microwave processing of natural biopolymers-studies on the properties of different starches

Note

Microwaveprocessingofnaturalbiopolymers—studiesonthe

propertiesofdifferentstarches

Anik´oSzepesa,MagdolnaHasznos-Nezdeia,J´ozsefKov´acsb,ZofiaFunkec,JoachimUlrichd,PiroskaSzab´o-R´ev´esza,∗

b

UniversityofSzeged,DepartmentofPharmaceuticalTechnology,E¨otv¨osu.6,SzegedH-6720,Hungary

UniversityofVeszpr´em,DepartmentofEnvironmentalEngineeringandChemicalTechnology,P.O.B.158,Veszpr´emH-8200,Hungary

cMartin-Luther-UniversityHalle-Wittenberg,InstituteofBioengineering,D-06099Halle,GermanydMartin-Luther-UniversityHalle-Wittenberg,InstituteofProcessEngineering,D-06099Halle,Germany

Received31May2005;accepted16June2005

Availableonline15August2005

a

Abstract

Inthisstudy,theinfluenceofmicrowaveirradiationonsomephysico-chemicalpropertiesandseveralpharmaceuticaltech-nologicalparametersofpotatoandmaizestarcheswasinvestigated.Changesintheirhabitswereobservedanddecreaseinmoisturecontentscausedbytheelectromagneticirradiationwasdetermined.Thecrystallinestructuresandthemicromorpho-logicalparametersofthestarcheswereaffectedbymicrowaveirradiationindifferentwaysdependingonthebotanicaloriginofthesamples.Thetensilestrengthsofthecompactscontainingstarchesweredecreased,theirwettingpropertieswereenhancedbythethermalprocessapplied.Furthermore,microwaveirradiationreducedthesurfacefreeenergyandthepolarityofthecompactssignificantly.Samplestreatedbyconventionalheatingwereusedtocomparetheeffectsofmicrowaveirradiationontheexaminedpropertiesandparametersofthesestarches.©2005ElsevierB.V.Allrightsreserved.

Keywords:Microwave;Starch;Scanning-electron-microscopy;Surfacefreeenergy;X-raypowderdiffraction

Applicationsofmicrowaveenergyhavebeendevel-opedprimarilyforcommunicationsandsomeareasofprocessing.Inpharmaceuticaltechnology,microwaveirradiationhasbeenusedbecauseofitsthermaleffectindryingprocesses(Joshietal.,1989;D´avidetal.,

Correspondingauthor.Tel.:+3662545570;fax:+3662545571.

E-mailaddress:revesz@pharm.u-szeged.hu(P.Szab´o-R´ev´esz).0378-5173/$–seefrontmatter©2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.ijpharm.2005.06.018

∗

2000;Panetal.,2001),forsterilisationofinjectionsandinfusionsandinafrozenstorage-microwavethawingsystemforintravenousinfusions(SewellandPalmer,1991a;Sewelletal.,1991b).Severalstudiesfocusedontheprocessparametersandthekineticsofmicrowavedryinghavebeencarriedoutbutsufficientdataabouttheeffectsofelectromagneticirradiationonthestruc-tureandphysico-chemicalpropertiesoffrequentlyusedpharmaceuticalmaterialsarenotavailable.

