《食品化学》课程教学资源（英文讲义）03 Carbohydrates part1

3/2/14carbohydratesCarbohydratesPartOneThemostabundantorganicmoleculesInitial sourceof ALLFOOD?Provide·Energy (~4Cal/g).Carbon.FiberSignificantcontributiontothepropertiesoffoodsWhereis Sugar in Food?Contributionsto FoodProperties-SweetnessNaturally found in:-Precursors ofaroma compoundsFruits, vegetables, grains, dairy products-Precursorsofcoloredcompounds-Provide textureAdded sugar found in:-CelluloseCandy, chocolate-StarchDesserts, baked goods, ice cream-PectinSoft drinks-Buildviscosityat lowconcentrationCondiments, snacksOn labels as sugar, sucrose, invert sugar,-Starchcorn syrup-Gums-Cellulosefragments

3/2/14& 1& Carbohydrates Part One Carbohydrates • The most abundant organic molecules • Initial source of ALL FOOD • Provide • Energy (~4 Cal/g) • Carbon • Fiber • Significant contribution to the properties of foods . Where is Sugar in Food? Naturally found in: Fruits, vegetables, grains, dairy products Added sugar found in: Candy, chocolate Desserts, baked goods, ice cream Soft drinks Condiments, snacks On labels as sugar, sucrose, invert sugar, corn syrup Contributions to Food Properties •Sweetness •Precursors of aroma compounds •Precursors of colored compounds •Provide texture •Cellulose •Starch •Pectin •Build viscosity at low concentration •Starch •Gums •Cellulose fragments

3/2/14Classificationsac.uPolysaccharides2carb/-Monosaccharides-Polysaccharides-Starch·Polyhydroxyaldehydes-Glucosepolymer,a-1,4-linkages,1.6branches-Polyhydroxyketones-Cellulose-Oligosaccharides-Glucosepolymer,β-1,4-linkages-Disaccharides-Pectin.Sucrose,Maltose,Lactose-Polygalacturonic acid (methyl esters)-Trisaccharides-GumsRaffinose-Carrageenans-Alginates-Tetrasaccharides-Locustbeangum-Stachyose'etc.TriosesNutritionalAvailabilitythe simplest sugars-H.6=0Readilyabsorbedandmetabolized-Glucose-FructoseHO-C-HH-C-OH-(Galactose)CH,OHCH,OH.0H.-Not Absorbed(HCOH)C-Polysaccharides (fiber)-Disaccharides (some diffusion)Glyceraldehyde(s)CH,OH-Some are hydrolyzed in the intestinal mucosaTwo possible isomersGlycoaldehyde-Prebiotic oligosaccharides (food for Probiotic bacteria)CH,OH-Fermentable oligosaccharides can lead to flatulence (gas-producingEnantiomers-c-oanaerobes)non super-imposableCH,OHmirror imagesEpimers --1,3-Dihydroxyacetonesugars that difer by configuration at one(optically inactive)carbon2

3/2/14& 2& Classifications •Monosaccharides •Polyhydroxy aldehydes •Polyhydroxy ketones •Oligosaccharides •Disaccharides •Sucrose, Maltose, Lactose •Trisaccharides •Raffinose •Tetrasaccharides •Stachyose http://www.chem.qmw.ac.uk/iupac/2carb/ Polysaccharides •Polysaccharides •Starch •Glucose polymer, α-1,4-linkages, 1,6 branches •Cellulose •Glucose polymer, β-1,4-linkages •Pectin •Polygalacturonic acid (methyl esters) •Gums •Carrageenans •Alginates •Locust bean gum •etc. Nutritional Availability •Readily absorbed and metabolized •Glucose •Fructose •(Galactose) •Not Absorbed •Polysaccharides (fiber) •Disaccharides (some diffusion) •Some are hydrolyzed in the intestinal mucosa •Prebiotic oligosaccharides (food for Probiotic bacteria) •Fermentable oligosaccharides can lead to flatulence (gas-producing anaerobes) Trioses the simplest sugars C H C H2OH O Glycoaldehyde (HCOH) C H C O C H2OH H OH C H C O C H2OH HO H Glyceraldehyde(s) Two possible isomers C H2OH C C H2OH O 1,3-Dihydroxyacetone (optically inactive) Enantiomers – non super-imposable mirror images Epimers – sugars that differ by configuration at one carbon

