Post on 10-Nov-2015
description
Beta glucano
Diagrama que muestra la orientacin y la ubicacin de diferentes vnculos de los beta-
glucanos.
Estructura tridimensional de celulosa, un -1, 4 glucano.
Los -Glucanos (beta-glucanos) son polisacridos de monmeros D-glucosa ligados con enlaces glucosdicos. Los beta-glucanos son un grupo muy diverso de molculas que
pueden variar en relacin a su masa molecular, solubilidad, viscosidad, y configuracin
tridimensional. Normalmente, se presentan como celulosa en las plantas, el salvado de los
granos de cereales, la pared celular de la levadura del panadero, algunos hongos, setas y
bacterias. Algunas formas de beta-glucanos son tiles en la nutricin humana como agentes
de textura y como suplementos de fibra soluble, pero pueden ser problemticos en el
proceso de elaboracin de la cerveza.
Levaduras, hongos medicinales son derivados de beta-glucanos notables por su capacidad
para modular el sistema inmunitario. Investigaciones han demostrado que beta-glucanos
insolubles (1,3 / 1,6), tienen mayor actividad biolgica que sus homlogos beta-glucanos
solubles (1,3 / 1,4).1 Las diferencias entre los enlaces de beta-glucano y su estructura
qumica, en relacin a la solubilidad, el modo de accin, y la actividad biolgica en general
son muy importantes.
ndice
1 Informacin general
2 Qumica de los Beta-glucanos
3 Fuentes de Beta-glucano en la naturaleza
4 Beta-glucano y el sistema inmunitario
5 Aplicaciones clnicas
o 5.1 Cncer
o 5.2 Prevencin de la infeccin
o 5.3 La exposicin a radiacin
o 5.4 El choque sptico
o 5.5 Ciruga
o 5.6 Cicatrizacin de heridas
o 5.7 La rinitis alrgica
o 5.8 Artritis
o 5.9 Aplicaciones adicionales
6 Absorcin de Beta-glucano
7 Beta glucano derivado de levadura
8 Aplicaciones mdicas
9 El papel del Beta-D-glucano en diagnsticos
10 Vase tambin
11 Referencias
12 Enlaces externos
Informacin general
Ejemplos de beta-glucanos con diferentes enlaces glucosdicos.
Glucanos son polisacridos que slo contienen glucosa como componentes estructurales, y
estn vinculados con enlaces glucosdicos .
En general, se distingue entre enlaces - y -glucosdicos dependiendo de si los grupos sustituyentes de los carbonos que flanquean el oxgeno del anillo estn apuntando en la
misma direccin o contraria en la forma estndar de elaboracin de los azcares. Un
vnculo -glucosdico de D-azcar deriva de un plano inferior de azcares, el hidrxido (u otro grupo sustituyente) deriva de otros puntos de carbono por encima del plano
(configuracin opuesta), mientras que un vnculo -glucosdico emana por encima del dicho plano.
Los nmeros 1,4 y 6 identifican los tomos de carbono en cada extremo del enlace
glucosdico. La numeracin se inicia junto al oxgeno del anillo (vase la glucosa).
Ejemplos de beta glucanos incluyen:
Nombre Enlace glucosdico Notas
celulosa -1,4
curdlan -1,3
laminarin -1,3 y -1,
chrysolaminarin -1,3
lentinan -1,6:-1,3 aislado de Lentinula edodes
lichenin -1,3 y -1,4
pleuran -1,3 y -1,6 aislado de Pleurotus ostreatus
zymosan -1,3
Qumica de los Beta-glucanos
Molecula de glucosa, visualizacin de la numeracin de los carbonos y la numeracin beta.
Por definicin, los beta-glucanos son cadenas de D-polisacridos de glucosa, unidas por
enlaces glucosdicos tipo beta. Estos anillos D-glucosa de seis caras pueden ser conectados
unos a otros, en una variedad de posiciones en la estructura del anillo de D-glucosa.
Algunos compuestos de beta-glucano, se repiten continuamente debido a la unin de D-
glucosa en posiciones especficas. Un ejemplo de esto sera la celulosa. La celulosa se
compone de una larga cadena de molculas de D-glucosa, unidas unas a otras, una y otra
vez, en la posicin beta (1,4).
Sin embargo, los beta-glucanos pueden ser ms diversos que molculas como la celulosa.
Por ejemplo, una molcula de beta-glucano puede estar compuesta de unidades repetidas de
D-glucosa unidas con enlaces glucosdicos beta, pero tienen ligaciones laterales de cadenas
de glucosa unidas a otras posiciones de la cadena principal de D-glucosa. Estas pequeas
cadenas laterales pueden ser separadas de la "columna vertebral" del beta-glucano (en el
caso de la celulosa, la columna vertebral seran cadenas de D-glucosa unidas en la posicin
(1,4)) y en otras posiciones como la 3 y 6. Adems, estas cadenas laterales pueden ser
conectadas a otros tipos de molculas, como las protenas. Un ejemplo de un beta-glucano
que se ha unido a protenas sera el Polisacrido-K.
La forma ms activa de los beta-glucanos son los que integran unidades de D-glucosa
unidas unas a otras en la posicin (1,3) con cadenas laterales de D-glucosa unidas a la
posicin (1,6). stas son referidas como beta - 1,3/1,6 glucano. Algunos investigadores han
sugerido que es la frecuencia, la ubicacin, y la longitud de la cadena lateral en lugar de la
columna vertebral de beta glucanos que determinan su actividad del sistema inmune. Otra
variable es el hecho de que algunos de estos compuestos contienen una nica cadena de
filamentos, mientras que las columnas vertebrales de otros 1,3 beta-glucanos existen en
forma de cadenas hlice dobles y triples. En algunos casos, las protenas vinculadas a la
columna vertebral del beta (1,3) glucano tambin pueden estar involucrado en actividades
teraputicas. Aunque estos compuestos tengan un potencial interesante para la mejora del
sistema inmunitario, se debe enfatizar que la investigacin est todava en el inicio. Hay
opiniones diferentes sobre qu peso molecular, forma, estructura, y fuente de beta (1,3)
glucanos proporcionan el mayor beneficio teraputico.
Fuentes de Beta-glucano en la naturaleza
Algunos hongos, como el Shiitake, contienen grandes cantidades de beta-glucanos.
Una de las fuentes ms comunes de la beta (1,3) D-glucano para el uso de suplementos se
deriva de la pared celular de la levadura (Saccharomyces cerevisiae). Sin embargo, los beta
(1,3) (1,4) glucanos tambin son extrados de los salvados de algunos granos como la avena
y cebada, y en un grado menor en el centeno y el trigo. La versin beta (1,3) D-glucanos de
la levadura son a menudo insolubles. Las que se extraen de los granos tienden a ser tanto
solubles como insolubles. Otras fuentes incluyen algunos tipos de algas2 y varias especies
de hongos, como reishi (Ganoderma lucidum), shiitake (Lentinus edodes), maitake (Grifola
frondosa), Schizophyllum commune, Trametes versicolor, Inonotus obliquus (seta chaga) y
enokitake (Flammulina velutipes).3
Beta-glucano y el sistema inmunitario
Beta-glucanos son conocidos como "modificadores de respuesta biolgica" por su
capacidad de activar el sistema inmunitario.4 Los inmunlogos de la Universidad de
Louisville, descubrieran que un receptor en la superficie de las clulas inmunes llamado
Receptor del Complemento 3 (CR3 o CD11b / CD18) es responsable de la unin a beta-
glucanos, permitiendo que las clulas inmunes las reconozcan como "no-yo."5 Sin embargo,
cabe sealar que la actividad de beta-glucanos es diferente de algunos frmacos que tienen
la capacidad de sobre-estimulacin del sistema inmunitario. Algunos frmacos tienen el
potencial de empujar al sistema inmune a una estimulacin excesiva, y por lo tanto estn
contraindicados en individuos con enfermedades autoinmunes, alergias o infecciones por
hongos. Beta-glucanos hacen el sistema inmunitario funcionar mejor sin llegar a ser
demasiado activo.6 Adems de mejorar la actividad del sistema inmunitario, los beta-
glucanos ayudan a normalizar los elevados niveles de colesterol LDL, ayudan en la
cicatrizacin de heridas, ayudan a prevenir infecciones, y tambin tienen potencial como
adyuvante en el tratamiento del cncer.
Aplicaciones clnicas
Cncer
Beta-glucanos, como lentinano (derivado del hongo shiitake) y polisacrido-K, han sido
utilizados como terapia inmunitaria para el cncer desde 1980, principalmente en Japn.
