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1. Food Chemistry
0711-2101
Carbohydrates
Department of Nutrition & Food Engineering
Daffodil International University

2. Contents
•Introduction to carbohydrates and its functions
•Classification of carbohydrates
•Monosaccharides and changes
•Introduction to common Oligosaccharides
•Polysaccharides and its classifications
•Starch-structure, gelatinization, retrogradation
•Modified starches
•Glycogen
•Chitin
•Cellulose
•Carbohydrate digesting enzymes

3. Carbohydrates
Introduction
Carbohydratesarethemostabundantanddiverseclassoforganiccompoundsoccurringin
nature.Theyarealsooneofthemostversatilematerialsavailable.
Carbohydrate-relatedtechnologieshaveplayedacriticalroleinthedevelopmentofnew
productsrangingfromfoods,nutraceuticals,pharmaceuticals,textiles,paper,and
biodegradablepackagingmaterials.
Carbohydratesareproducedduringtheprocessofphotosynthesis:
Thefirstcarbohydratesstudiedcontainedonlycarbon(C),hydrogen(H),andoxygen(O),with
theratioofH:Othesameasinwater,2:1,hencethenamecarbohydratesorhydratesof
carbon,C
x(H
2O)
y,wasgiven.Thecompositionofsomecarbohydratesisindeedcapturedby
theempiricalformula,butmostaremorecomplex.

4. Carbohydrates
Introduction
Carbohydratesarewidelydistributedbothinanimalandplanttissues,wheretheyfunctionas:
•Energyreserves(e.g.,starch,fructans,glycogen).
•Structuralmaterials(e.g.,cellulose,chitin,xylans,mannans).
•Protectivesubstances.Someplantcellwallpolysaccharidesareelicitorsofplantantibiotics
(phytoalexins).Insoybean,fragmentsofpecticpolysaccharides(α-4-linkeddodecagalacturonide)
inducesynthesisofaprotein(proteininhibitorinducerfactor)thatinhibitsinsectandmicrobial
proteinases.Arabinoxylanshavebeenpostulatedtoinhibitintercellulariceformation,thusensuring
wintersurvivalofcereals.
•Cellrecognitionmoieties.Oligosaccharidesconjugatedtoprotein(glycoproteins)ortolipids
(glycolipids)areimportantcomponentsofcellmembranesandcanbeactiveincelltocell
recognitionandsignaling.Itisrecognizedthatoligosaccharidemoietiesserveasprobesthrough
whichthecellinteractswithitsenvironment.Inaddition,theenvironmentdeliverssignalstothe
interiorofthecellthroughthecellsurfaceoligosaccharides.
•Informationtransferagents(nucleicacids)

5. Carbohydrates
AccordingtoamorecomprehensivedefinitionofRobyt(1998),carbohydratesarepolyhydroxy
aldehydesorketones,orcompoundsthatcanbederivedfromthemby-
•Reductionofthecarbonylgrouptoproducesugaralcohols
•Oxidationofthecarbonylgroupand/orhydroxylgroupstosugaracids
•Replacementofoneormoreofthehydroxylmoietiesbyvariouschemicalgroups,e.g.,
hydrogen(H)togivedeoxysugars,aminogroups(NH
2oracetyl-NH
2)togiveaminosugars
•Derivatizationofthehydroxylgroupsbyvariousmoieties,e.g.,phosphoricacidtogive
phosphorsugars,sulphuricacidtogivesulphosugars
•Theirpolymershavingpolymericlinkagesoftheacetaltype

6. Food Carbohydrates
Classifications
Foodcarbohydratesencompassawiderangeofmoleculesandcanbe
classifiedaccordingtotheirchemicalstructureintothreemaingroups:
•Lowmolecularweightmono-anddisaccharides
•Intermediatemolecularweightoligosaccharides
•Highmolecularweightpolysaccharides
Nutritionistsdividefoodcarbohydratesintotwoclasses:
•Available,orthosewhicharereadilyutilizedandmetabolized.Theymaybeeithermono-,di-,
oligo-orpolysaccharides,e.g.,glucose,fructose,sucrose,lactose,dextrins,starch.
•Unavailable,orthosewhicharenotutilizeddirectlybutinsteadbrokendownbysymbiotic
bacteria,yieldingfattyacids,andthusnotsupplyingthehostwithcarbohydrate.Thisincludes
structuralpolysaccharidesofplantcellwallsandmanycomplexpolysaccharides,e.g.,
cellulose,pectins,beta-glucans.

