Editing Hemicellulose

{{Short description|Class of plant cell wall polysaccharides}}
A '''hemicellulose''' (also known as '''polyose''') is one of a number of [[heteropolymer]]s (matrix polysaccharides), such as [[arabinoxylan]]s, present along with [[cellulose]] in almost all [[embryophyte|terrestrial plant]] [[cell wall]]s.<ref name="Scheller HV">Scheller HV, Ulvskov P.[https://www.ncbi.nlm.nih.gov/pubmed/20192742 Hemicelluloses.] // Annu Rev Plant Biol. 2010;61:263-89. [[doi: 10.1146/annurev-arplant-042809-112315]].</ref> Cellulose is crystalline, strong, and resistant to [[hydrolysis]]. Hemicelluloses are branched, shorter in length than cellulose, and also show a propensity to crystallize.<ref>{{Cite journal |last1=Smith |first1=Peter J. |last2=Curry |first2=Thomas M. |last3=Yang |first3=Jeong-Yeh |last4=Barnes |first4=William J. |last5=Ziegler |first5=Samantha J. |last6=Mittal |first6=Ashutosh |last7=Moremen |first7=Kelley W. |last8=York |first8=William S. |last9=Bomble |first9=Yannick J. |last10=Peña |first10=Maria J. |last11=Urbanowicz |first11=Breeanna R. |date=2022-07-13 |title=Enzymatic Synthesis of Xylan Microparticles with Tunable Morphologies |journal=ACS Materials Au |language=en |volume=2 |issue=4 |pages=440–452 |doi=10.1021/acsmaterialsau.2c00006 |issn=2694-2461 |pmc=9284610 |pmid=35856073}}</ref>  They can be hydrolyzed by dilute [[acid]] or [[Base (chemistry)|base]] as well as a myriad of [[Cellulase|hemicellulase]] enzymes.

[[File:Hemicellulose.png|thumb|Most common molecular motif of hemicellulose]]

==Composition==
Diverse kinds of hemicelluloses are known.  Important examples include [[xylan]], [[glucuronoxylan]], [[arabinoxylan]], [[glucomannan]], and [[xyloglucan]].

Hemicelluloses are [[polysaccharide]]s often associated with [[cellulose]], but with distinct compositions and structures. Whereas cellulose is derived exclusively from [[glucose]], hemicelluloses are composed of diverse sugars, and can include the five-carbon sugars [[xylose]] and [[arabinose]], the six-carbon sugars glucose, [[mannose]] and [[galactose]], and the six-carbon [[deoxy sugar]] [[rhamnose]]. Hemicelluloses contain most of the D-[[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]] and [[galacturonic acid]] can be present.<ref name="Ebringerová-2005" /><ref name="Heinze-2005" />

==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.<ref name="Gibson-2013">{{cite journal | author=Gibson LJ | title=The hierarchical structure and mechanics of plant materials | journal= [[Journal of the Royal Society Interface]] | volume=9 | issue=76 | year=2013 | pages=2749–2766 | pmc=3479918 | pmid=22874093 | doi=10.1098/rsif.2012.0341}}</ref> In addition, hemicelluloses may be branched [[polymer]]s, while cellulose is unbranched. Hemicelluloses are embedded in the cell walls of plants, sometimes in chains that form a '[[Matrix (biology)|ground]]' – they bind with [[pectin]] to cellulose to form a network of cross-linked fibres.<ref>{{Cite journal |last1=Zykwinska |first1=Agata W. |last2=Ralet |first2=Marie-Christine J. |last3=Garnier |first3=Catherine D. |last4=Thibault |first4=Jean-François J. |date=2005-09-01 |title=Evidence for In Vitro Binding of Pectin Side Chains to Cellulose |journal=Plant Physiology |language=en |volume=139 |issue=1 |pages=397–407 |doi=10.1104/pp.105.065912 |issn=1532-2548 |pmc=1203388 |pmid=16126855}}</ref>
[[File:Plant cell wall diagram-en.svg|thumb|Section of a cell wall; hemicellulose in green|alt=|195x195px]]

Based on the structural difference, like backbone linkages and side groups, as well as other factors, like abundance and distributions in plants, hemicelluloses can be categorized into four groups as following:<ref name="Heinze-2005">{{Cite book|title=Polysaccharides I : structure, characterisation and use|date=2005|publisher=Springer|last=Heinze|first=Thomas|isbn=978-3-540-31583-4|location=Berlin|oclc=262681325}}</ref> 1) xylans, 2) [[Mannan (polysaccharide)|mannan]]s; 3) [[Mixed-linkage glucan|mixed linkage β-glucans]]; 4) xyloglucans.

