Beta-glucan

{{short description|Class of chemical compounds}} {{Distinguish|betaglycan}} {{missing information|biosynthesis|date=August 2019}} {{Use dmy dates|date=March 2023}} {{CS1 config|display-authors=6|name-list-style=vanc}} [[Image:Callose.svg|class=skin-invert-image|thumb|Callose is an example of a (1→3)-β-D-glucan composed of glucose units]] '''Beta-glucans''', '''β-glucans''' comprise a group of β-D-glucose polysaccharides (glucans) naturally occurring in the cell walls of plants (including cereals), bacteria, algae and fungi, with significantly differing physicochemical properties dependent on source. Typically, β-glucans form a linear backbone with 1–3 β-glycosidic bonds but differ with respect to molecular mass, solubility, viscosity, branching structure, and gelation properties, with several physiological roles in these organisms and causing diverse physiological effects in any animals that consume them.

β-glucans are natural gums and are used as texturing agents in various nutraceutical and cosmetic products, and as soluble fiber supplements. At dietary intake levels of at least 3 g per day in humans, oat fiber β-glucan decreases blood levels of LDL cholesterol and so may reduce the risk of cardiovascular diseases.<ref name="ho">{{cite journal | pmid = 27724985 | year = 2016 | last1 = Ho | first1 = H. V | title = The effect of oat β-glucan on LDL-cholesterol, non-HDL-cholesterol and apoB for CVD risk reduction: A systematic review and meta-analysis of randomised-controlled trials | journal = British Journal of Nutrition | volume = 116 | issue = 8 | pages = 1369–1382 | last2 = Sievenpiper | first2 = J. L | last3 = Zurbau | first3 = A | last4 = Blanco Mejia | first4 = S | last5 = Jovanovski | first5 = E | last6 = Au-Yeung | first6 = F | last7 = Jenkins | first7 = A. L | last8 = Vuksan | first8 = V | doi = 10.1017/S000711451600341X | doi-access = free }}</ref>

== History == Cereal and fungal products have been used for centuries for medicinal and cosmetic purposes; however, the specific role of β-glucan was not explored until the 20th century. β-glucans were first discovered in lichens, and shortly thereafter in barley. A particular interest in oat β-glucan arose after a cholesterol lowering effect from oat bran reported in 1981.<ref> {{cite journal |vauthors=Kirby RW, Anderson JW, Sieling B, Rees ED, Chen WJ, Miller RE, Kay RM |title=Oat-bran intake selectively lowers serum low-density lipoprotein cholesterol concentrations of hypercholesterolemic men |journal=Am. J. Clin. Nutr. |volume=34 |issue=5 |pages=824–9 |year=1981 |pmid=6263072 |doi= 10.1093/ajcn/34.5.824|doi-access=free }}</ref>

In 1997, the FDA approved of a claim that intake of at least 3.0 g of β-glucan from oats per day decreased absorption of dietary cholesterol and reduced the risk of coronary heart disease. The approved health claim was later amended to include these sources of β-glucan: rolled oats (oatmeal), oat bran, whole oat flour, oatrim (the soluble fraction of alpha-amylase hydrolyzed oat bran or whole oat flour), whole grain barley and barley beta-fiber. An example of an allowed label claim: "Soluble fiber from foods such as oatmeal, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A serving of oatmeal supplies 0.75 grams of the 3.0 g of β-glucan soluble fiber necessary per day to have this effect." The claim language is in the Federal Register 21 CFR 101.81 Health Claims: "Soluble fiber from certain foods and risk of coronary heart disease (CHD)".<ref>https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=1&SID=4bf49f997b04dcacdfbd637db9aa5839&ty=HTML&h=L&mc=true&n=pt21.2.101&r=PART#se21.2.101_181 21 CFR 101.81 Health Claims: Soluble fiber from certain foods and risk of coronary heart disease (CHD)</ref>{{fcn|date=February 2026}}

