Am J Clin Nutr-1979-Saunders-1188-91

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Relationships       among crude fiber, neutral
detergent     fiber, in vitro dietary fiber, and                                                                                                                           in vivo
(rats) dietary     fiber in wheat foods1’2
R.     M.    Saunders,3                 Ph.D.,            and    E.     Hautala,4              B.S.

                           ABSTRACT                    The in vivo dietary              fiber contents          of wheat          milling        fractions        and wheat             foods,

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                           determined           in rat feeding      experiments,          were compared             with dietary              fiber      values      determined             in
                           vitro     with pronase            a-amylase       digestion.       Both      types of dietary               fiber      values      were compared                  with
                           crude      fiber and neutral           detergent      fiber values         in same
                                                                                                            the   materials.          Regression      analyses       indicated
                           close correlation            amongst       all values     determined.           It appears
                                                                                                                  that     laboratory           analysis        for crude        fiber,
                           neutral       detergent        fiber, or in vitro dietary             fiber accurately             predicts       in vivo dietary              fiber (rats)         for
                           wheat     milling      fractions      when the laboratory             result is adjustedy means
                                                                                                                     b                  of an appropriate               regression
                           equation.             Am. I. Clin.       Nuir. 32: 1188-1191,            1979.

     The        possible            health-related                    role       of dietary this laboratory,              and     by a modified       neutral
fiber5      (or       total          indigestible               residue)          food-
                                                                                     of        detergent     fiber       technique.      These  values        are
stuffs      has       been          reviewed              extensively               in recent compared       with crude           fiber and in vivo values
years       (1-4).         One        difficulty             in the          dietary     fiber determined       earlier.
question             is the         validity          its
                                                      of measurement                     in
different            foodstuffs,              by in vivo,      in vitro, Materials
                                                                         or                                           and           methods
chemical             techniques.              Goering    and Van Soest
                                                                              The     wheat                             milling         products,’           wheat      breads   and break-
(5) and   Southgate                        (6) have   published proce-   fast     foods,                            and       the      in vivo          procedure          to measure     total
dures   to measure                             “neutral          detergent               fiber” indigestible         residue          (dietary          fiber)        been described
and       “unavailable         carbohydrate,”                                         respec- earlier   (9). Pronase                and      crystalline           procine     pancreatic
tively,     whereas     Hellendoorn           et                             al. (7) havea-amylase            were purchased        from Sigma,        St. Louis,     Mo.
described       an enzymatic       procedure                                   to measure Crude         fiber      was  measured       by    AOAC      procedure       (10).
                                                                                              Neutral     detergent fiber     (NDF)      values   were     determined
“indigestible                 residue”.               Each         of            proce-
                                                                             these            for wheat       milling  fractions    by the method         that includes
dures        provides        a number                is
                                             that assumed     to
be an approximate                  measure       of dietary   fiber, ‘From       the Western       Regional         Research     Center,Sci-
and such           numbers         are widely       quoted   in the ence and Education         Administration,           United      States     De-
                                                                    partment   of Agriculture,       Berkeley,       California      94710.
literature.        With       one exception,        to our knowl-
                                                                        ‘Parts  of this work    were     presented         at Annual         Meet-
edge,       these     values     have not been interrelated         ings of the American       Association         of Cereal      Chemists,
to one another,                to in vivo measurements              of
                                                                    1976 and   1977.
dietary          fiber,       nor       systematically                  to chemically                  3Research        Leader,          Cereals       Research         Unit.
determined           crude        fiber-the          figure     that     ap- Research                Chemist,           Nutrient           and       Chemical            Analysis
pears    in food         tables       (8). The exception              con- ‘The term dietary                         fiber implies          the total         indigestible
sists of an earlier             report      from this laboratory fraction                 of the foodstuff,                  and includes               indigestible          solu-
where      crude      fiber was closely             correlated       with ble and insoluble polysaccharides,                                 lignin, and unavaila-
in vivo dietary            fiber in wheat            products,       mea- ble protein,           fat, starch,           and       micronutrients.
                                                                                 ‘When          wheat          is milled            into        flour,      the     residue         left
sured     in rats (9).
                                                                           after      flour       removal           is termed              millrun.           In commercial
    In this        paper       values        are determined               for
                                                                            practice,       millrun       is sually
                                                                                                           u              further        classified into subfrac-
dietary      fiber     in wheat-based          materials       by an tions: germ, bran (larger particles),                                         shorts      (intermediate
in vitro        enzymatic        procedure          developed          in particles),         and      red dog           (fines).