===Xylans===

Xylans usually consist of a backbone of β-(1→4)-linked xylose residues and can be further divided into homoxylans and heteroxylans. Homoxylans have a backbone of D-xylopyranose residues linked by β(1→4) glycosidic linkages. Homoxylans mainly have structural functions. Heteroxylans such as glucuronoxylans, glucuronoarabinoxylans, and complex heteroxylans, have a backbone of D-xylopyranose and short carbohydrate branches. For example, glucuronoxylan has a substitution with α-(1→2)-linked glucuronosyl and 4-O-methyl glucuronosyl residues. Arabinoxylans and glucuronoarabinoxylans contain arabinose residues attached to the backbone<ref name="Scheller-2010">{{Cite journal|last1=Scheller|first1=Henrik Vibe|last2=Ulvskov|first2=Peter|date=2010-06-02|title=Hemicelluloses|journal=Annual Review of Plant Biology|language=en|volume=61|issue=1|pages=263–289|doi=10.1146/annurev-arplant-042809-112315|pmid=20192742|issn=1543-5008}}</ref>[[File:Xylan hardwood.svg|thumb|279x279px|Xylan in hardwood<ref>{{Citation|last1=Nimz|first1=Horst H|title=Wood|date=2000-06-15|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|pages=a28_305|editor-last=Wiley-VCH Verlag GmbH & Co. KGaA|publisher=Wiley-VCH Verlag GmbH & Co. KGaA|language=en|doi=10.1002/14356007.a28_305|isbn=978-3-527-30673-2|last2=Schmitt|first2=Uwe|last3=Schwab|first3=Eckart|last4=Wittmann|first4=Otto|last5=Wolf|first5=Franz}}</ref>|alt=]]

===Mannans===

The mannan-type hemicellulose can be classified into two types based on their main chain difference, [[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.<ref name="Scheller HV" />

===Mixed linkage β-glucans===

The conformation of the mixed linkage [[glucan]] 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 (C<sub>18</sub>H<sub>32</sub>O<sub>16</sub>) and cellotraosyl (C<sub>24</sub>H<sub>42</sub>O<sub>21</sub>)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).<ref name="Scheller HV" /><ref name="Gibson-2013" />[[File:Beta-D-glucopyranose-2D-skeletal.svg|thumb|171x171px|Beta-D-glucopyranose with carbon positions.|alt=]]

===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.<ref name="Gibson-2013" />

The two most common types of xyloglucans in plant cell walls are identified as XXXG and XXGG.<ref name="Scheller HV" />

== Biosynthesis ==
Hemicelluloses are synthesised from sugar nucleotides in the cell's [[Golgi apparatus]].<ref name="Zhu-2019">{{Citation|last1=Zhu|first1=Xiaoyu|title=Cellulose and Hemicellulose Synthesis and Their Regulation in Plant Cells|date=2019|work=Extracellular Sugar-Based Biopolymers Matrices|volume=12|pages=303–353|editor-last=Cohen|editor-first=Ephraim|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-030-12919-4_7|isbn=978-3-030-12918-7|last2=Xin|first2=Xiaoran|last3=Gu|first3=Ying|s2cid=198238237|editor2-last=Merzendorfer|editor2-first=Hans}}</ref> 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.<ref name="Zhu-2019" /><ref name="Pauly-2013">{{Cite journal|last1=Pauly|first1=Markus|last2=Gille|first2=Sascha|last3=Liu|first3=Lifeng|last4=Mansoori|first4=Nasim|last5=de Souza|first5=Amancio|last6=Schultink|first6=Alex|last7=Xiong|first7=Guangyan|date=2013|title=Hemicellulose biosynthesis|journal=Planta|language=en|volume=238|issue=4|pages=627–642|doi=10.1007/s00425-013-1921-1|pmid=23801299|bibcode=2013Plant.238..627P |s2cid=17501948|issn=0032-0935}}</ref>

