★★不同贮藏条件下枇杷果实的生理反应及耐贮性研究

Physiologicalresponseofloquatfruittodifferentstorage

conditionsanditsstorability

ZhanshengDinga,b,ShipingTiana,∗,YoushengWanga,BoqiangLia,b,

ZhulongChana,b,JinHana,b,YongXua

a

KeyLaboratoryofPhotosynthesisandEnvironmentalMolecularPhysiology,InstituteofBotany,ChineseAcademyofSciences,Beijing100093,China

bGraduateSchoolofChineseAcademyofSciences,Beijing100039,China

Received16March2005;accepted25March2006

Abstract

Loquat(EriobotryajaponicaLindl.)fruitwerestoredinairat25◦C,modifiedatmospherepackaging(MAP,polyethylenebagof0.01mmthickness)at1and6◦C,controlledatmospheres(CA)of10%O2+1%CO2and,CAwith70%O2treatmentfor24hatfirst,thenstoredinCAwith10%O2+1%CO2at1◦C,todeterminetheeffectsofatmospheresandtemperaturesonqualityattributes,physiologicalpropertiesandstorabilityduringstorageperiods.TheresultsindicatedCAwith10%O2+1%CO2wasmoreeffectiveinreducingfruitdecay,SSC/TA,pH,activitiesofendo-PGandexo-PG,inhibitingethylacetateaccumulationinfruit,inducingethanolaccumulationinfruitatlaterstorageperiodincomparisonwithMAPtreatment.LoquatfruitcouldbestoredinthisCAconditionat1◦Cformorethan50dwithnormalflavourandlowdecayindexofabout7%.Shorttermhigh-O2treatmentatthebeginningofstoragehadlittleeffectonfruitflavor,butstimulatedethanolaccumulationinloquatfruit,andreducedactivitiesofendo-PGandexo-PG.MAPtreatmentshowedmoreeffectivenessinreducingfruitdecay,off-flavorandweightlossat1◦Cthanat6◦C.CAconditionsweremoreeffectiveforreducingtheactivitiesofPPOandoxidativestresscomparedtoothertreatments,whichmaybethereasonwhyloquatfruitstoredinCAconditionshadlowerdecayindexthanthatkeptinotherconditions.

©2006ElsevierB.V.Allrightsreserved.

Keywords:Loquat;Storagecondition;Physiologicalproperties;Qualityattributes;Storability

1.Introduction

Loquat(EriobotryajaponicaLindl.)iswidelycultivatedinsubtropicalregionsofChina,Japan,IndiaandMediter-raneanarea(Linetal.,1999).TheharvestseasonofloquatinChinalastsfromtheendofApriltothemiddleofJunewhenthemarketisshortoffreshfruit(QiuandZhang,1996),soloquatfruitusuallyhasahighmarketvalue.Butloquatfruitaresusceptibletodecay,moistureandnutritionallossesdur-ingtheirpostharvestlife.Forexample,storagetimeofthefruitinairatroomtemperatureisabout6–9d(Shaw,1980;Zhengetal.,2000).

Modifiedatmospherepackaging(MAP)andcontrolledatmosphere(CA)withlow-O2andhigh-CO2atlowtem-∗

Correspondingauthor.Tel.:+861062836559;fax:+861082594675.E-mailaddress:tsp@ibcas.ac.cn(S.Tian).

perature,havebeensuccessfullyusedtoreducedecay,main-tainqualityandextendstoragelifeinmanyfruit(Beaudry,1999;Brechtetal.,2003).ExposuretosuperatmosphericO2concentrationmaystimulate,havenoeffect,orreduceratesofrespirationandethyleneproduction,dependingonthecommodity,maturityandripenessstage,O2con-centration,storagetimeandtemperature,andconcentra-tionsofCO2andC2H4presentintheatmosphere;inhibitthegrowthofsomebacteriaandfungi(KaderandBen-Yehoshua,2000).CAconditionswithashorttimetreat-mentof70%O2showedtobeeffectivetopreventpeeloflongan(Tianetal.,2002),jujube(Linetal.,2004),andlitchifruit(Tianetal.,2005)frombrowning,andsignifi-cantlylimitethanolproductionoflitchiflesh.CAwith70%O2treatmentfor15dinducedsuperoxidedismutase(SOD)andcatalase(CAT)activitiesinpeachfruit(Wangetal.,2005).

