Beta Glucano Alfa Glucanos

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Beta glucano Diagrama que muestra la orientación y la ubicación de diferentes vínculos de los beta- glucanos. Estructura tridimensional de celulosa, un β-1, 4 glucano. Los β-Glucanos (beta-glucanos) son polisacáridos de monómeros D-glucosa ligados con enlaces glucosídicos. Los beta-glucanos son un grupo muy diverso de moléculas que pueden variar en relación a su masa molecular, solubilidad, viscosidad, y configuración 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 útiles en la nutrición humana como agentes de textura y como suplementos de fibra soluble, pero pueden ser problemáticos en el proceso de elaboración 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 biológica que sus homólogos beta-glucanos solubles (1,3 / 1,4). 1 Las diferencias entre los enlaces de beta-glucano y su estructura química, en relación a la solubilidad, el modo de acción, y la actividad biológica en general son muy importantes. Índice 1 Información general 2 Química de los Beta-glucanos 3 Fuentes de Beta-glucano en la naturaleza 4 Beta-glucano y el sistema inmunitario 5 Aplicaciones clínicas o 5.1 Cáncer o 5.2 Prevención de la infección o 5.3 La exposición a radiación o 5.4 El choque séptico

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Transcript of Beta Glucano Alfa Glucanos

  • 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

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    38. Cramer, DE; Allendorf DJ, Baran JT, Hansen R, Marroquin J, Li B, Ratajczak J, Ratajczak MZ, Yan J (15-01-2006). Beta-glucan enhances complement-mediated

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    46. Kirmaz, C; Bayrak P, Yilmaz O, Yuksel H. (June 2005). Effects of glucan treatment on the Th1/Th2 balance in patients with allergic rhinitis: a double-blind

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    evaluation of the (13)-D-glucan assay as an aid to diagnosis of fungal infections in humans. Clin Infect Dis 41: pp. 654659. doi:10.1086/432470.

    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

    10. Matthews, C. E.; K. E. Van Holde; K. G. Ahern (1999) Biochemistry. 3rd edition. Benjamin Cummings. ISBN 0-8053-3066-6

    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.

    External links

    Wikimedia Commons has media related to Carbohydrates.

    Carbohydrates, including interactive models and animations (Requires MDL

    Chime)

    IUPAC-IUBMB Joint Commission on Biochemical Nomenclature (JCBN):

    Carbohydrate Nomenclature

    Carbohydrates detailed

    Carbohydrates and Glycosylation The Virtual Library of Biochemistry and Cell Biology

    Functional Glycomics Gateway, a collaboration between the Consortium for

    Functional Glycomics and Nature Publishing Group

    Carbohydrate: Biochemistry Course

    [show]

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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