7. Food Carbohydrates
Classifications
Monosaccharides (1 unit), e.g.
Glucose (Glu), Fructose (Fru), Galactose (Gal)
Disaccharides (2 units), e.g. Sucrose (Glu-Fru),
Maltose (Glu-Glu), Lactose (Gal-Glu)
Oligosaccharides (3 –10 units), e.g. Maltotriose
(Glu-Glu-Glu), Raffinose (Gal-Glu-Fru), Lacto-oligos
(Gal-Gal-Glu
Polysaccharides (10+ units), e.g. Starch, Cellulose, Pectin, Carrageenan, Alginates,
Locust bean gum

8. Food Carbohydrates
Sources & Basic Functions in Food
Plants
•Sugar:Sugarcane,sugarbeetetc.
•Starch:Potatoes,grainsetc.
•Cellulose:Cellwalls
•Pectin:Fruitpomaceandpeels
•Gum:Arabic–acaciatree
Animals
•Glycogen:Chitinandchitosan
•Algaeandmicrobes:Gums-agar,carrageenan,alginate,xanthan
FunctionsinFood
•sweetening
•gelorpaste-forming
•thickeningagents
•stabilizersprecursorsforaromaandcoloringsubstances

9. Food Carbohydrates
Monosaccharides
Monosaccharidesarechiralpolyhydroxyaldehydesandpolyhydroxyketonesthatoftenexist
incyclichemiacetalforms.Theyaremonomericinnatureandcannotbedepolymerizedby
hydrolysistosimplersugars.
Monosaccharidesaredividedintotwomajorgroupsaccordingtowhethertheiracyclicforms
possessanaldehydeoraketogroup,thatis,intoaldosesandketoses,respectively.These,in
turn,areeachclassifiedaccordingtothenumberofcarbonsinthemonosaccharidechain
(usually3to9),intotrioses(C3),tetroses(C4),pentoses(C5),hexoses(C6),heptoses(C7),
octoses(C8),nonoses(C9).Byaddingtheprefixaldo-tothesenames,onecandefinemore
closelyagroupofaldoses,e.g.,aldohexose,aldopentose.Forketosesitiscustomarytoadd
theending-ulose

10. Food Carbohydrates
Monosaccharides-Aldoses
Thesimplestmonosaccharideisthethree-carbonglyceraldehyde(aldotriose).Ithasone
asymmetriccarbonatom(chiralcenter)andconsequently,ithastwoenantiomericforms.
•Glyceraldehydeisthesimplestthree-carbonsugarandexistsintwoforms:D-glyceraldehydeandL-
glyceraldehyde.Despitehavingthesamechemicalformula(C3H6O3),theyhavedifferentproperties.D-
glyceraldehyderotatespolarizedlighttotheright,whileL-glyceraldehyderotatesittotheleft.
•Whenweextendthecarbonchaintoformlongersugars,suchassix-carbonaldoseswith4chiralcarbons,
weintroducemorecomplexity.Eachnewcarboncreatesadditionalchiralcenters,leadingtoagreater
numberofpossiblearrangements.Forasix-carbonaldosewith4chiralcarbons,thereare16different
arrangementsineachseries:DandL.Thus,intotal,wehave16differentsugarsineachseries,DandL,
resultingfromthevariousarrangementsofchiralcarbons.

11. Food Carbohydrates
Monosaccharides-Aldoses (D/R)
.

12. Food Carbohydrates
Monosaccharides-Ketoses (D/R)
Theketotriose(dihydroxyacetone)hasno
chiralcenter,thefirstmonosaccharideinthe
ketoseseriesiserythrulose.