0925-5214/$–seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.postharvbio.2006.03.012

144Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150

Thepreviousreportshowedthatloquatfruitretainedinitialqualityandchemicalcomponentsfor30din0.15%perfo-ratedpolyethylenefilmpackagingat1and5◦C(Dingetal.,1998).LoquatfruitkeptinMAPwithlowergasperme-ancepolyethylenebagpackaging(0.02–0.05mmthickness)at5◦Chadhigherqualityandminimalriskofdisorderdevel-opment,andthefruitstoredinthinnerbagshowedalowerincidenceofdecay(Dingetal.,2002).Whensodiumcar-bonate(Na2CO3)wasaddedin0.06mmthickpolyethylenestoragebagstodecreaseCO2concentration,loquatfruitretainedhigherqualityat3◦Cfor40d(Liuetal.,1994).However,thereisnoanyreportabouteffectsofCAcondi-tiononphysiologyandstorabilityofloquatfruituptonow.Theobjectivesofthisstudyweretoinvestigatetheeffectsofdifferentstorageconditions,suchasCAwithlow-O2orCAwithashorttimeofhigh-O2shock,MAP(polyethylenebagof0.01mmthickness)atdifferenttemperatures,onphysio-logicalproperties,qualityattributesandstorabilityofloquatfruitduringstorageperiods,andtoevaluatetherelationshipbetweenfruitdecayandethyleneproduction,activitiesofpolyphenoloxidase(PPO),peroxidase(POD)andphenylala-nineammonium-lyase(PAL),andoxidativestressinloquatfruit.

2.Materialsandmethods2.1.Fruit

Loquat(E.japonicaLindl.cv.Wuxing)fruitwerehar-vestedfromanorchardinShuangliu,SichuanProvince,China.Thefruitwerehand-pickedatthematurestage(orangecolour),thenweretransportedtoBeijingbyair(4–6h)imme-diately.Fruitwithoutdisease,mechanicalinjuryanduni-formedinshapewereusedintheexperimentaccordingtodifferentstorageconditions.2.2.Storageconditions

Storageconditionsweredesignedasfollows:control,inairat25◦C;MAP,inpolyethylenefilmbags(0.01mmthick-ness,220mm×300◦mm,13–18%O2and2–4%CO2)at1±1◦Cor6±1C,therewere10fruitineachbag;CA-I,10%O2+1%CO2at1±1◦C;CA-II,fruittreatedwith70%O2for24h,thenstoredin10%O2+1%CO2at1±1◦C.Controlledatmospherecabinets(105cm×55cm×100cm),withCO2andethyleneabsorbers,werelinkedwithanatmosphereanalyzer(FC-701,Italy).InitialO2andCO2levelsinthecabinetswereestablishedbyaflow-throughsystem,mixingN2(100%)andO2(99.5%),orN2andCO2viapressureregulators,thenautomaticallycontrolledandregulatedbytheanalyzer.TheconcentrationsofO2andCO2intheMAPbagsweremeasuredbyanatmosphereanalyzer(CYES-II,Shanghai,China)each7dduringtheexperimentalperiods.ThefruitwerestoredinCAconditionsandMAPwithapproximately95%relativehumidity(RH).

Therewere50kgfruitineachCAcabinet,30kgfruitinMAPand10kgfruitinair,respectively,withthreereplications.Accordingtothetreatments,about5kgfruitwereusedforeachanalysisafterthespecifiedintervals.2.3.Determinationoffruitdecayandweightloss

Fruitdecayandweightlosswasdeterminedin30fruitwiththreereplications,respectively.Thedecaywasassessedbymeasuringtheextentofdecayedareaoneachfruit,andwasdeterminedas:0,nodecay;1,lessthan1/4decay;2,1/4–1/2decay;3,1/2–3/4decay.Thedecayindexwascalculatedusingthefollowingformula:[(1×N1+2×N2+3×N3)×100/(3×N)],whereNisthetotalnumberoffruitmeasuredandN1,N2andN3werethenumberoffruitshowingthedifferentdegreesofdecay.Weightlosswascalculatedbythefollowingformula:(A−B)/A×100,whereAisthefruitweightjustbeforestor-ageandBwasthefruitweightafterspecialstorageperiod.2.4.MeasurementsofpH,SSCandTA

ThepHandsolublesolidscontent(SSC)offruitweredeterminedusingapHanalyzer(pHanalyzer,CpHS-3B,Shanghai,China)andanAbberefractometer(10481S/N,USA),respectively.TAwasdeterminedbypotentiometrictitrationwith0.1mol/Lsodiumhydroxide(NaOH)uptopH8.1,using1mLofdilutedjuicein25mLdistilledH2O,whichcontainphenolphthalein.Therewerethreereplicatesforeachanalysispertreatment.

