Linamarin
Encyclopedia
Linamarin is a cyanogenic
glucoside
found in the leaves and roots of plants such as cassava
, lima bean
s, and flax
. It is a glucoside
of acetone cyanohydrin
. Upon exposure to enzyme
s and gut flora
in the human intestine
, linamarin and its methylated relative lotaustralin
can decompose to the toxic chemical hydrogen cyanide; hence food uses of plants that contain significant quantities of linamarin require extensive preparation and detoxification. Ingested and absorbed linamarin is rapidly excreted in the urine and the glucoside itself does not appear to be acutely toxic. Consumption of cassava products with low levels of linamarin is widespread in the low-land tropics. Ingestion of food prepared from insufficiently processed cassava roots with high linamarin levels has been associated with dietary toxicity, particularly with the upper motor neuron
disease known as konzo
to the African populations in which it was first described by Trolli and later through the research network initiated by Hans Rosling
. However, the toxicity is believed to be induced by ingestion of acetone cyanohydrin
, the breakdown product of linamarin. Dietary exposure to linamarin has also been reported as a risk factor in developing glucose intolerance and diabetes, although studies in experimental animals have been inconsistent in reproducing this effect and may indicate that the primary effect is in aggravating existing conditions rather than inducing diabetes on its own.
The generation of cyanide from linamarin is usually enzymatic
and occurs when linamarin is exposed to linamarase
, an enzyme normally expressed in the cell wall
s of cassava plants. Because the resulting cyanide derivatives are volatile, processing methods that induce such exposure are common traditional means of cassava preparation; foodstuffs are usually made from cassava after extended blanching, boiling
, or fermentation
. Food products made from cassava plants include garri
(toasted cassava tuber
s), porridge-like fufu
, the dough agbelima, and cassava flour
.
Recent research efforts have developed a transgenic cassava plant that stably downregulates linamarin production via RNA interference
.
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....
glucoside
Glucoside
A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes....
found in the leaves and roots of plants such as cassava
Cassava
Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...
, lima bean
Lima bean
Phaseolus lunatus is a legume. It is grown for its seed, which is eaten as a vegetable. It is commonly known as the lima bean or butter bean.-Origin and uses:...
s, and flax
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
. It is a glucoside
Glucoside
A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes....
of acetone cyanohydrin
Acetone cyanohydrin
Acetone cyanohydrin is an organic compound used in the production of methyl methacrylate, the monomer of the transparent plastic polymethyl methacrylate , also known as acrylic.-Preparation:...
. Upon exposure to enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s and gut flora
Gut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....
in the human intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
, linamarin and its methylated relative lotaustralin
Lotaustralin
Lotaustralin is a cyanogenic glucoside found in small amounts in Fabaceae Austral Trefoil , cassava , lima bean , roseroot and white clover , among other plants...
can decompose to the toxic chemical hydrogen cyanide; hence food uses of plants that contain significant quantities of linamarin require extensive preparation and detoxification. Ingested and absorbed linamarin is rapidly excreted in the urine and the glucoside itself does not appear to be acutely toxic. Consumption of cassava products with low levels of linamarin is widespread in the low-land tropics. Ingestion of food prepared from insufficiently processed cassava roots with high linamarin levels has been associated with dietary toxicity, particularly with the upper motor neuron
Upper motor neuron
Upper motor neurons are motor neurons that originate in the motor region of the cerebral cortex or the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle...
disease known as konzo
Konzo
Konzo is an epidemic paralytic disease first described by G. Trolli in 1938, who discovered it amongst the Kwango of the Belgian Congo . The outbreaks are associated with several weeks of almost exclusive consumption of insufficiently processed "bitter" cassava as a famine food...
to the African populations in which it was first described by Trolli and later through the research network initiated by Hans Rosling
Hans Rosling
Hans Rosling is a Swedish medical doctor, academic, statistician and public speaker. He is Professor of International Health at Karolinska Institute and co-founder and chairman of the Gapminder Foundation, which developed the Trendalyzer software system.-Study and career:From 1967 to 1974 Rosling...
. However, the toxicity is believed to be induced by ingestion of acetone cyanohydrin
Acetone cyanohydrin
Acetone cyanohydrin is an organic compound used in the production of methyl methacrylate, the monomer of the transparent plastic polymethyl methacrylate , also known as acrylic.-Preparation:...
, the breakdown product of linamarin. Dietary exposure to linamarin has also been reported as a risk factor in developing glucose intolerance and diabetes, although studies in experimental animals have been inconsistent in reproducing this effect and may indicate that the primary effect is in aggravating existing conditions rather than inducing diabetes on its own.
The generation of cyanide from linamarin is usually enzymatic
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
and occurs when linamarin is exposed to linamarase
Linamarase
Linamarase, or beta-D-glucosidase , is an enzyme found in many plants including cassava and the butter bean.In cassava it is found in the cell walls. When the plant is chewed or ground, it exposes the enzyme to compounds like linamarin and lotaustralin which release cyanide compounds that can be...
, an enzyme normally expressed in the cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s of cassava plants. Because the resulting cyanide derivatives are volatile, processing methods that induce such exposure are common traditional means of cassava preparation; foodstuffs are usually made from cassava after extended blanching, boiling
Boiling
Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. While below the boiling point a liquid...
, or fermentation
Fermentation (food)
Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...
. Food products made from cassava plants include garri
Garri
Garri is a popular West African food made from cassava tubers. The spelling 'garri' is mainly used in Nigeria, Cameroon, Sierra Leone and 'gari' in Ghana....
(toasted cassava tuber
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
s), porridge-like fufu
Fufu
Fufu, , is a staple snack of West and Central Africa. It is a thick paste usually made by boiling starchy root vegetables in water and pounding with a mortar and pestle until the desired consistency is reached...
, the dough agbelima, and cassava flour
Flour
Flour is a powder which is made by grinding cereal grains, other seeds or roots . It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history...
.
Recent research efforts have developed a transgenic cassava plant that stably downregulates linamarin production via RNA interference
RNA interference
RNA interference is a process within living cells that moderates the activity of their genes. Historically, it was known by other names, including co-suppression, post transcriptional gene silencing , and quelling. Only after these apparently unrelated processes were fully understood did it become...
.