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Tannins (or tannoids) are a class of
astringent 200px, A crystal of the astringent alum An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissue In biology Biology is the natural science that studies life and living organisms, including thei ...
,
polyphenol Polyphenols () are a large family of naturally occurring s characterized by multiples of units. They are abundant in plants and structurally diverse. Polyphenols include s, , and , some of which have been used historically as s and for . Et ...

polyphenol
ic
biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a Nobel Prize in Chemistry, Nobel Prize i ...
s that bind to and
precipitate In aqueous solution, precipitation is the process of transforming a dissolved substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a de ...
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s and various other organic compounds including
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
s and
alkaloid Alkaloids are a class of basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of ...
s. The term ''tannin'' (from
Anglo-NormanAnglo-Norman may refer to: *Anglo-Normans The Anglo-Normans ( nrf, Anglo-Normaunds, ang, Engel-Norðmandisca) were the medieval ruling class in England, composed mainly of a combination of ethnic Anglo-Saxons, Normans, Bretons, Flemish people, F ...
''tanner'', from
Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share ...
''tannāre'', from ''tannum'',
oak An oak is a tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including on ...

oak
bark Bark may refer to: * Bark (botany), an outer layer of a woody plant * Bark (sound), a vocalization of some animals Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, entertainment, and media * ''Bark'' (Jefferson Airp ...
) refers to the use of oak and other bark in
tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye to ...
animal hides into
leather Leather is a strong, flexible and durable material obtained from the tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of arti ...

leather
. By extension, the term ''tannin'' is widely applied to any large
polyphenol Polyphenols () are a large family of naturally occurring s characterized by multiples of units. They are abundant in plants and structurally diverse. Polyphenols include s, , and , some of which have been used historically as s and for . Et ...

polyphenol
ic compound containing sufficient
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...

hydroxyl
s and other suitable groups (such as
carboxyl A carboxylic acid is an organic acid An organic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

carboxyl
s) to form strong complexes with various
macromolecule A macromolecule is a very large molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in ...
s. The tannin compounds are widely distributed in many species of plants, where they play a role in protection from
predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical en ...

predation
(including as
pesticides Pesticides are substances that are meant to control pests Pest or The Pest may refer to: Science and medicine * Pest (organism), an animal or plant detrimental to humans or human concerns ** Weed, a plant considered undesirable * Infectious d ...
) and might help in regulating plant growth. The
astringency 200px, A crystal of the astringent alum An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, Witch haze ...
from the tannins is what causes the dry and puckery feeling in the mouth following the consumption of unripened fruit, red wine or tea. Likewise, the destruction or modification of tannins with time plays an important role when determining harvesting times. Tannins have
molecular weight A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...
s ranging from 500 to over 3,000 (
gallic acid Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acidTrihydroxybenzoic acid may refer to the following phenolic acids : * Gallic acid (3,4,5-trihydroxybenzoic acid) * Phloroglucinol carboxylic acid (2,4,6-trihydroxy ...

gallic acid
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
s) and up to 20,000 Daltons (
proanthocyanidin Proanthocyanidins are a class of polyphenol Polyphenols () are a large family of naturally occurring s characterized by multiples of units. They are abundant in plants and structurally diverse. Polyphenols include s, , and , some of which have ...

proanthocyanidin
s).


Structure and classes of tannins

There are three major classes of tannins: Shown below are the base unit or monomer of the tannin. Particularly in the flavone-derived tannins, the base shown must be (additionally) heavily hydroxylated and polymerized in order to give the high molecular weight
polyphenol Polyphenols () are a large family of naturally occurring s characterized by multiples of units. They are abundant in plants and structurally diverse. Polyphenols include s, , and , some of which have been used historically as s and for . Et ...

polyphenol
motif that characterizes tannins. Typically, tannin molecules require at least 12 hydroxyl groups and at least five phenyl groups to function as protein binders.
Oligostilbenoid Oligostilbenoids (oligo- or polystilbenes) are oligomeric forms of stilbenoids. Some molecules are large enough to be considered polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of ...
s (oligo- or polystilbenes) are oligomeric forms of
stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with Chalconoid, chalcones. Most stilbenoids ...
s and constitute a class of tannins.


