 2009 Cengage-Wadsworth 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 –RS 1 - plant cell walls –RS 2 - ungelatinized starch granules –RS 3 - retrograde starch from cooking & cooling or extruding foods –RS 4 - chemically modified starch RS 1 & RS 2 = dietary fibers, RS 3 & RS 4 = functional fibers

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

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