2.5.Ethanol,ethylacetateandethylenemeasurementEthanolandethylacetatecontentsandethyleneproductionrateoffruitweredeterminedbyheadspacegaschromatog-raphy(Shimadzu,GC-9A,Japan).Forethanolandethylacetate,15gfleshfromninefruitineachstorageconditionwerecollectedandhomogenizedin15mLofice-cold20%trichloroaceticacidwithaKinematicatissuegrinder.A5gsampleofthemixturewassealedina10mLvial,andthenincubatedinathermostatedbathat40◦Cfor60min.Forethy-leneproduction,20fruitwereselectedrandomlyfromeachtreatment,thenweightedandputinto10Lsealedcontainersandtheairincontainerswasanalyzedafteranhour.

A1mLsampleoftheheadspacegaswasremovedfromvialorcontainerbysyringeandinjectedintothegaschro-matographequippedwithaflameionizationdetector(FID)andglasscolumn(2mm×4m,thecolumnwaspackedwithpolymerofcinnameneanddi-vinyl-benzene,GDX-502,Tianjin,China).Theexperimentalconditionswere:85◦Coventemperature,130◦Cinjectortemperature,250◦Cdetec-tortemperature.Thecomponentswereidentifiedindividuallybycomparingretentiontimesagainststandards,concentra-tionsbeingdeterminedbyaregressionequationcalculatedonfoursamplesofstandardconcentrations.Experimentswereconductedthreetimeseach,induplicate.

Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150145

2.6.Measurementofenzymeactivity

Ineachtreatment,10gfleshfrom10fruitwascollectedandhomogenizedin25mLofice-coldextractionbufferand0.5gpolyvinylpolypyrrolidone(PVPP)withaKinemat-icatissuegrinder(Crl-6010,Kriens-LU,Switzerland).Forlipoxygenase(LOX),superoxidedismutase(SOD)andcata-lase(CAT)assay,theextractionbufferwas50mMsodiumphosphate(pH7.8).ForPPOandPOD,100mMsodiumphosphatebuffer(pH6.4)wasused.ForPALandpolygalac-turonase(PG)assay,thebufferwassodiumboratebuffer(100mM,pH8.9)and0.5Msodiumchloride(NaCl),respec-tively.Thehomogenatewascentrifugedat27,000×gfor50minat4◦Candtheresultingsupernatantswereuseddirectlyforassay.

DeterminationofLOX,SODandCATactivitieswasper-formedbythemethodofWangetal.(2005)withslightmodifications.ForLOX,thereactionmixturecontained2.8mLsodiumphosphatebuffer(100mM,pH6.0),0.1mLofsodiumlinoleicacidsolution(50mM)and0.1mLsam-ple.Theblankcontained2.9mLofsodiumphosphatebuffer(100mM,pH6.0)and0.1mLofsodiumlinoleicacid.Theincreaseinabsorbanceat234nmwasmeasured,usingaUV-160Spectrophotometer(Shimadzu,Japan).TheLOXspecificactivitywasexpressedasUkg−1,whereoneunitwasexpressedas1␮molhydroperoxideformedpermassoffreshfruitfleshperminat30◦C.

