Amylose-lipid-complex-formation-during-cooking-of-

Amylose-lipidcomplexformationduringcookingofrice¯ourKulwinderKaur,NarpinderSingh*DepartmentofFoodScienceandTechnology,GuruNanakDevUniversity,Amritsar143005,IndiaReceived18October1999;accepted20June2000AbstractThee€ectsofcookingrice¯ourinthepresenceofmyristic,palmiticandstearicacidonamylose-lipidcomplexformation,watersolubilityandpastingpropertieswerestudied.Di€erentfattyacidswereaddedtorice¯our,at1.5,3.0and4.5%levels,andcookedinVisco-amylographat95Cfor30,60and90min.Amylose-lipidcomplexformationincreasedandwater-solubilitydecreasedwiththeincreaseinlevelsofallthefattyacidsinricepastecookedfor30±90min.Complexingofamylosewithallthefattyacidsincreasedwiththeincreaseincookingtime.Myristicacidhadthehighestabilitytoformthecomplexandstearicacidthelowest.Iodinespectraofricepastecookedwithandwithoutlipidswerealsodeterminedtocon®rmtheformationofamylose-lipidcom-plexes.Bothlmaxandratiosofabsorbancesat630and520nmdecreasedwiththeincreaseinlevelsofallthefattyacids.Myristicacidcausedagreaterreductioninlmaxandratiosofabsorbance.Additionofallthefattyacidsincreasedthepastingtemperature,peakviscosity,viscosityat95Candviscosityat50Cofricepaste.Consistencycoecientand¯owbehaviourindicesofricepastescookedinthepresenceofdi€erentfattyacidswerealsodeterminedusingaBrook®eldviscometer.Consistencycoecientincreasedwiththeincreaseinlevelsofallthefattyacidsandtheincreasewasmorepronouncedwithmyristicacid.#2000ElsevierScienceLtd.Allrightsreserved.Keywords:Rice;Myristicacid;Palmiticacid;Stearicacid;Complexingindex;Pastingproperties1.IntroductionAdditionsoffattyacidsalterthephysicalandchemicalpropertiesofstarchyfoods(Singh,Cairns,Morris&Smith,1998).Thechangesbroughtaboutbytheminstarchyfoodshavebeenattributedtotheformationofcomplexesbetweenamyloseandlipids.Lipidshavebeenreportedtoforminclusioncompoundswithamylose,withthehydrocarbonportionofthelipidlocatedwithinthehelicalcavityofamylose(Banks&Greenwood,1972).Thecomplexhasbeenreportedtodecreasewater-solubilityandsusceptibilityofthestarchestoalphaamylasedigestion(Eliasson&Krog,1985;Sene-viratne&Biliaderis,1991).HooverandHadziyev(1981)usedswellingpowerandsolubilityteststoshowthatmyristicacidwasthemoste€ectivefattyacidinformingcomplexeswithstarches.LagendijkandPennigs(1970)foundthatcomplexingindexdecreasedasthenumberofdoublebondsincreased.Mercier,Charbonniere,GrebautandDeLaGueriviere(1980)showed,usingtwin-screwextrusion,thatvaluesforwater-solublecarbohydratesandretro-gradationdecreasedwhenoleicacidorlinoleicacidwereusedinplaceofstearicacid.HahnandHood(1987)reportedthatincreasingunsaturationresultedintolessbinding.NierleandElBaya(1990)studiedthee€ectofdi€erentlipidsonviscosityandpastingprop-ertiesofwheatstarch.Hibi(1994)reportedthee€ectofpalmiticacidandemulsi®ersonviscoelasticpropertiesofricestarchgel.Thepresentstudywasundertakentoexaminethee€ectsofcookingofrice¯ourinthepresenceofpalmi-tic,myristcandstearicacid(99%purity)oncomplexingindex,iodinespectra,solubility,pastingandrheologicalproperties.2.Materialsandmethods2.1.MaterialApaddysampleofvarietyPR-106wasprocuredfromthe1997harvest.Palmiticacid,myristicacidandstearicacidwereobtainedfromSigma(Poole,UK).0308-8146/00/$-seefrontmatter#2000ElsevierScienceLtd.Allrightsreserved.PII:S0308-8146(00)00202-8FoodChemistry71(2000)511±517*Correspondingauthor.E-mailaddress:[e-mail](N.Singh).2.2.PreparationofsamplesCleanpaddywasdehuskedandpolishedtoauniform6%degreeofpolishasdescribedearlier(Singh,Sekhon&Kaur,1990).MilledricewasobtainedandgroundinaBrabenderQuadrumatJuniorMill.2.3.PastingandcookingofricepastePastingpropertiesofricewithandwithoutlipidswerestudiedusingaBrabenderVisco-amylographequippedwith350cm-gsensitivecartridgeandcoolingcoil.A40gsample(14%,moisturebasis)wasblendedwith450mlofdistilledwatertoobtainedasmoothdispersion.Thedispersionwasheatedfrom30Cto95C(1.5C/min)andheldat95Cfor30,60and90minandthencooledto50C(1.5C/min).Di€erentfattyacids(palmitic,myristicandstearicacid)werealsoaddedat1.5,3.0and4.5%levels(on¯ourweightbasis)tostudytheire€ectsonpastingproperties.Thecookedricesampleswerealsoanalysedforcomplexingindex,water-solubility,iodinespectraandrheologicalproperties.2.4.ComplexingindexComplexingindex(CI)wasdeterminedusingthemethodofGilbertandSpragg(1964).Thismethodinvolvestheformationofstarch-iodinecomplexandmeasurementofstarchwhichisnotcomplexedwithlipids.Theabsorbanceisrelatedtotheportionofstarchthatiscomplexedtotheiodine.Theiodinesolutionusedforanalysiswaspreparedbydissolving2gofpotassiumiodideand1.3gofI2in50mlofdistilledwaterandallowingittodissolveforabout2h.Thenthe®nalvolumewasmadeto100mlusingdistilledwater.Acookedricepastesample(5g)wasmixedwith25mlofdistilledwaterinatesttube.Thetesttubewasvortexedfor2minandcentrifugedfor15minat3000rpm.Thesupernatant(500ml)anddistilledwaterwereaddedtoiodinesolution(2ml).Thetubewasinvertedseveraltimesandtheabsorbancewasmeasuredat690nm.CIwascalculatedfromtheequation.CI…%†ˆ…Absorbanceofcontrolÿabsorbanceofsample†100=absorbanceofcontrol:2.5.Water-solubilityFordeterminati