3/2/14AldosesTetrosesD-and L-IsomersAldoses0HHICOHH.b=0H.6=0CHOHHO-C-HH-C-OHD-(+)-glyceraldenydeH-C-OHH-C-OHCH2OHCH2OHH..0HOC-HD-(-ThreoseD-(-)-ErythroseCH2OHthe"conformationalC2EpimerL-(-)-glyceraldehydecarbon", highest-numbered asymmetric C Not an Enantiomer (complete mirror image)PentosesTetrosesAldosesKetoses-the"uloses"HH200CCH2OHCH2OHH-CH-C-OHOHHb=0H.b=0C=0C=0-OHHO-C-HH-CHO-CIHHO-CHH-C-OHHO-C-HH-C-OHH-C-OHH-COHHO-CHCH2OHCH2OHCH,OHCH,OHH-C-OHH-C-OHD-syloseCH,OHCH,OHD-glycero-tetruloseL-glycero-tetruloseD-ribose"D-erythrulose"D-arabinoseD-lyxose3

3/2/14& 3& Aldoses D- and L- Isomers D-(+)-glyceraldehyde L-(-)-glyceraldehyde C H C O C H2OH H OH C H C O C H2OH HO H the&
conforma1onal&& carbon,&highest8numbered&asymmetric&C& Tetroses Aldoses D-(-)-Threose D-(-)-Erythrose C H C O C HO H C H2OH H OH C H C O C C H2OH H OH H OH C2&Epimer &Not&an&Enan1omer&(complete&mirror&image)& Tetroses Ketoses - the
uloses D-glycero-tetrulose
D-erythrulose C H2OH C C C H2OH O H OH C H2OH C C C H2OH O HO H L-glycero-tetrulose Pentoses Aldoses D-ribose D-arabinose D-xylose D-lyxose C C C C C H2OH OH OH OH H H H H O C C C C C H2OH OH OH H H H O HO H C C C C C H2OH OH H OH H HO H H O C C C C C H2OH H H OH HO HO H H O

3/2/14PentosesHexosesKetosesAldoses-thereare8D-aldohexosesCH,OHCHOCHOCHOCHOCH,OHC-oCHOCHOCHOCHO0-0H-COHHO-C-HH-C-OHH-C-OHCH,OHCH,OHCH,OHCH,OHCH,OHCH,OHCH,OHCH,OHCH,OHCH,OH850me-(+)-0a50n6-(-)-0seeS0m6-(+)250e-(+)-098osD-ribuloseD-xylulosesouue-(+gsope-(-0e6-(+)(erythro-pentulose)40-(+)(threo-pentulose)aocHexosesbutonly 4D-ketohexoses,or hexulosesTable 2.5. Monosaccharide pricesPrice (SUS g l)Pice (SUS.gr)CH,OHCH,OHCH,OHCHOHD9L-Ooo0AldlyertoseKegycutoses0.47250430cryaro-Pentulose-68000.33threo-Pentilose1350RXylove-2.88Lyxosc一KerobexoneAldohesases189200900AllseI 1PsicostCH,OHCH,OHCH,OHCH,OHAltrose700Fructose0.05188984200.18GluconeSorbose0009(sd-(+)00e-(0MasnoscTagaoic13140Gulose.ldoseSeGlaconeoTaloxe15004

