HOME

TheInfoList




A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as
arabinoxylan Arabinoxylan is a hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant ce ...
s, present along with
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
in almost all
terrestrial plant A terrestrial plant is a plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiratio ...

terrestrial plant
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
s.Scheller HV, Ulvskov
Hemicelluloses.
// Annu Rev Plant Biol. 2010;61:263-89. doi: 10.1146/annurev-arplant-042809-112315.
While cellulose is crystalline, strong, and resistant to
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolysis
, hemicelluloses have random, amorphous structure with little strength. They are easily hydrolyzed by dilute
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
or
base Base or BASE may refer to: Brands and enterprises *Base (mobile telephony provider) Base (stylized as BASE) is the third largest of Belgium Belgium ( nl, België ; french: Belgique ; german: Belgien ), officially the Kingdom of Belgium, ...
as well as a myriad of hemicellulase enzymes.


Composition

Diverse kinds of hemicelluloses are known. Important examples include
xylan Xylan (; ) (CAS number A CAS Registry Number, also referred to as CASRN or CAS Number, is a unique numerical identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of ...

xylan
,
glucuronoxylan Glucuronoxylans are the primary components of hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrest ...

glucuronoxylan
,
arabinoxylan Arabinoxylan is a hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant ce ...
,
glucomannan Glucomannan is a water-soluble polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to ...
, and
xyloglucan Xyloglucan is a hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant ce ...
. Hemicelluloses are
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallograp ...
s often associated with
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
, but with distinct compositions and structures. Whereas cellulose is derived exclusively from
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
, hemicelluloses are composed of diverse sugars, and can include the five-carbon sugars
xylose Xylose ( grc, ξύλον, , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a of the type, which means that it contains five atoms and includes an . It is derived from , one of the main constituents o ...

xylose
and
arabinose Arabinose is an aldopentoseIn 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, behavio ...

arabinose
, the six-carbon sugars glucose,
mannose Mannose is a sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosaccharides joine ...

mannose
and
galactose Galactose (, '' galacto-'' + ''-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. Th ...
, and the six-carbon
deoxy sugar Deoxy sugars are sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycos ...
rhamnose Rhamnose (Rha, Rham) is a naturally occurring deoxy sugar. It can be classified as either a methyl-pentose or a 6-deoxy-hexose. Rhamnose occurs in nature in its L-form, L-form as L-rhamnose (6-deoxy-L-mannose). This is unusual, since most of the n ...
. Hemicelluloses contain most of the D-
pentose 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 in the ...

pentose
sugars, and occasionally small amounts of L-sugars as well. Xylose is in most cases the sugar monomer present in the largest amount, although in softwoods mannose can be the most abundant sugar. Not only regular sugars can be found in hemicellulose, but also their acidified forms, for instance
glucuronic acid Glucuronic acid (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is a ...

glucuronic acid
and
galacturonic acid -Galacturonic acid is a sugar acid, an oxidized form of -galactose. It is the main component of pectin Pectin (from grc, πηκτικός ', "congealed, curdled") is a structural acidic heteropolysaccharide contained in the primary and mid ...

galacturonic acid
can be present.


Structural comparison to cellulose

Unlike cellulose, hemicelluloses consist of shorter chains – 500–3,000 sugar units. In contrast, each polymer of cellulose comprises 7,000–15,000 glucose molecules. In addition, hemicelluloses may be branched
polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong inc ...

polymer
s, while cellulose is unbranched. Hemicelluloses are embedded in the cell walls of plants, sometimes in chains that form a '
ground Ground may refer to: * Soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body ...
' – they bind with
pectin Pectin (from grc, πηκτικός ', "congealed, curdled") is a structural acidic heteropolysaccharide contained in the primary and middle lamella The middle lamella is a layer that cements together the primary cell wall A cell wall is a ...

