even before the essential idea of "vitamins" in foods had been put forward, has been called the single most important piece of vitamin C research.  In 1915, New Zealand troops in the Gallipoli Campaign had a lack of vitamin C in their diet which caused many of the soldiers to contract scurvy. It is thought that scurvy is one of many reasons that the Allied attack on Gallipoli failed.  Vilhjalmur Stefansson, an arctic explorer who had lived among the Inuit, proved that the all-meat diet they consumed did not lead to vitamin deficiencies. He participated in a study in New York's Bellevue Hospital in February 1928, where he and a companion ate only meat for a year while under close medical observation, yet remained in good health.  In 1927, Hungarian biochemist Szent-Györgyi isolated a compound he called "hexuronic acid". Szent-Györgyi suspected hexuronic acid, which he had isolated from adrenal glands, to be the antiscorbutic agent, but he could not prove it without an animal-deficiency model. In 1932, the connection between hexuronic acid and scurvy was finally proven by American researcher Charles Glen King of the University of Pittsburgh. King's laboratory was given some hexuronic acid by Szent-Györgyi and soon established that it was the sought-after anti-scorbutic agent. Because of this, hexuronic acid was subsequently renamed "ascorbic acid."

21st century.

Rates of scurvy in most of the world are low. Those most commonly affected are malnourished people in the developing world and the homeless. There have been outbreaks of the condition in refugee camps. Case reports in the developing world of those with poorly healing wounds have occurred.

Human trials.

Notable human dietary studies of experimentally induced scurvy have been conducted on conscientious objectors during World War II in Britain and on Iowa state prisoner volunteers in the late 1960s. These studies both found that all obvious symptoms of scurvy previously induced by an experimental scorbutic diet with extremely low vitamin C content could be completely reversed by additional vitamin C supplementation of only 10 mg per day. In these experiments, no clinical difference was noted between men given 70 mg vitamin C per day (which produced blood levels of vitamin C of about 0.55 mg/dl, about of tissue saturation levels), and those given 10 mg per day (which produced lower blood levels). Men in the prison study developed the first signs of scurvy about 4 weeks after starting the vitamin C-free diet, whereas in the British study, six to eight months were required, possibly because the subjects were pre-loaded with a 70 mg/day supplement for six weeks before the scorbutic diet was fed.  Men in both studies, on a diet devoid or nearly devoid of vitamin C, had blood levels of vitamin C too low to be accurately measured when they developed signs of scurvy, and in the Iowa study, at this time were estimated (by labeled vitamin C dilution) to have a body pool of less than 300 mg, with daily turnover of only 2.5 mg/day.

Evolution.

The vast majority of animals and plants are able to synthesize vitamin C, through a sequence of enzyme-driven steps, which convert monosaccharides to vitamin C. However, some mammals have lost the ability to synthesize vitamin C, notably simians and tarsiers. These make up one of two major primate suborders, haplorrhini, and this group includes humans. The strepsirrhini (non-tarsier prosimians) can make their own vitamin C, and these include lemurs, lorises, pottos, and galagos. Ascorbic acid is also not synthesized by at least two species of caviidae, the capybara and the guinea pig. There are known species of birds and fish that do not synthesize their own vitamin C. All species that do not synthesize ascorbate require it in the diet. Deficiency causes scurvy in humans, and somewhat similar symptoms in other animals.  Animals that can contract scurvy all lack the -gulonolactone oxidase (GULO) enzyme, which is required in the last step of vitamin C synthesis. The genomes of these species contain GULO as pseudogenes, which serve as insight into the evolutionary past of the species.

Name.

In babies, scurvy is sometimes referred to as "Barlow's disease", named after Thomas Barlow, a British physician who described it in 1883. However, "Barlow's disease" may also refer to mitral valve prolapse (Barlow's syndrome), first described by John Brereton Barlow in 1966.

Scurvy is a disease resulting from a lack of vitamin C (ascorbic acid). Early symptoms of deficiency include weakness, feeling tired and sore arms and legs. Without treatment, decreased red blood cells, gum disease, changes to hair, and bleeding from the skin may occur. As scurvy worsens there can be poor wound healing, personality changes, and finally death from infection or bleeding. It takes at least a month of little to no vitamin C in the diet before symptoms occur. In modern times, scurvy occurs most commonly in people with mental disorders, unusual eating habits, alcoholism, and older people who live alone. Other risk factors include intestinal malabsorption and dialysis. While many animals produce their own vitamin C, humans and a few others do not. Vitamin C is required to make the building blocks for collagen. Diagnosis is typically based on physical signs, X-rays, and improvement after treatment. Treatment is with vitamin C supplements taken by mouth. Improvement often begins in a few days with complete recovery in a few weeks. Sources of vitamin C in the diet include citrus fruit and a number of vegetables (such as red peppers, broccoli, and potatoes). Cooking often decreases vitamin C in foods. Scurvy is rare compared to other nutritional deficiencies. It occurs more often in the developing world in association with malnutrition. Rates among refugees are reported at 5 to 45 percent. Scurvy was described as early as the time of ancient Egypt. It was a limiting factor in long-distance sea travel, often killing large numbers of people. During the Age of Sail, it was assumed that 50 percent of the sailors would die of scurvy on a given trip. A Scottish surgeon in the Royal Navy, James Lind, is generally credited with proving that scurvy can be successfully treated with citrus fruit in 1753. Nonetheless, it would be 1795 before health reformers such as Gilbert Blane persuaded the British Royal Navy to routinely give lemon juice to its sailors.