Investigaciones han demostrado que los beta-glucanos pueden ser antitumorales y ejercer
actividad anticncer.7 8 9 En un estudio con ratones, 1,3 beta glucanos han conseguido
inhibir los tumores y metstasis hepticas.10
En algunos estudios, los beta 1, 3 glucanos han
potenciado los efectos de la quimioterapia. En un experimento de cncer, utilizando
ratones, la administracin de ciclofosfamida, en conjunto con los beta 1, 3 glucanos
derivados de levadura result en la reduccin de la mortalidad.11
En pacientes humanos con
cncer gstrico avanzado, la administracin de beta 1, 3 glucanos derivados de setas
Shiitake, en conjunto con la quimioterapia result en tiempos de sobrevivencia
prolongada.12
Estudios preclnicos han demostrado que un producto de levadura glucano soluble, cuando se utiliza en combinacin con ciertos anticuerpos monoclonales o vacunas contra el
cncer, ofrece mejoras significativas en la sobrevivencia a largo plazo frente a anticuerpos
monoclonales solos.5 Este beneficio, sin embargo, no es resultado del Betafectin potenciar
la accin especfica de la muerte de anticuerpos. La actividad antitumoral es debida a un
mecanismo nico que consiste en matar a los neutrfilos que estn preparados con
Betafectin y que normalmente no estn implicados en la lucha contra el cncer.5 13
Una
investigacin reciente de Hong et al., demuestra que este mecanismo de accin es eficaz
contra una amplia gama de tipos de cncer cuando se utiliza en combinacin con
anticuerpos monoclonales especficos que activan el complemento que se une al tumor.14
El
complemento permite a estos neutrfilos encontrar el tumor y unirse a ello, lo que facilita
su muerte. Las clulas del sistema inmune son la primera lnea de defensa del cuerpo y
circulan en el organismo, ejerciendo una respuesta inmune contra organismos "extranjeros"
(bacterias, hongos, parsitos). En general, los neutrfilos no estn relacionados con la
destruccin del tejido canceroso, porque estas clulas inmunes identifican el cncer como
"yo" en vez de lo identificar como extranjero o "no yo". Actualmente, en la inmunoterapia
del cncer participan los anticuerpos monoclonales y tambin vacunas, que estimulan la
respuesta inmune adquirida, pero no hacen nada para cambiar la imagen del sistema
inmunitario innato del cncer como "yo". As, los anticuerpos monoclonales por s solos no
participan o no inician la posibilidad de matar del sistema inmunitario innato, que es
nuestro principal mecanismo de defensa contra las infecciones provocadas por bacterias y
levaduras (hongos).
Dr. Gordon Ross y Dr. Vclav Vetvicka, inmunlogos y investigadores respetados de
cncer en la Universidad de Louisville, descubrieran que un receptor en la superficie de
estas clulas de inmunidad innata llamado Receptor del Complemento 3 (CR3 o CD11b /
CD18) es el responsable de la unin a los hongos o a la levadura, permitiendo que las
clulas inmunes los reconozcan como "no yo."5 Este receptor es un receptor de ocupacin
doble, ya que tiene dos locales de unin. El primer local es el responsable de la unin a un
tipo de complemento, una protena soluble en la sangre, conocida como C3 (o iC3b). C3 se
adhiere a los agentes patgenos a que se han dirigido los anticuerpos especficos. El
segundo local de este receptor se une a un hidrato de carbono de la levadura o de las clulas
de los hongos, permitiendo que la clula inmune reconozca las levaduras y los hongos que
sean "no yo".13
15
Los dos locales de estos receptores deben ser ocupados de modo a activar
la clula inmune para destruir las levaduras u hongos. Existen dos obstculos que impiden
el uso de este mecanismo de accin contra el cncer por parte de los neutrfilos. En primer
lugar, el cuerpo no suele generar suficientes anticuerpos naturales para enlazar con el
tumor, y esto impide la activacin y el acoplamiento de lo complemento a la superficie de
la clula del cncer. Por lo tanto, los neutrfilos no se vinculan al cncer a partir del local
del primer receptor de CR3. El segundo obstculo es que cuando la respuesta de los
anticuerpos naturales se complementa con anticuerpos monoclonales (fijan el complemento
y el enlace se produce en el primer local), los tumores no contienen en su superficie
hidratos de carbono actuando como extranjeros y produciendo una "segunda seal" que
permitan a los neutrfilos a reconocer el cncer como "no yo".13
16
Otros receptores
humanos han sido identificados como siendo capases de recibir seales de beta-glucanos,
tales como Dectin-1, lactosylceramide, y scavenger receptores.[1]
El Dr. Ross descubri que un biofragmento procesado de Imprime PGG se une
especficamente al local del segundo receptor CR3 en los neutrfilos. Cuando los
neutrfilos se unen a los tumores, el Betafectin les permite "ver" el cncer como si fuera
una levadura o hongos patgenos y tambin proporciona la "segunda seal" para
desencadenar la muerte. En resumen, el Betafectin hace con que los neutrfilos luchen
contra el cncer, mejorando la eficacia del complemento de activacin de los anticuerpos
monoclonales y vacunas a travs de un mecanismo de diferentes muertes.
Diversas investigaciones han demostrado con xito que la forma oral de levadura de beta
1,3 D-glucano tiene efectos protectores similares a la versin de la inyeccin, incluyendo la
defensa contra las enfermedades infecciosas y el cncer.17
18
19
20
21
Recientemente, se
descubri que la ingesta de glucano por va oral puede aumentar significativamente la
proliferacin y activacin de los monocitos de sangre de pacientes con cncer de mama
avanzado.22
La tecnologa tiene una amplia aplicacin para el tratamiento del cncer. Cada clula de un
tumor canceroso tiene antgenos especficos en la suya superficie, y algunos de ellos son
comunes a otros tipos de cncer (Ejemplo: mucina 1 est presente en aproximadamente el
70% de todos los tipos de clulas cancerosas). Diversas inmunoterapias han demostrado
que existen diferentes antgenos para la unin de anticuerpos monoclonales en las clulas
tumorales. Esto se ha traducido en el desarrollo de cientos de anticuerpos monoclonales
dirigidos a un antgeno especfico diferente en las clulas cancerosas. En los estudios de
investigacin, el Betafectin ha mejorado la eficacia de todos los complementos testados que
activaban los anticuerpos monoclonales, incluyendo cncer de mama, de hgado y de
pulmn (datos de la empresa). La magnitud de xito vara de acuerdo con el anticuerpo
monoclonal especfico utilizado y el tipo de cncer.
Prevencin de la infeccin
Hasta ahora ha habido numerosos estudios y ensayos clnicos realizados con el -glucano de levadura soluble y con el glucano. Estos estudios van desde el impacto de -glucano en infecciones post-quirrgicas nosocomiales hasta la funcin de -glucanos de levadura en el tratamiento de las infecciones de carbunco.
Las infecciones post-quirrgicas son un grave problema despus de una ciruga mayor (en
25-27% de las cirugas hay infecciones post-ciruga).23
Las tecnologas de la Alfa-Beta
llevaran a cabo una serie de ensayos clnicos en humanos en la dcada de 1990 para evaluar
el impacto de la terapia con -glucano para el control de infecciones en pacientes de alto riesgo quirrgico.
23 En el ensayo inicial de 34 pacientes fueron aleatoriamente (doble ciego,
controlados con placebo) asignados a los grupos de tratamiento o placebo. Los pacientes
que recibieron la PGG-glucano tuvieron significativamente menos complicaciones
infecciosas que el grupo placebo (el grupo que recibi la PGG-glucano ha tenido 1,4
infecciones por paciente mientras que el grupo placebo ha tenido 3,4 infecciones por
paciente). Algunos datos adicionales del estudio clnico han revelado que los pacientes que
recibieron PGG-glucano tuvieran una necesidad menor de antibiticos intravenosos y
tuvieran tambin estancias ms cortas en la unidad de cuidados intensivos do que los
pacientes que recibieron el placebo.
Un ensayo clnico posterior en humanos24
estudi ms a fondo el impacto de -glucano en reducir la incidencia de infecciones en pacientes quirrgicos de alto riesgo. Los autores
encontraron un resultado similar con un dose-response trend (dosificaciones superiores
facilitaba mayor reduccin de incidencias de infecciones que dosificaciones baja). En el
ensayo clnico en humanos 67 pacientes fueron asignados aleatoriamente y recibieron un
placebo o una dosis de 0.1, 0.5, 1.0 o 2.0 mg PGG-Glucano por kg de peso corporal.
Infecciones graves ocurrieron en cuatro pacientes que recibieron el placebo, tres pacientes
que recibieron la dosis ms baja (0.1 mg/kg) de PGG-Glucano y solo una infeccin se
observ con la dosis ms alta de 2.0 mg/kg de PGG-Glucano.
