Chapter 4 Fiber 2009 Cengage-Wadsworth

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

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

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

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

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

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

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

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

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

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

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

Chitin & Chitosan Chitin Chitosan 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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