Kurděje (skorbut, Möllerova Barlowova choroba, avitaminóza C) je nemoc způsobená dlouhodobým nedostatkem vitamínu C ve stravě. Na rozdíl od většiny zvířat a rostlin totiž lidské tělo nedokáže syntetizovat tento vitamín, proto jej musí přijímat v potravě. Dnes už je tato choroba poměrně vzácná, vyskytuje se občas jen ve velmi chudých oblastech tzv. třetího světa. Dříve jí trpěli zejména chudí lidé, obzvláště v zimních měsících, nebo námořníci při dlouhých plavbách. Nemoc se projevuje především krvácením z dásní, pod kůži, do svalů, do nehtových lůžek, vnitřních orgánů, sníženou odolností proti nemocem a poruchou krvetvorby.


Occurrence.

Small amounts of methanol are present in normal, healthy human individuals. One study found a mean of 4.5 ppm in the exhaled breath of test subjects. The mean endogenous methanol in humans of 0.45 g/d may be metabolized from pectin found in fruit; one kilogram of apple produces up to 1.4 g methanol.  Methanol is produced by anaerobic bacteria and phytoplankton.

Interstellar medium.

Methanol is also found in abundant quantities in star-forming regions of space and is used in astronomy as a marker for such regions. It is detected through its spectral emission lines.  In 2006, astronomers using the MERLIN array of radio telescopes at Jodrell Bank Observatory discovered a large cloud of methanol in space, 288 billion miles (463 billion km) across. In 2016, astronomers detected methanol in a planet-forming disc around the young star TW Hydrae using ALMA radio telescope.

Toxicity.

Methanol has low acute toxicity in humans, but is dangerous because it is occasionally ingested in large volumes, often together with ethanol. As little as of pure methanol can cause permanent blindness by destruction of the optic nerve. is potentially fatal. The median lethal dose is, "i.e.", 1–2 mL/kg body weight of pure methanol. The reference dose for methanol is 0.5 mg/kg in a day. Toxic effects begin hours after ingestion, and antidotes can often prevent permanent damage. Because of its similarities in both appearance and odor to ethanol (the alcohol in beverages), it is difficult to differentiate between the two; such is also the case with denatured alcohol, adulterated liquors or very low quality alcoholic beverages. However, cases exist of methanol resistance, such as that of Mike Malloy who was the victim of a failed murder attempt by methanol in the early 1930s.  Methanol is toxic by two mechanisms. First, methanol can be fatal due to effects on the central nervous system, acting as a central nervous system depressant in the same manner as ethanol poisoning. Second, in a process of toxication, it is metabolized to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. Methanol is converted to formaldehyde via alcohol dehydrogenase (ADH) and formaldehyde is converted to formic acid (formate) via aldehyde dehydrogenase (ALDH). The conversion to formate via ALDH proceeds completely, with no detectable formaldehyde remaining. Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing hypoxia at the cellular level, and metabolic acidosis, among a variety of other metabolic disturbances. Outbreaks of methanol poisoning have occurred primarily due to contamination of drinking alcohol. This is more common in the developing world. In 2013 more than 1700 cases nonetheless occurred in the United States. Those affected are often adult men. Outcomes may be good with early treatment. Toxicity to methanol was described as early as 1856.  Because of its toxic properties, methanol is frequently used as a denaturant additive for ethanol manufactured for industrial uses. This addition of methanol exempts industrial ethanol (commonly known as "denatured alcohol" or "methylated spirit") from liquor excise taxation in the US and some other countries.

Applications.

Formaldehyde, acetic acid, methyl "tert"-butylether.

Methanol is primarily converted to formaldehyde, which is widely used in many areas, especially polymers. The conversion entails oxidation: Acetic acid can be produced from methanol. Methanol and isobutene are combined to give methyl "tert"-butyl ether (MTBE). MTBE is a major octane booster in gasoline.

Methanol to hydrocarbons, olefins, gasoline.

Condensation of methanol to produce hydrocarbons and even aromatic systems is the basis of several technologies related to gas to liquids. These include methanol-to-hydrocarbons (MTH), methanol to gasoline (MTG), and methanol to olefins (MTO), and methanol to propylene (MTP). These conversions are catalyzed by zeolites as heterogeneous catalysts. The MTG process was once commercialized at Motunui in New Zealand.

Gasoline additive.

The European Fuel Quality Directive allows fuel producers to blend up to 3% methanol, with an equal amount of cosolvent, with gasoline sold in Europe. China uses more than 4.5 billion Liters of methanol per year as a transportation fuel in low level blends for conventional vehicles, and high level blends in vehicles designed for methanol fuels.

Other chemicals.

Methanol is the precursor to most simple methylamines, methyl halides, and methyl ethers. Methyl esters are produced from methanol, including the transesterification of fats and production of biodiesel via transesterification.

Niche and potential uses.

Energy carrier.

Methanol is a promising energy carrier because, as a liquid, it is easier to store than hydrogen and natural gas. Its energy density is however low reflecting the fact that it represents partially combusted methane. Its energy density is 15.6 MJ/L, whereas ethanol's is 24 and gasoline's is 33 MJ/L.  Further advantages for methanol is its ready biodegradability and low toxicity. It does not persist in either aerobic (oxygen-present) or anaerobic (oxygen-absent) environments. The half-life for methanol in groundwater is just one to seven days, while many common gasoline components have half-lives in the hundreds of days (such as benzene at 10–730 days). Since methanol is miscible with water and biodegradable, it is unlikely to accumulate in groundwater, surface water, air or soil.