Los resultados de un ensayo clnico en humanos en fase III demostraron que terapia de
PGG-Glucano reduca graves infecciones post-operativas en un 39% despus de
operaciones no-colonrectales de alto riesgo.25
Este estudio se realiz en pacientes que ya
estaban caracterizados como alto riesgo por el tipo de operacin y eran ms susceptibles a
las infecciones y otras complicaciones.
En este punto del desarrollo de una forma inyectable de b-glucano (Betafectin PGG-
Glucano) la mayora de los cientficos ya concluan que b-glucano derivado de la levadura
promova la fagocitosis y la muerte posterior de las bacterias patgenas. Un ensayo clnico
en fase III se propuso y se llevo a cabo en treinta-y-nueve centros mdicos en los EE.UU.
participando 1,249 sujetos estratificados de acuerdo a pacientes quirrgicos de ciruga
colorectal o no-colorectal. El PGG-glucano fue dado una vez pre-operacin y tres veces
post-operacin en 0, 0.5 o 1.0 mg/kg de peso corporal. Dentro de 30 das despus de la
ciruga el resultado medido fue infeccin grave o la muerte de los sujetos. Los resultados
del ensayo clnico en humanos en fase III demostraron que la terapia inyectable de PGG-
Glucano reduca infecciones graves post-operativas con un 39% despus de operaciones
nocolorectal de alto riesgo.25
Se han realizado estudios con seres humanos y animales que aun ms apoyan la eficacia de
-glucano en la lucha contra diversas enfermedades infecciosas. Un estudio en humanos ha demostrado que el consumo de partculas enteras de glucano en forma oral ha incrementado
la capacidad de clulas inmunes a consumir un desafi bacteriana (fagocitosis). El numero
total de clulas fagocticas y la eficiencia de la fagocitosis en humanos sanos participantes
en el estudio increment mientras consuman partculas comerciales de levadura de -Glucano. Este estudio demostr el potencial de -glucano de levadura en incrementar la velocidad de reaccin del sistema inmune en los desafos infecciosos. El estudio concluy
que el consumo oral de partculas enteras de glucano mejora la inmunidad natural.
El carbunco es una enfermedad que no puede ser probado en estudios en seres humanos por
razones obvias. En un estudio realizado por el departamento de defensa canadiense, el Dr.
Kournikakis demostr que la administracin oral de levadura -glucano dada con o sin antibiticos protege ratones contra infecciones de carbunco.
17 Una dosis de antibiticos por
va oral junto con partculas enteras de glucano (2mg/kg de peso corporal o 20 mg/kg de
peso corporal) durante ocho das de la infeccin con Bacillus anthracis protega a los
ratones contra la infeccin de carbunco durante los 10 das siguientes del periodo test. Los
ratones tratados con solo antibitica no sobrevivieron.
Un segundo experimento fue realizado para investigar el efecto de -glucano de levadura por consumo en va oral despus de la exposicin de los ratones a B. anthracis. Los
resultados fueron similares a la exposicin anterior con un 80-90% de la tasa de sobre
vivencia a los ratones tratados con -glucano, pero slo el 30% para el grupo de control despus de 10 das de exposicin. La inferencia esperada es que resultados similares se
observen en los seres humanos.
La exposicin a radiacin
-glucano es un conocido modificador de la respuesta biolgica (BRM) aislado de los polisacridos de las paredes de las clulas de levadura y se compone enteramente de
glucosa mediante enlaces (1,3) en cadenas lineales con una frecuencia variable de enlaces (1,6) formando cadenas laterales.26 La especfica actividad hematopoitica se demostr por primera vez con -glucano a mediados de la dcada de 1980 en forma anloga de granulocyte monocyte-colony factor estimulante (GM-CSF).
27 La investigacin se realiz
inicialmente con partculas -glucano y ms tarde con -glucanos solubles, todos los cuales fueron administrados por va intravenosa a ratones.
28 29
30
Ratones expuestos a 500-900 cGy
(500-900 mrads) de la radiacin gamma mostr una recuperacin significativamente mayor
de leucocitos en la sangre, plaquetas y glbulos rojos cuando se administraba -glucano en va intravenosa.
31 Otros informes mostraron que el -glucano poda revertir la
mielosupresin producida con frmacos quimioterapeuticos como fluorouracil,25
carboplatinum o ciclophosphamide.32
Por otra parte, la actividad anti-infecciosa de -glucano combinado con su hematopoyesis actividad estimulante result en una mayor
sobrevivencia en los ratones que recibieron una dosis letal de 900-1200 cGy de
radiacin.International
journal of immunopharmacology (England: Elsevier Science) 11 (7): pp. 761769. doi:10.1016/0192-0561(89)90130-6. PMID 2599714.
22. Demir, G; Klein HO, Mandel-Molinas N, Tuzuner N (January 2007). Beta glucan induces proliferation and activation of monocytes in peripheral blood of patients
with advanced breast cancer. International immunopharmacology (Netherlands:
Elsevier Science) 7 (1): pp. 113116. doi:10.1016/j.intimp.2006.08.011. PMID 17161824. 23. Babineau, TJ; Marcello P, Swails W, Kenler A, Bistrian B, Forse RA (November
1994). Randomized phase I/II trial of a macrophage-specific immunomodulator
(PGG-glucan) in high-risk surgical patients. Annals of surgery (United States:
Lippincott Williams & Wilkins) 220 (5): pp. 601609. doi:10.1097/00000658-199411000-00002. PMID 7979607.
24. Babineau, TJ; Hackford A, Kenler A, Bistrian B, Forse RA, Fairchild PG, Heard S, Keroack M, Caushaj P, Benotti P (November 1994). A phase II multicenter,
double-blind, randomized, placebo-controlled study of three dosages of an
immunomodulator (PGG-glucan) in high-risk surgical patients. Archives of
surgery (Chicago, Ill. : 1960) (United States: American Medical Association) 129
(11): pp. 12041210. ISSN 0004-0010. PMID 7979954. 25. Dellinger, EP; Babineau TJ, Bleicher P, Kaiser AB, Seibert GB, Postier RG, Vogel
SB, Norman J, Kaufman D, Galandiuk S, Condon RE (September 1999). Effect of
PGG-glucan on the rate of serious postoperative infection or death observed after
high-risk gastrointestinal operations. Betafectin Gastrointestinal Study Group.
Archives of surgery (Chicago, Ill. : 1960) (United States: American Medical
Association) 134 (9): pp. 977983. doi:10.1001/archsurg.134.9.977. PMID 10487593. 26. Stone, Bruce A.; Clarke, Adrienne E. (enero de 1993). Chemistry and Biology of
(13)--Glucans. Victoria, Australia: La Trobe University Press. ISBN 978-1863244091.
27. Patchen, ML; MacVittie TJ (April 1983). Dose-dependent responses of murine pluripotent stem cells and myeloid and erythroid progenitor cells following
administration of the immunomodulating agent glucan. Immunopharmacology
(Netherlands: Elsevier/North-Holland) 5 (4): pp. 303313. doi:10.1016/0162-3109(83)90046-2. PMID 6853144.
28. Patchen, ML; DiLuzio NR, Jacques P, MacVittie TJ (December 1984). Soluble polyglycans enhance recovery from cobalt-60--induced hemopoietic injury.
Journal of biological response modifiers (United States: Raven Press) 3
(6): pp. 627633. ISSN 0732-6580. PMID 6512563. 29. Patchen, ML; MacVittie TJ, Wathen LM (15-11-1984). Effects of pre- and post-
irradiation glucan treatment on pluripotent stem cells, granulocyte, macrophage and
erythroid progenitor cells, and hemopoietic stromal cells. Experientia
(Switzerland: Birkhuser Verlag) 40 (11): pp. 12401244. doi:10.1007/BF01946654. PMID 6500009.
30. Petruczenko, A (May-June 1984). Glucan effect on the survival of mice after radiation exposure. Acta physiologica Polonica (Poland: Panstwowy Zaklad
Wydawnictw Lekarskich) 35 (3): pp. 231236. ISSN 0044-6033. PMID 6537716. 31. Patchen, ML; MacVittie TJ (febrero 1986). Comparative effects of soluble and
particulate glucans on survival in irradiated mice. Journal of biological response
modifiers (EE.UU.: Raven Press) 5 (1): pp. 4560. ISSN 0732-6580. PMID 3958754. 32. Patchen, ML; Vaudrain T, Correira H, Martin T, Reese D (diciembre 1998). In
vitro and in vivo hematopoietic activities of Betafectin PGG-glucan.. Experimental
hematology (Netherlands: Elsevier Science) 26 (13): pp. 12471254. ISSN 0301-472X. PMID 9845381.