Pseudo tannins

Pseudo tannins are low molecular weight compounds associated with other compounds. They do not change color during the
Goldbeater's skin Goldbeater's skin is the processed outer membrane of the intestine of an animal, typically an oxen, ox, valued for its strength against tearing. The term derives from its traditional use as durable layers interleaved between sheets of gold stock ...
test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * Test (2013 film), ''Test'' (2013 film), an American film * Test ( ...
, unlike hydrolysable and condensed tannins, and cannot be used as tanning compounds. Some examples of pseudo tannins and their sources are:


History

Ellagic acid Ellagic acid is a natural phenol In biochemistry, naturally occurring phenols refers to phenol functional group that is found in natural products. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenol ...

Ellagic acid
,
gallic acid Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acidTrihydroxybenzoic acid may refer to the following phenolic acids : * Gallic acid (3,4,5-trihydroxybenzoic acid) * Phloroglucinol carboxylic acid (2,4,6-trihydroxy ...

gallic acid
, and
pyrogallic acid Pyrogallol is an organic compound with the formula C6H3(OH)3. It is a white, water-soluble solid although samples are typically brownish because of its sensitivity toward oxygen. It is one of three isomeric benzenetriols. Production, occurrence, ...
were first discovered by chemist
Henri Braconnot Henri Braconnot (29 May 1780 – 13 January 1855) was a French chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical ...

Henri Braconnot
in 1831. Julius Löwe was the first person to synthesize ellagic acid by heating
gallic acid Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acidTrihydroxybenzoic acid may refer to the following phenolic acids : * Gallic acid (3,4,5-trihydroxybenzoic acid) * Phloroglucinol carboxylic acid (2,4,6-trihydroxy ...

gallic acid
with
arsenic acid Arsenic acid is the chemical compound with the chemical formula, formula H3AsO4. More descriptively written as AsO(OH)3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic aci ...

arsenic acid
or silver oxide. Maximilian Nierenstein studied natural phenols and tannins found in different plant species. Working with Arthur George Perkin, he prepared
ellagic acid Ellagic acid is a natural phenol In biochemistry, naturally occurring phenols refers to phenol functional group that is found in natural products. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenol ...

ellagic acid
from algarobilla and certain other
fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the ...

fruit
s in 1905. He suggested its formation from
galloyl Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula carbon, C6hydrogen, H2(hydroxide, OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, Witch-hazel, witch hazel, tea le ...
-
glycine Glycine (symbol Gly or G; ) is an amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond ...

glycine
by ''
Penicillium ''Penicillium'' () is a genus of ascomycetous Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest ...

Penicillium
'' in 1915.
Tannase In enzymology Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the ...

Tannase
is an enzyme that Nierenstein used to produce m- from
gallotanninA gallotannin is any of a class of molecules belonging to the hydrolysable tannins. Gallotannins are polymers formed when gallic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose. Meta ...
s. He proved the presence of
catechin Catechin is a flavan-3-ol, a type of natural phenol and antioxidant. It is a plant secondary metabolite. It belongs to the group of flavan-3-ols (or simply flavanols), part of the chemical family of flavonoids. The name of the catechin chemical ...

catechin
in
cocoa bean The cocoa bean or simply cocoa (), also called the cacao bean or cacao (), is the dried and fully fermented Fermentation is a metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Li ...
s in 1931. He showed in 1945 that
luteic acid Luteic acid is a natural phenol found in numerous fruits. It is a monolactonized tergalloyl group. Maximilian Nierenstein showed in 1945 that luteic acid was a molecule present in the myrobalanitannin, a tannin found in the fruit of ''Terminalia che ...

luteic acid
, a molecule present in the myrobalanitannin, a tannin found in the fruit of ''
Terminalia chebula ''Terminalia chebula'', commonly known as black- or chebulic myrobalan, is a species of '' Terminalia'', native to South Asia South Asia is the southern region of Asia, which is defined in both geography, geographical and culture, ethno-cultur ...