Fuel for vehicles.

Methanol is occasionally used to fuel internal combustion engines. It burns forming carbon dioxide and water: One problem with high concentrations of methanol in fuel is that alcohols corrode some metals, particularly aluminium. Methanol fuel has been proposed for ground transportation. The chief advantage of a methanol economy is that it could be adapted to gasoline internal combustion engines with minimum modification to the engines and to the infrastructure that delivers and stores liquid fuel. Its energy density is however only half that of gasoline, meaning that twice the volume of methanol would be required.

Other applications.

Methanol is a traditional denaturant for ethanol, the product being known as "denatured alcohol" or "methylated spirit". This was commonly used during the Prohibition to discourage consumption of bootlegged liquor, and ended up causing several deaths.  Methanol is used as a solvent and as an antifreeze in pipelines and windshield washer fluid. Methanol was used as an automobile coolant antifreeze in the early 1900s. As of May 2018, methanol was banned in the EU for use in windscreen washing or defrosting due to its risk of human consumption.  In some wastewater treatment plants, a small amount of methanol is added to wastewater to provide a carbon food source for the denitrifying bacteria, which convert nitrates to nitrogen gas and reduce the nitrification of sensitive aquifers.  Methanol is used as a destaining agent in polyacrylamide gel electrophoresis.  Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, which lets them be greatly miniaturized. This, combined with the relatively easy and safe storage and handling of methanol, may open the possibility of fuel cell-powered consumer electronics, such as laptop computers and mobile phones.  Methanol is also a widely used fuel in camping and boating stoves. Methanol burns well in an unpressurized burner, so alcohol stoves are often very simple, sometimes little more than a cup to hold fuel. This lack of complexity makes them a favorite of hikers who spend extended time in the wilderness. Similarly, the alcohol can be gelled to reduce risk of leaking or spilling, as with the brand "Sterno".  Methanol is mixed with water and injected into high performance diesel and gasoline engines for an increase of power and a decrease in intake air temperature in a process known as water methanol injection.

Production.

From synthesis gas.

Carbon monoxide and hydrogen react over a catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper and zinc oxides, supported on alumina, as first used by ICI in 1966. At 5–10 MPa (50–100 atm) and, the reaction is characterized by high selectivity (>99.8%):  The production of synthesis gas from methane produces three moles of hydrogen for every mole of carbon monoxide, whereas the synthesis consumes only two moles of hydrogen gas per mole of carbon monoxide. One way of dealing with the excess hydrogen is to inject carbon dioxide into the methanol synthesis reactor, where it, too, reacts to form methanol according to the equation:  In terms of mechanism, the process occurs via initial conversion of CO into CO, which is then hydrogenated: where the HO byproduct is recycled via the water-gas shift reaction This gives an overall reaction, which is the same as listed above.

Biosynthesis.

The catalytic conversion of methane to methanol is effected by enzymes including methane monooxygenases. These enzymes are mixed-function oxygenases, i.e. oxygenation is coupled with production of water and NAD.  CH + O + NADPH + H → CHOH + HO + NAD  Both Fe- and Cu-dependent enzymes have been characterized. Intense but largely fruitless efforts have been undertaken to emulate this reactivity. Methanol is more easily oxidized than is the feedstock methane, so the reactions tend not to be selective. Some strategies exist to circumvent this problem. Examples include Shilov systems and Fe- and Cu containing zeolites. These systems do not necessarily mimick the mechanisms employed by metalloenzymes, but draw some inspiration from them. Active sites can vary substantially from those known in the enzymes. For example, a dinuclear active site is proposed in the sMMO enzyme, whereas a mononuclear iron (alpha-Oxygen) is proposed in the Fe-zeolite.

Safety.

Methanol is highly flammable. Its vapours are heavier than air, can travel and ignite. Methanol fires should be extinguished with dry chemical, carbon dioxide, water spray or alcohol-resistant foam.

Quality specifications and analysis.

Methanol is available commercially in various purity grades. Commercial methanol is generally classified according to ASTM purity grades A and AA. Methanol for chemical use normally corresponds to Grade AA. In addition to water, typical impurities include acetone and ethanol (which are very difficult to separate by distillation). UV-vis spectroscopy is a convenient method for detecting aromatic impurities. Water content can be determined by the Karl-Fischer titration.

History.