A.Szepesetal./InternationalJournalofPharmaceutics302(2005)166–171167

Theobjectiveofthepresentworkwastoinvesti-gatethemorphologicalparametersandthestructuralchangesofpotato(PS)andmaize(MS)starchestreatedbymicrowaveirradiation.Theinfluenceoftheelectro-magneticirradiationonthetensilestrengthsandsurfacefreeenergiesofcompactspressedfromthemodifiedPSandMSwasalsostudied.Theinitialsamplesandsamplestreatedbyconventionalheatingwereusedtocomparetheeffectsofmicrowaveirradiationontheexaminedpropertiesandparametersofthesestarches.PSandMSwereusedasexperimentalmaterials(Hungaropharma,Budapest,Hungary).Physicalmod-ificationswereachievedintwodifferentways:•bymicrowaveirradiationfor15mininaSharpR4P58(450W)microwaveoven(PSbyconventionalheatingat130◦mwandMSmw);•Cfor2h(PS130◦CandMS130◦C)inadryingovenwithoutairflow(Fortunaetal.,1998;Palasinskietal.,2000).Inbothcases,100.0gpowderwasmodified.Theini-tialandthetreatedsampleswerestoredinwell-closedvesselsatroomtemperature(20±2◦C;45±5%RH).Themoisturecontentsofthesamplesweredeter-minedbyusingtheHR73HalogenMoistureAnalyzer(Mettler-ToledoGmbH,Greifensee,Switzerland)at60◦C.

TheparticleformandparticlesurfaceofthestarcheswereinvestigatedbySEM(PhilipsXL30ESEM).Themicromorphologicalparametersofthesam-plesweredeterminedusingMicromeriticsASA2000equipment(InstrumentCorp.,Norcross,GA,USA)fromthedataofnitrogenadsorptionanddesorptionisothermsattheboilingpointofliquidnitrogenunderatmosphericpressure(−196◦C).Thespecificsurfaceareas(FBET)andmesoporediameters(D(4V/F))werecalculatedinthevalidityrangeoftheBET-isotherm.Themesoporevolumes(VP1.7–300nm)werecalculatedviatheBJH-method.

Theparticlesizeanditsdistributionforallsamplesweremeasuredbylaserdiffraction(MalvernMaster-sizer2000,MalvernLtd.,Worcestershire,UK).

ThepowderX-raydiffractionprofilesweretakenusinganX-raydiffractometer(PhilipsPW1050/70PW1710)underthefollowingconditions:radiationsource:CuK␣,scanspeed:0.0352θs−1,stepsize:0.0352θs−1,timeperstep:1.0s.

Binarypowdermixtureswerepreparedbymix-ing80%(w/w)microcrystallinecellulose(Avicel®PH101,FMCCorp.,Philadelphia,USA)and20%(w/w)starchinaTurbulamixer(WillyA.Bachofen,Maschinenfabrik,Basel,Switzerland)at50rpmdur-ing2min.Compactswerecompressedwithaninstru-mentedeccentrictablettingmachine(KorschEK0,Berlin,Germany).

ThecrushingstrengthsofthetabletsweremeasuredusingHeberleinequipment(HeberleinandCo.AG,Z¨urich,Switzerland),whiletensilestrengthswerecal-culatedviatheequationofFellandNewton(FellandNewton,1970).

Thesurfacefreeenergiesofthetabletsweredeter-minedbycontactanglemeasurementswithpolar(bidistilledwater)andnon-polar(diiodomethane,MerckKGaA,Darmstadt,Germany)liquids,usingtheOCA20OpticalContactAngleMeasuringSystem(Dataphysics,Filderstadt,Germany)withthesessiledropmethod.SurfacefreeenergieswerecalculatedviatheOwens–Wendtequation(OwensandWendt,1969).Porosityparametersofthetabletsweredeterminedbyahigh-pressuremercuryporosimeter(PASCAL140+440,PorotecGmbH,Hofheim,Germany).

Thedifferencebetweensamplemeanswasdeemedstatisticallysignificantifthe95%confidenceintervalsforthemeansdidnotoverlap.

TheparticlesoftheinitialPS(23–75␮m)wereovoidandhadasmoothsurface(Fig.1a).Themicro-scopicpicturesofthemicrowavedPSdidnotrevealnoteworthy◦changes(Fig.1b).Heatingofpotatostarchat130Ccausedcracksinthesurfaceoftheparticles(Fig.1c).

TheparticlesoftheMSweresmaller(9–23␮m)andhadacrystallineappearance(Fig.2a).TheunmodifiedMSsampleconsistedofnon-agglomeratedcrystallineparticles.Theparticlesweredeformedaftermicrowaveirradiation(Fig.2b)andconventionalheating,andformedlooseagglomerates(Fig.2c).Theseobserva-tionsareingoodagreementwiththeresultsobtainedbyPalasinskietal.(2000).