==Structure== Glucans are arranged in six-sided D-glucose rings connected linearly at different carbon positions depending on the compound, although most commonly β-glucans include a 1-3 glycosidic link in their backbone. They generally contain 20 - 30 D-glucose rings. Although technically β-glucans are chains of D-glucose polysaccharides linked by β-type glycosidic bonds, by convention not all β-D-glucose polysaccharides are categorized as β-glucans.<ref>{{Cite journal|title = Natural and Modified (1→3)-β-D-Glucans in Health Promotion and Disease Alleviation|last = Zeković|first = Djordje B.|date = 10 October 2008|journal = Critical Reviews in Biotechnology|doi = 10.1080/07388550500376166|pmid = 16419618|volume=25|issue = 4|pages=205–230|s2cid = 86109922}}</ref> Cellulose is not conventionally considered a β-glucan, as it is insoluble and does not exhibit the same physicochemical properties as other cereal or yeast β-glucans.<ref>{{Cite journal|title = Identification of high b-glucan oat lines and localization and chemical characterization of their seed kernel b-glucans|last = Sikora|first = Per|date = 14 June 2012|journal = Food Chemistry|doi = 10.1016/j.foodchem.2012.10.007|pmid = 23199994|volume=137|issue = 1–4|pages=83–91}}</ref> class=skin-invert-image|thumb|Glucose molecule, showing carbon numbering notation and β orientation.

Some β-glucan molecules have branching glucose side-chains attached to other positions on the main D-glucose chain, which branch off the β-glucan backbone. In addition, these side-chains can be attached to other types of molecules, like proteins, as in polysaccharide-K.

The most common forms of β-glucans are those comprising D-glucose units with β-1,3 links. Yeast and fungal β-glucans contain 1-6 side branches, while cereal β-glucans contain both β-1,3 and β-1,4 backbone bonds, but no β-1,3 branching.<ref name="pmid29491277">{{cite journal | vauthors=Nakashima A, Yamada K, Suzuki K | title=β-Glucan in Foods and Its Physiological Functions | journal=Journal of Nutritional Science and Vitaminology | volume=64 | issue=1 | pages=8–17 | year=2018 | doi = 10.3177/jnsv.64.8 | pmid=29491277 | doi-access=free }}</ref> Seaweeds glucans consist of a backbone that is primarily β-1,3-glucan, but with some β-1,6-glucan in the backbone as well as in side chains.<ref name="pmid29491277" />

Glucans have a significant role in carbon storage especially in marine algae and they are estimated to account for about 25% of world-wide organic carbon production.<ref name="Becker_et_al_2020">{{cite journal |last1=Becker |first1=Stefan |last2=Tebben |first2=Jan |first3=Sarah |last3=Coffinet |first4=Karen |last4=Wiltshire |first5=Morten Hvitfeldt |last5=Iversen |first6=Tilmann |last6=Harder |first7=Kai-Uwe |last7=Hinrichs |first8=Jan-Hendrik |last8=Hehemann |title=Laminarin is a major molecule in the marine carbon cycle. |journal=Proc. Natl. Acad. Sci. U.S.A. |date=2020 |volume=117 |issue=12 |pages=6599–6607 |doi=10.1073/pnas.1917001117 |doi-access=free |pmid=32170018 |pmc=7104365 }}</ref> They are also cell wall components and can act in communication between fungi, plants and animals, notably in symbiotic or pathogenic interactions.<ref name="Gow_et_al_2017">{{cite journal |last1=Gow |first1=N A R |last2=Latge |first2=J-P |last3=Munro |first3=C A |title=The fungal cell wall: Structure, biosynthesis, and function. |journal=Microbiology Spectrum |date=2017 |volume=5 |issue=3 |article-number=5.3.01 |doi=10.1128/microbiolspec.FUNK-0035-2016 |pmid=28513415 |pmc=11687499 }}</ref> The frequency, location, and length of the side-chains may play a role in immunomodulation. Differences in molecular weight, shape, and structure of β-glucans dictate the differences in biological activity.<ref name=":0">{{Cite book|title = Oats Nutrition and Technology|last = Chu|first = YiFang|publisher = Wiley Blackwell|year = 2014|isbn = 978-1-118-35411-7|location = Barrington, Illinois}}</ref><ref name=":2">{{Cite journal|title = Dietary modulation of immune function by β-glucans|last = Volman|first = Julia J|date = 20 November 2007|journal = Physiology & Behavior|volume = 94|issue = 2|pages = 276–284|doi = 10.1016/j.physbeh.2007.11.045|pmid = 18222501|s2cid = 24758421}}</ref>