ForSOD,thereactionmixture(3mL)contained65mMsodiumphosphatebuffer(pH7.8),13mMmethionine,75␮Mnitrobluetetrazolium(NBT),10␮MEDTA,2␮Mriboflavinand0.1mLoftheenzymeextract.Themixtureswereilluminatedbylight(60molm−2s−1)for10minandtheabsorbancewasthendeterminedat560nm.Identicalsolutionsheldinthe−dark1servedasblank.SODactivitywasexpressedasUkg,whereoneunitwasdefinedastheamountofenzymethatcauseda50%decreaseoftheSOD-inhibitableNBTreductionpermassoffreshfruitflesh.ForCAT,thereactionmixtureconsistedof2.8mLH2O2(40mM,in50mMsodiumphosphatebuffer,pH7.0)and0.2mLenzymeextract.ThedecompositionofH2O2wasmeasuredbythedeclineinabsorbanceat240nmduring120s.ThespecificactivitywasexpressedasUkg−1,whereoneunitofcatalaseconvertslmolofH2O2permassoffreshfruitfleshperminat30◦C.

PPOandPODactivitiesweremeasuredat30◦Canddeterminedbymonitoringtheincreaserateofabsorbanceat398and460nm,respectively,accordingtothemethodol-ogydescribedbyTianet−1al.(2005).PPOandPODactivitieswereexpressedasUkg,whereoneunitwasexpressedastheincreaserateofabsorbencypermassoffreshfruitfleshpermin.

PALactivitywasassayedaccordingtothemethodofAssisetal.(2001),withslightmodification.Enzymeextract(1mL)wasincubatedwith2mLofboratebuffer(50mM,pH8.8)and1mLofl-phenylalanine(20mM)for60minat37◦C.Thereactionwasstoppedwith1mL1Mhydrochloricacid

(HCl).PALactivitywasdeterminedbytheproductionofcinnamate,whichwasmeasuredbyabsorbanceat290nm.Theblankwasthecrudeenzymepreparationmixedwithl-phenylalaninewithzerotimeincubation.Specificenzymeactivitywasdefinedbytheproductionofcinnamicacidpermassoffreshfruitfleshwithunitsofnmolkg−1s−1.

PGsactivitiesweremeasuredaccordingtothemethodofZhouetal.(2000),withslightmodification.Forendo-PGassay,1mLenzymeextractwasmixedwith0.1mL1%chloramphenicol,0.5mL0.2Msodiumacetate(pH4.0)and1mL1%polygalacturonicacid.Forexo-PGassay,1mLenzymeextractwasmixedwith0.1mL1%chlorampheni-col,0.1mL0.02Mcalciumchloride(CaCl2),0.5mL0.2Msodiumacetate(pH5.5)and1mL1%polygalacturonicacid.After12h,themixturewasboiledfor3min,cooledtoroomtemperature,◦andthencentrifugedat20,000×gfor10minat4C.Thegalacturonicacidintheresultingsupernatantwasmeasuredbyanthronereagentat620nm.Galacturonicacidwasusedasastandard,andcontrolsofboiledextractwererun.Oneactivityunitwasexpressedasthemolaramountofgalacturonicacidreleased−1permassoffreshfruitfleshpersecond,␮molkg−1s.2.7.Statisticalanalysis

AllstatisticalanalyseswereperformedwithSPSS11.0(SPSSInc.,Chicago,IL,USA).OneANOVAwasusedtocomparemorethantwomeans,andLevene’stestwasfirstperformedforhomogeneityofvariancetestofthemeans,thenDuncan’stestwasappliedtomeanswithequalvariance,Dunnett’sT3testwasperformedtomeanswithunequalvari-ance.Inaddition,independent-samplesT-testwasappliedtocomparetwomeans.DifferencesatP=0.05wereconsideredtobesignificant.

3.Results

3.1.Effectsofatmospheresandtemperaturesondecayindexandweightloss

Fruitdecayindexgraduallyincreasedwithstoragetimeinallstorageconditions(Fig.1).FruitstoredinCA-IandCA-IIpresenteddecayindexesof6.7and5.6%after50dof

Fig.1.Decayindexofloquatfruitindifferentconditionsduringstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

146Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150

Fig.2.Weightlossofloquatfruitindifferentconditionsduringstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

storage,butthefruitstoredinMAP(13–18%O2and2–4%CO2)at1and6◦C,showedsignificantlyhigherdecayindexesof16.7and27.8%on49d.TheresultindicatedCAstoragewasmoreeffectivelyinreducingloquatfruitdecaythanMAP,and1◦Ctemperaturewasmorefavorabletostoreloquatfruitcomparedto6◦C.

