TABLE 9-2
Composition and Properties of Dietary Fiber with Respect to Human Nutrition
Type of Dietary Fiber
and Food Sources
Chemical Composition
Properties
Cellulose
Whole-wheat flour, Bran, Cabbage family, Dried
peas/beans, Apples, Root vegetables
Polymer of glucose with /3(1—>4) linkages.
Not digested in the small intestine; a significant
amount is digested by the bacterial flora of the
large intestine.
Hemicellulose
Bran, Cereals, Whole grains
Heterogeneous group of polysaccharides; the major
group consists of pentose polymers (pentosans),
xylans, and arabinosylans; the second group con-
sists of hexose polymers, galactans, and mannans; and
the third group consists of uronic acid polymers
containing either galacturonic or glucuronic acid.
Associated with cellulose in plant tissues not
digested in the small intestine but digested by
the bacterial flora of the large intestine. Can be
extracted from cell walls by alkaline solutions.
Pectins
Apples, Citrus fruits, Strawberries
Mixture of galactouronan [a polymer of galacturonic
acid linked in /3(1—»4) linkages] and galactan and
arabinan in varying proportions depending on the
source. Carboxylate groups of the uronic acids are
either free or esterified with methyl groups.
Function as intercellular cementing material in
plant tissues. When solubilized, the product has
a characteristic gel texture (viscous and sticky
properties). Not digested in the small intestine but
digested to a small extent by the bacterial flora of
the large intestine. Pectins are extracted by acidic
solutions or solutions containing chelating agents.
Gums and Alginates
Oatmeal, Dried beans, Other legumes
Heterogeneous group of polysaccharides. Some
gums are galactomannans (e.g., guar gum).
Alginates are polymannuronic acids.
Gums form viscous solutions; alginates are used
as thickening agents and stabilizers in food. Not
digested in the small intestine but digested to varying
extents by the bacterial flora of the large intestine.
Lignins
Mature vegetables, Wheat
Nonpolysaccharide polymer found in woody plant
tissues. The nature of the monomers is not com-
pletely known, but appears to involve coniferyl
and sinapyl or related alcohols.
Totally indigestible even by ruminants.