In their embalming process, the ancient Egyptians used a mixture of substances, including methanol, which they obtained from the pyrolysis of wood. Pure methanol, however, was first isolated in 1661 by Robert Boyle, when he produced it via the distillation of buxus (boxwood). It later became known as "pyroxylic spirit". In 1834, the French chemists Jean-Baptiste Dumas and Eugene Peligot determined its elemental composition.  They also introduced the word "methylène" to organic chemistry, forming it from Greek "methy" = "alcoholic liquid" + "hȳlē" = "forest, wood, timber, material". "Methylène" designated a "radical" that was about 14% hydrogen by weight and contained one carbon atom. This would be CH, but at the time carbon was thought to have an atomic weight only six times that of hydrogen, so they gave the formula as CH. They then called wood alcohol (l'esprit de bois) "bihydrate de méthylène" (bihydrate because they thought the formula was CHO = (CH)(HO)). The term "methyl" was derived in about 1840 by back-formation from "methylene", and was then applied to describe "methyl alcohol". This was shortened to "methanol" in 1892 by the International Conference on Chemical Nomenclature. The suffix -yl, which, in organic chemistry, forms names of carbon groups, is from the word "methyl".  In 1923, the German chemists Alwin Mittasch and Mathias Pier, working for Badische-Anilin & Soda-Fabrik (BASF), developed a means to convert synthesis gas (a mixture of carbon monoxide, carbon dioxide, and hydrogen) into methanol. US patent 1,569,775 () was applied for on 4 Sep 1924 and issued on 12 January 1926; the process used a chromium and manganese oxide catalyst with extremely vigorous conditions: pressures ranging from 50 to 220 atm, and temperatures up to 450 °C. Modern methanol production has been made more efficient through use of catalysts (commonly copper) capable of operating at lower pressures. The modern low pressure methanol (LPM) process was developed by ICI in the late 1960s with the technology patent since long expired.  During World War II, methanol was used as a fuel in several German military rocket designs, under the name M-Stoff, and in a roughly 50/50 mixture with hydrazine, known as C-Stoff.  The use of methanol as a motor fuel received attention during the oil crises of the 1970s. By the mid-1990s, over 20,000 methanol "flexible fuel vehicles" capable of operating on methanol or gasoline were introduced in the U.S. In addition, low levels of methanol were blended in gasoline fuels sold in Europe during much of the 1980s and early-1990s. Automakers stopped building methanol FFVs by the late-1990s, switching their attention to ethanol-fueled vehicles. While the methanol FFV program was a technical success, rising methanol pricing in the mid- to late-1990s during a period of slumping gasoline pump prices diminished interest in methanol fuels.  In the early 1970s, a process was developed by Mobil for producing gasoline fuel from methanol.  Between the 1960s and 1980s methanol emerged as a precursor to the feedstock chemicals acetic acid and acetic anhydride. These processes include the Monsanto acetic acid synthesis, Cativa process, and Tennessee Eastman acetic anhydride process.

Methanol, also known as methyl alcohol amongst other names, is a chemical with the formula CHOH (a methyl group linked to a hydroxyl group, often abbreviated MeOH). It is a light, volatile, colourless, flammable liquid with a distinctive alcoholic odour similar to that of ethanol (drinking alcohol). A polar solvent, methanol acquired the name wood alcohol because it was once produced chiefly by the destructive distillation of wood. Today, methanol is mainly produced industrially by hydrogenation of carbon monoxide.

Methanol (mimo chemii dle pravidel českého pravopisu metanol), methylalkohol, karbinol je nejjednodušší alifatický alkohol. Používá se pro něj též dnes již zastaralý název dřevný líh či dřevitý líh. Jde o bezbarvou, alkoholicky páchnoucí kapalinu, neomezeně mísitelnou s vodou. Je těkavý, hořlavý a silně jedovatý, což je problém při záměně s ethanolem. Methanol vzniká i při alkoholovém kvašení, avšak nikoliv v množství ohrožujícím život (povolené množství je 15 gramů na litr).


Definition.

In general usage, a cuesta is a hill or ridge with a gentle slope (backslope) on one side, and a steep slope (frontslope) on the other. The word is from Spanish: "flank or slope of a hill; hill, mount, sloping ground". In geology and geomorphology, cuesta refers specifically to an asymmetric ridge with a long and gentle backslope called a dip slope that conforms with the dip of a resistant stratum or strata, called caprock. The outcrop of the caprock forms a steeper or even cliff-like frontslope (escarpment), cutting through the dipping strata that comprise the cuesta.

Formation.

Cuestas are the expression of extensive outcrops of gently dipping strata, typically sedimentary strata, that consist of alternating beds of weak or loosely cemented strata, i.e. shale, mudstone, and marl and hard, well-lithified strata, i.e. sandstone and limestone. The surfaces of the hard, erosion-resistant rock strata form the caprock of the backslope (dip-slope) of the cuesta, where erosion has preferentially removed the weaker strata. The frontslope of the cuesta consists of an escarpment that cuts across the bedding of the strata comprising it. Because of the gently dipping nature of the strata that forms a cuesta, a significant shift in horizontal location will take place as the landscape is lowered by erosion. Because the slope of a cuesta dips in the same direction as the sedimentary strata, the dip angle of this bedding (θ) can be calculated by ("v" / "h") = tan(θ) where "v" is equal to the vertical distance and "h" is equal to the horizontal distance perpendicular to the strike of the beds.  Cuestas, homoclinal ridges, and hogbacks comprise a sequence of landforms that form a gradational continuum. These landforms differ only on the steepness of their backslopes and the relative differences in the inclination of their backslopes and frontslopes. These differences depend upon whether the dip of the strata from which they have been eroded are either nearly vertical, moderately dipping, or gently dipping. Because of their gradational nature, the exact angle of the backslope that separates these landforms is arbitrary and some differences in the specific angles used to define these landforms occur in the scientific literature. It also can be difficult to sharply distinguish immediately adjacent members of this series of landforms because of their gradational nature.

Examples.