ThelossoffruitweightgraduallyincreasedwithstoragetimeincontrolandMAPtreatments(Fig.2).Totalweightlossoffruitstoredat25◦Cwas15.6%after9d,whilethatoffruitstoredat6and1◦Cwas8.0and4.4%,respectively,after49dofstorage.WeightlossoffruitstoredinCAconditionswasverylow,below2%(datanotshown).

3.2.EffectsofatmospheresandtemperaturesonSSC/TAandpH

ThevalueofSSC/TAiscloselyrelatedtofruitflavour,andthelowervalueismorefavourable.SSC/TAoffruitincreasedmoreslowlywiththestoragetimeinCAconditionsthaninMAPandcontrol(Fig.3A).SSC(%)offruitinalltreatmentschangedslightlywithstoragetime,buttitratableacidity(%)decreasedwithdifferentspeedsamongthetreatments,which

Fig.3.SSC/TA(A)andpH(B)ofloquatfruitindifferentconditionsdur-ingstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

Fig.4.Ethanol(A),ethylacetate(B)contentsandethyleneproductionrate(C)ofloquatfruitindifferentconditionsduringstorageperiods.Barsrep-resentstandarderrorsofthemeanwiththreereplications.

mightaccountforthedifferenceoffruitSSC/TAunderdif-ferentstorageconditions(datanotshown).

pHinfruitshowedagradualincreasewithstoragetimeinalltreatments(Fig.3B).Thevalue,changedfrom3.73atharvestto4.28,4.47,4.55and4.83attheendofstorageinCA,MAPat1and6◦Candcontrolcondition,respectively.ThechangeofpHwasapproximatelycoincidentalwithSSC/TA,becausepHincreasemightresultfromdecreaseoftitratableacidcontentinfruit.

3.3.Effectsofatmospheresandtemperatureson

ethanol,ethylacetatecontentsandethyleneproductionTheethanolcontentofloquatfruitincreasedslightlywithstoragetimeincontrol,butitincreasedsignificantlyinMAPandCA,especiallyafteramonthinstorage(Fig.4A).Loquatfruit◦accumulatedmoreamountofethanolinCAthaninMAPat1Cabouton50d,andhigh-O2treatmentforshorttimestimulatedaccumulationofethanol.Attheendofstorage,ethanolcontentinloquatfruitstoredinMAPshowedtobehigherat6◦Cthanat1◦C.

EthylacetatecontentofloquatfruitstoredincontrolandCAconditionschangedslightlyduringstorageperiods,butfluctuatedsignificantlyinfruitkeptinMAPcondition(Fig.4B).Duringstorageperiods,loquatfruitstoredinCAconditionsaccumulatedlesseramountofethylacetatethan

Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150147

Fig.5.ChangesinLOX(A),SOD(B)andCAT(C)activitiesofloquatfruitindifferentconditionsduringstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

thatkeptinMAP,andshorttermofhigh-oxygenshockhadlittleeffectonit.TherewasnosignificantdifferenceinethylacetatecontentinfruitstoredinMAPbothat1and6◦C.Ethyleneproduction−1rateofloquatfruitincreased−1from0.34nmolkg−1satinitialdayto0.72nmolkgs−1after3dofstoragethendecreasedrapidlyincontrol,butchangedslightlyatfirstthendecreasedrapidlyafter7or10dand,retainedbelow0.2nmolkg−1s−1inMAPandCAtreatments(Fig.4C).High-oxygenshockandstoragetemperatureshadlittleeffectontheethyleneproductionoffruit.3.4.EffectsofatmospheresandtemperaturesonLOX,SODandCATactivities

TheactivityofLOXchangeddifferentlyunderdifferentstorageconditionsduringstorageperiods(Fig.5A).Com-paredwiththeactivityonday0,itincreasedsignificantlyon6dincontrol,butchangedlittleinMAPduringstorageperiods,increasedon30dinCA-I,anddecreasedon50dinCA-II.SODactivitysignificantlydecreasedon9dincon-trolfruit,whilefluctuatedinMAPandincreasedgraduallyinCAexcepton30d(Fig.5B).AsignificantlyhigheractivityofSODwasfoundinfruitstoredinCAconditionsthaninMAPafter30dofstorage.Shorttermofhigh-oxygenshockandstoragetemperaturesdidnotsignificantlyaffectSODactivity.TheactivityofCATfluctuatedincontrolandMAP,

increasingatfirstthendecreasingwithstoragetimeunderCAconditions(Fig.5C).CATactivityinMAPat1◦Cwashigherthanthatat6◦Cafter42d,andshorttermhigh-oxygenshockhadlittleeffectontheactivityofCAT.