Thephysicaltreatmentsapplieddidnotcauseremarkablechangesinparticlesizeandparticlesizedistributionofthestarches(Table1).

ThemicromorphologicalparametersofthePSandMSwereentirelydifferent(Table1),whichcanberelatedtothestructuraldifferencesofthesamples(SwarbrickandBoylan,2002).ThemicromeriticsofPSwerechangedslightlyduringthethermalpro-cesses.ThespecificsurfaceareaoftheMSmodified

168A.Szepesetal./InternationalJournalofPharmaceutics302(2005)166–171

Fig.1.SEMpicturesofpotatostarch.(a)PS;(b)PSmw;(c)PS130◦.

Fig.2.SEMpicturesofmaizestarch.(a)MS;(b)MSmw;(c)MS130◦.

Table1

Parametersofstarchsamples(n=3)SamplesPSPSmwPS130◦CMSMSmwMS130◦C

Moisturecontent(%)9.66±0.200.07±0.000.60±0.116.84±0.140.00±0.000.01±0.01

D10%(␮m)23.4723.1623.829.399.339.34

±±±±±±0.080.020.300.220.010.02

D90%(␮m)75.62±0.0773.86±0.0773.16±0.0423.02±0.3122.51±0.0722.41±0.14

FBET(m2/g)0.12±0.0020.10±0.0030.11±0.0020.27±0.0040.30±0.0030.38±0.003

VP1.7–300nm(×10−4m3/g)1.831.661.739.119.1711.60

D(4V/F)(nm)11.57.558.4713.5013.009.42

A.Szepesetal./InternationalJournalofPharmaceutics302(2005)166–171169

Fig.3.Cumulativemesoporevolumedistributionsofstarchsamplesasafunctionofaveragemesoporediameter(D).

byconventionalheating(MS130◦C)became40%largerandasimilarsignificantincreasewasobservedonevaluationofthemesoporevolumedata(30%).ThechangesinmicromorphologyofMSwereconsiderablesmalleraftermicrowaveirradiation(MSmw).Differ-encesbetweenthemicrostructuresofthestarchsam-plesarewelldemonstratedbythecumulativemesoporevolumedistributioncurves(Fig.3).

ThecrystallinityofPSincreasedduringmicrowaveirradiation,whileconventionalheatingtendedtodestroythecrystallinestructure(Table2).Theunmodi-fiedMScontainedahighercrystallinefraction(84.6%).Thisfellto30%duringmicrowaveirradiationandto33%duringconventionalheating(Table2).TheseresultsareinagreementwithpreviousinvestigationswhichprovedthatthecrystalstructureofthePS

Table2

ResultsofX-rayexaminationsofstarchsamplesSamples

2Θ(◦)

Intensity/crystallinepart(cps)577661473906611521162490

Intensity/amorphouspart(cps)466531145227111649564970

PSPSmwPS130◦CMSMSmwMS130◦C17.18517.13516.90522.85022.75522.860

2Θ:reflectionangle.

changedfromtheBpatterntotheApattern.Typi-cally,tuberstarchesexhibittheBtypeofcrystallinity,whereascerealstarchesdisplaytheAtypeofcrystalstructure(Lewandowiczetal.,1997,2000;SwarbrickandBoylan,2002).

Ascomparedwiththecompactsconsistingofmicro-crystallinecelluloseonly(AV),theapplicationoftheinitialstarchesfortabletformulationdecreasedtheten-silestrengthsofthecompacts,andthetensilestrengthswerealsodecreasedafterphysicaltreatments(Table3).Theextentofthedecreasedidnotdependonthetypeofstarchapplied,buttheeffectsofthethermalmodificationsonthetensileparametersdiffered.Thedecreaseinthetensilestrengthcausedbytheappli-cationofthermallymodifiedPSwasmoresignificantthanthedecreasesinthestrengthparametersofthecomprimatescontainingphysicallytreatedMS.TheexperimentalresultsofMScouldberelatedtoitsspecialstructure.MSismoreresistanttowardsmod-ifyingagentsthanisPS,whichisprobablyduetotheoccurrenceoflipidsinthesurfaceandhelicalamylosecomplexes(Fortunaetal.,1998).