1188                                     The     American         Journal        of Clinical          Nutrition 32: JUNE        1979,     pp.      1188-1191. Printed           in   U.S.A.
                                                                           DIETARY                      FIBER              IN        WHEAT                         FOODS                                                                        1189

TABLE      I
Crude fiber, neutral                             detergent         fiber,     and       dietary          fiber        measured                   by         in     vivo           and        in    vitro
techniques   in wheat                            milling           fractions”

                                                                                                                                                         Dietary          fiber
                    Material                                                      NDF                                                                                                                                   Crude         fiber
                                                                                                                                          In vitro                                            In vivo


Bran                                                                    49.66 (0.64)’                                        52.41             (0.77)’                                       52.7’                            12.2’
Shorts                                                                  41.97 (1.00)’                                        47.16             (0.76)’                                       41.2’                             9.8’
Germ                                                                    26.47 (0.54)’<                                       32.36            (1.38y’                                        23.9’                             5.8’
Red dog                                                                 19.33 (0.36)’                                        24.50             (0.45)”                                        18.8’                            4.6’
Flour                                                                      1.84     (0.06)”                                    3.88            (0.14)”                                         2.1’                            0.6’
AACC          bran’                                                     45.42       (0.41)’                                  43.85             (0.39)’                                       46.7’                            10.0’

    “All        figures        on    moisture-free          basis.    SD     of   sample                                                                     is    in               6 Average
                                                                                                                                                                           parentheses.         value                                     for          six
determinations.             ‘Average       value     for two determinations.      d Average                                                                    value     for three determinations.                                    e   Single
determination.             ‘<Average     value     for five determinations.     ‘Certified                                                                    food-grade         wheat    bran. American                                     Associa-
tion of Cereal          Chemists,     St. Paul,       Minn.

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TABLE               2
Crude       fiber       and            dietary             fiber      measured            by      in vivo            and        in vitro                techniques                      in   wheat         breads     and
breakfast           foods”
                                                                                                                                Dietary         fiber
                               Wheat       food                                                                                                                                                                     Crude      fiber<
                                                                                                         In vitro’                                                         In vivo

Breads                                                                                                       %
   White      1                                                                                    5.98  (0.57)                                                              1.73                                               0.60
   White     2                                                                                     6.62  (0.13)                                                             4.40                                                0.40
   White/germ                                                                                      5.84 (0.10)                                                              2.29                                                0.74
   Mixed     grains                                                                                6.57 (0.14)                                                              3.00                                                 1.06
   Whole      wheat                1                                                              10.46 (0.16)                                                              7.78”
   Whole      wheat                2                                                              11.83 (0.06)                                                              7.78                                                1.47
   Whole      wheat                3                                                              12.14 (0.47)                                                              9.27                                                2.45
   Whole      wheat                4                                                              12.85 (0.27)                                                              7.77                                                2.34

Breakfast       food
    Wheat-processed                                                                               11.79          (0.21)                                                     8.80                                                 1.85
    Wheat-natural                                                                                  9.37          (0.26)’                                                   4.35                                                 1.17
    Bran                                                                                          33.64          (0.43)’                                                  37.90                                                 8.62

     “All     figures             on       moisture-free                   basis.         SD       of     sample            is in parentheses.                      “Average                      value      from     three        determina-
tions.           ‘Single                determination.                   “Average              value        for two          determinations.                          ‘Average                     value     for six determinations.

adding       a-amylase            (11).        We      foundthe earlier           NDF        was gently          stirred      overnight          at room     temperature.          The
method       (5), which         does not contain           amylase, unsatisfac-              mixture        was centrifuged              at 2000 x g for 5 mm and the
tory    for wheat        milling         fractions        containing          large     quan-supernatant         was removed             by aspiration.        The solids were
tities   of starch,       and both        NDF        methods,         either     with or twice           suspended          in water          (40 ml), mixed,         centrifuged,
without      a-amylase,          unsatisfactory             breads
                                                            for         and break-           and      aspirated.         The      final solids     remaining      were      dried
fast foods.                                                                                  overnight        at 100 C and weighed.                The residue     corresponds
      A procedure          using        pronase         (a fungal         protease)        and the in vitro
                                                                                             to                        dietary      fiber.
porcine     pancreas        a-amylase        was used to measure               in vitro
dietary      fiber.     Earlier,          this     method         had      been      used       to
measure          protein       digestibility           (12)       but      was     modified
                                                                                                                           Results                      and         discussion
herein       by addition         of an ether extraction                    to remove       the
bulk      of the fat, as follows:            Air-dried        substrate         (about      I     The in vitro       procedure       to measure          dietary
g sampled          by quartering)           was stirred          in ether (40 ml) for         fiber described         here is considerably             easier     to
 15 mm then allowed                 to settle        for 10 mm.              Most of the      operate    than the in vitro procedure                 described
ether      was removed             by aspiration,              then       the last tracesby Hellendoorn                et al. (7). Only water             is used
were removed               by air-drying.          Water        (10 ml) added  was
and the mixture               was heated           at 70 C for 10 mm. After
                                                                                              as a solvent,        no     buffers     are    required,          and
cooIin,        125 units of a-amylase                 and 30 ml of water were
added,          and      the    mixture was        gently         stirred      at room            7One  unit  is defined       as the amount       of a-amylase
temperature           for 2 hr.Pronase           (5 mg) in I ml of water                      required to liberate      I mg of maltose     from starch        in 10
and     two     drops       of toluene        were       added, nd
                                                              a         the mixture                       C.
                                                                                              mm at 37#{176}
1190                                                                  SAUNDERS                AND        HAUTALA