Mannan chain backbones are synthesized by cellulose synthase-like protein family A (CSLA) and possibly enzymes in cellulose synthase-like protein family D (CSLD).<ref name="Zhu-2019" /><ref name="Pauly-2013" /> Mannan synthase, a particular enzyme in CSLA, is responsible for the addition of mannose units to the backbone.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> The galactose side-chains of some mannans are added by galactomannan galactosyltransferase.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> [[Acetylation]] of mannans is mediated by a mannan O-acetyltransferase, however, this enzyme has not been definitively identified.<ref name="Pauly-2013" />

Xyloglucan backbone synthesis is mediated by cellulose synthase-like protein family C (CSLC), particularly [[glucan synthase]], which adds glucose units to the chain.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> Backbone synthesis of xyloglucan is also mediated in some way by [[xylosyltransferase]], but this mechanism is separate to its transferase function and remains unclear.<ref name="Pauly-2013" /> Xylosyltransferase in its transferase function is, however, utilized for the addition of xylose to the side-chain.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> Other enzymes utilized for side-chain synthesis of xyloglucan include [[galactosyltransferase]] (which is responsible for the addition of [galactose and of which two different forms are utilized), [[fucosyltransferase]] (which is responsible for the addition of fucose), and [[acetyltransferase]] (which is responsible for acetylation).<ref name="Zhu-2019" /><ref name="Pauly-2013" />

Xylan backbone synthesis, unlike that of the other hemicelluloses, is not mediated by any cellulose synthase-like proteins.<ref name="Pauly-2013" /> Instead, xylan synthase is responsible for backbone synthesis, facilitating the addition of xylose.<ref name="Pauly-2013" /> Several genes for xylan synthases have been identified.<ref name="Pauly-2013" /> Several other enzymes are utilized for the addition and modification of the side-chain units of xylan, including [[glucuronosyltransferase]] (which adds [glucuronic acid units), xylosyltransferase (which adds additional xylose units), [[arabinosyltransferase]] (which adds arabinose), [[methyltransferase]] (responsible for [[methylation]]), and acetyltransferase] (responsible for acetylation).<ref name="Pauly-2013" /> 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.<ref name="Pauly-2013" /> Backbone synthesis is mediated by enzymes in cellulose synthase-like protein families F and H (CSLF and CSLH), specifically glucan synthase.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> Several forms of glucan synthase from CSLF and CSLH have been identified.<ref name="Zhu-2019" /><ref name="Pauly-2013" /> 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.<ref name="Zhu-2019" /><ref name="Pauly-2013" />

==Applications==
In the [[sulfite process|sulfite pulp process]] the hemicellulose is largely hydrolysed by the acid pulping liquor ending up in the brown liquor where the fermentable [[hexose]] sugars (around 2%) can be used for producing [[ethanol]]. This process was primarily applied to calcium sulfite brown liquors.<ref>{{Cite web |title=Sulfite Process - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/engineering/sulfite-process |access-date=2022-09-08 |website=www.sciencedirect.com}}</ref>
; [[Arabinogalactan]]
:Arabinogalactans can be used as [[emulsifier]]s, [[Stabilizer (chemistry)|stabilizers]] and [[Binder (material)|binders]] according to [https://uscode.house.gov/view.xhtml?path=/prelim@title21/chapter9&edition=prelim the Federal Food, Drug and Cosmetic Act]. Arabinogalactans can also be used as bonding agent in [[Sugar substitute|sweeteners]].<ref>Whistler, R. L. (1993). Hemicelluloses. In Industrial Gums (pp. 295–308). Elsevier. https://doi.org/10.1016/b978-0-08-092654-4.50015-2</ref>
; Xylan
:The films based on xylan show low oxygen permeability and thus are of potential interest as packaging for oxygen-sensitive products.<ref>Gröndahl, M., & Gatenholm, P. (2007). Oxygen Barrier Films Based on Xylans Isolated from Biomass. In ACS Symposium Series (pp. 137–152). American Chemical Society. https://doi.org/10.1021/bk-2007-0954.ch009</ref>
[[File:Agar plate with colonies.jpg|thumb|right|A Petri dish with [[bacteria]]l colonies on an [[agar]]-based [[growth medium]]]]
; [[Agar]]
:Agar is used in making jellies and puddings. It is also growth medium with other nutrients for [[microorganisms]].<ref name="Spiridon-2008">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</ref>
; [[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.<ref name="Spiridon-2008"/>
; [[beta-glucan]]
:b-glucans have an important role in [[food supplement]] while b-glucans are also promising in health-related issues, especially in immune reactions and the treatment of cancer.<ref>Vetvicka, V., Vannucci, L., Sima, P., & Richter, J. (2019). Beta Glucan: Supplement or Drug? From Laboratory to Clinical Trials. Molecules, 24(7), 1251. https://doi.org/10.3390/molecules24071251</ref>
; [[Xanthan gum|Xanthan]]
:Xanthan, with other [[polysaccharides]] can form gels that have high solution [[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.<ref>Navarrete, R. C., Himes, R. E., & Seheult, J. M. (2000). Applications of Xanthan Gum in Fluid-Loss Control and Related Formation Damage. SPE Permian Basin Oil and Gas Recovery Conference. SPE Permian Basin Oil and Gas Recovery Conference. https://doi.org/10.2118/59535-ms</ref>
; [[Alginic acid|Alginate]]
:Alginate has an important role in the development of [[antimicrobial]] textiles due to its characteristics of environmental friendliness, and high industrialization level as a sustainable [[biopolymer]].<ref>Li, J., He, J., & Huang, Y. (2017). Role of alginate in antibacterial finishing of textiles. International Journal of Biological Macromolecules, 94, 466–473. https://doi.org/10.1016/j.ijbiomac.2016.10.054</ref>