13. Food Carbohydrates
Monosaccharides-Structures & Stereochemistry
Isomer:Oneoftwoormoremoleculesthat
havethesamechemicalformulabuthavea
differentstereochemical(special)arrangement
oftheiratoms.
Epimer:Diastereomericmonosaccharidesthat
differsatonlyonecarbonposition
Enantiomer:Apairofchiralisomers
(stereoisomers)thataredirect,nonsuperimposable
mirrorimagesofeachother.

14. Food Carbohydrates
Monosaccharides-Physical Properties
Mostmonosaccharideshaveasweettaste(fructoseissweetest;73%sweeterthansucrose).
•Theyaresolidsatroomtemperature.
•Theyareextremelysolubleinwater.
ThepresenceoflargenumbersofOHgroupsmakethemonosaccharidesmuchmorewater
solublethanmostmoleculesofsimilarMW.Glucosecandissolveinminuteamountsofwater
tomakeasyrup(1g/1mlH
2O).

15. Food Carbohydrates
Monosaccharides-Occurrence
ThemajorityofthenaturallyoccurringcarbohydrateshavetheD-configuration.L-
monosaccharidesarelessabundantinnature,althoughL-arabinoseandL-galactoseare
presentascarbohydrateunitsinmanycarbohydratepolymers(polysaccharides).
Thepyranoseformsdominateinaqueoussolutionofmostmonosaccharides,itisquite
commontofindfuranoseformwhenthesugarisincorporatedintoabiomolecule.
Thepopularnamesofsugarsoftenindicatetheirprincipalsourcesandtheiropticalrotary
properties.
SynonymsforD-glucosearedextrose,grapesugar,andstarchsugar.
Synonymsforfructosearelevulose,honeysugar,fruitsugar.

16. Food Carbohydrates
Monosaccharides-Ring Forms of Sugar
D-glucoseexistsintwoforms,αandβ,duetointramolecularreactions.Thisoccurswhenthehydroxyloxygen
atomattachedtoC-5reactswiththecarbonylgroup,formingahemiacetal.Thisprocess,calledcyclization,
convertstheachiralC-1carbonatomintoachiralhemiacetalcarbonatom,resultingintwoisomericforms
knownasanomers:αandβ.Theseanomershavedifferentspecificrotationsandarerelatedtothestructureof
pyranose.

17. Food Carbohydrates
Monosaccharides-Ring Forms of Sugar
Afive-memberedringcanalsobeformedfromtheintramolecularnucleophilicattackbythe
hydroxyloxygenatomattachedtoC-4onthecarbonylgroupandhemiacetalformation.The
five-memberedringisrelatedtotetrahydrofuranandis,therefore,designatedasfuranose.
TheanomericcarbonofketosesisC-2.

18. Food Carbohydrates
Monosaccharides-Mutarotation
•When sugar molecules like D-glucose dissolve in water, they undergo a series of rearrangements,
resulting in a mixture of different forms. This process is called mutarotation.
•For example, when α-D-glucopyranoseor β-D-glucopyranoseare dissolved in water, they form an
equilibrium solution with a specific rotation value of around +52.7°. This solution contains five
different forms of glucose: α-D-glucopyranose, β-D-glucopyranose, α-D-glucofuranose, β-D-
glucofuranose, and the open-chain free aldehyde form. These forms can interconvert with each
other through molecular rearrangements.
Themutarotationprocessisslow(itmaytakeseveralhourstoreachequilibrium)if
conductedinwaterat20°C.Therateofmutarotationincreases,however,1.5to3
timeswitheach10°Cincreaseinthetemperature.Bothacidsandbasesincreasethe
rateofmutarotation.Certainenzymes,suchasmutarotasewillalsocatalyzethe
mutarotationreactions.Therateandtherelativeamountofproductsarealso
affectedbythepolarityofthesolvent,withlesspolarsolventsdecreasingtherateof
mutarotation.