Terminalia chebula
'', is an intermediary compound in the synthesis of
ellagic acid Ellagic acid is a natural phenol In biochemistry, naturally occurring phenols refers to phenol functional group that is found in natural products. Phenolic compounds are produced by plants and microorganisms. Organisms sometimes synthesize phenol ...

ellagic acid
. At these times, molecule formulas were determined through
combustion analysis Combustion analysis is a method used in both organic chemistry and analytical chemistry to determine the chemical element, elemental composition (more precisely empirical formula) of a pure organic compound by combusting the sample under conditions ...
. The discovery in 1943 by Martin and Synge of
paper chromatography Paper chromatography is an analytical method used to separate coloured chemicals or substances. Erwin Chargaff credits in Weintraub's history of the man the 1944 article by Consden, Gordon and Martin with sparking his discovery of Chargaff's rul ...

paper chromatography
provided for the first time the means of surveying the phenolic constituents of plants and for their separation and identification. There was an explosion of activity in this field after 1945, including prominent work by Edgar Charles Bate-Smith and Tony Swain at
Cambridge University The University of Cambridge is a collegiate university, collegiate research university in Cambridge, Cambridge, United Kingdom. Founded in 1209 and granted a royal charter by Henry III of England, Henry III in 1231, Cambridge is the second-oldest ...
. In 1966,
Edwin Haslam Edwin Haslam (1932 – 3 October 2013)Edwin ...
proposed a first comprehensive definition of plant polyphenols based on the earlier proposals of Bate-Smith, Swain and Theodore White, which includes specific structural characteristics common to all phenolics having a tanning property. It is referred to as the White–Bate-Smith–Swain–Haslam (WBSSH) definition.


Occurrence

Tannins are distributed in species throughout the
plant kingdom Plants are mainly multicellular Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, prope ...

plant kingdom
. They are commonly found in both
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also ...
s and
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...

angiosperm
s. Mole studied the distribution of tannin in 180 families of
dicotyledon The dicotyledons, also known as dicots (or more rarely dicotyls), are one of the two groups into which all the flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "a ...
s and 44 families of
monocotyledon Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. Th ...
s (Cronquist). Most families of dicot contain tannin-free species (tested by their ability to precipitate proteins). The best known families of which all species tested contain tannin are: , Actinidiaceae,
Anacardiaceae The Anacardiaceae, commonly known as the cashew family or sumac family, are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families ...
,
Bixaceae The Bixaceae are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the ...
,
Burseraceae The Burseraceae are a moderate-sized family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its memb ...
,
Combretaceae The Combretaceae, often called the white mangrove family, are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship) ...
,
Dipterocarpaceae The Dipterocarpaceae are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maint ...
,
Ericaceae The Ericaceae are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of soci ...
,
Grossulariaceae ''Ribes'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...
,
Myricaceae The Myricaceae are a small family of dicotyledonous shrubs and small trees in the order Fagales. There are three genera in the family, although some botanists separate many species from ''Myrica'' into a fourth genus ''Morella''. About 55 species ...
for dicot and Najadaceae and
Typhaceae The Typhaceae () are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typical ...
in Monocot. To the family of the oak,
Fagaceae Fagaceae is a family of flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anythin ...
, 73% of the species tested contain tannin. For those of acacias,
Mimosaceae The Mimosoideae are a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendan ...
, only 39% of the species tested contain tannin, among
Solanaceae The Solanaceae , or nightshades, are a family (biology), family of flowering plants that ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of agricultural crops, medicinal plants, spice ...
rate drops to 6% and 4% for the
Asteraceae The family (biology), family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the Order (biology), order Asterales. Commonly referred to as the aster, daisy, composite, o ...