In general, β-1,3 linkages are created by 1,3-beta-glucan synthase, and β-1,4 linkages are created by cellulose synthase. The process leading to β-1,6 linkages is poorly understood: although genes important in the process have been identified, not much is known about what each of them do.<ref>{{cite journal | vauthors = Ruiz-Herrera J, Ortiz-Castellanos L | title = Analysis of the phylogenetic relationships and evolution of the cell walls from yeasts and fungi | journal = FEMS Yeast Research | volume = 10 | issue = 3 | pages = 225–43 | date = May 2010 | pmid = 19891730 | doi = 10.1111/j.1567-1364.2009.00589.x | doi-access = free }}</ref> {| class="wikitable skin-invert-image" |+β-Glucan Structure by Source !Source (Example) !Backbone !Branching !Solubility in Water |- |Bacteria (Curdlan) |β-1,3 centre|135px |None |Insoluble<ref>{{Cite journal|title = Curdlan and other bacterial (1→3)-β-D-glucans|last = Mcintosh|first = M|date = 19 October 2004|journal = Applied Microbiology and Biotechnology|doi = 10.1007/s00253-005-1959-5|pmid = 15818477|volume=68|issue = 2|pages=163–173|s2cid = 13123359}}</ref> |- |Fungus |β-1,3 centre|135px |Short β-1,6 branching |Insoluble<ref>{{Cite journal|title = Solubilization of water-insoluble β-glucan isolated from Ganoderma lucidum|last = Han|first = Man Deuk|date = March 2008|journal = Journal of Environmental Biology}}</ref> |- |Yeast |β-1,3 centre|135px |Long β-1,6 branching |Insoluble<ref name=":2" /> |- |Cereal (Mixed-linkage glucan) |β-1,3-1,4 centre|225px |None |Soluble<ref name=":0" /> |}

Bacteria make a variety of β-1,3 glycans. Linear β-1,3 glycans and derivatives with β-1,2 branches are commonly found in the bacterial capsule. Cyclic β-1,3-1,6 glycans are mostly found in the periplasm with an osmotic adaptation role. They are most commonly found in soil bacteria and pathogenic bacteria.<ref name="pmid15818477">{{cite journal | vauthors = McIntosh M, Stone BA, Stanisich VA | title = Curdlan and other bacterial (1-->3)-beta-D-glucans | journal = Appl Microbiol Biotechnol | volume = 68 | issue = 2 | pages = 163–73 | year = 2005 | pmid = 15818477 | doi = 10.1007/s00253-005-1959-5 | s2cid = 13123359 }}</ref>

==β-glucan types used in the human diet==

One of the most common sources of β-glucan for supplement use is derived from the cell wall of baker's yeast (''Saccharomyces cerevisiae''). β-glucans found in the cell walls of this yeast contain a β-1,3 glucose backbone with elongated β-1,6 glucose branches.<ref>{{Cite journal|title = The Structure of a β-(1→3)-D-Glucan from Yeast Cell Walls|last = Manners|first = David J.|date = 2 February 1973|journal = Biochemical Journal|doi =10.1042/bj1350019 |pmc=1165784|pmid=4359920|volume=135|issue = 1|pages=19–30}}</ref> Other sources include seaweed,<ref>{{cite journal | last = Teas | first = J | year = 1983 | title = The dietary intake of Laminarin, a brown seaweed, and breast cancer prevention | journal = Nutrition and Cancer | volume = 4 | issue = 3 | pages = 217–222 | issn = 0163-5581 | pmid = 6302638 | doi = 10.1080/01635588209513760 }}</ref> and various mushrooms, such as lingzhi, shiitake, chaga, and maitake, which are under preliminary research for their potential immune effects.<ref>{{cite journal|pmid=23739801|pmc=3775562|year=2013|last1=Vannucci|first1=L|title=Immunostimulatory properties and antitumor activities of glucans (Review)|journal=International Journal of Oncology|volume=43|issue=2|pages=357–64|last2=Krizan|first2=J|last3=Sima|first3=P|last4=Stakheev|first4=D|last5=Caja|first5=F|last6=Rajsiglova|first6=L|last7=Horak|first7=V|last8=Saieh|first8=M|doi=10.3892/ijo.2013.1974}}</ref>

