9/12/2014 1 Carbohydrates I: Structures • Macro Nutrients – Water – Carbohydrates – Proteins and Amino Acids – Lipids – Energy • Micronutrients – Vitamins – Minerals Carbohydrates • Plant: structural and stored energy • Animal: – energy source in diet – minor role as stored energy (glycogen) – Derived products Typically the most abundant class of nutrients in the diet. non-ruminants: starch ruminants, herbivores: starch, cellulose, other non-starch polysaccharides.9/12/2014 2 Classification Monosaccharides: glucose, fructose galactose, mannose Discaccharides: lactose, sucrose, maltose Oligosaccharides: (3-10) raffinose, stachyose maltotriose FOS, MOS, GOS Polysaccharides: (10 + ) starch, cellulose, pectins, hemicellulose Structures • Carbohydrate: hydrated carbon C n(H2O)n : Glucose = C 6(H2O)6 = C 6H12O6 • Smallest carbohydrate is 3 carbons Triose (3 C) C 3H6O3 glyceraldeyde Tetrose (4 C) C 4H8O4 erythrose pentose (5 C) C 5H10O5 ribose, xylose, arabinose Hexose (6 C) C 6H12O6 glucose, fructose, galactose Carbohydrates: Isomerism • Isomers: molecules with the same chemical formula, but different physical structure. • 5 forms (α-D-glucopyranose = reference) – Mirror image – Ring structure – Anomer – Epimer – Aldose-ketose9/12/2014 3 1. Mirror Image: D vs L Glucose 2. Ring structure: - pyran 6 member - furan 5 member Glucose most stable as Pyranose 3. Anomer: -orientation of hydroxyl on #1 carbon Glucose in solution: Pyranose forms: α = 62% (down) β = 38% (up) Furanose forms: < 0.3% Open chain < 1% Anomer: -orientation of hydroxyl on #1 carbon β anomer more abundant Anomer and ring structure variation with fructose Fructose: most stable as furanose9/12/2014 4 4. Epimer: - orientation of hydroxyl on carbon # 2, 3, or 4 Stereoisomerism: Depends on presence of chiral centers. Glucose has 4. 5. Aldose (#1 C is aldehyde, glucose) and Ketose (#2 C is ketone, fructose) Disaccharides • Maltose = glucose + glucose – Linked α 1→4 – Digested by Maltase – Continued linkage in this way produces starch – Isomaltose = glucose + glucose (α 1→6) • Cellobiose = glucose + glucose – Linked β 1→4 – Not digested by animals – Continued linkage produces cellulose9/12/2014 5 Disaccharides • Sucrose = glucose + fructose – Linked α 1→2 – Digested by sucrase – Table sugar, fruits • Lactose = galactose + glucose – Linked β 1→4 – digested by lactase – Difference between lactose and cellobiose is #4 position on galactose. Nutritionally Important Disaccharides Cellobiose = glucose + glucose β1→4 Lactose = galactose + glucose Oligosaccharides • 3-10 monosaccharides • Prebiotics • Anti-nutritional • Intermediates in polysaccharide digestion9/12/2014 6 Oligosaccharides • Prebiotics: – Prebiotics are defined as non-digestible food ingredients that may beneficially affect the host by selectively stimulating the growth and/or the activity of a limited number of bacteria in the colon. – Compounds that favor the growth on non-pathogens in the gut – May substitute for antibiotics – Examples: • FOS = fructo-oligosaccharides • MOS = mannan-oligosaccharides • GOS = galacto-oligosaccharides Oligosaccharides • Anti-nutritional – Oligosaccharides (particularly in soybean meal) may decrease digestibility of other nutrients in the diet – Raffinose: galactose-glucose-fructose – Stachyose: gal-gal-glu-fru – 5-10% of the weight of soybean meal – Function in the seed is to hold water (hygroscopic) Sucrose Raffinose Stachyose α 1→ 6 galactose to glucose9/12/2014 7 Oligosaccharides and Soybean meal Crude Protein Crude Fiber Fat ME, kcal/kg Poultry ME, kcal/kg Swine Soybean meal Corn Isolated soy protein 49 8 84 3.9 2.2 0.2 1.0 3.9 0.2 2440 3350 3500 3380 3420 3500 Differences in energy value in poultry vs swine are due to oligosaccharides Solutions: ethanol extraction enzyme treatment Oligosaccharide Content of Legumes (mg/g DM) Raffinose Ciceritol Stachyose Verbascose Total Soybeans 60 - 35 - 95 Lentils 29 39 39 4 96 Chickpeas 50 68 27 - 145 Green Peas 30 - 35 15 80 Raffinose = Gal-Glu-Fru Ciceritol = Gal-Gal-Inositol Stachyose = Gal-Gal-Glu-Fru Verbascose = Gal=Gal-Gal-Glu-Fru Polysaccharides: • Digestible carbohydrates vs fiber (sugars + starch) vs other • Starch vs non-starch polysaccharides (NSP) • Homo-polyglycans vs hetero-polyglycans9/12/2014 8 Polysaccharides: Starch Amylose = α 1→4 linked glucose - water soluble Amylopectin = α 1→4, α 1→6 linked glucose - not soluble Glycogen found in animal liver and muscle is structurally similar to amylopectin Source Starch GranuleDiameter, micronsAmylose %Amylopectin%Corn, normal Waxy High Amylose12-25 28170729930Rice 3-8 22 78Wheat small - 10large - 3526 74Potato 100 20 80Starch Characterization in Selected Plants9/12/2014 9 Homopolysaccharides: • Starch • Cellulose • 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 nature • Beta-glucans: – Found in barley and oats, less in rye and wheat – Consist of β1→4/ β1→3(soluble), and β1→3 /β1→6 (insoluble) Heteropolysaccharides (contains more than one type of sugar unit) • Hemicellulose • complex mixture of glucose, mannose, arabinose, and galactose • β1-4 linkage • principal component of plant cell wall degraded only by microbial enzymes • Insoluble in water, soluble in dilute base and degraded by dilute acid • Pectin • polymers of 1-4 linked glucose, galacturonic and uronic acids • degraded only by microbial enzymes • found primarily in the space between cell walls • Arabinoxylans • β 1-4 linked arabinose and xylose9/12/2014 10 Dietary Fiber Chemical composition Colonic function Nutritional / clinical effects Cellulose Homopolyglycan β (1→4) glucose Nondigestive, partially fermentable, imbibes water, laxative Dilution of colonic excretory metabolites, prevents diverticulitis Hemicellulose Heteropolyglycan (250 known polymers) β1→4 xyloside backbone, arabinose, glucuronic acid side chains Partially fermentable, imbibes water, laxative Dilution of colonic excretory metabolites, prevents diverticulitis Pectins Heteropolyglycan, β1→4 linkage of galacturonic