ThesolidscontainingtheinitialPShadsmallercon-tactanglesthanthosecompressedfromtheunmodifiedMS(Table4).ThelowerhydrophilicityofMScouldbeattributedtothelipidcontentandthespecialstruc-tureofthisstarchtype(vanOss,1995).TheeffectsofthemicrowavedPSandMSonthecontactangleswere

170A.Szepesetal./InternationalJournalofPharmaceutics302(2005)166–171

Table3

Influenceofstarchesonphysicalparametersofcompactscontaining20%starchand80%microcrystallinecellulose(Avicel®PH101)(com-pressionforce=2±0.5kN)(n=10)Compacts

Avicel®PH101(AV)AV/PSAV/PSmwAV/PS130◦CAV/MSAV/MSmwAV/MS130◦C

Averagemass(g)0.2157±0.00500.2149±0.00120.2237±0.00120.2172±0.00110.2099±0.00310.2158±0.00730.2224±0.0011

Averageheight(mm)2.33±0.022.51±0.022.64±0.012.79±0.012.34±0.042.40±0.052.48±0.02

Averagetensilestrength(MPa)5.46±0.094.60±0.244.00±0.223.46±0.134.83±0.444.31±0.354.43±0.14

Table4

Contactanglesandsurfacefreeenergiesofcompactswithaporosityof10±2%containing20%starchand80%microcrystallinecellulose(Avicel®PH101)(compressionforce=20±1kN)(n=10)Compacts

Avicel®PH101(AV)AV/PSAV/PSmwAV/PS130◦CAV/MSAV/MSmwAV/MS130◦C

Θwater(◦)38.83±1.7733.00±1.4047.20±1.9744.84±1.0234.47±1.7845.03±1.4853.51±1.76

Θdiiodomethane(◦)25.02±0.6624.46±0.7033.08±0.7737.59±1.6525.24±1.1233.13±1.2032.05±1.53

γd(mN/m)33.6932.7231.8131.8733.2131.4430.90

γp(mN/m)27.8131.7223.2825.2130.6025.3320.19

γ(mN/m)61.4964.4455.0957.0863.8056.7751.09

Polaritya(%)45.2349.2242.2644.1747.9644.6239.52

γ:surfacefreeenergy;γd:surfacefreeenergydispersepart;γp:surfacefreeenergypolarpart;Θ:contactangle.aPolarity=(γp/γ)×100(OhandLuner,1999).

significantandhadthesamescale,whileapplicationoftheMStreatedbyconductiveheatingresultedinlargerchangesinthecontactanglesthanthoseforthePS.Thedecreasedhydrophilicityoftheprocessedstarchescouldbeexplainedbythefactthatthermaltreatmentdecreasesthecontentofthemorehydrophilicstruc-turepolymer(“amylose-escape”)(Lewandowiczetal.,1997,2000;Palasinskietal.,2000).

Boththemicrowaveirradiationandtheconventionalheatingreducedthesurfacefreeenergyandthepolarityofthecompacts,whichwasduetothewaterlossfromthestarchescausedbythethermaltreatment(Table1).Thedisperseandpolarpartsofthesurfacefreeenergiesoftheinitialsampleswerenearlyequal.Afterthether-malprocesses,thepolarcomponentsfelldrastically,whereasthedispersepartdidnotdecreasesignificantly(Table4).