===Fermentable fiber=== {{Main|Dietary fiber}}

In the diet, β-glucans are a source of soluble, fermentable fiber – also called ''prebiotic fiber'' – which provides a substrate for microbiota within the large intestine, increasing fecal bulk and producing short-chain fatty acids as byproducts with wide-ranging physiological activities.<ref name="mcrorie">{{cite journal|pmid=27863994|year=2017|last1=McRorie Jr|first1=J. W|title=Understanding the Physics of Functional Fibers in the Gastrointestinal Tract: An Evidence-Based Approach to Resolving Enduring Misconceptions about Insoluble and Soluble Fiber|journal=Journal of the Academy of Nutrition and Dietetics|volume=117|issue=2|pages=251–264|last2=McKeown|first2=N. M|doi=10.1016/j.jand.2016.09.021|url=http://jandonline.org/article/S2212-2672(16)31187-X/fulltext|doi-access=free}}</ref> This fermentation impacts the expression of many genes within the large intestine,<ref>{{cite journal|last1=Keenan |first1=M. J. |last2=Martin |first2=R. J.|last3=Raggio |first3=A. M. |last4=McCutcheon |first4=K. L. |last5=Brown |first5=I. L.|last6=Birkett |first6=A. |last7=Newman |first7=S. S. |last8=Skaf |first8=J. |last9=Hegsted |first9=M. |last10=Tulley|first10=R. T. |last11=Blair |first11=E. |last12=Zhou |first12=J.|title=High-Amylose Resistant Starch Increases Hormones and Improves Structure and Function of the Gastrointestinal Tract: A Microarray Study |journal=Journal of Nutrigenetics and Nutrigenomics |date=2012 |volume=5 |issue=1 |pages=26–44 |doi=10.1159/000335319 |pmid=22516953|pmc=4030412 }}</ref> which further affects digestive function and cholesterol and glucose metabolism, as well as the immune system and other systemic functions.<ref name=mcrorie/><ref>{{cite journal|last1=Simpson|first1=H. L.|last2=Campbell|first2=B. J.|title=Review article: dietary fibre–microbiota interactions |journal=Alimentary Pharmacology & Therapeutics |date=2015 |volume=42 |issue=2 |pages=158–79 |doi=10.1111/apt.13248 |pmid=26011307 |pmc=4949558}}</ref>

thumb|Oatmeal is a common food source of β-glucans

===Cereal=== {{Main|Mixed-linkage glucan|Oat beta-glucan}}

Cereal β-glucans from oat, barley, wheat, and rye have been studied for their effects on cholesterol levels in people with normal cholesterol levels and in those with hypercholesterolemia.<ref name=ho/> Intake of oat β-glucan at daily amounts of at least 3 grams lowers total and low-density lipoprotein cholesterol levels by 5 to 10% in people with normal or elevated blood cholesterol levels.<ref>{{cite journal|pmid=21631511|year=2011|last1=Othman|first1=R. A|title=Cholesterol-lowering effects of oat β-glucan|journal=Nutrition Reviews|volume=69|issue=6|pages=299–309|last2=Moghadasian|first2=M. H|last3=Jones|first3=P. J|doi=10.1111/j.1753-4887.2011.00401.x|doi-access=free}}</ref>

Oats and barley differ in the ratio of trimer and tetramer 1-4 linkages. Barley has more 1-4 linkages with a degree of polymerization higher than 4. However, the majority of barley blocks remain trimers and tetramers. In oats, β-glucan is found mainly in the endosperm of the oat kernel, especially in the outer layers of that endosperm.<ref name=":0" />