Two well-known cuestas in western New York and southern Ontario are the Onondaga escarpment and the Niagara Escarpment, respectively. The dip of the Onondaga is about 40 feet per mile (about 7.6 m/km) to the south. The escarpment edge faces north, and in its most populated section, runs roughly parallel to the southern Lake Ontario shoreline.  The Gulf Coastal Plain in Texas is punctuated by a series of cuestas that parallel the coast, as are most coastal plains. The Reynosa Plateau is the most coast-ward cuesta, which has surface expression with the Bordes-Oakville escarpment, on the northwest side and a low ridge on the eastern boundary, called the Reynosa Cuesta, where the deposits dip below later Pliocene-Pleistocene deposits of the Willis and Lissie Formations.  Cuestas have less dramatic expression in the United Kingdom, with two notable examples being the northwest-facing escarpment of the Cretaceous chalk White Horse Hills and the similarly aligned escarpment of the Jurassic limestones in the Cotswolds, sometimes called the Cotswold Edge.  In continental Europe, the Swabian Alb offers particularly good views of cuestas in Jurassic rock. In France, the term for a cuesta is the same as for a coastline: "côte". Notable French cuestas are the wine-growing regions of Côte d'Or and Côtes du Rhône.  The Machinchang Formation outcrops in the Langkawi islands off the coast of northwestern Malaysia. The formation is one of the oldest exposed rock units in Southeast Asia and has an extensive eroded anticline cuesta topography—dating back to Cambrian.

A cuesta (from Spanish "cuesta" "slope") is a hill or ridge with a gentle slope on one side, and a steep slope on the other. In geology the term is more specifically applied to a ridge where a harder sedimentary rock overlies a softer layer, the whole being tilted somewhat from the horizontal. This results in a long and gentle backslope called a dip slope that conforms with the dip of resistant strata, called caprock. Where erosion has exposed the frontslope of this, a steep slope or escarpment occurs. The resulting terrain may be called scarpland.

Kuesta (ze špan. "cuesta" - kopec, stráň) je geomorfologický termín, označující asymetrický vrchol hory nebo hřebenu, tvořeného mírně ukloněnými vrstvami odolných hornin (do 7°), které se střídají s vrstvami méně odolných hornin. Typická je pro oblasti pánví, tabulí a plochých antiklinál, budovaných mírně ukloněnými sedimentárními horninami s různým stupněm odolnosti, najdeme je však i v oblastech s vulkanity, kde se střídají lávové příkrovy s polohami tufů. Toky stékající po čelním svahu označujeme jako resekventní, naopak toky stékající v souladu s vrstevními plochami označujeme jako konsekventní.


Evolutionary advantage: Succulents.

Cuttings are used as a method of asexual reproduction in succulent horticulture, commonly referred to as vegetative reproduction. A cutting can also be referred to as a propagule. Succulents have evolved with the ability to use adventitious root formation in reproduction to increase fitness in stressful environments. Succulents grow in shallow soils, rocky soils, and desert soils. Seedlings from sexual reproduction have a low survival rate; however, plantlets from the excised stem cuttings and leaf cuttings, broken off in the natural environment, are more successful. Cuttings have both water and carbon stored and available, which are resources needed for plant establishment. The detached part of the plant remains physiologically active, allowing mitotic activity and new root structures to form for water and nutrient uptake. Asexual reproduction of plants is also evolutionarily advantageous as it allows plantlets to be better suited to their environment though retention of epigenetic memory, heritable patterns of phenotypic differences that are not due to changes in DNA but rather histone modification and DNA methylation. Epigenetic memory is heritable through mitosis, and thus advantageous stress response priming is retained in plantlets from excised stem.

Physiology.

Adventitious root formation refers to roots that form from any structure of a plant that is not a root; these roots can form as part of normal development or due to a stress response. Adventitious root formation from the excised stem cutting is a wound response.  At a molecular level when a cutting is first excised at the stem there is an immediate increase in jasmonic acid, known to be necessary for adventitious root formation. When the cutting is excised from the original root system the root inhibiting hormones, cytokinin and strigolactone, which are made in the root and transported to the stem, decrease in concentration. Polyphenol degradation decreases, increasing auxin concentration. The increased auxin concentration increases nitric oxide concentration which initiates root formation through a MAPK signal cascade and a cGMP-dependent pathway that both regulate mitotic division and are both necessary for the initiation of adventitious root formation. The root primordia form from cambial cells in the stem. In propagation of detached succulent leaves and leaf cuttings, the root primordia typically emerges from the basal callous tissue after the leaf primordia emerges.  It was known as early as 1935 that when indolyl-3-acetic acid (IAA), also known as auxin, is applied to the stem of root cuttings, there is an increase the average number of adventitious roots compared to cuttings that are not treated. Researchers also applied this compound to stems without leaves that normally would not have any root formation and found that auxin induced root formation, thus determining auxin is necessary for root formation. Identification of this hormone has been important to industries that rely on vegetative propagation, as it is sometimes applied to fresh cuttings to stimulate root growth.

Technique.