Asteraceae
. Some families like the
Boraginaceae Boraginaceae, the borage or forget-me-not ''Myosotis'' ( ) is a genus of flowering plants in the family (biology), family Boraginaceae. The name comes from the Ancient Greek "mouse's ear", which the foliage is thought to resemble. In the no ...
,
Cucurbitaceae The Cucurbitaceae, also called cucurbits or the gourd family, are a plant family (biology), family consisting of about 965 species in around 95 genera, of which the most important to humans are: *''Cucurbita'' – Squash (plant), squash, pumpkin, ...

Cucurbitaceae
,
Papaveraceae The Papaveraceae are an economically important family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial o ...
contain no tannin-rich species. The most abundant polyphenols are the
condensed tannin Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are biopolymer, polymers formed by the Condensation reaction, condensation of flavans. They do n ...
s, found in virtually all families of plants, and comprising up to 50% of the dry weight of leaves.


Cellular localization

In all vascular plants studied, tannins are manufactured by a
chloroplast A chloroplast is a type of membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structure ...

chloroplast
-derived
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
, the
tannosomeTannosomes are organelles found in plant cells of vascular plants. Formation and functions Tannosomes are formed when the chloroplast membrane forms pockets filled with tannin. Slowly, the pockets Budding, break off as tiny vacuoles that carry tan ...
. Tannins are mainly physically located in the
vacuole A vacuole () is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts ...
s or surface wax of plants. These storage sites keep tannins active against plant predators, but also keep some tannins from affecting plant metabolism while the plant tissue is alive. Tannins are classified as ergastic substances, i.e., non-protoplasm materials found in cells. Tannins, by definition, precipitate proteins. In this condition, they must be stored in organelles able to withstand the protein precipitation process.
Idioblast An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. ...
s are isolated plant cells which differ from neighboring tissues and contain non-living substances. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin or pigments etc. They also can contain tannins. In Japanese persimmon (''
Diospyros kaki ''Diospyros kaki'', the Oriental persimmon, Chinese persimmon, Japanese persimmon or kaki persimmon, is the most widely cultivated species of the genus ''Diospyros''. Although its first botanical description was not published until 1780,Published ...

Diospyros kaki
'') fruits, tannin is accumulated in the vacuole of tannin cells, which are idioblasts of parenchyma cells in the flesh.


Presence in soils

The
convergent evolution Convergent evolution is the independent evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; eit ...
of tannin-rich plant communities has occurred on nutrient-poor acidic soils throughout the world. Tannins were once believed to function as anti-herbivore defenses, but more and more ecologists now recognize them as important controllers of decomposition and nitrogen cycling processes. As concern grows about global warming, there is great interest to better understand the role of polyphenols as regulators of carbon cycling, in particular in northern boreal forests. Leaf litter and other decaying parts of kauri (''
Agathis australis ''Agathis australis'', commonly known by its Māori language, Māori name kauri, is a Pinophyta, coniferous tree of Araucariaceae in the genus ''Agathis'', found north of 38°S in the northern regions of New Zealand's North Island, New Zealand ...
''), a tree species found in New Zealand, decompose much more slowly than those of most other species. Besides its acidity, the plant also bears substances such as waxes and phenols, most notably tannins, that are harmful to
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
s.


Presence in water and wood

The leaching of highly
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
soluble In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence i ...

soluble
tannins from decaying vegetation and leaves along a stream may produce what is known as a
blackwater river A blackwater river is a type of river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its co ...
. Water flowing out of
bog A bog or bogland is a wetland A wetland is a distinct ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are lin ...

bog
s has a characteristic brown color from dissolved
peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, ...
tannins. The presence of tannins (or
humic acid Humic substances are organic compounds that are important components of humus, the major organic compound, organic fraction of soil, peat, and coal (and also a constituent of many upland river, streams, dystrophic lakes, and ocean water). For a long ...

humic acid
) in
well water A well is an excavation or structure created in the ground by digging Digging, also referred to as excavation, is the process of using some implement such as claws, hands, manual tool A tool is an object that can extend an individual ...

well water
can make it smell bad or taste bitter, but this does not make it unsafe to drink. Tannins leaching from an unprepared driftwood decoration in an aquarium can cause pH lowering and coloring of the water to a tea-like tinge. A way to avoid this is to boil the
wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...

