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Doughthermomechanicalpropertiesinfluenceofsodiumchloride,mixingtimeandequipmentA.Angioloni,M.DallaRosaAbstractThermomechanicalpropertiesofdoughspreparedfromcommonwheatflourwereinvestigatedunderdifferentkneadingconditionsandwithdifferentamountsofsodiumchloride.Dynamicmechanicalthermalanalysisshowedthathighspeedmixingandtheadditionofsalttodoughslowedheatinducedreactionssuchasstarchgelatinisationandproteincoagulation.Theeffectofdoughmixingtechnologywasmoresignificantthantheamountofsodiumchlorideinmodifyingdoughrheologicalcharacteristics.q2004ElsevierLtd.Allrightsreserved.KeywordsDoughMixingSodiumchlorideThermomechanicalpropertiesStarchgelatinization1.IntroductionThefirststepinabakingprocessismixingthedoughhowthemixingisperformedandtheingredientsareincorporatedanddispersedlargelydeterminethefinalqualityofthebakedproductAamodtetal.,2003BasaranandGo¨cmen,2003.Theproductionofwheatdoughisaprocessinwhichrawmaterialsmainlyflour,water,saltandyeastaremixedandsubjectedtoalargerangeofstrainsituations.Doughisacomplexmixtureofstarch,protein,fatandsalt.Mixinghasthreeimportantfunctionsiitblendstheingredientsintoamacroscopicallyhomogeneousmass,iiitdevelopsthedoughintoathreedimensionalviscoelasticstructurewithgasretainingpropertiesandiiiitincorporatesairwhichwillformnucleiforgasbubblesthatgrowduringdoughfermentationBloksma,1990ColladoandLeyn,2000DobraszczykandMorgenstern,2003HoseneyandRogers,1990Naeemetal.,2002.Bothmixingintensityandmixingenergymustbeaboveaminimumcriticalleveltodevelopthedoughproperly,thelevelvaryingwithflourandmixertypeKilbornandTipples,1972MacRitchie,1986Skeggs,1985Zhengetal.,2000.ThetimerequiredforoptimumdoughdevelopmentispositivelycorrelatedwiththepolymericproteincompositionandthebalancebetweenproteinpolymersandmonomersDobraszczykandMorgenstern,2003MacRitchie,1992Millar,2004.Rheologicalpropertieschangeduringeverystageofthedoughmakingprocessstressconditionsarehighwhenthedoughismixedinhighspeedmixers,tobecomeanelasticandcoherentmass.Mixingspeedandenergyworkinputmustbehigherthanacertainvaluetodeveloptheglutennetworkandtoproduceasuitablebreadmakingdough.Ontheotherhand,anoptimalmixingtimehasbeenrelatedtooptimumbreadmakingperformancewhichvariesdependingonmixertypeandingredientsDobraszczykandMorgenstern,2003Manietal.,1992.Forexample,kneadingdoughstoreachoptimumdevelopmentusingelongationalflowinsheeting,requiredonly10–15oftheenergygenerallyimpartedbyconventionalhighspeedshearmixers,suggestingthatmuchhigherratesofworkinputcanbeachievedduetotheimprovedstrainhardeningofdoughunderextensionDobraszczykandMorgenstern,2003KilbornandTipples,1974Millar,2004Starch,themajorcomponentofwheatflour,makingupabout80ofitsdryweight,influencesdoughrheologicalproperties,especiallyuponheatinginthepresenceofwaterwhenstarchgelatinisesLiandYeh,2001.Thegelatinizationprocessincludesanumberofchangesabsorptionofwaterandswellingofthegranules,changeinsizeandshapeofthegranules,lossofbirefringenceandXraydiffractionpattern,leachingofamylosefromthegranulesintothesolventandtheformationofapasteAtwelletal.,1988.Atreducedwatercontents,suchasindough,thechangesresultingfromgelatinisationarestronglydependentontheamountofwateravailableEliasson,1983Seetharamanetal.,2004.Theincreaseinviscosityduetostarchgelatinisationhasbeensuggestedtomodifystructuralpropertiesofdough.Inaddition,thepresenceofsodiumchlorideisknowntoaffectdoughpropertiessalttoughenstheproteinandhelpsinconditioningthedoughbyimprovingitstolerancetomixingtheadditionofsaltproducedamorestableandstiffdoughGalaletal.,1978ShiuandYeh,2001.Moreoveritisknownthatwhensaltisaddedtothedough,heatinducedreactionssuchasstarchgelatinisationandproteincoagulation,areslowed.Theaimofthepresentworkwastoanalysetheeffectsofincreasingsodiumchlorideconcentrationanddifferentkneadingconditionsonseveraldoughthermomechanicalproperties,usingadynamicalstressstraincontrolledrheometer.2.MaterialsandmethodsCommercialwheatflourwasfromMulinoPivettiItaly,sodiumchloride,fromCarloErbaItaly.AACC2000methodswereusedtodeterminemoisture4419,ash0801,protein4610andgluten3812intheflouranditsAlveographcharacteristics.Doughsampleswith50moisturewerepreparedinaccordancewithAlveographmethodAACC5430A2000,usingtwodifferentmixersandmixingtimes.InthefirstsampleAtheAlveographmixerwasusedwithstandardconditions250gofflourwasmixedwithwaterfor7mintoformthedough.InthesecondsampleMaprototypemixerwasusedwheretheingredientswerekneadedforonly15sbutathighspeed1500rpm.Inthiswayhighamountsofenergyweretransferredtothedough.Theprototypemixerhadaparallelpipedshape12812cmwithtwoverticalarmsoperatedbya1.5kWmotorGamars.r.l.,VEItaly.Sodiumchloride,0–4.5,drybasisd.b.wasadded,foreachdifferentkneadingconditionandmixertypeTable1.Beforerheologicalanalysisalldoughswererestedfor30minatroomtemperatureinaplasticcontainer.Doughtemperaturesattheendofkneadingwere26–288CforsampleAandw358CforsampleMalthoughtheuseofprototypemixerrapidlyThermomechanicaltestsweremadeusingacontrolledstressstrainrheometerMCR300,Physica/AntonPaarMesstechnik,Ostfildern,Germany,usingparallelplategeometry25mmplatediameter,2mmplategap.Theupper,serrated25mmplatewaslowereduntilthethicknessofsamplewas2mmandexcesswastrimmedoff.Theexposedsurfacewascoveredwithathinlayerofmineraloiltopreventmoisturelossduringtesting.Thesamplewasrestedanother15minintherheometer,beforeeachmeasurement,allowingrelaxationofstressesinducedduringsampleloadingtorelax.Allmeasurementswereperformedataheatingrateof0.88C/minatfixedfrequencyof1Hzwiththeoscillationamplitudesmallenoughtoensurelinearviscoelasticity.Thedataarereportedasmeansofmeasurementsmadeonthreesamples,whereeachsamplewasobtainedfromaseparatelypreparedbatchofdoughforeachformulationandforthedifferentmixersused.SignificantdifferencesinstoragemodulusG0at1HzweredeterminedbyLeastSignificantDifferenceanalysiswithP0.05.AllstatisticalanalyseswereperformedwiththeStatSoftVersion6.3.Resultsanddiscussion3.1.FlourchemicalandphysicalpropertiesThechemicalcompositionandrheologicalpropertiesoftheflourareshowninTable2.AnalysisofAlveographdatacategorisestheflourusedasweak,andasseenbytheP/Lratio,theglutenisricheringliadinsthaningluteninsTheresistanceofaglutendoughtoextensiondecreasesandextensibilityincreaseswithanincreasinggliadintogluteninratioGrasbergeretal.,2003Kimetal.,1988Uthayakumuranetal.,2000.3.2.ThermomechanicalpropertiesofdoughsThesameamountsofsalt0,2.5,3.5,4.5d.b.wereaddedtobothsamplesAMtochecktheeffectofsaltanddifferentkneadingconditionsonsamplebehaviourduringdynamicmechanicalthermalanalysis.Thismeasurementsimulatesthephysicochemicalchangesthattakeplaceduringthermaltreatmentofdough.Figs.1and2showtheeffectofsaltadditiononthestoragemodulusG0duringanoscillatorytemperatureramp.Below558C,G0,forbothsamples,graduallydecreasedastemperatureincreased,indicatingsofteningofthedough.Thereafter,thestoragemodulusincreasedfrom55–60to808Candthenslowlydecreased.TheabruptincreasecanbeattributedtothegelatinizationofstarchtheswellinganddistortionofstarchgranulesduringgelatinizationwereresponsiblefortherapidincreaseofG0notonlybytheiractionasafillerintheglutennetwork,butalsobypromotingeffectivecrosslinkinginthesystemDreeseet
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