pectin
to cellulose to form a network of cross-linked fibres. Based on the structural difference, like backbone linkages and side groups, as well as other factors, like abundance and distributions in plants, hemicelluloses could be categorized into four groups as following: 1) xylans, 2) mannans; 3) mixed linkage β-glucans; 4) xyloglucans. Xylans Xylans usually consist of backbone of β-(1→4)-linked xylose residues. And it could be further divided into homoxylans and heteroxylans. Homoxylans have a backbone of D-xylopyranose residues linked by β(1→3) or mixed ,β(1→3, 1→4)-glycosidic linkages. Homoxylans mainly carry structural functions. Heteroxylans such as glucuronoxylans, glucuronoarabinoxylans, and complex heteroxylans, have a backbone of D-xylopyranose and short carbohydrate branches. For examples, glucuronoxylan has substitution with α-(1→2)-linked glucuronosyl and 4-O-methyl glucuronosyl residues. And arabinoxylans and glucuronoarabinoxylans contain arabinose residues attached to the backbone Mannans The mannan-type hemicellulose can be classified into two types based on their main chain difference,
galactomannan Galactomannans are polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suc ...

galactomannan
s and glucomannans. Galactomannans have only β-(1→4) linked D-mannopyranose residues in linear chains. Glucomannans consist of both β-(1→4) linked D-mannopyranose and β-(1→4) linked D-glucopyranose residues in the main chains. As for the side chains, D-galactopyranose residues tend to be 6-linked to both types as the single side chains with various amount. Mixed linkage β-glucans The conformation of the mixed linkage
glucan A glucan is a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () using as catalyst, whi ...
chains usually contains blocks of β-(1→4) D-Glucopyranose separated by single β-(1→3) D-Glucopyranose. The population of β-(1→4) and β-(1→3) are about 70% and 30%. These glucans primarily consist of cellotriosyl (C18H32O16) and cellotraosyl (C24H42O21)segments in random order. There are some study show the molar ratio of cellotriosyl/cellotraosyl for oat (2.1-2.4), barley (2.8-3.3), and wheat (4.2-4.5). Xyloglucans Xyloglucans have a backbone similar to cellulose with α-D-xylopyranose residues at position 6. To better describe different side chains, a single letter code notation is used for each side chain type. G -- unbranched Glc residue; X -- α-d-Xyl-(1→6)-Glc. L -- β-Gal , S -- α-l-Araf, F-- α-l-Fuc. These are the most common side chains. The two most common types of xyloglucans in plant cell walls are identified as XXXG and XXGG.


Biosynthesis

Hemicelluloses are synthesised from sugar nucleotides in the cell's
Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that stu ...

Golgi apparatus
. Two models explain their synthesis: 1) a '2 component model' where modification occurs at two transmembrane proteins, and 2) a '1 component model' where modification occurs only at one transmembrane protein. After synthesis, hemicelluloses are transported to the plasma membrane via Golgi vesicles. Each kind of hemicellulose is biosynthesized by specialized enzymes. Mannan chain backbones are synthesized by cellulose synthase-like protein family A (CSLA) and possibly enzymes in cellulose synthase-like protein family D (CSLD). Mannan synthase, a particular enzyme in CSLA, is responsible for the addition of mannose units to the backbone. The galactose side-chains of some mannans are added by galactomannan galactosyltransferase.
Acetylation Acetylation (or in IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents che ...