wood
in water several times, discarding the water each time. Using peat as an aquarium substrate can have the same effect. Many hours of boiling the driftwood may need to be followed by many weeks or months of constant soaking and many water changes before the water will stay clear. Adding
baking soda Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt (chemistry), salt composed of a sodium cation (Sodium, Na+) and a bica ...

baking soda
to the water to raise its
pH level In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they ...
will accelerate the process of leaching, as the more
alkaline In chemistry, an alkali (; from ar, القلوي ''al-qaly'' "ashes of the saltwort") is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
solution can draw out tannic acid from the wood faster than the pH-neutral water. Softwoods, while in general much lower in tannins than hardwoods, are usually not recommended for use in an aquarium so using a hardwood with a very light color, indicating a low tannin Concentration, content, can be an easy way to avoid tannins. Tannic acid is brown in color, so in general white woods have a low tannin content. Woods with a lot of yellow, red, or brown coloration to them (like cedar, redwood, red oak, etc.) tend to contain a lot of tannin.


Extraction

There is no single protocol for Extraction (chemistry), extracting tannins from all plant material. The procedures used for tannins are widely variable.''The Tannin Handbook'', Ann E. Hagerman, 1998
book
)
It may be that acetone in the extraction solvent increases the total yield by inhibiting interactions between tannins and
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s during extraction or even by breaking hydrogen bonds between tannin-protein complexes.


Tests for tannins

There are three groups of methods for the analysis of tannins: precipitation of proteins or alkaloids, reaction with phenolic rings, and depolymerization.


Alkaloid precipitation

Alkaloids such as caffeine, cinchonine, quinine or strychnine, precipitates polyphenols and tannins. This property can be used in a quantitation method.


Goldbeater's skin test

When goldbeater's skin or ox skin is dipped in Hydrochloric acid, HCl, rinsed in water, soaked in the tannin solution for 5 minutes, washed in water, and then treated with 1% Iron(II) sulfate, FeSO4 solution, it gives a blue black color if tannin was present.


Ferric chloride test

Ferric chloride test, Use of ferric chloride (FeCl3) tests for natural phenol, phenolics in general. Powdered plant leaves of the test plant (1.0 g) are weighed into a beaker and 10 ml of distilled water are added. The mixture is boiled for five minutes. Two drops of 5% FeCl3 are then added. Production of a greenish precipitate is an indication of the presence of tannins. Alternatively, a portion of the water extract is diluted with distilled water in a ratio of 1:4 and few drops of 10% ferric chloride solution is added. A blue or green color indicates the presence of tannins (Evans, 1989).


Other methods

The hide-powder method is used in tannin analysis for
leather Leather is a strong, flexible and durable material obtained from the tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of arti ...

leather
tannin and the Stiasny method for wood adhesives. Statistical analysis reveals that there is no significant relationship between the results from the hide-powder and the Stiasny methods. ;Hide-powder method 400 mg of sample tannins are dissolved in 100 ml of distilled water. 3 g of slightly chromated hide-powder previously dried in vacuum for 24h over CaCl2 are added and the mixture stirred for 1 h at ambient temperature. The suspension is filtered without vacuum through a sintered glass filter. The weight gain of the hide-powder expressed as a percentage of the weight of the starting material is equated to the percentage of tannin in the sample. ;Stiasny's method 100 mg of sample tannins are dissolved in 10 ml distilled water. 1 ml of 10M HCl and 2 ml of 37% formaldehyde are added and the mixture heated under reflux for 30 min. The reaction mixture is filtered while hot through a sintered glass filter. The precipitate is washed with hot water (5× 10 ml) and dried over CaCl2. The yield of tannin is expressed as a percentage of the weight of the starting material.


