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Retrogradation behaviour of milled and brown rice pastes during ageing

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Retrogradationbehaviourofmilledandbrownricepastesduringageing

M.Mariotti*,N.Sinelli,F.Catenacci,M.A.Pagani,M.Lucisano

DepartmentofFoodScienceandMicrobiology(DiSTAM),UniversityofMilan,ViaG.Celoria2,20133Milan,Italy

articleinfo

Articlehistory:Received1January2008Receivedinrevisedform9July2008Accepted5September2008

Keywords:RiceGelRetrogradationViscoamylographDynamicrheologicaltestFT-NIRspectroscopyabstract

Retrogradationofgelatinisedstarchisthemainphenomenonthatinfluencesthetextureofcookedrice.Therateofretrogradationisaffectedbyseveralfactorsincludingamyloseandamylopectinratio,proteinandfibre.TheobjectiveofthisstudywastoanalysethepastingpropertiesandtheretrogradationbehaviourofsixtraditionalandfivearomaticItalianricevarieties.Thepastedgels,aftercooling,wereevaluatedbydynamicrheologicalmeasurementsforupto7daysofstorageat4󰀂C.ThesampleswerealsoanalysedbyaNIRspectrometer.Thepastingpropertiesandtheretrogradationbehaviourofmilledricefloursstronglydependedonthericevarieties.Duringgelageing,anoticeableincreaseofG0andG00

wasobservedonlyforthemilledricevarietiesAsia,Gange,FragranceandVialoneNano,characterisedbyahighamylosecontent.Nofurtherhardeningwasfoundeitherfortheothermilledvarietiesorforallthebrownsamples.Themethodsusedinthiswork(dynamicoscillatoryrheometryandFT-NIRspectros-copy)turnedouttobeveryusefulinthedefinitionofricestarchgelsageing.Ó2008ElsevierLtd.Allrightsreserved.

1.Introduction

Duringgelatinisation,starchgranulesswelltoseveraltimes

theirinitialsizeastheresultofthelossofcrystallineorderand

waterabsorption;theyarepartiallyruptured,releasingamylose,

andformathree-dimensionalnetworkwiththeswollengranules

embeddedintothematrix.Astarchpastecanthereforeberegar-

dedasacompositematerialconsistingofswollengranules

dispersedinacontinuousbiopolymermatrix(Noeletal.,1993).

Thepropertiesofeachphaseandtheinteractionsbetweenthe

componentsareimportantelementsindeterminingtherheolog-

icalbehaviourofpastedgels.Thesepropertiesdependonseveral

factors,includingthetypeandtheconcentrationofstarch,the

amylose/amylopectinratio,thetemperatureprofileappliedtothe

pastes,andthepresenceandconcentrationofothersolubleand

insolublecompoundssuchasprotein,salts,lipids,andfibre(Lii

etal.,1995,2004).

Theswollenstarchgranulesformastrongpackedgelstructure

withahighshearresistancewhoseintensityincreasesoncooling

duetostarchretrogradation.Infact,ifthestarchconcentrationis

sufficientlyhigh,thepastecanconvertintogeluponcooling(TesterandMorrison,1990).Retrogradationofgelatinisedstarchinvolves

thereorderingoftheamylosechainsinshort-termageing(Dou-

blierandChoplin,1989)andaslowerreorganisationofamylopectin

afterlongerperiods(BiliaderisandZawistowski,1990;Laietal.,

2000).

TheBrabenderMicro-Visco-Amylograph(MVA)andtheRapid

ViscoAnalyser(RVA)arecurrentlyusedasstandardanalyticaltools

toassessthepastingcharacteristicsofstarchandfloursuspensions

inwater.Severalparametersevaluatedfromthepastingprofilesof

milledriceflourhavebeenshowntocorrelatewiththeeating

quality(Bergmanetal.,2004)andwiththeend-useofriceflour.

Relationshipshavebeenobservedbetweentheamylographic

measurementsandtheamyloseandproteincontent(SandhyaRani

andBhattacharya,1989)andtheinstrumentalparametersusedto

measurethetexturalpropertiesofriceflourpastes.

Dynamicoscillatoryrheometryisusefulformonitoringstruc-

turedevelopmentduringgellingandageingwithoutbreakingthe

structuralelementsformedinthesampleuponageing.In

adynamictest,thestoragemodulus(G0),lossmodulus(G00),

complexmodulus(G*)orcomplexviscosity(h*)aredetermined

usingasinusoidalstraincycle.Manyauthorshaveusedrheological

methodstomonitorthechangesthatoccurduringtheheatingof

starchesandflours(HageninaandDing,2005;Hamedetal.,2008;

Liietal.,1995,1996;Raoetal.,1997;SvegmarkandHermansson,

1991)andtoevaluatetheviscoelasticityofstarchpastes(Liietal.,

1995;SandhyaRaniandBhattacharya,1989;Yoo,2006)andgels

(BiliaderisandZawistowski,1990;ChunandYoo,2004).

Anotherinterestingmethodforacquiringinformationabout

molecularchangesduringgelageingisnearinfrared

reflectanceAbbreviations:FT-NIR,Fouriertransformnearinfraredreflectance;G0,storagemodulus;G00,lossmodulus;MSC,multiplicativescattercorrection;MVA,BrabenderMicro-Visco-Amylograph;NIR,nearinfraredreflectance;PCA,principalcomponentanalysis;Ricevarieties:AP,Apollo;AS,Asia;AU,Augusto;BA,Balilla;FR,Fragrance;GA,Gange;GI,Giano;GL,Gladio;RO,Roma;SE,Selenio;VN,VialoneNano;RVA,RapidViscoAnalyser.*Correspondingauthor.Tel.:þ390250319186;fax:þ390250319190.E-mailaddress:manuela.mariotti@unimi.it(M.

Mariotti).ContentslistsavailableatScienceDirect

JournalofCerealScience

journalhomepage:

www.elsevier.com/locate/jcs

0733-5210/$–seefrontmatterÓ2008ElsevierLtd.Allrightsreserved.

doi:10.1016/j.jcs.2008.09.005JournalofCerealScience49(2009)171–177