Fiber

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Chapter 4

• Fiber

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Definitions of Dietary Fiber Functional Fiber

• Dietary fiber - nondigestible CHO lignin that
  are intact intrinsic in plants
• Functional fiber - nondigestible CHO that are
  isolated, extracted, or manufactured known to
  have physiological benefits

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Fiber and Plants

• gt95 of fibers from cell wall
• Primary wall
• Secondary wall
• Fiber-related components
• Cellulose
• Hemicellulose
• Lignin
• Pectins
• Suberin
• Cutin

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Chemistry Characteristics of Dietary
Functional Fibers

• Varieties
• Cellulose
• Hemicellulose
• Pectins
• Lignin
• Gums
• ?-glucans

• Fructans
• Resistant starch
• Chitin chitosan
• Polydextrose polyols
• Psyllium
• Resistant dextrins

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Cellulose

• Dietary functional fiber
• Long, linear polymer of ? 1-4 linked glucose
  units
• Main component of plant cell walls
• Sources bran, legumes, nuts, peas, root
  vegetables, cabbage family, outer covering of
  seeds, apples

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Hemicellulose

• Dietary fiber
• Heterogenous group of polysaccharide substances
• Sugars in backbone side chains
• Xylose, mannose, galactose (backbone)
• Arabinose, glucoronic acid, galactose (side
  chains)
• Sources bran, whole grains, nuts, legumes, some
  vegetables fruits

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Pectins

• Dietary functional fiber
• Complex group of polysaccharides called
  galacturonoglycans
• Backbone galacturonic acid
• Cell wall middle lamella in plants
• Water-soluble, gel-forming
• Sources apples, strawberries, citrus

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Lignin

• Dietary functional fiber
• Highly-branched polymer composed of phenol units
  with strong bonding
• Structural components of plants - found in stems,
  seeds, bran layer
• Sources wheat, mature root vegetables, fruits
  with edible seeds

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Gums (Hydrocolloids)

• Dietary functional fibers
• Group of substances secreted at site of plant
  injury
• Tree exudates gum arabic, gum karaya, gum ghatti
• Shrub exudate gum tragacanth
• Composed of sugars derivatives
• Sources oatmeal, barley, legumes

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?-Glucans

• Dietary functinal fibers
• Homopolymers of glucopyranose units
• Water-soluble, highly fermentable
• Sources cereal brans, especially oats barley

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Fructans--Inulin, Oligofructose,
Fructooligosaccharides

• Dietary fibers
• Fructose units in chains of varying length
• Prebiotics
• Sources chicory, asparagus, onions, garlic,
  artichokes, tomatoes, bananas

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Resistant Starch

• Starch that cannot be digested by humans
• Types
• RS1 - plant cell walls
• RS2 - ungelatinized starch granules
• RS3 - retrograde starch from cooking cooling or
  extruding foods
• RS4 - chemically modified starch
• RS1 RS2 dietary fibers, RS3 RS4
  functional fibers

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Chitin Chitosan

• Chitin
• Amino-polysaccharide polymer containing ? 1-4
  linked glucose units
• Cells walls of some lower plants
• Chitosan
• Deacetylated form of chitin polysaccharide made
  of glucosamine N-acetyl glucosamine

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Polydextrose Polyols

• Polydextrose
• Polysaccharide of glucose sorbitol units that
  have been polymerized at high temperatures
  partial vacuum
• Polyols
• Polyglycitol malitol
• Found in syrups

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Psyllium

• Functional fiber
• Mucilage from husk of psyllium seeds
• Used as laxative
• Must ingest plenty of fluids

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Resistant Dextrins

• Functional fibers
• Generated by treating cornstarch with heat acid
  then with amylase
• Glucose polymers containing ? 1-4 ? 1-6
  glucosidic bonds ? 1-2 ? 1-3 bonds

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Selected Properties Physiological Effects of
Fiber

• Important properties include
• Solubility in water
• Water-holding capacity viscosity
• Adsorption or binding ability
• Degradability/fermentability

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Solubility in Water

• Classifications
• Soluble - dissolve in hot water
• Insoluble - dont dissolve in hot water
• Water-soluble some hemicelluloses, pectin, gums,
  ?-glucans
• Water-insoluble cellulose, lignin, some
  hemicelluloses, chitosan, chitin

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Solubility in Water

• Soluble
• Delay gastric emptying
• Increase transit time
• Decrease nutrient absorption

• Insoluble
• Decrease transit time
• Increase fecal bulk

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Water-Holding/Hydration Capacity Viscosity

• Ability of fiber to bind water
• Delayed (slowed) gastric emptying
• Reduced mixing of gastrointestinal contents with
  digestive enzymes
• Reduced enzyme function
• Decreased nutrient diffusion rate--attenuation of
  the blood glucose response
• Altered small intestine transit time

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Adsorption or Binding Ability

• Diminished absorption of lipids
• Increased fecal bile acid excretion
• Lowered serum cholesterol concentrations
  (hypocholesterolemic properties)
• Altered mineral carotenoid absorption

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Degradability/Fermentability

• Fermentable fibers
• Fermentable fibers as prebiotics
• Short-chain fatty acid generation
• Increased water sodium absorption in the colon
• Mucosal cell proliferation
• Provision of energy
• Acidification of luminal environment

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Degradability/Fermentability

• Nonfermentable fibers
• Detoxification
• Increased fecal volume (bulk)

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Roles of Fiber in Disease Prevention Management

• Hypoglycemic hypolipidemic effects of soluble
  fibers
• For diabetes high serum cholesterol
• Insoluble, nonfermentable fibers for GI diseases
• Diverticular disease, gallstones, IBS,
  constipation
• Health claims for fiber

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Roles of Fiber in Disease Prevention Management

• Mechanisms
• Adsorb bile acids, promote excretion
• Increase fecal bulk
• Provide fermentable substrates for bacteria in
  colon
• Shortened fecal transit time
• Decreases interluminal pH
• Fermentation may release fiber-bound calcium
• Butyric acid appears to hinder cancer cells
• Insoluble fibers bind carcinogens

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Recommended Fiber Intake

• Adequate Intakes
• Adults
• 19-50 25 g for women, 38 g for men
• 51 or gt 21 g for women, 31 g for men
• Children
• 1-3 19 g 4-8 25 g
• Girls 9-18 26 g
• Boys 9-13 31 g boys 14-18 38 g

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Perspective 4

• Phytochemicals Herbal Supplements in Health
  Disease

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Phytochemicals Herbals

• Phytochemicals
• Echinacea
• Garlic
• Ginkgo biloba
• Ginseng
• Milk thistle
• St. Johns wort
• Regulation of herbal supplements