Reaction with phenolic rings

The bark tannins of ''Commiphora angolensis'' have been revealed by the usual color and precipitation reactions and by quantitative determination by the methods of Löwenthal-Procter and of DeijsChemical study of bark from Commiphora angolensis Engl. Cardoso Do Vale, J., Bol Escola Farm Univ Coimbra Edicao Cient, 1962, volume 3, page 128
abstract
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(formalin-hydrochloric acid method). Colorimetric methods have existed such as the Neubauer-Löwenthal method which uses potassium permanganate as an oxidizing agent and Indigo dye, indigo sulfate as an indicator, originally proposed by Löwenthal in 1877. The difficulty is that the establishing of a titer for tannin is not always convenient since it is extremely difficult to obtain the pure tannin. Neubauer proposed to remove this difficulty by establishing the titer not with regard to the tannin but with regard to crystallised oxalic acid, whereby he found that 83 g oxalic acid correspond to 41.20 g tannin. Löwenthal's method has been criticized. For instance, the amount of indigo used is not sufficient to retard noticeably the oxidation of the non-tannins substances. The results obtained by this method are therefore only comparative. A modified method, proposed in 1903 for the quantification of tannins in wine, Feldmann's method, is making use of calcium hypochlorite, instead of potassium permanganate, and indigo sulfate.


Food items with tannins


Pomegranates


Accessory fruits

Strawberries contain both hydrolyzable and condensed tannins.


Berries

Most berries, such as cranberry, cranberries, and Blueberry, blueberries, contain both hydrolyzable and condensed tannins.


Nuts

Nut (fruit), Nuts vary in the amount of tannins they contain. Some species of acorns of
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oak
contain large amounts. For example, acorns of Quercus robur and Quercus petraea in Poland were found to contain 2.4–5.2% and 2.6–4.8% tannins as a proportion of dry matter, but the tannins can be removed by leaching in water so that the acorns become edible. Other nuts – such as hazelnuts, walnuts, pecans, and almonds – contain lower amounts. Tannin concentration in the crude extract of these nuts did not directly translate to the same relationships for the condensed fraction.


Herbs and spices

Cloves, tarragon, cumin, thyme, vanilla, and cinnamon all contain tannins.


Legumes

Most legumes contain tannins. Red-colored beans contain the most tannins, and white-colored beans have the least. Peanuts without shells have a very low tannin content. Chickpeas (garbanzo beans) have a smaller amount of tannins.


Chocolate

Chocolate liquor contains about 6% tannins.


Drinks with tannins

Principal human dietary sources of tannins are tea and coffee. Most wines aged in charred oak barrels possess tannins absorbed from the wood. Soils high in clay also contribute to tannins in wine grapes.Oz Clarke ''Encyclopedia of Grapes'' pp. 155–162 Harcourt Books 2001 This concentration gives wine its signature astringent, astringency. Coffee pulp has been found to contain low to trace amounts of tannins.


Fruit juices

Although citrus fruits do not contain tannins, orange-colored juices often contain tannins from food colouring. Apple, grape and berry juices all contain high amounts of tannins. Sometimes tannins are even added to juices and ciders to create a more astringent feel to the taste.


Beer

In addition to the alpha acids extracted from hops to provide bitterness in beer, condensed tannins are also present. These originate both from malt and hops. Trained brewmasters, particularly those in Germany, consider the presence of tannins to be a flaw. However, in some styles, the presence of this astringency is acceptable or even desired, as, for example, in a Flanders red ale. In lager type beers, the tannins can form a precipitate with specific haze-forming proteins in the beer resulting in turbidity at low temperature. This chill haze can be prevented by removing part of the tannins or part of the haze-forming proteins. Tannins are removed using Polyvinylpolypyrrolidone, PVPP, haze-forming proteins by using silica or tannic acid.