19. Food Carbohydrates
Monosaccharides-Mutarotation
.

20. Food Carbohydrates
Monosaccharides-Enolization and Isomerization
Inthepresenceofalkali,sugarsarerelativelyeasilyinterconverted.Thetransformation
involvesepimerizationofbothaldosesandketosesaswellasaldoseketoseisomerization.
Theenolizationreactionisageneralreactionofacarbonylcompoundhavinganα-hydrogen
atom.Startingwithaldehydo-D-glucose,the1,2enediolisfirstformed,whichcanbeconverted
intoanotheraldose(withoppositeconfigurationatC-2)andthecorrespondingketose.
Therefore,byenolizationandisomerization,D-glucose,D-mannose,andD-fructosecanbe
easilyinterconverted.Eitherabaseoranenzymecatalyzesisomerization,anditwillalso
occurunderacidorneutralconditions,althoughatamuchslowerrate.

21. Food Carbohydrates
Monosaccharides-Chemical Modifications
In

22. Food Carbohydrates
Oligosaccharides-Disaccharides
Disaccharidesareglycosidesinwhichtheaglyconconstitutesanother
monosaccharideunit.
Alcoholgroupsofonecarbohydrate(monosaccharide)canreactwithahemiacetal
hydroxylgroupofanothercarbohydrate(monosaccharide)andformaglycoside
betweentwocarbohydrateunits.
Disaccharidescanbedividedintoheterogeneousandhomogeneoustypesaccording
totheirmonosaccharidecomposition,andintoreducingornon-reducing
disaccharides,dependingwhethertheypossessafreeanomericcarbon.
Homodisaccharides containtwoidenticalmonosaccharide units,whereas
heterodisaccharidesarecomposedoftwodifferentmonomers.
Reducingdisaccharides,incontrasttonon-reducingones,containareactive
hemiacetalcenterthatcanbeeasilymodifiedchemically(e.g.,viaoxidationor
reduction).

23. Food Carbohydrates
Oligosaccharides-Disaccharides
Thetwomostimportantnaturallyoccurringheterodisaccharidesaresucroseandlactose.
Sucrose(commonlyknownassugarortablesugar)occursinallplants,butitiscommercially
obtainedfromsugarcaneandsugarbeets.Itiscomposedofanα-D-glucopyranosylunitanda
β-D-fructofuranosylunitlinkedreducingendtoreducingend,thusitisanon-reducingsugar.
Itschemicalnameisα-D-glucopyranosyl-β-D-fructofuranoside.
Sucroseistheworld’smainsweeteningagent.Sucroseiscommoninmanybakedproducts,
breakfastcereals,deserts,andbeverages.SucroseishydrolyzedintoD-glucoseandD-
fructosebytheenzymesucrase,whichispresentinthehumanintestinaltract,andtherefore
canbeutilizedbyhumansforenergy.Monosaccharides(D-glucoseandD-fructose)donot
needtoundergodigestionbeforetheyareabsorbed.Theplantenzymeinvertaseisableto
hydrolyzesucroseintoitstwoconstituentsugarsinequimolarmixtureofD-glucoseandD-
fructose;themixturehasadifferentvalueofspecificrotation,andistermedinvertsugar.

24. Food Carbohydrates
Oligosaccharides-Disaccharides
Lactoseoccursinthemilkofmammals,whereitservesasanenergysourcefordeveloping
mammals.Theconcentrationoflactoseinmilkmayvaryfrom2to8%,dependingonthe
source.Lactoseisalsoabyproductinthemanufactureofcheese.Lactoseiscomposedof
twodifferentsugarresidues:β-D-galactopyranoseandD-glucopyranoselinkedviaβ-1→4
linkage.Itschemicalnameisβ-D-galactopyranosyl-D-glucopyranoside.
OthercommonnaturallyoccurringdisaccharidesaremaltoseandCellobiose.

25. Food Carbohydrates
Oligosaccharides-Disaccharides
.

26. Food Carbohydrates
Oligosaccharides
AccordingtoIUPAC,oligosaccharidescontain3to9sugarresidues,determiningtheirdegreeof
polymerization.Raffinose,anon-reducingtrisaccharide,isformedfromsucrosebyaddingα-D-
galactopyranosetotheC-6ofglucose.It'sfoundinvariousplantsandcommerciallyderivedfrom
beetmolassesandcottonseeds.Stachyose,anothersucrosederivative,occursfreelyinlegumes
andpulses.