Accordingtopreviousstudies,thesusceptibilityofstarchestothehydrothermalprocessesdependedontheirbotanicalorigin.Ourresultsallowtheconclu-sionthatthedifferenceinresponseofPSandMStothemicrowaveirradiationwasrelatedtothestruc-turaldifferenceoftheinitialstarches.Furthermore,the

samplesrespondeddifferentlytothetwohydrothermaltreatments,againthecrystallinitymightbeadecisivefactor.Thechangesintensilestrength,wettabilityandsurfacefreeenergycouldbeattributedtothewaterloss(dehydration)duringmicrowavetreatment.Ontheotherhand,irreversiblestructuralchangescausedbythephysicaltreatments,suchascrystalline–amorphoussolidphasetransitionand“amylose-escape”mayhaveaninfluenceontheaboveproperties.Acknowledgements

ThisstudywassupportedbytheGermanAca-demicExchangeServiceandtheHungarianSchol-¨Project2003/2004),arshipCommittee(DAAD-MOB

furthermorebytheHungarianNationalResearchFoun-dation(OTKAT-047166).References

´Benk´´´D´avid,A.,oczy,Z.,Acs,Z.,Greskovits,D.,D´avid,A.Z.,2000.Thetheoreticalbasisforscaling-upbyuseofthemethod

A.Szepesetal./InternationalJournalofPharmaceutics302(2005)166–171

171

ofmicrowavegranulation.Drug.Dev.Ind.Pharm.26,943–951.

Fell,J.T.,Newton,J.M.,1970.Determinationoftabletstrengthby

diametral-compressiontest.J.Pharm.Sci.59,688–691.

Fortuna,T.,Juszczak,L.,Palasinski,M.,1998.Changeingran-uleporosityonmodificationofstarch.Zywnosc.Technologia.Jakosc.4,124–130.

Joshi,H.N.,Kral,M.A.,Topp,E.M.,1989.Microwavedryingof

aqueoustabletfilmcoatings:astudyonfreefilms.Int.J.Pharm.51,19–25.

Lewandowicz,G.,Fornal,J.,Walkowski,A.,1997.Effectof

microwaveradiationonphysico-chemicalpropertiesandstruc-tureofpotatoandtapiocastarches.Carbohyd.Polym.34,213–220.

Lewandowicz,G.,Jankowski,T.,Fornal,J.,2000.Effectof

microwaveradiationonphysico-chemicalpropertiesandstructureofcerealstarches.Carbohyd.Polym.42,193–199.

Oh,E.,Luner,P.E.,1999.Surfacefreeenergyofethylcellulosefilms

andtheinfluenceofplasticizers.Int.J.Pharm.188,203–219.

Owens,D.K.,Wendt,R.C.,1969.Estimationofthesurfacefree

energyofpolymers.J.Appl.Polym.Sci.13,1741–1747.

Palasinski,M.,Fortuna,T.,Juszczak,L.,Fornal,J.,2000.Changes

insomephysico-chemicalpropertiesofstarchgranulesinducedbyheatingandmicrowaveradiation.Pol.J.FoodNutr.Sci.9,17–22.

Pan,X.,Liu,H.,An,Z.,Wang,J.,Niu,G.,2001.Microwave-enhanceddehydrationandsolventwashingpurificationofpeni-cillinGsulfoxide.Int.J.Pharm.220,33–41.

Sewell,G.J.,Palmer,A.J.,1991a.Thechemicalandphysicalstabil-ityoftreeintravenousinfusionssubjectedtofrozenstorageandmicrowavethawing.Int.J.Pharm.72,57–63.

Sewell,G.J.,Palmer,A.J.,Tidy,P.J.,1991b.Characterizationofa

frozenstorage-microwavethawingsystemforintravenousinfu-sions.Int.J.Pharm.70,119–127.

Swarbrick,J.,Boylan,J.C.,2002.EncyclopediaofPharmaceutical

Technology,vol.2.MarcelDekker,NewYork.

vanOss,C.J.,1995.Hydrophobicityofbiosurfaces—origin,quanti-tativedeterminationandinteractionenergies.ColloidSurf.B5,91–110.