Properties for animal nutrition

Tannins have traditionally been considered Antinutrient, antinutritional, but it is now known that their beneficial or antinutritional properties depend upon their chemical structure and dosage. The new technologies used to analyze molecular and chemical structures have shown that a division into condensed and hydrolyzable tannins is too simplistic. Recent studies have demonstrated that products containing chestnut tannins included at low dosages (0.15–0.2%) in the diet of chickens may be beneficial. Some studies suggest that chestnut tannins have positive effects on silage quality in the Baler#Silage or haylage bales, round bale silages, in particular reducing Non-protein nitrogen, NPNs (non-protein nitrogen) in the lowest wilting level. Improved fermentability of Soybean, soya meal nitrogen in the rumen may occur. Studies conducted in 2002 on ''in vitro'' ammonia release and dry matter degradation of soybean meal comparing three different types of tannins (quebracho tannin, quebracho, acacia and chestnut) demonstrated that chestnut tannins are more efficient in protecting soybean meal from ''in vitro'' degradation by rumen bacteria. Condensed tannins inhibit herbivore digestion by binding to consumed plant proteins and making them more difficult for animals to digest, and by interfering with protein absorption and digestive enzymes (for more on that topic, see plant defense against herbivory). Many tannin-consuming animals secrete a tannin-binding protein (mucin) in their saliva. Tannin-binding capacity of salivary mucin is directly related to its proline content. Salivary proline-rich proteins (PRPs) are sometimes used to inactivate tannins. One reason is that they inactivate tannins to a greater extent than do dietary proteins resulting in reduced fecal nitrogen losses. PRPs additionally contain non-specific nitrogen and non-essential amino acids making them more convenient than valuable dietary protein. Histatins, another type of salivary proteins, also precipitate tannins from solution, thus preventing alimentary adsorption.


Tannin market

Tannin production began at the beginning of the 19th century with the industrial revolution, to produce tanning material for the need for more leather. Before that time, processes used plant material and were long (up to six months). There was a collapse in the vegetable tannin market in the 1950s–1960s, due to the appearance of synthetic tannins, which were invented in response to a scarcity of vegetable tannins during World War II. At that time, many small tannin industry sites closed. Vegetable tannins are estimated to be used for the production of 10–20% of the global leather production. The cost of the final product depends on the method used to extract the tannins, in particular the use of solvents, alkali and other chemicals used (for instance Glycerite, glycerin). For large quantities, the most cost-effective method is hot water extraction. Tannic acid is used worldwide as clarifying agent in alcoholic drinks and as aroma ingredient in both alcoholic and soft drinks or juices. Tannins from different botanical origins also find extensive uses in the wine industry.


Uses

Tannins are an important ingredient in the process of tanning leather. Tanbark from
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oak
, mimosa, chestnut and quebracho tree has traditionally been the primary source of Tanning (leather), tannery tannin, though inorganic Leather tanning, tanning agents are also in use today and account for 90% of the world's leather production. Tannins produce different colors with ferric chloride (either blue, blue black, or green to greenish-black) according to the type of tannin. Iron gall ink is produced by treating a solution of tannins with iron(II) sulfate. Tannins can also be used as a mordant, and is especially useful in natural dyeing of cellulose fibers such as cotton. The type of tannin used may or may not have an impact on the final color of the fiber. Tannin is a component in a type of industrial particleboard adhesive developed jointly by the Tanzania Industrial Research and Development Organization and Forintek Labs Canada. ''Pinus radiata'' tannins has been investigated for the production of Wood glue, wood adhesives. Condensed tannins, e.g., quebracho tannin, and Hydrolyzable tannins, e.g., chestnut tannin, appear to be able to substitute a high proportion of synthetic phenol in phenol-formaldehyde resins for wood particleboard. Tannins can be used for production of anti-corrosion, corrosive primer, sold under brand-name "Nox Primer" for treatment of rusted steel surfaces prior to painting, rust converter to transform oxidized steel into a smooth sealed surface and rust inhibitor. The use of resins made of tannins has been investigated to remove Mercury (element), mercury and methylmercury from solution. Immobilized tannins have been tested to recover uranium from seawater.


See also

* Polyphenol


References


External links


Tannins: fascinating but sometimes dangerous molecules
*   * {{Authority control Tannins, Nutrition Oenology Organic polymers Wine terminology Astringent flavors Phenol antioxidants Wood products Food stabilizers Phytochemicals