==β-glucan absorption== Enterocytes facilitate the transportation of β(1,3)-glucans and similar compounds across the intestinal cell wall into the lymph, where they begin to interact with macrophages to activate immune function.<ref>{{cite journal | vauthors = Frey A, Giannasca KT, Weltzin R, Giannasca PJ, Reggio H, Lencer WI, Neutra MR | date = 1 September 1996 | title = Role of the glycocalyx in regulating access of microparticles to apical plasma membranes of intestinal epithelial cells: implications for microbial attachment and oral vaccine targeting | journal = The Journal of Experimental Medicine | volume = 184 | issue = 3 | pages = 1045–1059 | pmid = 9064322 | doi = 10.1084/jem.184.3.1045 | pmc = 2192803 }}</ref> Radiolabeled studies have verified that both small and large fragments of β-glucans are found in the serum, which indicates that they are absorbed from the intestinal tract.<ref>{{cite journal | vauthors = Tsukagoshi S, Hashimoto Y, Fujii G, Kobayashi H, Nomoto K, Orita K |date=June 1984 | title = Krestin (PSK) | journal = Cancer Treatment Reviews | volume = 11 | issue = 2 | pages = 131–155 | pmid = 6238674 | doi = 10.1016/0305-7372(84)90005-7 }}</ref> M cells within the Peyer's patches physically transport the insoluble whole glucan particles into the gut-associated lymphoid tissue.<ref name="Hong 04">{{cite journal | last = Hong | first = F |author2=Yan J|author3=Baran JT|author4=Allendorf DJ|author5=Hansen RD|author6=Ostroff GR|author7=Xing PX|author8=Cheung NK|author9=Ross GD | date = 15 July 2004 | title = Mechanism by which orally administered β-1,3-glucans enhance the tumoricidal activity of antitumor monoclonal antibodies in murine tumor models | journal = Journal of Immunology | volume = 173 | issue = 2 | pages = 797–806 | issn = 0022-1767 | pmid = 15240666 | doi=10.4049/jimmunol.173.2.797 | doi-access = free }}</ref>