27. Food Carbohydrates
Oligosaccharides
.

28. Food Carbohydrates
Polysaccharides
Polysaccharidesarethecarbohydrateswhichcontainmorethan10monosaccharideunits.
Theycanbehydrolyzedintohundredoreventhousandsofmonosaccharideunits.Thesuffix–
oseinsugarischangedto–anstodescribethecorrespondingpolysaccharide.
Examples:
(1)Pentosans-(a)Arabans,(b)Xylans
(2)Hexosans-(a)Glucansàstarch,dextrin,glycogen,cellulose,inulin;(b)Mannans;(c)
Galactans
(3)Complexpolysaccharides-(a)Pectinsorpecticsubstances,(b)Gums,(c)Mucilages,(d)
Algalpolysaccharides-Alginicacidandcarrageenan,(e)Bacterialpolysaccharides-Xanthan
gum.
Polysaccharidescommonlypresentinfoodsarestarch,glycogen,cellulose,hemicellulose,
pecticsubstances,gums.

29. Food Carbohydrates
Classification of Polysaccharides
Polysaccharidescomeintwomaintypes:homopolysaccharidesandheteropolysaccharides.
Homopolysaccharides:Thesecontainthesamebuildingblocksthroughout,likestarch,glycogen,
fructans,andmannans.Theycanbeeitherperfectlylinearorbranched,withvaryingcomplexitiesof
branchingandlinkagesbetweenunits.
•PerfectlyLinearPolysaccharides:Thesehaveasingletypeofsugarunitandlinkage,making
theminsolubleinwaterandpronetoprecipitatingout.Theycanformstickypastesundercertain
conditionsbutarenotverysoluble.
•BranchedPolysaccharides:Thesearemoresolubleinwatercomparedtolinearonesbecause
theirbranchingreduceschain-chaininteractions.Theyhavelowerviscosityandarelesslikelyto
precipitate.Branchedpolysaccharidescanformstickypastesathigherconcentrations,making
themusefulasbindersoradhesives.
Heteropolysaccharides:containmultipletypesofsugarunits.Forexample,arabinoxylans,
glucomannans,etc.Thesepolymerscanbelinearorbranched,withvarioustypesofbranchpoints.
CommonsugarunitsfoundinfoodheteropolysaccharidesincludeD-fructose(Fru),D-mannose
(Man),D-glucose(Glc),D-mannuronicacid(ManA),D-glucuronicacid(GluA),D-xylose(Xyl),D-
galactose(Gal),L-arabinose(Ara),D-galacturonicacid(GalA),andL-rhamnose(Rha).

30. Food Carbohydrates
Homopolysaccharides Occurring/Used in Foodstuffs

31. Food Carbohydrates
Heteropolysaccharides Occurring/Used in Foodstuffs

32. Food Carbohydrates
Starch
Starch,anaturalpolymerofD-glucose,iswidespreadintheplantkingdomandservesasavital
energysourceinfood.Over80%offoodcropsarecomposedofstarch-richcerealsandvegetables.
Innature,starchexistsassmallgranuleswithuniquesizesandshapescharacteristictoeachplant
species.Thesegranulesexhibitahighlyorderedcrystallinestructure,observableunderlight
microscopyandX-raydiffraction.
Starchcomprisestwomainpolymers:amyloseandamylopectin.Amyloseisalinearpolymer
consistingofover2000glucoseunitslinkedbyα-1,4-glycosidicbonds.Amylopectin,ontheother
hand,ishighlybranched,withbranchescomposedof20to30glucoseunits.Eachamylopectin
moleculecontainsnumerousbrancheslinkedbyα-1,4-glycosidicbonds,withbranchpoints
connectedviaα-1,6-glycosidiclinkages.
Theimportantsourcesofstarchare(i)Cerealsandmillets(65to85%)e.g.maize,wheat,rice;
(ii)Rootsandtubes(19to35%)e.g.potato,tapioca
Cerealstarchesdifferfromrootandtuberstarchesintheirphysicalproperties.Acerealstarchpaste
(5%)setstoathickjellyoncoolingwhereasaturberstarchpaste(5%)remainsasafluidanddoes
notsettoathickjelly.
Incerealsmoisturecontentislowandthestarchgranulesareembeddedinahard,proteinaceous
matrix,whichrequirespreliminarysofteningbeforestarchextraction.Potatocontainshighmoisture
andnopreliminarysofteningisrequired.