33. Turnbull, JL; Patchen ML, Scadden DT (1999). The polysaccharide, PGG-glucan, enhances human myelopoiesis by direct action independent of and additive to early-
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48. Keogh, GF; Cooper GJ, Mulvey TB, McArdle BH, Coles GD, Monro JA, Poppitt SD (October 2003). Randomized controlled crossover study of the effect of a
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59. Odabasi Z, Mattiuzzi G, Estey E, et al. (2004). Beta-D-glucan as a diagnostic adjunct for invasive fungal infections: validation, cutoff development, and
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receiving intravenous amoxicillinclavulanic acid. 354. pp. 28342835.
ALFA-GLUCANOS
Diagrama que muestra la orientacin y la ubicacin de diferentes vnculos de los Alfa-
glucanos.
Carbohydrate
From Wikipedia, the free encyclopedia
Lactose is a disaccharide found in milk. It consists of a molecule of D-galactose and a
molecule of D-glucose bonded by beta-1-4 glycosidic linkage. It has a formula of
C12H22O11.
A carbohydrate is a large biological molecule, or macromolecule, consisting of carbon
(C), hydrogen (H), and oxygen (O) atoms, usually with a hydrogen:oxygen atom ratio of
2:1 (as in water); in other words, with the empirical formula Cm(H2O)n (where m could be
different from n).[1]
Some exceptions exist; for example, deoxyribose, a sugar component of
DNA,[2]
has the empirical formula C5H10O4.[3]
Carbohydrates are technically hydrates of
carbon;[4]
structurally it is more accurate to view them as polyhydroxy aldehydes and
ketones.[5]
The term is most common in biochemistry, where it is a synonym of saccharide. The
carbohydrates (saccharides) are divided into four chemical groups: monosaccharides,
disaccharides, oligosaccharides, and polysaccharides. In general, the monosaccharides and
disaccharides, which are smaller (lower molecular weight) carbohydrates, are commonly
referred to as sugars.[6]
The word saccharide comes from the Greek word (skkharon), meaning "sugar." While the scientific nomenclature of carbohydrates is
complex, the names of the monosaccharides and disaccharides very often end in the suffix -
ose. For example, grape sugar is the monosaccharide glucose, cane sugar is the disaccharide
sucrose, and milk sugar is the disaccharide lactose (see illustration).
Carbohydrates perform numerous roles in living organisms. Polysaccharides serve for the
storage of energy (e.g., starch and glycogen), and as structural components (e.g., cellulose
in plants and chitin in arthropods). The 5-carbon monosaccharide ribose is an important
component of coenzymes (e.g., ATP, FAD, and NAD) and the backbone of the genetic
molecule known as RNA. The related deoxyribose is a component of DNA. Saccharides
and their derivatives include many other important biomolecules that play key roles in the
immune system, fertilization, preventing pathogenesis, blood clotting, and development.[7]
In food science and in many informal contexts, the term carbohydrate often means any food
that is particularly rich in the complex carbohydrate starch (such as cereals, bread, and
pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts).
Contents
1 Structure
2 Monosaccharides
o 2.1 Classification of monosaccharides
o 2.2 Ring-straight chain isomerism
o 2.3 Use in living organisms
3 Disaccharides
4 Nutrition
o 4.1 Classification
5 Metabolism
o 5.1 Catabolism
6 Carbohydrate chemistry
7 See also
8 References
9 External links
Structure
Formerly the name "carbohydrate" was used in chemistry for any compound with the
formula Cm (H2O) n. Following this definition, some chemists considered formaldehyde
(CH2O) to be the simplest carbohydrate,[8]
while others claimed that title for
glycolaldehyde.[9]
Today the term is generally understood in the biochemistry sense, which
excludes compounds with only one or two carbons.
Natural saccharides are generally built of simple carbohydrates called monosaccharides
with general formula (CH2O)n where n is three or more. A typical monosaccharide has the
structure H-(CHOH)x(C=O)-(CHOH)y-H, that is, an aldehyde or ketone with many
hydroxyl groups added, usually one on each carbon atom that is not part of the aldehyde or
ketone functional group. Examples of monosaccharides are glucose, fructose, and
glyceraldehydes. However, some biological substances commonly called
"monosaccharides" do not conform to this formula (e.g., uronic acids and deoxy-sugars
such as fucose), and there are many chemicals that do conform to this formula but are not
considered to be monosaccharides (e.g., formaldehyde CH2O and inositol (CH2O)6).[10]
The open-chain form of a monosaccharide often coexists with a closed ring form where the
aldehyde/ketone carbonyl group carbon (C=O) and hydroxyl group (-OH) react forming a
hemiacetal with a new C-O-C bridge.
Monosaccharides can be linked together into what are called polysaccharides (or
oligosaccharides) in a large variety of ways. Many carbohydrates contain one or more
modified monosaccharide units that have had one or more groups replaced or removed. For
example, deoxyribose, a component of DNA, is a modified version of ribose; chitin is
composed of repeating units of N-acetyl glucosamine, a nitrogen-containing form of
glucose.
Monosaccharides
Main article: Monosaccharide
D-glucose is an aldohexose with the formula (CH2O)6. The red atoms highlight the
aldehyde group, and the blue atoms highlight the asymmetric center furthest from the
aldehyde; because this -OH is on the right of the Fischer projection, this is a D sugar.
Monosaccharides are the simplest carbohydrates in that they cannot be hydrolyzed to
smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups.
The general chemical formula of an unmodified monosaccharide is (CH2O) n, literally a "carbon hydrate." Monosaccharides are important fuel molecules as well as building blocks
for nucleic acids. The smallest monosaccharides, for which n=3, are dihydroxyacetone and
D- and L-glyceraldehydes.
Classification of monosaccharides
The and anomers of glucose. Note the position of the hydroxyl group (red or green) on the anomeric carbon relative to the CH2OH group bound to carbon 5: they either have
identical absolute configurations (R,R or S,S) (), or opposite absolute configurations (R,S or S,R) ().[11]
Monosaccharides are classified according to three different characteristics: the placement of
its carbonyl group, the number of carbon atoms it contains, and its chiral handedness. If the
carbonyl group is an aldehyde, the monosaccharide is an aldose; if the carbonyl group is a
ketone, the monosaccharide is a ketose. Monosaccharides with three carbon atoms are
called trioses, those with four are called tetroses, five are called pentoses, six are hexoses,
and so on.[12]
These two systems of classification are often combined. For example, glucose
is an aldohexose (a six-carbon aldehyde), ribose is an aldopentose (a five-carbon aldehyde),
and fructose is a ketohexose (a six-carbon ketone).
Each carbon atom bearing a hydroxyl group (-OH), with the exception of the first and last
carbons, are asymmetric, making them stereo centers with two possible configurations each
(R or S). Because of this asymmetry, a number of isomers may exist for any given
monosaccharide formula. Using Le Bel-van't Hoff rule, the aldohexose D-glucose, for
example, has the formula (CH2O) 6, of which four of its six carbons atoms are stereogenic,
making D-glucose one of 24=16 possible stereoisomers. In the case of glyceraldehydes, an
aldotriose, there is one pair of possible stereoisomers, which are enantiomers and epimers.
1, 3-dihydroxyacetone, the ketose corresponding to the aldose glyceraldehydes, is a
symmetric molecule with no stereo centers. The assignment of D or L is made according to
the orientation of the asymmetric carbon furthest from the carbonyl group: in a standard
Fischer projection if the hydroxyl group is on the right the molecule is a D sugar, otherwise
it is an L sugar. The "D-" and "L-" prefixes should not be confused with "d-" or "l-", which
indicate the direction that the sugar rotates plane polarized light. This usage of "d-" and "l-"
is no longer followed in carbohydrate chemistry.[13]
Ring-straight chain isomerism
Glucose can exist in both a straight-chain and ring form.
The aldehyde or ketone group of a straight-chain monosaccharide will react reversibly with
a hydroxyl group on a different carbon atom to form a hemiacetal or hemiketal, forming a
heterocyclic ring with an oxygen bridge between two carbon atoms. Rings with five and six
atoms are called furanose and pyranose forms, respectively, and exist in equilibrium with
the straight-chain form.[14]
During the conversion from straight-chain form to the cyclic form, the carbon atom
containing the carbonyl oxygen, called the anomeric carbon, becomes a stereogenic center
with two possible configurations: The oxygen atom may take a position either above or
below the plane of the ring. The resulting possible pair of stereoisomers is called anomers.
In the anomer, the -OH substituent on the anomeric carbon rests on the opposite side (trans) of the ring from the CH2OH side branch. The alternative form, in which the CH2OH
substituent and the anomeric hydroxyl are on the same side (cis) of the plane of the ring, is
called the anomer.
Use in living organisms
Monosaccharides are the major source of fuel for metabolism, being used both as an energy
source (glucose being the most important in nature) and in biosynthesis. When
monosaccharides are not immediately needed by many cells they are often converted to
more space-efficient forms, often polysaccharides. In many animals, including humans, this
storage form is glycogen, especially in liver and muscle cells. In plants, starch is used for
the same purpose. The most abundant carbohydrate, cellulose, is a structural component of
the cell wall of plants and many forms of algae. Ribose is a component of RNA.
