Effect of moisture uptake on amorphous inulin propertie
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1Gembloux Agricultural University, Dcpanmcnt of Food Technology (Head: Prof.C.Deroanne),URL:hllp:llw •••vw.Isagx.ac.be/ta2Gembloux Agricultural University. Dcpanment of IndusrriatBiological Chenustry (Head: Prof.M.Paquet). Passage desDéportés.2.B-5030 Gembloux. Belgium.
3 CosucraGroupe Warcoing SA.Ruedelasucrerie. L8-7740 Warcoing. Belgium
cosucra
GrOUpeWarcoingIntroduction
lnulinisa naruralstorage carbohydratecomposed of achainof fructose unitswithgenerallyaterminal glucose unit.industriallyextracted Fromchicoryrootandcommercially available in the powdered fonn.ln a previous study,we engineered physical propertiesandcontrolled the amorphouslcrystallinity contentof inulin by selecting appropriate feedtemperatureand/or inlet air temperatureofthespray-drier,
Unlikea crystalline structure,the amorphousstate hasa kinelicallynon-equilibrium structure.Amorphous solidsare commonly fonned throughrapid cooling ofaliquid melt to a certain temperaturesothat themoleculesinthemelt donot have enough rimetorearrangeandarefrozen in theiroriginal position.Anamorphous solid is also calledaglass,and is characterizedbya glasstransition,which referstothephase transitionwhena glassischangedinto asupercooled melt.Theglass transition is an important parameter for understanding themechanisrns of transformation processes in foods and for controllingtheirshelf-Iife.Depending on themoisture and/or thestoragetemperature, theamorphousproductcan physicallychange inorder to attain a morethenno-dynamical stable state.For thisreason,theaimof thepresent paper wasto determinethekineticof thephysicalchangesof amorphousinu1in powderstoredat highrelative humidity.Thephysicalparameters investigated were theglasstransitiontemperature (Tg) and the crystallinity index,determined byModulated Differential Scanning Calorimetry(MDSC) and WideAngleXcray Scattering (WAXS),respectively. Temperature-resolved W AXS wasused to understand theMDSC thermograrns whencrystallization occurred.lnaddition, surface analysiswasusedto correlatetherneasuredparameterstothe observed macroscopic propertychanges of the amorphouspowder.
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The powder X-ray difTractome1er uscd was aPW3710 Philips Analytical X-ray B.V.withaNi-filtered Cul(.. radiation. gencratc:d by ananode ëevice operating al 40kVand30mA inccnjunction with aproportionnai detector. Thepatterns werereoorded withaIixedlime ofOAs persreporO.02° in the4<29<30° range.
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120 140 160 180 -50 50 100 150 200 Tem rature COq 'rem ratureThestartlng materiatand theinulin storedup 101h H minonlyprcsented aglass transition alaround IWC. Although the samplcs storedat2hand2h30minwere still
amorphous. the:irthermaJ properties weredifferent fromthosc:conditioncd up to1h 45 min.At 2h-2h30min.theTg of the amorphous product wasbelow thesrcragc temperature (20"C}. due to the plasticizing efTect of water, asdeterrnined by the
reversingbeatûow using berrretic pans. After 3h.anendothennic peak waspresent aboyethe glasstransition temperature œserved for the amorphous samples.
Temperature Resolved \VAXS ofa crystallized inulin
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The MDse rreasuremenrs were realized byusing a osc 2920CE TAInstruments in hermetic and non hermetie aluminium pans.Heating raie was of 1.5°C.rnin·1 and theose cel! waspurged with 70
cmê.min-'drynitrogen. Tg - water content state diagram 160
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140 120 I()() Û "-80~
60 4ùThe reletionship bctween watercontent, crystallization and thermal properties, permitted thedctermination ofthree zonesin the state diagram. Zone 1 wasthe plesticizaticn effect of water by dcprcssing Tg, without physical propert)' changes likeheatcapecityjump,crystallinity index orcaking astheproduct was
still inapowder form.Zone Ilcharactcrizcd theproduct with aTgdown 10the
storagc temperature withsorne mecroscopic andthermal property changes, but
withacrystalliniry index equa! 10zero as inzone 1.Stereomicroscopy analysis showcdsome cracking, probably due10thespecifie volume decreesc eboveTg
and thus the retraction of the powdcr. Moreover, inthcsc fully amorphous
samplcs, sorne parts of the arnorphous phase werembbery andetherswerein the powdered form. During storage in the zone Il,theglassy 1rubbery amorphous inulin ratio dccreased, allowing anincreasc in themoleeular mobility andthus thecrystallization ofinulin in thedefined zone III.
25 0 20 III
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~' lOê Hcnnctic containers Satumtcdsalt turion(KNOl) Inulin wasstored over PlOsforone ••••eek al20°C 10œtain adehydratedproduct. tbenconditioned overKNO) fordifferentlimes.
Crystallinityevolution 100 20 10
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0.1 10 100 Steregelime(h) 1000 Stability of thepowder in the 3 zones···
lncornparison totheMDse results. the:beginning andthe: endof theendothennie peakcorresponded tothetransition observedintheTempcrarure-Resolved Widc Angle X-ray Scauering experiment (145 and 165°C for onset and endset temperature. respectivety). Indeed. upro 1~5°e. crystallizcd amorphous inulin showed diffraction peaks: while ebove this value. the crystallintty decreascddrastically. as showed by the drop of the crystallinity index. A compterely
amorphous sample wasobservedal 166°e.
Conclusions
The samples wereconsidered completety amorphous up to astorage limeof2 h30min(crystalliniry index"" 00/.), whilethecrystallinity indexes increased up10 a plateau limitof92-93% after 24h ofstorage, andcan beconsidered asreaching anequilibrium state.
Theeffectofmoisture uptakeduring storageon amorphous inulin propertieshasbeen investigated. Watercontent, crystallînity indexes,thermalproperties and glasstransition ternperature evolution pennitted the understanding of thephysicaland behaviourchanges ofthe arnorphousrnaterial.The Tg-water contentstate diagramallowed ustopointout three zones.Zone1was theplasticizationeffectofwateronTgwith inulin inapowderedamorphous state,The definedzoneIlwasan intennedîate state betweenglassyamorphcusand crystallized inulin,withsorne macroscopic and thermalpropertychanges. lnzoneIII,the productcrystallized,cakedand no glasstransitionwasobserved.Anendothermicpeakappearedat the initialglasstransition,which wasattributed tothernelting ofinulincrystals,asconfinned byTemperature-Resolved WideAngle XcrayScattering.
Acknowledgments
Financia1 support wasprovided for this stud)'bytheWal100n Region ofBclgium (DGTRE) andCosucraGroupe Warcoing SA.The: authors aregrarefulto MrsLynn Doran fortechnicalassistance. MIs.Bernadette NorbergandProf.JohanWouters from the:'Department ofStructuraJ Biologica1 ChemiSlry' orthe 'Facultés uni"ersilaircs NOlre DamedelaPaix' (Namur, Bclgium) for theuseof theWAXSand theTemperalure-Rcsol\'ed WAXS, andJeanDetryfor rushelpon the: Slereomicroscope.