Some plants form roots much more easily than others. Stem cuttings from woody plants are treated differently, depending on the maturity of the wood:  Most plant cuttings are stem pieces, and have no root system of their own, and are therefore likely to die from dehydration if the proper conditions are not met. They require a moist medium, which, however, cannot be too wet lest the cutting rot. A number of media are used in this process, including but not limited to soil, perlite, vermiculite, coir, rock wool, expanded clay pellets, and even water given the right conditions. Most succulent cuttings can be left in open air until the cut surface dries, which may improve root formation when the cutting is later planted.  In temperate countries, stem cuttings may be taken of soft (green or semi-ripe) wood and hard wood, which have specific differences in practice. Certain conditions lead to more favorable outcomes for cuttings; timing, size, location on the plant, and amount of foliage are all important. Stem cuttings of young wood should be taken in spring from the upper branches, while cuttings of hardened wood should be taken in winter from the lower branches. Common bounds on the length of stem cuttings are between for soft wood and between for hard wood. Soft wood cuttings do best when about two thirds of the foliage are removed, while hard wood stem cuttings need complete foliage removal. The cut needs to be done either immediately below a node, or up to 1/2 inch below a node.  The environment for cuttings is generally kept humid—often attained by placing the cuttings under a plastic sheet or in another confined space where the air can be kept moist—and in partial shade to prevent the cutting from drying out. Cuttings in the medium are typically watered with a fine mist to avoid disturbing the plants. Following the initial watering, the aim is to keep the soil moist but not wet or waterlogged; the medium is allowed to almost dry out before misting again.  A rooting hormone may be administered to "encourage" growth and can increase the success rate of plant growth. Though not essential, several compounds may be used to promote the formation of roots through the signaling activity of plant hormone auxins. Among the commonly used chemicals is indole-3-butyric acid (IBA) used as a powder, liquid solution, or gel. This compound is applied either to the cut tip of the cutting or as a foliar spray. Rooting hormone can be manufactured naturally, such as soaking the yellow-tipped shoots of a weeping willow tree in water, or by preparing a tea from the bark of a willow tree. Shoots or bark do better when soaked for 24 hours prior to using. The extract obtained from the crushing of leaves and bulbs of coco-grass ("Cyperus rotundus") is used as an excellent rooting of cuttings and seedlings of various plant species. Honey, though it does not contain any plant hormones, can also aid in rooting success through its natural antiseptic and antifungal properties. Cinnamon or an Aspirin tablet in water can also aid the rooting process.

Types.

Many vegetative parts of a plant can be used. The most common methods are:  Although some species, such as willow, blackberry and pelargoniums can be grown simply by placing a cutting into moist ground, the majority of species require more attention. Most species require humid, warm, partially shaded conditions to strike, thus requiring the approach above to be followed. Particularly difficult species may need cool air above and warm soil. In addition, with many more difficult cuttings, one should use the type of cutting that has the most chance of success with that particular plant species.

Improving results.

There are ways of improving the growth of stem cutting propagations. Intensifying light allows cuttings to root and sprout faster, though the heat thus generated could cause the propagation material distress. Azalea cuttings can be mildly heated in water to disinfect it from the fungus pathogen Rhizoctonia, and this could potentially be used for other plants.

Providing the right soil.

Depending on the type of soil being used, several additives may need adding to create good soil for cuttings. These additions may include:  For example, with plain potting soil, a third of the container should be filled with sand, to make suitable soil for cuttings.

Providing the right humidity.

Although several options can be used here, usually semi-white plastic is used to cover the cuttings. The soil below and from the cuttings themselves is kept moist, and should be aerated once in a while to prevent formation of molds. A plastic bottle can be used as a small greenhouse to provide the right humidity level.

Plant propagation by cutting.

Plants which can be propagated from stem, leaf and/or tip cuttings include:  To note, some plants listed above, such as Coleus, Maranta, Nerium and Golden Pothos, among others, may require water for them to root before they can be transplanted to soil.

A plant cutting is a piece of a plant that is used in horticulture for vegetative (asexual) propagation. A piece of the stem or root of the source plant is placed in a suitable medium such as moist soil. If the conditions are suitable, the plant piece will begin to grow as a new plant independent of the parent, a process known as striking. A stem cutting produces new roots, and a root cutting produces new stems. Some plants can be grown from leaf pieces, called leaf cuttings, which produce both stems and roots. The scions used in grafting are also called cuttings.

Řízkování rostlin je způsob vegetativního rozmnožování pomocí částí rostlin. Nejčastějším druhem řízkování je množení pomocí bylinných (zelených) nebo dřevitých řízků. Nová rostlina, která vznikne řízkováním, je klonem mateřské rostliny, má stejné vlastnosti je geneticky shodná s mateřskou rostlinou. Řízkování má výhody i nevýhody oproti jiným způsobům množení a tyto vlastnosti se mohou výrazně lišit podle druhu rostliny. Řízkování je široce používáno v květinářství, ovocném i okrasném školkařství.


Etymology.

The word "starch" is from its Germanic root with the meanings "strong, stiff, strengthen, stiffen". Modern German "Stärke" (strength) is related and referring for centuries main application, the use in textile: sizing yarn for weaving and starching linen. The Greek term for starch, "amylon" (ἄμυλον), which means "not milled", is also related. It provides the root amyl, which is used as a prefix for several 5-carbon compounds related to or derived from starch (e.g. amyl alcohol).

History.

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. 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 since 700 CE.

Starch industry.

In addition to starchy plants consumed directly, by 2008 66 million tonnes of starch were being produced per year worldwide. In 2011, production was increased to 73 million ton.  In the EU the starch industry produced about 8.5 million tonnes in 2008, with around 40% being used for industrial applications and 60% for food uses, most of the latter as glucose syrups. In 2017 EU production was 11 million ton of which 9,4 million ton was consumed in the EU and of which 54% were starch sweeteners.  The US produced about 27.5 million tons of starch in 2017, of which about 8.2 million tons was high fructose syrup, 6.2 million tons was glucose syrups, and 2.5 million tons were starch products. The rest of the starch was used for producing ethanol (1.6 billion gallons).

Energy store of plants.

