1/30/20131DR. JOSIE COVERDALEANSC/NUTR 303CarbohydratesCarbohydrate Digestion & Absorption Are all carbohydrates the same? Size Composition  Bonding Goals of digestion? Enzymatic Fermentation Method of absorption? Dependent on end product of digestion Location Use of carbohydrates in the animal body?1/30/20132Carbohydrates (CHO) C:H:O (1:2:1) Glucose C6H12O6 Sources Sugars Starch Cellulose Gums Primarily from plant sourcesComponents of Feed CHOSoluble sugars and pectinCelluloseHemicelluloseLigninNon-Structural Carbohydrate (NSC)StructuralCarbohydratePotentiallydegradedIndigestible1/30/20133Classification Number of sugar molecules Monosaccharide – 1 sugar unit Disaccharide – 2 Oligosaccharide – 3 - 10 Polysaccharide - >10 Most plants contain different types of carbohydratesMonosaccharides - Isomerism Compounds with same structural formula but different spatial configurations D/L D is natural form racemic α/β1/30/20134Monosaccharides (CnH2nOn) Classified by the number of carbon atoms: 3C Triose 4C Tetrose 5C Pentose 6C HexoseNutritional importanceSugars that contain 4 or more carbons exist primarily in cyclic formMonosaccharides Hexoses (6C) Glucose Component of starch, cellulose, glycogen End product of CHO digestion  monogastrics Primary form of sugar used for energyGlucose, fructose, and galactose are among the most important monosaccharides in living organisms.1/30/20135Monosaccharides Hexoses cont. Fructose 75% of sugars in honey fruits and cane sugar Galactose component of milk sugar (lactose) metabolized to glucose Mannose found in hydrolysis of plant mannosans and gums; legumesDisaccharides 2 monosaccharide molecules linked by a glycosidic (acetal) bond Lactose (glucose + galactose) Β 1-4 linkage milk sugar found only in milk Sucrose (glucose + fructose) α 1-2 bond Common table sugar Produced in leaves and stems of plants Found in sugar cane and sugar beets1/30/20136Disaccharides Maltose (glucose + glucose) Intermediate product of starch hydrolysis α 1-4 linkage fundamental for starch found in starch from the malting of barley Isomaltose similar but with α 1-6 bond Cellobiose (glucose + glucose) Beta 1-4 linkage fundamental for cellulose Does not exist freely in natureDue to differences in bond type these are not digested the same way!PolysaccharidesHomopolysaccharides One type of monosaccharide unit Starch basic unit: alpha-D-glucoseprincipal sugar form in cereals and animal storage3 Forms Amylose Amylopectin Glycogen1/30/20137Starch Three forms of starch:1. Amylose alpha 1-4 linkages of glucose straight chain 14-30% of total plant starchStarch2. Amylopectin alpha 1-4 linkages with alpha 1-6 linkage at branch points 70-85% total plant starch 3. Glycogen animal starch small amounts in liver and muscle highly branched1/30/20138Polysaccharides Homopolysaccharides cont. Cellulose (beta linkage) basic unit: beta-D-glucose straight chain, beta 1-4 linkage highly stable 25-30% of fibrous plants cotton is the purest form most abundant CHO in naturePolysaccharidesHeteropolysaccharides Contains more than one type of sugar unit Hemicellulose complex mixture of glucose, mannose, arabinose, and galactose beta 1-4 linkage principal component of plant cell wall degraded only by microbial enzymes1/30/20139Polysaccharides Heteropolysaccharides cont. Pectinpolymers of 1-4 linked glucosedegraded only by microbial enzymesfound primarily in the space between cell wallsplant glueAbundant in alternative foragesStructural Non-Carbohydrates Lignin polymers of phenylpropane units encases cellulose and hemicellulose  enhance rigidity to plant cells lignification reduces digestibility  barrier to the plant carbohydrates no animal or bacteria can break1/30/201310How is it digested?CHO Enzymatic Fermentation Both NoneCelluloseStarchLactoseLigninPectinSucroseCarbohydrate DigestionMonogastric RuminantFeed CHOGlucose in small intestineAbsorption into bloodstreamDigestive EnzymesMicrobial FermentationVFA in rumen (acetic, propionic, butyric)1/30/201311Carbohydrate DigestionThe MonogastricNon-Ruminant CHO Digestion Only monosaccharides can be absorbed Mouth Salivary α-amylase Breaks starches down to dextrins Small role in digestion Ruminants and horses do not have this enzyme Stomach No enzymatic activity for CHO digestion Low pH alters amylase activity1/30/201312Monogastric Digestion of CHO – Small Intestine Pancreatic α-amylase Brush Border Enzymes (disaccharidases)Polysaccharide DisaccharidesPancreatic α-amylaseDisaccharideMonosaccharidesspecific brush border enzymeExample: Amylopectin Maltose and IsomaltosePancreatic α-amylaseExample: Maltose Glucose and GlucoseMaltaseIsomaltose Glucose and GlucoseIsomaltasePancreatic α-amylase Produced in pancreas Secreted into duodenum via pancreatic duct Specifically hydrolyzes α 1,4 glycosidic bond β 1, 4 is resistant α 1,6 is resistant Effect of α-amylase on common dietary polysaccharides? Cellulose Starch Amylose Amylopectin1/30/201313Small Intestinal CHO Digestion Small Intestine Primary site of non-structural carbohydrate digestion1. Pancreatic α-amylase Hydrolyzes alpha 1-4 linkages Produces monosaccharides and disaccharides• Hydrolyzes starch and glycogen to maltose, isomaltose and glucose2. Brush border enzymes Created in brush border, function locally Enzymes specific for disaccharides• Types and activities are species specific•Exception is β 1-4 bond of cellobioseDigestion in Small Intestine Maltose Glucose + GlucoseMaltaseLactoseLactaseGlucose + Galactose* Poultry do not have lactase.SucroseGlucose + FructoseSucrase* Ruminants do not have sucrase.IsomaltoseIsomaltaseGlucose + Glucose1/30/201314Digestion in Large Intestine Fermentative digestion Non-structural CHO Escapes small intestine digestion Structural CHO (fiber) Microbes produce cellulase Hydrolyzes β 1-4 bonds Microbial action on fiber Volatile Fatty Acids• Acetate •Propionate•ButyrateExtent of fermentation in large intestine