Deoxyribose is a component of DNA. Lyxose is a component of lyxoflavin found in human
heart.[15]
Ribulose and xylulose occurs in the pentose phosphate pathway. Galactose, a
component of milk sugar lactose, is found in galactolipids in plant cell membranes and in
glycoproteins in many tissues. Mannose occurs in human metabolism, especially in the
glycosylation of certain proteins. Fructose, or fruit sugar, is found in many plants and in
humans, it is metabolized in the liver, absorbed directly into the intestines during digestion,
and found in semen. Trehalose, a major sugar of insects, is rapidly hydrolyzed into two
glucose molecules to support continuous flight.
Disaccharides
Sucrose, also known as table sugar, is a common disaccharide. It is composed of two
monosaccharides: D-glucose (left) and D-fructose (right).
Main article: Disaccharide
Two joined monosaccharides are called a disaccharide and these are the simplest
polysaccharides. Examples include sucrose and lactose. They are composed of two
monosaccharide units bound together by a covalent bond known as a glycosidic linkage
formed via a dehydration reaction, resulting in the loss of a hydrogen atom from one
monosaccharide and a hydroxyl group from the other. The formula of unmodified
disaccharides is C12H22O11. Although there are numerous kinds of disaccharides, a handful
of disaccharides are particularly notable.
Sucrose, pictured to the right, is the most abundant disaccharide, and the main form in
which carbohydrates are transported in plants. It is composed of one D-glucose molecule
and one D-fructose molecule. The systematic name for sucrose, O--D-glucopyranosyl-(12)-D-fructofuranoside, indicates four things:
Its monosaccharides: glucose and fructose
Their ring types: glucose is a pyranose, and fructose is a furanose
How they are linked together: the oxygen on carbon number 1 (C1) of -D-glucose is linked to the C2 of D-fructose.
The -oside suffix indicates that the anomeric carbon of both monosaccharides
participates in the glycosidic bond.
Lactose, a disaccharide composed of one D-galactose molecule and one D-glucose
molecule, occurs naturally in mammalian milk. The systematic name for lactose is O--D-galactopyranosyl-(14)-D-glucopyranose. Other notable disaccharides include maltose (two D-glucoses linked -1,4) and cellulobiose (two D-glucoses linked -1,4). Disaccharides can be classified into two types.They are reducing and non-reducing
disaccharides. If the functional group is present in bonding with another sugar unit, it is
called a reducing disaccharide or biose.
Nutrition
Grain products: rich sources of carbohydrates
Carbohydrate consumed in food yields 3.87 calories of energy per gram for simple
sugars,[16]
and 3.57 to 4.12 calories per gram for complex carbohydrate in most other
foods.[17]
High levels of carbohydrate are often associated with highly processed foods or
refined foods made from plants, including sweets, cookies and candy, table sugar, honey,
soft drinks, breads and crackers, jams and fruit products, pastas and breakfast cereals.
Lower amounts of carbohydrate are usually associated with unrefined foods, including
beans, tubers, rice, and unrefined fruit.[18]
Foods from animal carcass have the lowest
carbohydrate, but milk does contain lactose.
Carbohydrates are a common source of energy in living organisms; however, no
carbohydrate is an essential nutrient in humans.[19]
Humans are able to obtain most of their
energy requirement from protein and fats, though the potential for some negative health
effects of extreme carbohydrate restriction remains, as the issue has not been studied
extensively so far.[19]
However, in the case of dietary fiber indigestible carbohydrates which are not a source of energy inadequate intake can lead to significant increases in mortality.
[20]
Following a diet consisting of very low amounts of daily carbohydrate for several days will
usually result in higher levels of blood ketone bodies than an isocaloric diet with similar
protein content.[21]
This relatively high level of ketone bodies is commonly known as
ketosis and is very often confused with the potentially fatal condition often seen in type 1
diabetics known as diabetic ketoacidosis. Somebody suffering ketoacidosis will have much
higher levels of blood ketone bodies along with high blood sugar, dehydration and
electrolyte imbalance.
Long-chain fatty acids cannot cross the bloodbrain barrier, but the liver can break these down to produce ketones. However the medium-chain fatty acids octanoic and heptanoic
acids can cross the barrier and be used by the brain, which normally relies upon glucose for
its energy.[22][23][24]
Gluconeogenesis allows humans to synthesize some glucose from
specific amino acids: from the glycerol backbone in triglycerides and in some cases from
fatty acids.
Organisms typically cannot metabolize all types of carbohydrate to yield energy. Glucose is
a nearly universal and accessible source of calories. Many organisms also have the ability
to metabolize other monosaccharides and disaccharides but glucose is often metabolized
first. In Escherichia coli, for example, the lac operon will express enzymes for the digestion
of lactose when it is present, but if both lactose and glucose are present the lac operon is
repressed, resulting in the glucose being used first (see: Diauxie). Polysaccharides are also
common sources of energy. Many organisms can easily break down starches into glucose,
however, most organisms cannot metabolize cellulose or other polysaccharides like chitin
and arabinoxylans. These carbohydrate types can be metabolized by some bacteria and
protists. Ruminants and termites, for example, use microorganisms to process cellulose.
Even though these complex carbohydrates are not very digestible, they represent an
important dietary element for humans, called dietary fiber. Fiber enhances digestion, among
other benefits.[25]
Based on the effects on risk of heart disease and obesity,[26]
the Institute of Medicine
recommends that American and Canadian adults get between 4565% of dietary energy from carbohydrates.
[27] The Food and Agriculture Organization and World Health
Organization jointly recommend that national dietary guidelines set a goal of 5575% of total energy from carbohydrates, but only 10% directly from sugars (their term for simple
carbohydrates).[28]
Classification
Nutritionists often refer to carbohydrates as either simple or complex. However, the exact
distinction between these groups can be ambiguous. The term complex carbohydrate was
first used in the U.S. Senate Select Committee on Nutrition and Human Needs publication
Dietary Goals for the United States (1977) where it was intended to distinguish sugars from
other carbohydrates (which were perceived to be nutritionally superior).[29]
However, the
report put "fruit, vegetables and whole-grains" in the complex carbohydrate column,
despite the fact that these may contain sugars as well as polysaccharides. This confusion
persists as today some nutritionists use the term complex carbohydrate to refer to any sort
of digestible saccharide present in a whole food, where fiber, vitamins and minerals are also
found (as opposed to processed carbohydrates, which provide calories but few other
nutrients). The standard usage, however, is to classify carbohydrates chemically: simple if
they are sugars (monosaccharides and disaccharides) and complex if they are
polysaccharides (or oligosaccharides).[30]
In any case, the simple vs. complex chemical distinction has little value for determining the
nutritional quality of carbohydrates.[30]
Some simple carbohydrates (e.g. fructose) raise
blood glucose slowly, while some complex carbohydrates (starches), especially if
processed, raise blood sugar rapidly. The speed of digestion is determined by a variety of
factors including which other nutrients are consumed with the carbohydrate, how the food
is prepared, individual differences in metabolism, and the chemistry of the carbohydrate.[31]
The USDA's Dietary Guidelines for Americans 2010 call for moderate- to high-
carbohydrate consumption from a balanced diet that includes six one-ounce servings of
grain foods each day, at least half from whole grain sources and the rest from enriched.[32]
The glycemic index (GI) and glycemic load concepts have been developed to characterize
food behavior during human digestion. They rank carbohydrate-rich foods based on the
rapidity and magnitude of their effect on blood glucose levels. Glycemic index is a measure
of how quickly food glucose is absorbed, while glycemic load is a measure of the total
absorbable glucose in foods. The insulin index is a similar, more recent classification
method that ranks foods based on their effects on blood insulin levels, which are caused by
glucose (or starch) and some amino acids in food.
Metabolism
Main article: Carbohydrate metabolism
This section requires expansion. (June 2008)
Catabolism
Catabolism is the metabolic reaction which cells undergo to extract energy. There are two
major metabolic pathways of monosaccharide catabolism: glycolysis and the citric acid
cycle.
In glycolysis, oligo/polysaccharides are cleaved first to smaller monosaccharides by
enzymes called glycoside hydrolases. The monosaccharide units can then enter into
monosaccharide catabolism. In some cases, as with humans, not all carbohydrate types are
usable as the digestive and metabolic enzymes necessary are not present.
Carbohydrate chemistry
Carbohydrate chemistry is a large and economically important branch of organic chemistry.