3/2/14& 4& Pentoses Ketoses D-ribulose (erythro-pentulose) D-xylulose (threo-pentulose) C H2OH C C C C H2OH OH OH H H O C H2OH C C C C H2OH H OH O HO H Hexoses Aldoses - there are 8 D-aldohexoses D-(+)-allose CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH CHO C H2OH D-(+)-mannose D-(-)-gulose D-(-)-idose D-(+)-galactose D-(+)-talose D-(+)-altrose D-(+)-glucose Hexoses but only 4 D-ketohexoses, or hexuloses C H2OH O C H2OH C H2OH O C H2OH C H2OH O C H2OH C H2OH O C H2OH D-(+)-psicose D-(-)-fructose D-sorbose Natural isomer appears to be L￾D-(-)-tagatose

3/2/14TwoCarbonyls?No Carbonyls?Oddly-placedCarbonyls?Sugar alcoholsDialdoses"-odialdose"instead of"-ose"CH,OHCH,OHCHOHCH,OHCH,OHe.g.,glucodialdoseKetoses atC2"-ulose"e.g.,xyluloseCH,OHCH,OHKetoseselsewhereCH,OHe.g.,at C3,called a 3-ketose or hexo-3-uloseCH,OHCH,OHErythritolThreitolDiketoseXyitolDiulosesSorbitolMannitolMixedketoseandaldosesymtricalaldoketoses,aldosulosesSugar AlcoholsXylitol:5 carbon sugar alcohol.?Many sugar alcohols exist naturally in nature:approximate sweetness of-especiallyplantssucrose.? anti-& non-cariogenice.g. sorbitol, mannitol, xylitol, etcproperties?notmetabolized byinsulin2:presentlyfairly expensive..Canalsobemadeartificially

3/2/14& 5& Two Carbonyls? Oddly-placed Carbonyls? Dialdoses
-odialdose instead of
-ose e.g., glucodialdose Ketoses at C2
-ulose e.g., xylulose Ketoses elsewhere e.g., at C3, called a 3-ketose or hexo-3-ulose Diketose Diuloses - Mixed ketose and aldose aldoketoses, aldosuloses No Carbonyls? Sugar alcohols Erythritol Threitol Sorbitol Mannitol Xylitol C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH C H2OH (symmetrical)& Sugar&Alcohols& • Many&sugar&alcohols&exist&naturally&in&nature& —&especially&plants& • e.g.&&sorbitol,&mannitol,&xylitol,&etc& • Can&also&be&made&ar1ficially&& Xylitol • 5&carbon&sugar&alcohol.& • approximate&sweetness&of& sucrose.& • an18&&&non8cariogenic& proper1es& • not&metabolized&by&insulin& • presently&fairly&expensive.&

3/2/14FamousreactionsXylitol-ExamplesCondensationsRRNTEWnicyanohydrinsICNOHOCmNTrident1OmCRRMutR2oenRHO-C-O-R*acetats, ketals-O=RRiminesRR09HHORC=N-R'SINRO=RHhydraaonesaD.(Shiff base)FamousreactionsSugarAcidsChain lengthening - Cyanohydrin (Kiliani-Fischer) SynthesisZ"O1-acids "onic acids", e.g-, gluconic acidZ-OOHpyranoses tend to form lactones,OHe.g..-gluconolactoneICNehydrolyze slowty -gradual acidification-OHH-HO-H6-acids'uronic acidseg. glucuronic acdH--OH-OHH-OHH-cyanide adduct1,-diacids "aric acids", e-g- glucaric acidCH,OHCH,OHCH,OH0.00OHCOOHCHOCOOHOadH20Na/Hg.0gH-OHH-OOHH-O-OHH-C-OHCHOHCHOHHO-d-HHO-d-HHO--HO-0-Hhydrolyze the nitrileH-C-OHH--OHH-C-OHH-C-OHH.OHreduction withH-OHH-OHH-0H-COHH-COHsodium amalgamCH,OHCH,OHCH,OHCH,OHCOOHCOOHerythroseolthreoseC