Most green plants store energy as starch, which is packed into semicrystalline granules. The extra glucose is changed into starch which is more complex than glucose (by plants). Young plants live on this stored energy in their roots, seeds, and fruits until it can find suitable soil in which to grow. An exception is the family Asteraceae (asters, daisies and sunflowers), where starch is replaced by the fructan inulin. Inulin-like fructans are also present in grasses such as wheat, in onions and garlic, bananas, and asparagus.  In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The glucose is used to generate the chemical energy required for general metabolism, to make organic compounds such as nucleic acids, lipids, proteins and structural polysaccharides such as cellulose, or is stored in the form of starch granules, in 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. The semicrystalline granules generally consist of concentric layers of amylose and amylopectin which can be made bioavailable upon cellular demand in the plant.  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.  The amylose/amylopectin ratio, molecular weight and molecular fine structure influences the physicochemical properties as well as energy release of different types of starches. In addition, cooking and food processing significantly impacts starch digestibility and energy release. Starch can be classified as rapidly digestible, slowly digestible and resistant starch. Raw starch granules resist digestion by human enzymes and do not break down into glucose in the small intestine - they reach the large intestine instead and function as prebiotic dietary fiber. When starch granules are fully gelatinized and cooked, the starch becomes easily digestible and releases glucose quickly within the small intestine. When starchy foods are cooked and cooled, some of the glucose chains re-crystallize and become resistant to digestion again. Slowly digestible starch can be found in raw cereals, where digestion is slow but relatively complete within the small intestine.

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. The ADP-glucose is almost certainly added to the non-reducing end of the amylose polymer, as the UDP-glucose is added to the non-reducing end of glycogen during glycogen synthesis.  Starch branching enzyme introduces 1,6-alpha glycosidic bonds between the amylose 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 similar 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 (analogous to starch).  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 cellobiose. Cellobiose phosphorylase cleaves to glucose 1-phosphate and glucose; the other enzyme—potato alpha-glucan phosphorylase can add a glucose unit from glucose 1-phosphorylase to the non-reducing ends of starch. In it, phosphate is internally recycled. The other product, glucose, can 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.

Degradation.

Starch is synthesized in plant leaves during the day and stored as granules; it serves as an energy source at night. The insoluble, highly branched starch chains have to be phosphorylated in order to be accessible for degrading enzymes. The enzyme glucan, water dikinase (GWD) 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 (PWD) 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 (sex) phenotype, and because starch cannot be phosphorylated, it accumulates in the plastids.  After the phosphorylation, the first degrading enzyme, beta-amylase (BAM) can 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 fewer molecules, BAM cannot release maltose. A second enzyme, disproportionating enzyme-1 (DPE1), 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 (ISA) is required.  The products of starch degradation are predominantly maltose and smaller amounts of glucose. These molecules are exported from the plastid to the cytosol, maltose via the maltose transporter, which if mutated (MEX1-mutant) results in maltose accumulation in the plastid. Glucose is exported via the plastidic glucose translocator (pGlcT). These two sugars act as a precursor for sucrose synthesis. Sucrose can then be used in the oxidative pentose phosphate pathway in the mitochondria, to generate ATP at night.

Properties.

Structure.

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".

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;  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 (Malting, Mashing).  Given a heat of combustion of glucose of whereas that of starch is per mole of glucose monomer, hydrolysis releases about per mole, or per gram of glucose product.

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. (Pyro)dextrins are mainly yellow to brown in color and dextrinization is partially responsible for the browning of toasted bread.

Chemical tests.

A triiodide (I) solution formed by mixing iodine and iodide (usually from potassium iodide) is used to test for starch; a dark blue color indicates the presence of starch. The details of this reaction are not fully known, but recent scientific work using single crystal x-ray crystallography and comparative Raman spectroscopy suggests that the final starch-iodine structure is similar to an infinite polyiodide chain like one found in a pyrroloperylene-iodine complex. 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. Benedict's test and Fehling's test is also done to indicate the presence of starch.  Starch indicator solution consisting of water, starch and iodide 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 (I) ions break up into three iodide ions, disassembling the starch-iodine complex. Starch solution was used as indicator for visualizing the periodic formation and consumption of triiodide intermediate in the Briggs-Rauscher oscillating reaction. The starch, however, changes the kinetics of the reaction steps involving triiodide ion. A 0.3% w/w solution is the standard concentration for a starch indicator. It is made by adding 3 grams of soluble starch to 1 liter of heated water; the solution is cooled before use (starch-iodine complex becomes unstable at temperatures above 35 °C).  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 (also known as extinction cross and birefringence).

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 (rice, wheat, and maize) and the root vegetables (potatoes and cassava). Many other starchy foods are grown, some only in specific climates, including acorns, arrowroot, arracacha, bananas, barley, breadfruit, buckwheat, canna, colocasia, 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 is digested poorly in the duodenum and small intestine, while bacterial degradation takes place mainly in the colon. When starch is cooked, the digestibility is increased.  Starch gelatinization during cake baking can be impaired by sugar competing for water, preventing gelatinization and improving texture.  Before the advent of processed foods, people consumed large amounts of uncooked and unprocessed starch-containing plants, which contained high amounts of resistant starch. Microbes within the large intestine fermented the starch, produced short-chain fatty acids, which are used as energy, and support the maintenance and growth of the microbes. More highly processed foods are more easily digested and release more glucose in the small intestine—less starch reaches the large intestine and more energy is absorbed by the body. 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.

Starch production.

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, arrowroot, and wheat, rice, and potato starches. To a lesser extent, sources of refined starch are sweet potato, sago and mung bean. 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 as dextrins. 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.  These starch sugars are by far the most common starch based food ingredient and are used as sweeteners in many drinks and foods. They include:

Modified starches.