33. Food Carbohydrates
Starch-Amylose
ThisisalongunbranchedchainofD-glucosemoleculeslinkedtogetherbyα-1,4linkage,
similartothatpresentinmaltose.
Molecularweightofamyloserangefrom10
5
to10
6
daltonsandonemoleculeofamylosemay
contain500to5000glucosemolecules.
Thesolutiononkeepingturnsturbidduetotheprecipitationsofamylosebyaprocessknown
asretrogradation.Amyloseismainlyresponsibleforthestiffeningofcookedriceonstanding.
Amylosegivesabluecolorwithiodine.Amylosecontentofastarchcanvaryconsiderably
dependingonthebotanicalspecies.Cerealstarchessuchaswheatstarchcontains25–30%
amylose,cornstarch(amylomaize)contains40–80%amylose.Waxymaizecontain0%starch.

34. Food Carbohydrates
Starch-Amylopectin
Amylopectinisbranchedchainpolysaccharidecomponentofstarch.Inthispolysaccharide
shortchains(20to30molecules)ofD-glucoselinkedbyα-1,4linkages.Thesechainsare
linkedtoeachotherbyα-1,6linkages.Molecularweightofamylopectinrangefrom10
7
to10
8
daltons,andonemoleculeofamylopectinmaycontain50000to500000moleculesofD-
glucose.Amylopectingivesapurplecolorwithiodine.

35. Food Carbohydrates
Starch-Gelatinization
Starchgelatinizationisaprocessthatbreaksdowntheintermolecularbondsofstarch
moleculesinthepresenceofwaterandheat,allowingthehydrogenbondingsites(the
hydroxylhydrogenandoxygen)toengagemorewater.
Asthetemperatureincreases,starchgranulesabsorbwater,causingthemtoswell.Thisleadstothedisruption
ofthegranularstructureandthereleaseofamyloseandamylopectinmoleculesintothesurroundingwater.
Itresultsintheformationofaviscousgel,whichisusefulinvariousfoodapplicationsforthickening,stabilizing,
andimprovingtexture.
Gelatinizationisinfluencedbyanumberoffactors.Thegelatinizationtemperatureandthe
lengthofheating,planttype(wheatandcornstarchshowdifferentbehaviorpatterns)andthe
amountofwaterpresent,pH,sizeofstarchgranule.

36. Food Carbohydrates
Starch-Retrogradation of Starch
Retrogradationistheprocessbywhichgelatinizedstarchmoleculesundergoreassociationandrecrystallization
uponcooling.
Also,Theprocessofdissolvedstarchbecominglesssolubleiscalledretrogradation.
Aftergelatinization,whenthegelcoolsdown,theamyloseandamylopectinmoleculesstarttorealignand
formnewbondswitheachother.
Thisprocessleadstotherearrangementofstarchmoleculesintoamoreorderedstructure,resultinginthe
formationofinsolubleamyloseandamylopectincomplexes.
Whenstarchisheatedwithwaterandformsagel,itinitiallyhasasmoothtexture.Overtime,especiallywhen
cooled,thegel-likesubstancemadewithstarchstartstobecomefirmerandlesssmooth.
Retrogradationisresponsibleforthestalingofstarch-basedfoodslikebreadorpastries,wheretheybecome
harderandlessfreshovertime.
Therateofretrogradationdependsonseveralvariables,includingmolecularratioofamylose
toamylopectin;botanicalsourceofstarch;temperature;starchconcentration;salts;
surfactants.