TABLE         3
Linear    regression      equations     and correlation coefficients                         for relationships                among    in vivo    dietary
fiber (rats),     in vitro dietary     fiber, modified        neutral                        detergent     fiber            value,  and crude
fiber in materials        derived   from wheat

                                 .                                                                                                        .                    Correlation
                          Expenmental        values                                                            Regression      equation

Wheat    milling   fractions
  ln vivo dietary       fiber (y) versus crude         fiber                                               y   -    4.48x      -       1.19                       0.996
  ln vivo dietary     fiber(y)      versus in vitro dietary                                                y   -     1.05w         -   4.76                       0.976
  fiber (w)
  In vivo dietary fiber        (y) versus    NDF    (z)                                                    y   -     1.05z     -       1.29                       0.996
  NDF     (z) versus     crude     fiber (x)                                                               z         4.26x     +       0.26                       0.995

Wheat    foods
  In vivo dietary               fiber     (y) versuscrude             fiber                                y   -    4.36x      -       0.19                       0.989
  In vivo dietary              fiber(y)         versus     in vitro      dietary                           y   -     1.28w         -   6.15                       0.991
  fiber (w)

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when        compared                    in this          laboratoryto pepsin- fractions               a reasonably                 accurate        assessment            of
type      in      vitro         procedures,                   gave                   in
                                                                                    re- vivo
                                                                              analogous              dietary          fiber       can be predicted                  from
sults. Like the Hellendoorn                          method         the draw- analyses                 for crude               fiber,      NDF,         or in vitro
back       is that        undigested              water-soluble                poly-indigestible              residue;          and, for wheat              foods,       in
saccharides             are       lost      in the rocedure.
                                                     p                        In vivo dietary                 fiber can be predicted                   by analysis
wheat        products          where         these      polysaccharides              for crude         fiber or in vitro indigestible                         residue.
occur       in only small              quantities,          the loss is not          We should              not expect             such predictability                  for
serious.         However,               if these polysaccharides                     some        wheat-based                  foods       in which           wheat         is
were      present         in large          quantities          the method the minor                     component.                 Ultimately,          of course,
would         be unsuitable                 for measuring dietary                    it remains           to be established                 if in vivo dietary
fiber.     This error            in part could              be correctable fiber values                       determined              for the rat are appli-
by dialyzing           the enzymatic               digests      rather        than cable        to humans.              Not until then can one look
removing           them        by aspiration.               However,             thisat values             determined                 by these           laboratory
would         not correct              for any          oligosaccharides             techniques            and recommend                     with certainty                a
dialyzable          but not digestible.                                              dietary       fiber value              for wheat         foods       in human
     Values       determined              for modified             NDF          and nutrition.                                                                    C!
in vitro        dietary        fiber      in wheat           millingmate-
rials     are listed         in Table             1, where           they        are References
compared            with earlier             values       reported         for in
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vivo     (rats)       dietary         fiber      and      crude        fiber.        In human
                                                                                                       nutrition.        Crit. Rev.Food      Sci. Nutr.        7: 39,
vivo and in vitro dietary                      fiber, and crude               fiber        1975.
for wheat-based                   breads        and breakfast               foods 2. DowNING,               D. L. The role of fiber in the diet. New
are listed         in Table            2. The calculated                  regres-         York     State       Agricultural         Expt.   Station.     Special       Re-
sion      equations             and       correlation            coefficients             port no. 21, 1976.
                                                                                                    3.   EASTWOOD,         M. A. The role of vegetable                  dietary       fiber
interrelating                 these        different              values            for     wheat        in human         nutrition,        Med. Hypoth.            1: 46, 1975.
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in Table     3.                                                                                          food. Baker’s          Digest 49: 34, 1975.
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                                                                                                         Analyses.       Agricultural          Handbook          no. 379. Washing-
highly          significant.                These             data,     for limited
                                                                                                         ton, D.C.: United             States     Department          of Agriculture,
number             of wheat-derived                           materials        establish                  1970.
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                                                                 7.                                      HELLENDOORN,             E. W., M. G. NORDHOFF                     AND      J.
vivo with rats. Though it is advisable           to carry
                                                                                                         SLAGMAN.         Enzymatic          determination           of indigestible
out     further      exhaustive      analyses     on      other                                          residue      (dietary       fiber)     content       of human               J.
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                                                    DIETARY               FIBER            IN   WHEAT FOODS                                                         1191

 8. Composition        of Foods.            Agriculture         Handbook          no. 8.      Chemists,          1975.
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