Some of the main organic reactions that involve carbohydrates are:
Carbohydrate acetalisation
Cyanohydrin reaction
Lobry-de Bruyn-van Ekenstein transformation
Amadori rearrangement
Nef reaction
Wohl degradation
KoenigsKnorr reaction
See also
Bioplastic
Fermentation
Gluconeogenesis
Glycoinformatics
Glycolipid
Glycoprotein
Low-carbohydrate diet
Macromolecule
No-carbohydrate diet
Nutrition
Pentose phosphate pathway
Photosynthesis
Saccharic acid
Sugar
Carbohydrate NMR
References
1. Western Kentucky University (May 29, 2013). "WKU BIO 113 Carbohydrates". wku.edu.
2. Eldra Pearl Solomon, Linda R. Berg, Diana W. Martin; Cengage Learning (2004). Biology. google.books.com. p. 52. ISBN 978-0534278281.
3. National Institute of Standards and Technology (2011). "Material Measurement Library D-erythro-Pentose, 2-deoxy-". nist.gov.
4. Long Island University (May 29, 2013). "The Chemistry of Carbohydrates". brooklyn.liu.edu.
5. Purdue University (May 29, 2013). "Carbohydrates: The Monosaccharides". purdue.edu.
6. Flitsch, Sabine L.; Ulijn, Rein V (2003). "Sugars tied to the spot". Nature 421 (6920): 21920. doi:10.1038/421219a. PMID 12529622.
7. Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993). Human Biology and
Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. pp. 5259. ISBN 0-13-981176-1.
8. John Merle Coulter, Charler Reid Barnes, Henry Chandler Cowles (1930), A Textbook of Botany for Colleges and Universities"
9. Carl A. Burtis, Edward R. Ashwood, Norbert W. Tietz (2000), Tietz fundamentals of clinical chemistry
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11. http://www.ncbi.nlm.nih.gov/books/NBK1955/#_ch2_s4_ 12. Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring
Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6.
13. Pigman, Ward; Horton, D. (1972). "Chapter 1: Stereochemistry of the Monosaccharides". In Pigman and Horton. The Carbohydrates: Chemistry and
Biochemistry Vol 1A (2nd ed.). San Diego: Academic Press. pp. 167. 14. Pigman, Ward; Anet, E.F.L.J. (1972). "Chapter 4: Mutarotations and Actions of
Acids and Bases". In Pigman and Horton. The Carbohydrates: Chemistry and
Biochemistry Vol 1A (2nd ed.). San Diego: Academic Press. pp. 165194. 15. "lyxoflavin". Merriam-Webster. 16. http://ndb.nal.usda.gov/ndb/foods/show/6202 17. http://www.fao.org/docrep/006/y5022e/y5022e04.htm 18. http://www.diabetes.org.uk/upload/How%20we%20help/catalogue/carb-reference-
list-0511.pdf
19. Westman, EC (2002). "Is dietary carbohydrate essential for human nutrition?". The American journal of clinical nutrition 75 (5): 9513; author reply 9534. PMID 11976176.
20. Park, Y; Subar, AF; Hollenbeck, A; Schatzkin, A (2011). "Dietary fiber intake and mortality in the NIH-AARP diet and health study". Archives of Internal Medicine
171 (12): 10618. doi:10.1001/archinternmed.2011.18. PMC 3513325. PMID 21321288.
21. http://ajcn.nutrition.org/content/83/5/1055.full.pdf+html 22. http://www.jneurosci.org/content/23/13/5928.full 23. http://www.nature.com/jcbfm/journal/v33/n2/abs/jcbfm2012151a.html 24. MedBio.info > Integration of Metabolism Professor em. Robert S. Horn, Oslo,
Norway. Retrieved on May 1, 2010. [1]
25. Pichon, L; Huneau, JF; Fromentin, G; Tom, D (2006). "A high-protein, high-fat, carbohydrate-free diet reduces energy intake, hepatic lipogenesis, and adiposity in
rats". The Journal of nutrition 136 (5): 125660. PMID 16614413. 26. Tighe, P; Duthie, G; Vaughan, N; Brittenden, J; Simpson, WG; Duthie, S; Mutch,
W; Wahle, K; Horgan, G; Thies, F. (2010). "Effect of increased consumption of
whole-grain foods on blood pressure and other cardiovascular risk markers in
healthy middle-aged persons: a randomized, controlled trial". The American journal
of clinical nutrition 92 (4): 73340. doi:10.3945/ajcn.2010.29417. PMID 20685951. 27. Food and Nutrition Board (2002/2005). Dietary Reference Intakes for Energy,
Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids.
Washington, D.C.: The National Academies Press. Page 769. ISBN 0-309-08537-3.
28. Joint WHO/FAO expert consultation (2003). [2] (PDF). Geneva: World Health Organization. pp. 5556. ISBN 92-4-120916-X.
29. Joint WHO/FAO expert consultation (1998), Carbohydrates in human nutrition, chapter 1. ISBN 92-5-104114-8.
30. "Carbohydrates". The Nutrition Source. Harvard School of Public Health. Retrieved 3 April 2013.
31. Jenkins, David; Alexandra L. Jenkins, Thomas M.S. Woleve, Lilian H. Thompson and A. Venkat Rao (February 1986). "Simple and Complex Carbohydrates".
Nutrition Reviews 44 (2).
32. DHHS and USDA, Dietary Guidelines for Americans 2010.
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Types of carbohydrates
Starch
From Wikipedia, the free encyclopedia
For the Urhobo cuisine dish known as starch see usi (food)
Starch
Identifiers
CAS number 9005-25-8
EC-number 232-679-6
RTECS number GM5090000
Properties
Molecular formula
(C
12H
22O
11) n
Molar mass variable
Appearance white powder
Density 1.5 g/cm3
Melting point decomp.
Solubility in water insoluble (see starch
gelatinization)
Hazards
MSDS ICSC 1553
EU Index not listed
Except where noted otherwise, data are given for
materials in their standard state (at 25 C (77 F),
100 kPa)
(verify) (what is: / ?)
Infobox references
Structure of the amylose molecule
Structure of the amylopectin molecule
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined
by glycosidic bonds. This polysaccharide is produced by most green plants as an energy
store. It is the most common carbohydrate in human diets and is contained in large amounts
in such staple foods as potatoes, wheat, maize (corn), rice, and cassava.
Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or
alcohol. It consists of two types of molecules: the linear and helical amylose and the
branched amylopectin. Depending on the plant, starch generally contains 20 to 25%
amylose and 75 to 80% amylopectin by weight.[1]
Glycogen, the glucose store of animals, is
a more branched version of amylopectin.
Starch is processed to produce many of the sugars in processed foods. Dissolving starch in
warm water gives wheatpaste, which can be used as a thickening, stiffening or gluing agent.
The biggest industrial non-food use of starch is as adhesive in the papermaking process.
Starch can be applied to parts of some garments before ironing, to stiffen them.
Contents
1 Etymology
2 History
3 Energy store of plants
o 3.1 Biosynthesis
o 3.2 Degradation
4 Properties
o 4.1 Structure
o 4.2 Hydrolysis
o 4.3 Dextrinization
o 4.4 Chemical tests
5 Food
o 5.1 Starch industry
5.1.1 Starch sugars
5.1.2 Modified starches
5.1.3 Use as food additive
6 Industrial applications
o 6.1 Papermaking
o 6.2 Corrugated board adhesives
o 6.3 Clothing starch
o 6.4 Other
7 See also
8 References
9 External links
Etymology
The word "starch" is from a Germanic root with the meanings "strong, stiff, strengthen,
stiffen".[2]
Modern German Strke (starch) is related.
"Amylum" for starch is from the Greek , "amylon" which means "not ground at a mill". The root amyl is used in biochemistry for several compounds related to starch.
History
Starch grains from the rhizomes of Typha (cattails, bullrushes) as flour have been identified
from grinding stones in Europe dating back to 30,000 years ago.[3]
Starch grains from
sorghum were found on grind stones in caves in Ngalue, Mozambique dating up to 100,000
years ago.[4]
Pure extracted wheat starch paste was used in Ancient Egypt possibly to glue papyrus.[5]
The extraction of starch is first described in the Natural History of Pliny the Elder around
AD 77-79.[6]
Romans used it also in cosmetic creams, to powder the hair and to thicken
sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. Rice
starch as surface treatment of paper has been used in paper production in China, from 700
AD onwards.[7]
In addition to starchy plants consumed directly, 66 million tonnes of starch were being
produced per year world-wide by 2008. In the EU this was around 8.5 million tonnes, with
around 40% being used for industrial applications and 60% for food uses,[8]
most of the
latter as glucose syrups.[9]
Energy store of plants
This section does not cite any references or sources. Please help improve this
section by adding citations to reliable sources. Unsourced material may be
challenged and removed. (March 2012)
Most green plants use starch as their energy store. An exception is the family Asteraceae
(asters, daisies and sunflowers), where starch is replaced by the fructan inulin.