3/2/14& 6& Xylitol&8&Examples& Famous reactions Condensations cyanohydrins acetals, ketals imines hydrazones (Shiff base) R C R' O C N R HO C C N R' R C R' O R C R' O O R" H R HO C O R' R" N H H R" C R' N R R" R HO C N R' R" H Famous reactions Chain lengthening - Cyanohydrin (Kiliani-Fischer) Synthesis C OH C H2OH O H H C N OH C H2OH H H OH C N H OH C H2OH H HO H C N & H2O CHOH OH C H2OH H C O O Na/Hg CHOH OH C H2OH H C O H cyanide adduct hydrolyze the nitrile reduction with sodium amalgam erythrose or threose Sugar Acids 1-acids
onic acids, e.g., gluconic acid pyranoses tend to form lactones, e.g., δ-gluconolactone hydrolyze slowly - gradual acidification 6-acids
uronic acids, e.g., glucuronic acid 1,6-diacids
aric acids, e.g., glucaric acid COOH C C C C C H2OH OH HO OH OH H H H H CHO C C C C COOH OH HO OH OH H H H H C C C C C C H2OH OH HO OH H H H H O O COOH C C C C COOH OH HO OH OH H H H H

3/2/14CyclizationCyclizationhemiacetals,hemiketalsmutarotationThe carbonyl carbon that was attacked is called3.HCH.OHthe anomeric carbonHO-C-OCHthe reducing carbonCH,OHCHOHThe potentially reducing groupa and p anomers are in equlibrium (mutarotation)hemiacetaldetermined by relative stabilityIntereoversion rate determined by T, pH, etc.Intramolecular hemiacetal (or hemiketal) is stablea and p anomers are differentmp, solubility, crystal habil, etc.HOHHOHCH.OHExcellent example: lactosedHaandβanomersTble 24The pecestage comgositions of sugas in aqeousolationat eqilibeiumpCyclizationCyli ornsAcyelicfuranoses and pyranosesSugrTemperature o-Pytanose β-Pyranose α-Furanose 8-Furanosecarbonyform (%)(C)(%)(%)(%)(%)HRiose#扫列打58.53213.5Ba#菜0#3pyran0.03CH,OH150.5lyreCH,OH002062.820.416.8pdhoPratalbse二2618.162.319.6OHshrro-PentifoseHO-C-H0H二5牌135nmβ-D-fructopyranoseH-C-OHaanH-C-OHHO-CHOnGlaoose0.6Mastose64.934.20.005CH.OHfuranI业#302115#H,OH2.53.50.028OHTaose42130.03β-D-fructofuranoseE批升En202334255-2383a anomers also exist in solution7

3/2/14& 7& Cyclization hemiacetals, hemiketals C H O C H2OH C C H2OH HO H OH C C H2OH HO H OCH3 H2O C H3OH hydrate hemiacetal α$ β$ Intramolecular hemiacetal (or hemiketal) is stable OH C H2OH O H O C H2OH OH OH OH H H H H OH H O C H2OH OH OH OH H H H H OH H or α and β anomers Cyclization mutarotation The carbonyl carbon that was attacked is called the anomeric carbon the reducing carbon The potentially reducing group α and β anomers are in equilibrium (mutarotation) determined by relative stability Interconversion rate determined by T, pH, etc. α and β anomers are different mp, solubility, crystal habit, etc. Excellent example: lactose O H OH H H H H OH OH OH C H2OH C H2OH C O C C C C H2OH HO H OH OH H H O C H2OH HO C H2 OH OH H H H OH O O Cyclization furanoses and pyranoses β-D-fructopyranose furan β-D-fructofuranose pyran α anomers also exist in solution