3.5.EffectsofatmospheresandtemperaturesonPPO,PODandPALactivities

PPOactivitypresentedobviouschangesduringstorageperiodsinalltreatments(Fig.6A).Incontrolfruit,itincreasedsignificantlyon3d,andthenchangedlittleafterwards.Althoughitfluctuatedwithstorageperiods,itwassignifi-canthigherthantheactivityon0d,andhadlittledifferencebetweenat1and6◦CinMAP.ComparedtothechangesinMAP,ithadaspikeon30dinCAconditions,andchangedsimilarlybetweenCA-IandCA-II.

TheactivityofPODfluctuatedduringstorageperiodsinallconditions(Fig.6B).ItdidnotchangesignificantlyinfruitstoredinairandinMAPat6◦C,onlyincreasedsignificantlyon49dinMAPat1◦C,incomparisonwiththeactivityon0d.InCA-I,itsignificantlyincreasedbefore30dandon50d,whileonlyincreasedon50dinCA-II.

PALactivityincreasedatfirst,andthendecreasedwithstoragetimeinalltheconditionsexceptCA-II(Fig.6C).Itreachedaclimaxvalueof4.3nmolkg−1s−1after3dincontrolfruit,andreachedthepeakvalueof2.0and

Fig.6.ChangesinPPO(A),POD(B)andPAL(C)activitiesofloquatfruitindifferentconditionsduringstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

148Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150

Fig.7.Changesinendo-PG(A)andexo-PG(B)activitiesofloquatfruitindifferentconditionsduringstorageperiods.Barsrepresentstandarderrorsofthemeanwiththreereplications.

2.5nmolkg−1s−1after14dinMAPat1and6◦C,respec-tively.PeakvalueofPALactivityinfruitstoredinCA-Iwas2.6nmolkg−1s−1,andappearedafter20dofstorage.ItchangedlittleduringstorageperiodsinCA-II.3.6.Effectsofatmospheresandtemperaturesonendo-PGandexo-PGactivities

Infruitstoredunderdifferentconditions,activitiesofendo-PGandexo-PGchangedsimilarlyduringstorageperi-ods(Fig.7).PGactivitiessignificantlyincreasedwithstoragetimeincontrolfruitwithin9d,butdidnotchangesignifi-cantlyinfruitstoredinMAPbefore14dandinCAbefore20d,soMAPandCAsignificantlyinhibitedtheincreaseofPGactivitiesatthebeginningperiodofstorage.PGactivitiesinfruitstoredinCAconditionsat30and50dweresignificantlowerthanthatinMAPat28and49d,respectively,soCAhadmoreeffectonretardingtheincreaseofPGsactivitiesthanMAP.DifferenttemperatureshadlittleeffectonPGactivi-ties,buthigh-oxygenshockdecreasedthemfrom30to50d.PGsarerelatedwiththecellwallsubstancemetabolism,andincreaseoftheiractivitiescanmakecellwalldecomposedandleadtofruitsoftening.Inthisstudy,fruitfirmnessdecreasedwithstoragetimeunderalltheconditions,butCAcondi-tionsweremorebeneficialformaintainingfruitfirmnessascomparedtoMAP(datanotshow).

4.Discussion

Decayisthemainfactorinfluencingpostharvestqualityandstoragelifeofloquatfruit(Shaw,1980).Ingeneral,ethy-leneiscloselyrelatedwiththeripening,senescenceanddecayoffruit,andlowethyleneproductionoffruitstoredinlow-O2orhigh-CO2atmosphereisbeneficialtodelaytheripening