Acetylation
of mannans is mediated by a mannan O-acetyltransferase, however, this enzyme has not been definitively identified. Xyloglucan backbone synthesis is mediated by cellulose synthase-like protein family C (CSLC), particularly glucan synthase, which adds glucose units to the chain. Backbone synthesis of xyloglucan is also mediated in some way by
xylosyltransferase Xylosyltransferase are transferase '' complexed with α-amanitin (in red). Despite the use of the term "polymerase," RNA polymerases are classified as a form of nucleotidyl transferase. A transferase is any one of a class of enzymes that enact ...
, but this mechanism is separate to its transferase function and remains unclear. Xylosyltransferase in its transferase function is, however, utilized for the addition of xylose to the side-chain. Other enzymes utilized for side-chain synthesis of xyloglucan include galactosyltransferase (which is responsible for the addition of alactose and of which two different forms are utilized), fucosyltransferase (which is responsible for the addition of fucose), and acetyltransferase (which is responsible for acetylation). Xylan backbone synthesis, unlike that of the other hemicelluloses, is not mediated by any cellulose synthase-like proteins. Instead, xylan synthase is responsible for backbone synthesis, facilitating the addition of xylose. Several genes for xylan synthases have been identified. Several other enzymes are utilized for the addition and modification of the side-chain units of xylan, including
glucuronosyltransferase Uridine 5'-diphospho-glucuronosyltransferase ( UDP-glucuronosyltransferase, UGT) is a microsomal glycosyltransferase () that catalyzes the transfer of the glucuronic acid component of UDP-glucuronic acid to a small hydrophobic molecule. This is a ...
(which adds lucuronic acid units), xylosyltransferase (which adds additional xylose units), arabinosyltransferase (which adds arabinose), methyltransferase (responsible for methylation), and acetyltransferase] (responsible for acetylation). Given that mixed-linkage glucan is a non-branched homopolymer of glucose, there is no side-chain synthesis, only the addition of glucose to the backbone in two linkages, β1-3 and β1-4. Backbone synthesis is mediated by enzymes in cellulose synthase-like protein families F and H (CSLF and CSLH), specifically glucan synthase. Several forms of glucan synthase from CSLF and CSLH have been identified. All of them are responsible for addition of glucose to the backbone and all are capable of producing both β1-3 and β1-4 linkages, however, it is unknown how much each specific enzyme contributes to the distribution of β1-3 and β1-4 linkages.


Applications

In the sulfite pulp process the hemicellulose is largely hydrolysed by the acid pulping liquor ending up in the brown liquor where the fermentable
hexose 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: their composition, structure, properties, behavior and the changes they undergo during a ...
sugars (around 2%) can be used for producing
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
. This process was primarily applied to calcium sulfite brown liquors. *
ArabinogalactanArabinogalactan is a biopolymer Biopolymers are natural polymers produced by the cells of Organism, living organisms. Biopolymers consist of monomeric units that are Covalent_bond, covalently bonded to form larger molecules. There are three main cl ...

Arabinogalactan
Arabinogalactans can be used as
emulsifier An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter In classical phys ...
s, stabilizers and binders according t
the Federal Food, Drug and Cosmetic Act
Arabinogalactans can also be used as bonding agent in
sweeteners A sugar substitute is a food additive that provides a sweetness, sweet taste like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie (non-nutritive) or low-calorie sweetener. Artif ...
. *Xylan The films based on xylan show low oxygen permeability and thus are of potential interest as packaging for oxygen-sensitive products. *
Agar Agar ( or ), or agar-agar, is a jelly-like substance, obtained from red algae Red algae, or Rhodophyta ( , ; ), are one of the oldest groups of eukaryotic algae Algae (; singular alga ) is an informal term for a large and diverse group of ...
Agar is used in making jellies and puddings. It is also growth medium with other nutrients for
microorganisms 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 ...

microorganisms
.Spiridon, I., & Popa, V. I. (2008). Hemicelluloses: Major Sources, Properties and Applications. In Monomers, Polymers and Composites from Renewable Resources (pp. 289–304). Elsevier. https://doi.org/10.1016/b978-0-08-045316-3.00013-2 *
Curdlan Curdlan is a water-insoluble linear beta-1,3-glucan, a high-molecular-weight polymer of glucose. Curdlan consists of β-(1,3)-linked glucose residues and forms elastic gels upon heating in aqueous suspension (chemistry), suspension. It was reporte ...

Curdlan
Curdlan can be used in fat replacement to produce diet food while having a taste and a mouth feel of real fat containing products. *
beta-glucan β-Glucans (beta-glucans A glucan is a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with wat ...
b-glucans have an important role in
food supplement A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill Pill or The Pill may refer to: Drugs * Pill (pharmacy) A tablet is a pharmaceutical A medication (also referred to as medicine, ...
while b-glucans are also promising in health-related issues, especially in immune reactions and the treatment of cancer. *
Xanthan Xanthan gum () is a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its s ...
Xanthan, with other
polysaccharides Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like mo ...
can form gels that have high solution
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

viscosity
which can be used in the oil industry to thicken drilling mud. In the food industry, xanthan is used in products such as dressings and sauces. *
Alginate Alginic acid, also called algin, is a polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the f ...
Alginate is an important role in the development of
antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All orga ...
textiles due to its characteristics of environmental friendliness, and high industrialization level as a sustainable
biopolymer Biopolymers are natural polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries ...
.