It is also abundantly found in cereal hull/husk, bran, and straw. A number of proposed processes aim to break it down into the above-mentioned parts for utilization.<ref>{{cite journal |last1=Arzami |first1=Anis N. |last2=Ho |first2=Thao M. |last3=Mikkonen |first3=Kirsi S. |title=Valorization of cereal by-product hemicelluloses: Fractionation and purity considerations |journal=Food Research International |date=January 2022 |volume=151 |pages=110818 |doi=10.1016/j.foodres.2021.110818|doi-access=free }}</ref>

==Natural functions==
[[File:Hemicellulose acting in the plant cell wall.jpg|thumb|Hemicellulose contribution to structural support within plant cells]]
As a [[Polysaccharides|polysaccharide]] compound in plant cell walls similar to cellulose, hemicellulose helps cellulose in the strengthening of plant cell walls.<ref name="Scheller-2010" /> Hemicellulose interacts with the [[cellulose]] by providing cross-linking of [[cellulose]] [[microfibrils]]: hemicellulose will search for voids in the cell wall during its formation and provide support around cellulose [[fibrils]] in order to equip the cell wall with the maximum possible strength it can provide.<ref name="Scheller-2010" /> Hemicellulose dominates the [[middle lamella]] of the plant cell, unlike [[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]] to provide structural tissue support of more vascular plants.<ref name="Ebringerová-2005">{{Citation|last1=Ebringerová|first1=Anna|title=Hemicellulose|date=2005|work=Polysaccharides I: Structure, Characterization and Use|pages=1–67|editor-last=Heinze|editor-first=Thomas|series=Advances in Polymer Science|publisher=Springer|language=en|doi=10.1007/b136816|isbn=978-3-540-31583-4|last2=Hromádková|first2=Zdenka|last3=Heinze|first3=Thomas}}</ref><ref>{{Cite journal|doi = 10.1016/j.trac.2015.02.022|title = Pressurized hot water extraction of bioactives|year = 2015|last1 = Plaza|first1 = Merichel|last2 = Turner|first2 = Charlotta|journal = Trends in Analytical Chemistry|volume = 71|pages = 39–54|doi-access = free}}</ref>