37. Food Carbohydrates
Modified Starches
Thebehaviorofpastesofthecommonnativestarcheswhensubjected
totheeffectsofheatandshearusedinmodernfoodtechnologyis
oftenunsatisfactory.
Consequentlymodifiedstarchesandstarchderivativeswithmore
sophisticatedstabilitycharacteristicshavebeendeveloped.Modified
starchesinclude-
•Acidmodifiedstarches
•Pre-gelatinizedstarches
•Cross-linkedstarches
•Esters&ethersofstarch
•Starchphosphates
•Hydroxyalkylsubstitutedstarch

38. Food Carbohydrates
Acid Modified Starches
Acid-modifiedstarchesaremadebyheatingstarchgranuleswithdilutedhydrochloricacid
attemperaturesbelowgelatinization.Thisprocessresultsingranulesthatswelllessduring
gelatinization,reducingvolumeandviscosity.
Thesestarchesdissolvemoreeasilyinhotwater,withsolubilitydependingontheextentof
acidtreatment.Theyarecommonlyusedinmakingfruitgumsduetotheirclear,stronggels,
unlikeunmodifiedstarches.
Gelsmadefromacid-modifiedstarchhavelowerviscosity,makingthemeasytopourinto
molds.Theacidtreatmentimprovesgelstrengthandclarity,likelyduetopreferential
degradationofamylopectin.

39. Food Carbohydrates
Pre-gelatinized Starches
Pre-gelatinizedstarchisstarchthathasbeencookedtodestroyitsgranularstructure,
reducingitsviscosity.Itisthendriedintoapowderforeasyuse.
Thispowderedstarchquicklyrehydratesincoldwaterbutmaynotyieldthesametextureas
freshlypreparedpasteduetostarchdegradation.
Pre-gelatinizedstarchiscommonlyusedininstantpuddings,whereit'smixedwithcoldmilk
tomakeaquickdessert.It'salsousedinfrozenfruitpiefillingstokeepfruitsuspendedand
retainflavorwithoutheating.

40. Food Carbohydrates
Cross-linked and Other Derivatized Starches
Starchderivativeslikestarchphosphatesandcross-linkedphosphateestersareimportant
additivesinthefoodindustry.Theyincreaseandstabilizepasteviscositybyintroducing
negativelychargedphosphategroups,preventingmoleculeaggregation.
Thesederivativesareusedasthickeningandtexturizingagentsinvariousfoods,especially
frozenfoods,duetotheirhighviscosityandclarity.
Cross-linkedphosphateestersarepreparedcommerciallybyesterificationwith
trimetaphosphate.Theextentofcross-linkingaffectsthepastingpropertiesofthe
derivatives.
Hydroxyalkylsubstituents,likehydroxypropylstarch,increasesolubilityandprevent
molecularaggregation.Theygelatinizeatlowertemperaturesandshowlittletendencyto
formgels,makingthemusefulinfoodtexturalmodification.

41. Food Carbohydrates
Glycogen
Glycogenthereservecarbohydrateisapolysaccharidefoundintheanimalbody.Itisfoundmainlyinthe
muscles(0.5to1percent)andliver(3to7percent).Glycogenresemblesstarchinitschemicalproperties.
Itisformedbythecondensationofalargenumber(5000-10000)ofglucosemolecules.Itisabranched
chainpolysaccharide,resemblingamylopectin.Thechainlengthvariesfrom8to12glucoseunits.The
molecularweightofglycogenfromdifferentsourcesrangefrom10
5
to10
8
daltons.

42. Food Carbohydrates
Cellulose
Celluloseisthemostabundantpolysaccharideinnature,sinceone-thirdofallhigherplantsconsists
ofthisbiopolymerwhichfunctionsasthemainstructuralmaterial.ItisalinearpolymerofD-glucose
unitslinked(1,4)intheβ–configuration.Thecellulosechainsareunbranchedandmaycontainas
manyas5000glucoseunits.
Cellulosechainsalignside-by-sideandformstrongbonds,creatingcrystallineregions.Becauseofthesebonds,
celluloseisinsolubleinwaterandeveninstrongsolutionslikesodiumhydroxide.
Thecelluloseisresponsiblefortheformandgrosstextureinallfoodstuffspreparedfrom
plants.Beinginsoluble,itislittleaffectedbyanycookingprocessanddoesnotdisperse.On
ingestion,itisunaffectedbyenzymesinthedigestivetractanddoesnothydrate.