Natural functions

Hemicellulose in Plant Cells * Along with
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
in plant cell walls, hemicellulose helps to strengthen the cell wall ** Hemicellulose are also a
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallograp ...
compound in plant cell walls similar to cellulose * The hemicellulose compound interacts with the
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
by providing cross-linking of
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
microfibrils ** Hemicellulose will search for voids in the cell wall during its formation and provide support around cellulose
fibrils Fibrils (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman ...
*** This process is done by hemicellulose in order to equip the cell wall with the maximum possible strength it can provide ** Hemicellulose dominates the middle lamella of the plant cell, unlike
cellulose Cellulose 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: their composition, structure, properties, behavior ...

cellulose
which is primarily found in the secondary layers. *** This allows for hemicellulose to provide middle-ground support for the cellulose on the outer layers of the plant cell * In few cell walls, hemicellulose will also interact with
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and Bark (botany), bark, because they l ...

lignin
to provide structural tissue support of more vascular plants


Extraction

There are many ways to obtain hemicellulose; all of these rely on extraction methods through hardwood or softwood trees milled into smaller samples. In hardwoods the main hemicellulose extract is glucuronoxlyan (acetylated xylans), while galactoglucomannan is found in softwoods. Prior to extraction the wood typically must be milled into wood chips of various sizes depending on the reactor used. Following this, a hot water extraction process, also known as autohydrolysis or hydrothermal treatment, is utilized with the addition of acids and bases to change the yield size and properties. The main advantage to hot water extraction is that it offers a method where the only chemical that is needed is water, making this environmentally friendly and cheap. The goal of hot water treatment is to remove as much hemicellulose from the wood as possible. This is done through the hydrolysis of the hemicellulose to achieve smaller oligomers and xylose. Xylose when dehydrated becomes furfural. When xylose and furfural are the goal, acid catalysts, such as formic acid, are added to increase the transition of polysaccharide to monosaccharides. This catalyst also has been shown to also utilize a solvent effect to be aid the reaction. One method of pretreatment is to soak the wood with diluted acids (with concentrations around 4%). This converts the hemicellulose into monosaccharides. When pretreatment is done with bases (for instance sodium or potassium hydroxide) this destroys the structure of the lignin. This changes the structure from crystalline to amorphous. Hydrothermal pretreatment is another method. This offers advantages such as no toxic or corrosive solvents are needed, nor are special reactors, and no extra costs to dispose of hazardous chemicals. The hot water extraction process is done in batch reactors, semi-continuous reactors, or slurry continuous reactors. For batch and semi-continuous reactors wood samples can be used in conditions such as chips or pellets while a slurry reactor must have particles as small as 200 to 300 micrometers. While the particle size decreases the yield production decreases as well. This is due to the increase of cellulose. The hot water process is operated at a temperature range of 160 to 240 degrees Celsius in order to maintain the liquid phase. This is done above the normal boiling point of water to increase the solubilization of the hemicellulose and the depolymerization of polysaccharides. This process can take several minutes to several hours depending on the temperature and pH of the system. Higher temperatures paired with higher extraction times lead to higher yields. A maximum yield is obtained at a pH of 3.5. If below, the extraction yield exponentially decreases. In order to control pH, sodium bicarbonate is generally added. The sodium bicarbonate inhibits the autolysis of acetyl groups as well as inhibiting glycosyl bonds. Depending on the temperature and time the hemicellulose can be further converted into oligomers, monomers and lignin.


See also

*
Cellulose Cellulose 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: their composition, structure, properties, behavior ...

Cellulose
*
Lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and Bark (botany), bark, because they l ...

Lignin
*
Polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallograp ...
s


References


External links


Structure and Properties of Hemicellulose
/David Wang's Wood Chemistry Class {{Wood products Polysaccharides Cell biology