In photosynthesis, plants use light energy to produce glucose from carbon dioxide. The
glucose is stored mainly in the form of starch granules, in plastids such as chloroplasts and
especially amyloplasts. Toward the end of the growing season, starch accumulates in twigs
of trees near the buds. Fruit, seeds, rhizomes, and tubers store starch to prepare for the next
growing season.
Glucose is soluble in water, hydrophilic, binds with water and then takes up much space
and is osmotically active; glucose in the form of starch, on the other hand, is not soluble,
therefore osmotically inactive and can be stored much more compactly.
Glucose molecules are bound in starch by the easily hydrolyzed alpha bonds. The same
type of bond is found in the animal reserve polysaccharide glycogen. This is in contrast to
many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are
bound by beta bonds and are much more resistant to hydrolysis.
Biosynthesis
Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the
enzyme glucose-1-phosphate adenylyltransferase. This step requires energy in the form of
ATP. The enzyme starch synthase then adds the ADP-glucose via a 1,4-alpha glycosidic
bond to a growing chain of glucose residues, liberating ADP and creating amylose. Starch
branching enzyme introduces 1,6-alpha glycosidic bonds between these chains, creating the
branched amylopectin. The starch debranching enzyme isoamylase removes some of these
branches. Several isoforms of these enzymes exist, leading to a highly complex synthesis
process.[10]
Glycogen and amylopectin have the same structure, but the former has about one branch
point per ten 1,4-alpha bonds, compared to about one branch point per thirty 1,4-alpha
bonds in amylopectin.[11]
Amylopectin is synthesized from ADP-glucose while mammals
and fungi synthesize glycogen from UDP-glucose; for most cases, bacteria synthesize
glycogen from ADP-glucose (analogous to starch).[12]
In addition to starch synthesis in plants, starch can be synthesized from non-food starch
mediated by an enzyme cocktail.[13]
In this cell-free biosystem, beta-1,4-glycosidic bond-
linked cellulose is partially hydrolyzed to cellobioase. Cellobiose phosphorylase cleaves to
glucose 1-phosphate and glucose; the other enzymepotato alpha-glucan phosphorylase can add glucose unit from glucose 1-phosphorylase to the non-ruducing ends of starch. In
it, phosphate is internally recycled. The other productglucosecan be assimilated by a yeast. This cell-free bioprocessing does not need any costly chemical and energy input, can
be conducted in aqueous solution, and does not have sugar losses.[14]
As a result, cellulosic
starch could be used to feed the world because cellulose resource is about 50 times of starch
resource.[15][16]
Degradation
Starch is synthesized in plant leaves during the day, in order to serve as an energy source at
night. Starch is stored as granulates. These insoluble highly branched chains have to be
phosphorylated in order to be accessible for degrading enzymes. The enzyme glucan, water
dikinase (GWD) phosphorylates at the C-6 position of a glucose molecule, close to the
chains 1,6-alpha branching bonds. A second enzyme, phosphoglucan, water dikinase
(PWD) phosphorylates the glucose molecule at the C-3 position. A loss of these enzymes,
for example a loss of the GWD, leads to a starch excess (sex) phenotype.[17]
Because starch
cannot be phosphorylated, it accumulates in the plastid.
After the phosphorylation, the first degrading enzyme, beta-amylase (BAM) is able to
attack the glucose chain at its non-reducing end. Maltose is released as the main product of
starch degradation. If the glucose chain consists of three or less molecules, BAM cannot
release maltose. A second enzyme, disproportionating enzyme-1 (DPE1), combines two
maltotriose molecules. From this chain, a glucose molecule is released. Now, BAM can
release another maltose molecule from the remaining chain. This cycle repeats until starch
is degraded completely. If BAM comes close to the phosphorylated branching point of the
glucose chain, it can no longer release maltose. In order for the phosphorylated chain to be
degraded, the enzyme isoamylase (ISA) is required.[18]
The products of starch degradation are to the major part maltose and to a less extensive part
glucose. These molecules are now exported from the plastid to the cytosol. Maltose is
exported via the maltose transporter. If this transporter is mutated (MEX1-mutant), maltose
accumulates in the plastid.[19]
Glucose is exported via the plastidic glucose translocator
(pGlcT).[20]
Now, these two sugars act as a precursor for sucrose synthesis. Sucrose can the
be used in the oxidative pentose phosphate pathway in the mitochondria, in order to
generate ATP at night.[18]
Properties
Structure
Starch, 800x magnified, under polarized light, showing characteristic extinction cross
Rice starch seen on light microscope. Characteristic for the rice starch is that starch
granules have an angular outline and some of them are attached to each other and form
larger granules
While amylose was traditionally thought to be completely unbranched, it is now known that
some of its molecules contain a few branch points.[21]
Although in absolute mass only about
one quarter of the starch granules in plants consist of amylose, there are about 150 times
more amylose molecules than amylopectin molecules. Amylose is a much smaller molecule
than amylopectin.
Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant
species has a unique starch granular size: rice starch is relatively small (about 2m) while potato starches have larger granules (up to 100m).
Starch becomes soluble in water when heated. The granules swell and burst, the semi-
crystalline structure is lost and the smaller amylose molecules start leaching out of the
granule, forming a network that holds water and increasing the mixture's viscosity. This
process is called starch gelatinization. During cooking, the starch becomes a paste and
increases further in viscosity. During cooling or prolonged storage of the paste, the semi-
crystalline structure partially recovers and the starch paste thickens, expelling water. This is
mainly caused by retrogradation of the amylose. This process is responsible for the
hardening of bread or staling, and for the water layer on top of a starch gel (syneresis).
Some cultivated plant varieties have pure amylopectin starch without amylose, known as
waxy starches. The most used is waxy maize, others are glutinous rice and waxy potato
starch. Waxy starches have less retrogradation, resulting in a more stable paste. High
amylose starch, amylomaize, is cultivated for the use of its gel strength and for use as a
resistant starch (a starch that resists digestion) in food products.
Synthetic amylose made from cellulose has a well-controlled degree of polymerization.
Therefore, it can be used as a potential drug deliver carrier.[13]
Hydrolysis
The enzymes that break down or hydrolyze starch into the constituent sugars are known as
amylases.
Alpha-amylases are found in plants and in animals. Human saliva is rich in amylase, and
the pancreas also secretes the enzyme. Individuals from populations with a high-starch diet
tend to have more amylase genes than those with low-starch diets;[22]
chimpanzees have
very few amylase genes.[22]
It is possible that turning to a high-starch diet was a significant
event in human evolution.[23]
Beta-amylase cuts starch into maltose units. This process is important in the digestion of
starch and is also used in brewing, where amylase from the skin of seed grains is
responsible for converting starch to maltose (Malting, Mashing).[citation needed]
Dextrinization
If starch is subjected to dry heat, it breaks down to form dextrins, also called "pyrodextrins"
in this context. This break down process is known as dextrinization. (Pyro)dextrins are
mainly yellow to brown in color and dextrinization is partially responsible for the browning
of toasted bread.[citation needed]
Chemical tests
Main article: Iodine test
Granules of wheat starch, stained with iodine, photographed through a light microscope
Iodine solution is used to test for starch; a dark blue color indicates the presence of starch.
The details of this reaction are not yet fully known, but it is thought that the iodine (I3 and
I5 ions) fit inside the coils of amylose, the charge transfers between the iodine and the
starch, and the energy level spacings in the resulting complex correspond to the absorption
spectrum in the visible light region. The strength of the resulting blue color depends on the
amount of amylose present. Waxy starches with little or no amylose present will color red.
Starch indicator solution consisting of water, starch and iodine is often used in redox
titrations: in the presence of an oxidizing agent the solution turns blue, in the presence of
reducing agent the blue color disappears because triiodide (I3) ions break up into three
iodide ions, disassembling the starch-iodine complex. A 0.3% w/w solution is the standard
concentration for a starch indicator. It is made by adding 3 grams of soluble starch to 1 liter
of heated water; the solution is cooled before use (starch-iodine complex becomes unstable
at temperatures above 35 C).
Each species of plant has a unique type of starch granules in granular size, shape and
crystallization pattern. Under the microscope, starch grains stained with iodine illuminated
from behind with polarized light show a distinctive Maltese cross effect (also known as
extinction cross and birefringence).
Food
Starch is the most common carbohydrate in the human diet and is contained in many staple
foods. The major sources of starch intake worldwide are the cereals (rice, wheat, and
maize) and the root vegetables (potatoes and cassava).[24]
Many other starchy foods are
grown, some only in specific climates, including acorns, arrowroot, arracacha, bananas,
barley, breadfruit, buckwheat, canna, colacasia, katakuri, kudzu, malanga, millet, oats, oca,
polynesian arrowroot, sago, sorghum, sweet potatoes, rye, taro, chestnuts, water chestnuts
and yams, and many kinds of beans, such as favas, lentils, mung beans, peas, and
chickpeas.
Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta,
porridge and tortilla.
Digestive enzymes have problems digesting crystalline structures. Raw starch will digest
poorly in the duodenum and small intestine, while bacterial degradation will take place
mainly in the colon. When starch is cooked, the digestibility is increased. Hence, before
humans started using fire, eating grains was not a very useful way to get energy.
Starch gelatinization during cake baking can be impaired by sugar competing for water,
preventing gelatinization and improving texture.
Starch industry
The starch industry extracts and refines starches from seeds, roots and tubers, by wet
grinding, washing, sieving and drying. Today, the main commercial refined starches are
cornstarch, tapioca, wheat, rice and potato starch. To a lesser extent, sources include rice,
sweet potato, sago and mung bean. Historically, Florida arrowroot was also
commercialized. To this day, starch is extracted from more than 50 types of plants.
Untreated starch requires heat to thicken or gelatinize. When a starch is pre-cooked, it can
then be used to thicken instantly in cold water. This is referred to as a pregelatinized starch.
Starch sugars
Starch can be hydrolyzed into simpler carbohydrates by acids, various enzymes, or a
combination of the two. The resulting fragments are known as dextrins. The extent of
conversion is typically quantified by dextrose equivalent (DE), which is roughly the
fraction of the glycosidic bonds in starch that have been broken.
These starch sugars are by far the most common starch based food ingredient and are used
as sweetener in many drinks and foods. They include:
Maltodextrin, a lightly hydrolyzed (DE 1020) starch product used as a bland-tasting filler and thickener.
Various glucose syrups (DE 3070), also called corn syrups in the US, viscous solutions used as sweeteners and thickeners in many kinds of processed foods.
Dextrose (DE 100), commercial glucose, prepared by the complete hydrolysis of
starch.
High fructose syrup, made by treating dextrose solutions with the enzyme glucose
isomerase, until a substantial fraction of the glucose has been converted to fructose.
In the United States sugar prices are two to three times higher than in the rest of the
world,[25]
which makes high fructose corn syrup significantly cheaper, so that it is
the principal sweetener used in processed foods and beverages.[26]
Fructose also has
better microbiological stability. One kind of high fructose corn syrup, HFCS-55, is
sweeter than sucrose because it is made with more fructose, while the sweetness of
HFCS-42 is on par with sucrose.[27][28]
Sugar alcohols, such as maltitol, erythritol, sorbitol, mannitol and hydrogenated
starch hydrolysate, are sweeteners made by reducing sugars.
Modified starches
A modified starch is a starch that has been chemically modified to allow the starch to
function properly under conditions frequently encountered during processing or storage,
such as high heat, high shear, low pH, freeze/thaw and cooling.
The modified food starches are E coded according to the International Numbering System
for Food Additives (INS):[29]
1400 Dextrin
1401 Acid-treated starch
1402 Alkaline-treated starch
1403 Bleached starch
1404 Oxidized starch
1405 Starches, enzyme-treated
1410 Monostarch phosphate
1412 Distarch phosphate
1413 Phosphated distarch phosphate
1414 Acetylated distarch phosphate
1420 Starch acetate
1422 Acetylated distarch adipate
1440 Hydroxypropyl starch
1442 Hydroxypropyl distarch phosphate
1443 Hydroxypropyl distarch glycerol
1450 Starch sodium octenyl succinate
1451 Acetylated oxidized starch
INS 1400, 1401, 1402, 1403 and 1405 are in the EU food ingredients without an E-number.
Typical modified starches for technical applications are cationic starches, hydroxyethyl
starch and carboxymethylated starches.
Use as food additive
As an additive for food processing, food starches are typically used as thickeners and
stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad
dressings, and to make noodles and pastas.
Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in
the conventional sense. A tray is filled with native starch and leveled. A positive mold is
then pressed into the starch leaving an impression of 1,000 or so jelly beans. The jelly mix
is then poured into the impressions and put into a stove to set. This method greatly reduces
the number of molds that must be manufactured.
Resistant starch is starch that escapes digestion in the small intestine of healthy individuals.
High amylose starch from corn has a higher gelatinization temperature than other types of
starch and retains its resistant starch content through baking, mild extrusion and other food
processing techniques. It is used as an insoluble dietary fiber in processed foods such as
bread, pasta, cookies, crackers, pretzels and other low moisture foods. It is also utilized as a
dietary supplement for its health benefits. Published studies have shown that Type 2
resistant corn helps to improve insulin sensitivity,[30]
increases satiety[31]
and improves
markers of colonic function.[32]
It has been suggested that resistant starch contributes to the
health benefits of intact whole grains.[33]
In the pharmaceutical industry, starch is also used as an excipient, as tablet disintegrant or
as binder.
Industrial applications
Starch adhesive
Papermaking
Papermaking is the largest non-food application for starches globally, consuming millions
of metric tons annually.[8]
In a typical sheet of copy paper for instance, the starch content
may be as high as 8%. Both chemically modified and unmodified starches are used in
papermaking. In the wet part of the papermaking process, generally called the "wet-end",
the starches used are cationic and have a positive charge bound to the starch polymer.
These starch derivatives associate with the anionic or negatively charged paper fibers /
cellulose and inorganic fillers. Cationic starches together with other retention and internal
sizing agents help to give the necessary strength properties to the paper web formed in the
papermaking process (wet strength), and to provide strength to the final paper sheet (dry
strength).
In the dry end of the papermaking process, the paper web is rewetted with a starch based
solution. The process is called surface sizing. Starches used have been chemically, or
enzymatically depolymerized at the paper mill or by the starch industry (oxidized starch).
The size - starch solutions are applied to the paper web by means of various mechanical
presses (size presses). Together with surface sizing agents the surface starches impart
additional strength to the paper web and additionally provide water hold out or "size" for
superior printing properties. Starch is also used in paper coatings as one of the binders for
the coating formulations which include a mixture of pigments, binders and thickeners.
Coated paper has improved smoothness, hardness, whiteness and gloss and thus improves
printing characteristics.
Corrugated board adhesives
Corrugated board adhesives are the next largest application of non-food starches globally.
Starch glues are mostly based on unmodified native starches, plus some additive such as
borax and caustic soda. Part of the starch is gelatinized to carry the slurry of uncooked
starches and prevent sedimentation. This opaque glue is called a SteinHall adhesive. The
glue is applied on tips of the fluting. The fluted paper is pressed to paper called liner. This
is then dried under high heat, which causes the rest of the uncooked starch in glue to
swell/gelatinize. This gelatinizing makes the glue a fast and strong adhesive for corrugated
board production.
Clothing starch
Clothing or laundry starch is a liquid that is prepared by mixing a vegetable starch in water
(earlier preparations also had to be boiled), and is used in the laundering of clothes. Starch
was widely used in Europe in the 16th and 17th centuries to stiffen the wide collars and
ruffs of fine linen which surrounded the necks of the well-to-do. During the 19th century
and early 20th century, it was stylish to stiffen the collars and sleeves of men's shirts and
the ruffles of girls' petticoats by applying starch to them as the clean clothes were being
ironed. Aside from the smooth, crisp edges it gave to clothing, it served practical purposes
as well. Dirt and sweat from a person's neck and wrists would stick to the starch rather than
to the fibers of the clothing, and would easily wash away along with the starch. After each
laundering, the starch would be reapplied. Today, the product is sold in aerosol cans for
home use.
Other
Another large non-food starch application is in the construction industry, where starch is
used in the gypsum wall board manufacturing process. Chemically modified or unmodified
starches are added to the stucco containing primarily gypsum. Top and bottom heavyweight
sheets of paper are applied to the formulation, and the process is allowed to heat and cure to
form the eventual rigid wall board. The starches act as a glue for the cured gypsum rock
with the paper covering, and also provide rigidity to the board.
Starch is used in the manufacture of various adhesives or glues[34]
for book-binding,
wallpaper adhesives, paper sack production, tube winding, gummed paper, envelope
adhesives, school glues and bottle labeling. Starch derivatives, such as yellow dextrins, can
be modified by addition of some chemicals to form a hard glue for paper work; some of
those forms use borax or soda ash, which are mixed with the starch solution at 5070 C to create a very good adhesive. Sodium silicate can be added to reinforce these formulae.
Textile chemicals from starch: warp sizing agents are used to reduce breaking of
yarns during weaving. Starch is mainly used to size cotton based yarns. Modified
starch is also used as textile printing thickener.
In oil exploration, starch is used to adjust the viscosity of drilling fluid, which is
used to lubricate the drill head and suspend the grinding residue in petroleum
extraction.
Starch is also used to make some packing peanuts, and some drop ceiling tiles.
In the printing industry, food grade starch[35]
is used in the manufact