3/2/14Conformationallsomers60440twistboatboatchait20Chair forms tend to be more stable - boat would have eclipsedsubstituents, chair had gauche interactions.But two chair forms are possible; which is preferred?20406080Temperature("C)OHCH,OHFig, 4.5, Temperature dependence of the mutaro-tation eguilibriumofD-fructose,(β-D-fructo-pyranose,-β-D-fructofuranose,--a-D-fruc-tofuranose)(accordingtoShallenbergerand Birch,1975)Stabilityof ConformersStabilityofConformerssteric interaction energiesnomenclature,interaction energies4C1CADecreasing order of unfavorabilityCH,OHCH.OHInteractionkJmole10.456.27O-O.3.76H-C1.88".O.-C..O_-C.1.46O-O.O..-O.2.30Anomeric O-OC24.18AnomericO.OC210.038

3/2/14& 8& Conformational Isomers boat twist boat chair Chair forms tend to be more stable - boat would have eclipsed substituents, chair had gauche interactions. But two chair forms are possible; which is preferred? H HO HO H H H C H2OH OH H OH O O C H2OH H OH H OH OH H H OH H Stability of Conformers steric interaction energies Decreasing order of unfavorability Interaction kJ/mole Oax - Cax 10.45 Oax - Oax 6.27 Hax - Cax 3.76 Hax - Oax , Oeq - Ceq, Oax - Ceq 1.88 Oeq - Oeq, Oax - Oeq 1.46 Anomeric O - OC2eq 2.30 Anomeric O - OC2ax 4.18 Stability of Conformers nomenclature, interaction energies H HO HO H H H C H2OH OH H OH O H HO HO H H H C H2OH H OH OH O O C H2OH H OH H OH OH H H OH H O C H2OH H OH H H OH OH H OH H 1C4 4C1 β$ α$ 8.53 33.44 10.03 27.38

3/2/14SummaryofIsomersFoodSweetenersEnantiomers,Epimers,AnomersSweetness is 1 of 5 taste modalities.Structural IsomersMany compounds may have a"sweet"taste.aldoses -ketoses(glucose - fructose)E.g. hydroxy compounds- glycols, sugarsthere are others however!Configurational Isomers-berylfium saltsenantiomers (miror image)leadsahsepimerssome other amino acidsD & L-isomerssynthetics-Cydamate,sacchaanomers *epimers" at the reducing carbonConformational Isomers (conformers)Boat-Chair, C,.PerCapita SugarConsumptionBASICTASTESRCATAOSWETNJOWFEQUaLBitterSaltySourSweetUmami??o

3/2/14& 9& Summary of Isomers Enantiomers, Epimers, Anomers - • Structural Isomers • aldoses – ketoses (glucose – fructose) • Configurational Isomers • enantiomers (mirror image) • epimers • D & L- isomers • anomers
epimers at the reducing carbon • Conformational Isomers (conformers) • Boat • Chair, 4C1. Food&Sweeteners • Sweetness&is&1&of&5&taste&modali1es.& • Many&compounds&may&have&a&
sweet&taste.& • E.g.&&hydroxy&compounds&8&glycols,&sugars& there&are&others&however!& – beryllium&salts& – lead&salts& – some&other&amino&acids& – synthe1cs&8&Cyclamate,&saccharin,&aspartame,&etc.& Umami&??& Per&Capita&Sugar&Consump1on&

3/2/14THERELATIVESWEETNESSOFSUGARSSweetnessAs"Crystaline"MaterialSugar-D-FructoseSucroseα-D-GlucoseB-D-Glucoseα-D-Galactoseβ-D-Galactoseα-D-Mannoseβ-D-Mannosta-D-Lactose3-D-tosβ-D-Maltose10RaffinoseStachyose:Shallenberger andAeree (1971)14012060O-Fructost100801820D-GlucoseD-Galactose4020406080Temperature("C)204060Temperature (*C)Fig.4.5. Temperature dependence of the mutaro-Fig, 4.4, Temperature dependence of the relativetation equilibrium ofp-fructose,β-D-fructo-sweetness of some sugars (based on saccharose100 at each temperature;pyranose,---β-D-fructofuranose,.-.a-D-fruc-tofuranose)(accordingtoShallenbergerand Birch,1975)10

3/2/14& 10& D8Fructose& D8Glucose& D8Galactose