43. Food Carbohydrates
Chitin
Chitinisahomopolysaccharidethatoccursasastructuralcompoundinlobster,
shrimp,andcrabshellsaswellasinsomeinsects,andfungi.
Theshellscontaincalciumcarbonate,proteins,andothercompounds,butthis
polysaccharideismainlyresponsiblefortherigidityofthetissue.
Itiseasilyextracted.Therepeatingunitinchitinis2-N-acetylglucosamine,linkedβ-1,4.

44. Food Carbohydrates
Pectins
Thepectinsorpecticsubstancesarefounduniversallyintheprimarycellwalls&intercellularlayersin
plants.
Theyaremostabundantinyoungtissue.Theyarecharacteristicconstituentoffruitse.g.citrusfruits
contain30%pectin.Thepecticsubstancesareafamilyofverycloselyassociatedpolysaccharides
whichareverydifficulttoseparate.Theterm‘pectin’isusedinrelationtowater-insoluble
polysaccharides.
D-galacturonicacidistheprincipalconstituentwhichisesterifiedasmethylesterandpossess
considerablegellingpower.
OtherconstituentsincludeD-galactose,L-arabinose,D-xylose,L-rhamnoseandL-fucose.Three
typesofhomopolysaccharidesarealsopresent–D-galacturonan,D-galactan,andL-arabinan.
Pectiniswidelyusedinmarmaladeandjellypreparation.High-methoxylpectinsolutionsgel
sufficientacidandsugararepresent.Low-methoxylpectinsolutionsgelonlyinthepresence
ofcalciumions,whichprovidecrossbridges.

45. Food Carbohydrates
Carbohydrate Digesting Enzymes
Degradationofpolysaccharidesisnowlargelyreplacedbyenzymaticprocessesasacid
hydrolysisrequirestheuseofcorrosionresistantmaterialswhichgivesrisetohighcolor,salt
andashcontent(afterneutralization),needsmoreenergyforheatingandisrelativelydifficult
tocontrol.
Amylases
Enzymesinvolvedindegradationofstarchbelongtohydrolases(Glycosidases).Amylasesarethe
mostimportantstarchdegradingenzymes.Theyhydrolyzethestarchtooligosaccharidesandsimple
sugars.Ofthetwocomponentsofstarch,amylopectinpresentsthegreatchallengetohydrolytic
enzymesystems.Thisisduetotheresiduesinvolvedinα-1,6-glycosidicbranchpointswhich
constituteabout4-6%oftheglucosepresent.Whilemosthydrolyticenzymestargetα-1,4-glucosidiclinks,
completehydrolysisofamylopectintoglucoserequirescleavageofα-1,6-glucosidiclinksaswell.
α-amylase
α-amylaseisanendoenzyme.Ithydrolyzestheα-1,4glycosidicbondsrandomlyalongthechain.
Amylopectinishydrolyzedtooligosaccharidesthatcontaintwotosixglucoseunits.Amixtureofamylose
andamylopectinishydrolyzedintoamixtureofdextrins,maltoseandglucose.Amyloseiscompletely
hydrolyzedtomaltose.Calciumionsarerequiredforitsactivation.
Enzymatichydrolysisisincreasedbythegelatinizationofstarch.α-amylasehydrolyzestheα-1,4-bondsof
amyloseandamylopectininarandommanner,liberatingsmallunitswithfreenon-reducingendgroups.
Lowmolecularweightdextrinsareformed

46. Food Carbohydrates
Carbohydrate Digesting Enzymes
β-amylase
β-amylasealsohydrolyzestheα-1,4-bondsofamyloseandamylopectin,removingmaltose
unitsfromthenon-reducingendofstarchinanorderlyfashion.Theα-amylaseandβ-amylase
donotcleavetheα-1,6-linkageesinamylopectin.
Glucoamylase
Glucoamylaseisusedincombinationwithanα-amylasetoproduceD-glucosesyrupsand
crystallineD-glucose.Theenzymeactsuponfullygelatinizedstarchsequentiallyreleasing
singleD-glucosylunitsfromthenonreducingendsofamyloseandamylopectinmolecules.
Pullulanase
Pullulanasehydrolyzesα-1,6glucosidicbondsinpolysaccharides,e.g.inamylopectin,
glycogen,andpullulan.Linearamylosefragmentsareformedfromamylopectin.