== Presence in blood == An assay to detect the presence of (1,3)-β-D-glucan in blood is marketed as a means of identifying invasive or disseminated fungal infections.<ref>{{cite journal |vauthors=Obayashi T, Yoshida M, Mori T | title=Plasma (13)-beta-D-glucan measurement in diagnosis of invasive deep mycosis and fungal febrile episodes | journal=Lancet | year=1995 | volume=345 | pages=17–20 | doi=10.1016/S0140-6736(95)91152-9 | pmid=7799700 | issue=8941 | s2cid=27299444 | display-authors=etal }}</ref><ref>{{cite journal |vauthors=Ostrosky-Zeichner L, Alexander BD, Kett DH | title=Multicenter clinical evaluation of the (1→3)β-D-glucan assay as an aid to diagnosis of fungal infections in humans | journal=Clin Infect Dis | year=2005 | volume=41 | pages=654–659 | doi=10.1086/432470 | pmid=16080087 | issue=5 | display-authors=etal | doi-access= }}</ref><ref>{{cite journal |vauthors=Odabasi Z, Mattiuzzi G, Estey E | title=Beta-D-glucan as a diagnostic adjunct for invasive fungal infections: validation, cutoff development, and performance in patients with acute myelogenous leukemia and myelodysplastic syndrome | journal=Clin Infect Dis | year=2004 | volume=39 | pages=199–205 | doi=10.1086/421944 | pmid=15307029 | issue=2 | display-authors=etal | doi-access=free }}</ref> This test can aid in the detection of ''Aspergillus'', ''Candida'', and ''Pneumocystis jirovecii''.<ref>{{Cite journal|last1=Lahmer|first1=Tobias|last2=da Costa|first2=Clarissa Prazeres|last3=Held|first3=Jürgen|last4=Rasch|first4=Sebastian|last5=Ehmer|first5=Ursula|last6=Schmid|first6=Roland M.|last7=Huber|first7=Wolfgang|date=4 April 2017|title=Usefulness of 1,3 Beta-D-Glucan Detection in non-HIV Immunocompromised Mechanical Ventilated Critically Ill Patients with ARDS and Suspected Pneumocystis jirovecii Pneumonia|journal=Mycopathologia|doi=10.1007/s11046-017-0132-x|issn=1573-0832|pmid=28378239|volume=182|issue=7–8|pages=701–708|s2cid=3870306}}</ref><ref>{{Cite journal|last1=He|first1=Song|last2=Hang|first2=Ju-Ping|last3=Zhang|first3=Ling|last4=Wang|first4=Fang|last5=Zhang|first5=De-Chun|last6=Gong|first6=Fang-Hong|date=August 2015|title=A systematic review and meta-analysis of diagnostic accuracy of serum 1,3-β-D-glucan for invasive fungal infection: Focus on cutoff levels|journal=Journal of Microbiology, Immunology, and Infection = Wei Mian Yu Gan Ran Za Zhi|volume=48|issue=4|pages=351–361|doi=10.1016/j.jmii.2014.06.009|issn=1995-9133|pmid=25081986|doi-access=free}}</ref><ref>{{Cite journal|last1=Kullberg|first1=Bart Jan|last2=Arendrup|first2=Maiken C.|date=8 October 2015|title=Invasive Candidiasis|journal=The New England Journal of Medicine|volume=373|issue=15|pages=1445–1456|doi=10.1056/NEJMra1315399|issn=1533-4406|pmid=26444731|hdl=2066/152392|s2cid=43788 |hdl-access=free}}</ref> This test cannot be used to detect ''Mucor'' or ''Rhizopus'', the fungi responsible for mucormycosis, as they do not produce (1,3)-beta-D-glucan.<ref>{{Cite journal|last1=Ostrosky-Zeichner|first1=Luis|last2=Alexander|first2=Barbara D.|last3=Kett|first3=Daniel H.|last4=Vazquez|first4=Jose|last5=Pappas|first5=Peter G.|last6=Saeki|first6=Fumihiro|last7=Ketchum|first7=Paul A.|last8=Wingard|first8=John|last9=Schiff|first9=Robert|date=1 September 2005|title=Multicenter clinical evaluation of the (1→3) beta-D-glucan assay as an aid to diagnosis of fungal infections in humans|journal=Clinical Infectious Diseases |volume=41|issue=5|pages=654–659|doi=10.1086/432470|issn=1537-6591|pmid=16080087|doi-access=}}</ref>

This test should be interpreted within the broader clinical context, however, as a positive test does not render a diagnosis, and a negative test does not rule out infection. False positives may occur because of fungal contaminants in various fungus-derived antibiotics such as the penicillin derivatives amoxicillin-clavulanate and piperacillin/tazobactam.<ref>{{cite journal | vauthors=Mennink-Kersten MA, Warris A, Verweij PE | title=1,3-β-D-Glucan in patients receiving intravenous amoxicillin–clavulanic acid | journal=NEJM | year=2006 | volume=354 | issue=26 | pages=2834–2835 | doi=10.1056/NEJMc053340 | pmid=16807428 | doi-access=free }}</ref> False positives can also occur with presence (bacteremia or sample contamination) of the bacteria ''Streptococcus pneumoniae'', ''Pseudomonas aeruginosa'', and ''Agrobacterium'',{{efn|Source uses the name ''Alcaligenes faecalis'' due to a widespread misidentification of the curdlan-producing ''Agrobacterium'' originating in the 1960s. True ''Alcaligenes faecalis'' is classified in a different class from ''Agrobacterium''.}} which also produce (1→3)β-D-glucan.<ref>{{cite journal |vauthors=Mennink-Kersten MA, Ruegebrink D, Verweij PE|title=''Pseudomonas aeruginosa'' as a cause of 1,3-β-D-glucan assay reactivity|journal=Clin Infect Dis|year=2008|volume=46|issue=12|pages=1930–1931|doi=10.1086/588563|pmid=18540808 |doi-access=free}}</ref>

== References == {{notelist}} {{Reflist|30em}}

== External links == * {{MeshName|beta-Glucans}}

Category:Edible thickening agents Category:Food additives Category:Medicinal fungi Category:Natural gums Category:Polysaccharides