== 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.<ref name="Gallina-2018">{{Cite journal|last1=Gallina|first1=Gianluca|last2=Cabeza|first2=Álvaro|last3=Grénman|first3=Henrik|last4=Biasi|first4=Pierdomenico|last5=García-Serna|first5=Juan|last6=Salmi|first6=Tapio|date=2018-03-01|title=Hemicellulose extraction by hot pressurized water pretreatment at 160°C for 10 different woods: Yield and molecular weight|url=http://uvadoc.uva.es/handle/10324/35166|journal=The Journal of Supercritical Fluids|series=Biomass Fractionation by Subcritical and Supercritical Water|language=en|volume=133|pages=716–725|doi=10.1016/j.supflu.2017.10.001|issn=0896-8446}}</ref><ref name="Li-2013">{{Cite web|url=https://bioresources.cnr.ncsu.edu/|title=Hot water extraction of hemicelluloses from aspen wood chips of different sizes :: BioResources|last=Li Z, Qin M, Xu C, and Chen X|date=2013|website=bioresources.cnr.ncsu.edu|access-date=2020-04-24}}</ref> 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.<ref name="Gallina-2018" /><ref name="Li-2013" /> 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.<ref>{{cite journal |last1=Gianluca Gallinaa Álvaro Cabezaa Henrik Grénmanbc Pierdomenico Biasibd Juan García-Sernaa Tapio Salmi |title=Hemicellulose extraction by hot pressurized water pretreatment at 160 °C for 10 different woods: Yield and molecular weight |journal=The Journal of Supercritical Fluids |date=March 2018 |volume=133 |issue=Part 2 |pages=716–725 |doi=10.1016/j.supflu.2017.10.001 |url=https://research.abo.fi/files/25488060/Gallina-woods-160C-UVaDocs.pdf |access-date=7 October 2017}}</ref>

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.<ref name="Tunc-2008">{{Cite journal|last1=Tunc|first1=M. Sefik|last2=van Heiningen|first2=Adriaan R. P.|date=2008-09-17|title=Hemicellulose Extraction of Mixed Southern Hardwood with Water at 150 °C: Effect of Time|journal=Industrial & Engineering Chemistry Research|volume=47|issue=18|pages=7031–7037|doi=10.1021/ie8007105|issn=0888-5885}}</ref>  When xylose and furfural{{typo help inline|date=December 2020}} 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.<ref name="Tunc-2008" />

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.<ref name="Li-2013" /> This changes the structure from crystalline to amorphous. Hydrothermal pretreatment is another method.{{explain|date=July 2021}} 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.<ref name="Gallina-2018" />

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.<ref name="Li-2013" /> While the particle size decreases the yield production decreases as well.<ref>{{Cite journal|last=Ayrilmis N, Kwon J, Han T|date=October 2017|title=Effect of Wood Chip Size on Hemicellulose Extraction and Technological Properties of Flakeboard|journal=Turkish Journal of Agriculture & Forestry|volume=41|pages=331–337|doi=10.3906/tar-1704-63|doi-access=free}}</ref> This is due to the increase of cellulose.{{Cn|date=February 2021}}

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.<ref name="Tunc-2008" /> This process can take several minutes to several hours depending on the temperature and pH of the system.<ref name="Li-2013" /> Higher temperatures paired with higher extraction times lead to higher yields. A maximum yield is obtained at a pH of 3.5.<ref name="Gallina-2018" /> If below, the extraction yield exponentially decreases. In order to control pH, sodium bicarbonate is generally added.<ref name="Gallina-2018" /> The sodium bicarbonate inhibits the [[autolysis (biology)|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.<ref name="Gallina-2018" />

Solid bits of wood remain after autohydrolysis, as the lignin is largely untouched. A proper degree of autohydrolysis can preserve the lignin well enough to be used for paper production. This is useful for the [[Kraft process]], which normally does not recover wood hemicellulose into useful products.<ref>Vila, C., Romero, J., Francisco, J. L., Santos, V., and Parajó, J. C. (2012). "On the recovery of hemicellulose before kraft pulping," BioRes. 7(3), 4179-4189. https://bioresources.cnr.ncsu.edu/resources/on-the-recovery-of-hemicellulose-before-kraft-pulping/</ref>

==See also==
* [[Cellulose]]
* [[Lignin]]
* [[Polysaccharide]]s

==References==
{{Reflist}}

==External links==
* [http://web.nchu.edu.tw/pweb/users/taiwanfir/lesson/10393.pdf Structure and Properties of Hemicellulose] /David Wang's Wood Chemistry Class

{{carbohydrates}}
{{Wood products}}

[[Category:Polysaccharides]]
[[Category:Cell biology]]