A modified starch is a starch that has been chemically modified to allow the starch to function properly under conditions frequently encountered during processing or storage, such as high heat, high shear, low pH, freeze/thaw and cooling.  The modified food starches are E coded according to the International Numbering System for Food Additives (INS):  INS 1400, 1401, 1402, 1403 and 1405 are in the EU food ingredients without an E-number. Typical modified starches for technical applications are cationic starches, hydroxyethyl starch and carboxymethylated starches.

Use as food additive.

As an additive for food processing, food starches are typically used as thickeners and stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, and to make noodles and pastas. They function as thickeners, extenders, emulsion stabilizers and are exceptional binders in processed meats.  Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in the conventional sense. A tray is filled with native starch and leveled. A positive mold is then pressed into the starch leaving an impression of 1,000 or so jelly beans. The jelly mix is then poured into the impressions and put onto a stove to set. This method greatly reduces the number of molds that must be manufactured.

Use in pharmaceutical industry.

In the pharmaceutical industry, starch is also used as an excipient, as tablet disintegrant, and as binder.

Resistant starch.

Resistant starch is starch that escapes digestion in the small intestine of healthy individuals. High amylose starch from corn has a higher gelatinization temperature than other types of starch and retains its resistant starch content through baking, mild extrusion and other food processing techniques. It is used as an insoluble dietary fiber in processed foods such as bread, pasta, cookies, crackers, pretzels and other low moisture foods. It is also utilized as a dietary supplement for its health benefits. Published studies have shown that resistant starch helps to improve insulin sensitivity, increases satiety, reduces pro-inflammatory biomarkers interleukin 6 and tumor necrosis factor alpha and improves markers of colonic function. It has been suggested that resistant starch contributes to the health benefits of intact whole grains.

Industrial applications.

Papermaking.

Papermaking is the largest non-food application for starches globally, consuming many millions of metric tons annually. In a typical sheet of copy paper for instance, the starch content may be as high as 8%. Both chemically modified and unmodified starches are used in papermaking. In the wet part of the papermaking process, generally called the "wet-end", the starches used are cationic and have a positive charge bound to the starch polymer. These starch derivatives associate with the anionic or negatively charged paper fibers / cellulose and inorganic fillers. Cationic starches together with other retention and internal sizing agents help to give the necessary strength properties to the paper web formed in the papermaking process (wet strength), and to provide strength to the final paper sheet (dry strength).  In the dry end of the papermaking process, the paper web is rewetted with a starch based solution. The process is called surface sizing. Starches used have been chemically, or enzymatically depolymerized at the paper mill or by the starch industry (oxidized starch). The size/starch solutions are applied to the paper web by means of various mechanical presses (size presses). Together with surface sizing agents the surface starches impart additional strength to the paper web and additionally provide water hold out or "size" for superior printing properties. Starch is also used in paper coatings as one of the binders for the coating formulations which include a mixture of pigments, binders and thickeners. Coated paper has improved smoothness, hardness, whiteness and gloss and thus improves printing characteristics.

Corrugated board adhesives.

Corrugated board adhesives are the next largest application of non-food starches globally. Starch glues are mostly based on unmodified native starches, plus some additive such as borax and caustic soda. Part of the starch is gelatinized to carry the slurry of uncooked starches and prevent sedimentation. This opaque glue is called a SteinHall adhesive. The glue is applied on tips of the fluting. The fluted paper is pressed to paper called liner. This is then dried under high heat, which causes the rest of the uncooked starch in glue to swell/gelatinize. This gelatinizing makes the glue a fast and strong adhesive for corrugated board production.

Clothing starch.

Clothing or laundry starch is a liquid prepared by mixing a vegetable starch in water (earlier preparations also had to be boiled), and is used in the laundering of clothes. Starch was widely used in Europe in the 16th and 17th centuries to stiffen the wide collars and ruffs of fine linen which surrounded the necks of the well-to-do. During the 19th and early 20th century it was stylish to stiffen the collars and sleeves of men's shirts and the ruffles of women's petticoats by applying starch to them as the clean clothes were being ironed. Starch gave clothing smooth, crisp edges, and had an additional practical purpose: dirt and sweat from a person's neck and wrists would stick to the starch rather than to the fibers of the clothing. The dirt would wash away along with the starch; after laundering, the starch would be reapplied. Today, in many cultures, starch is sold in aerosol cans for home use, but in others it remain available in granular form for mixing with water.

Other.

Another large non-food starch application is in the construction industry, where starch is used in the gypsum wall board manufacturing process. Chemically modified or unmodified starches are added to the stucco containing primarily gypsum. 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.  Starch is used in the manufacture of various adhesives or glues for book-binding, wallpaper adhesives, paper sack production, tube winding, gummed paper, envelope adhesives, school glues and bottle labeling. Starch derivatives, such as yellow dextrins, can be modified by addition of some chemicals to form a hard glue for paper work; some of those forms use borax or soda ash, which are mixed with the starch solution at to create a very good adhesive. Sodium silicate can be added to reinforce these formula.

Occupational safety and health.

The Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for starch exposure in the workplace as 15 mg/m total exposure and 5 mg/m respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended exposure limit (REL) of 10 mg/m total exposure and 5 mg/m respiratory exposure over an 8-hour workday.

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 (corn), rice, and cassava, as well as in the grain Emmer wheat (Triticum amyleum), from which is produced a cultivated white starch.

Škrob ("amylum") je makromolekulární látka (konkrétně směs polysacharidů glukanů) syntetizovaná rostlinami. Je to bílý prášek bez chuti a vůně, nerozpustný ve studené vodě. Jedná se o konečný produkt fotosyntézy rostlin.