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Chapter 4

Chapter 4. Fiber. 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. Fiber and Plants.

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Chapter 4

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  1. Chapter 4 Fiber 2009 Cengage-Wadsworth

  2. 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 2009 Cengage-Wadsworth

  3. Fiber and Plants • >95% of fibers from cell wall • Primary wall • Secondary wall • Fiber-related components • Cellulose • Hemicellulose • Lignin • Pectins • Suberin • Cutin 2009 Cengage-Wadsworth

  4. Varieties: Cellulose Hemicellulose Pectins Lignin Gums -glucans Fructans Resistant starch Chitin & chitosan Polydextrose & polyols Psyllium Resistant dextrins Chemistry & Characteristics of Dietary & Functional Fibers 2009 Cengage-Wadsworth

  5. 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 2009 Cengage-Wadsworth

  6. 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 2009 Cengage-Wadsworth

  7. 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 2009 Cengage-Wadsworth

  8. 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 2009 Cengage-Wadsworth

  9. 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 2009 Cengage-Wadsworth

  10. -Glucans • Dietary & functinal fibers • Homopolymers of glucopyranose units • Water-soluble, highly fermentable • Sources: cereal brans, especially oats & barley 2009 Cengage-Wadsworth

  11. Fructans--Inulin, Oligofructose, & Fructooligosaccharides • Dietary fibers • Fructose units in chains of varying length • Prebiotics • Sources: chicory, asparagus, onions, garlic, artichokes, tomatoes, bananas 2009 Cengage-Wadsworth

  12. 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 2009 Cengage-Wadsworth

  13. 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 2009 Cengage-Wadsworth

  14. Polydextrose & Polyols • Polydextrose • Polysaccharide of glucose & sorbitol units that have been polymerized at high temperatures & partial vacuum • Polyols • Polyglycitol & malitol • Found in syrups 2009 Cengage-Wadsworth

  15. Psyllium • Functional fiber • Mucilage from husk of psyllium seeds • Used as laxative • Must ingest plenty of fluids 2009 Cengage-Wadsworth

  16. 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 2009 Cengage-Wadsworth

  17. Selected Properties & Physiological Effects of Fiber • Important properties include: • Solubility in water • Water-holding capacity & viscosity • Adsorption or binding ability • Degradability/fermentability 2009 Cengage-Wadsworth

  18. Solubility in Water • Classifications: • Soluble - dissolve in hot water • Insoluble - don’t dissolve in hot water • Water-soluble: some hemicelluloses, pectin, gums, -glucans • Water-insoluble: cellulose, lignin, some hemicelluloses, chitosan, chitin 2009 Cengage-Wadsworth

  19. Soluble Delay gastric emptying Increase transit time Decrease nutrient absorption Insoluble Decrease transit time Increase fecal bulk Solubility in Water 2009 Cengage-Wadsworth

  20. 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 2009 Cengage-Wadsworth

  21. Adsorption or Binding Ability • Diminished absorption of lipids • Increased fecal bile acid excretion • Lowered serum cholesterol concentrations (hypocholesterolemic properties) • Altered mineral & carotenoid absorption 2009 Cengage-Wadsworth

  22. 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 2009 Cengage-Wadsworth

  23. Degradability/Fermentability • Nonfermentable fibers • Detoxification • Increased fecal volume (bulk) 2009 Cengage-Wadsworth

  24. 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 2009 Cengage-Wadsworth

  25. 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 2009 Cengage-Wadsworth

  26. Recommended Fiber Intake • Adequate Intakes • Adults: • 19-50: 25 g for women, 38 g for men • 51 or >: 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 2009 Cengage-Wadsworth

  27. Perspective 4 Phytochemicals & Herbal Supplements in Health & Disease 2009 Cengage-Wadsworth

  28. Phytochemicals & Herbals • Phytochemicals • Echinacea • Garlic • Ginkgo biloba • Ginseng • Milk thistle • St. John’s wort • Regulation of herbal supplements 2009 Cengage-Wadsworth

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