andsenescenceoffruit.Ithasbeenreportedthatethylenepro-ductionrateoffennelstoredinMAPat0◦Cdroppedrapidlyatfirstandthenremainedatlowlevel,atthesametime,fen-nelbrowningwasreduced(Escalonaetal.,2004).G´omezandArt´es(2004)alsoreportedthatbothethyleneproductionandqualitydecreasewereinhibitedingreencelerystoredinCAwithlow-O2andhigh-CO2.Inpresentstudy,MAPandCAstorageconditionswereeffectiveinmaintainingfruitqualityandreducingfruitdecayandethyleneproduction,soreducingethyleneproductionmightbeoneofthereasonswhyMAPandCAsignificantlyreduceddecayindexesandimprovedstorabilityofloquatfruit.Meanwhile,thedecayindexesofloquatfruitstoredat6◦Cand1◦CinMAPweredifferent,buttheirethyleneproductionrateweresimilar,sotheremightbeotherfactorsinfluencingthedecayofloquatfruitbesidesethylene.Theethyleneresponseisnotonlyrelatedtoitspro-ductionbutalsotheO2concentrationinstorageatmosphere,andmaybeinhibitedinlower-O2conditions(Beaudry,1999).Inthepresentexperiment,betweenMAPat1◦CandCAtreatments,theethyleneproductionratesweresimilar,whilethedecayindexesweresignificantlydifferent,sothefactthatCAmoreeffectivelyreducedthedecayindexofloquatfruitthanMAPmaybeduetolowerO2concentrationinCA(10%)thanthatinMAP(13–18%).KlaustermeyerandMorris(1975)foundsuper-atmosphericO2levelsincreasedethyleneproductionandtheincidenceandseverityofpinkribandC2H4-inducedrussetspottingonlettuce.Incontrast,KaderandBen-Yehoshua(2000)consideredthatexposureto80or100kPaO2reducedethyleneproductionratesanddelayed◦ripeningofmature-greenandbreakertomatoesat20C.Inthisstudy,wefoundthathigh-oxygenshockfor24hatthebeginningofstoragehadlittleeffectontheethy-leneproductionrateanddecayinloquatfruit.Sotheeffectofhigh-oxygenmaybedependedondifferentcommunities,etc.

Fleshbrowningwasoneofthesymptomsofloquatfruitdecay.Tissuebrowning,duetooxidativereactionsofphe-noliccompoundsbyoxidases(PPOandPOD)andthereac-tionproducts,o-quinones,tovariouspolymerizedproducts,resultsfromlossofcompartmentalizationwithinthecellswhenexposedtophysicaland/orphysiologicalstresses.PALisakeyenzymeinthephenyl-propanoidbiosynthesispath-way,andcloselyrelatedwiththesynthesisofphenoliccom-poundsintissue.Therearedifferentopinionsabouttherela-tionshipbetweenPPOactivityandfleshbrowning.WhitakerandLee(1995)consideredthatenzymaticbrowningwaspri-marilyresponsibleforthebrowningoffruitandvegetables.ButChengandCrisosto(1995)indicatedthatPPOactiv-itywasnotalimitingfactorinenzymaticbrowning.IthasbeenreportedthatCAwith5%O2+10%CO2moresignif-icantlyinhibitedtheenzymaticactivitiesofPPOandPOD,andeffectivelypreventedfleshbrowningofsweetcherryfruit(Tianetal.,2004).Inaddition,comparedwithMAPwith15–19%O2+2–4%CO2,CAof4%O2+5%CO2inhibitedPPOactivity,preventedpeelbrowninganddecreaseddecayoflonganfruit(Tianetal.,2002).Inthepresentstudy,MAP

Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150149

significantlydelayedtheactivityincreaseofPPOandPALandhadlittleeffectonthePODactivitycomparedtocontrol,sotheinhibitioneffectofMAPonthedecayandbrown-ingofloquatfruitwasrelated◦toPPOandPAL,ratherthanPOD.Loquatfruitstoredat6Cwereshowedfleshbrowningmorereadilythanfruitstoredat1◦CinMAP.ThismightbeduetothePALactivitybeinghigherat6◦Cthanat1◦C.IncomparisonwithMAP,CAreducedPPOactivity,increasedPODactivity,andhadlittleeffectonthePALactivity,sotheincreasedeffectivenessofCAonreducingthebrowningofloquatfruitmightbepartiallyduetothereductionofPPOactivity.High-oxygenshockhadlittleeffectonthebrowningofloquatfruit,atthesametime,slightlyaffectedtheactivitiesofPPOandPAL.

Oxidativestressoccurswhenactiveoxygenspecies(AOS)areinexcessofthetissuescavengingcapacityoffreshpro-duce;andoxidativestressoffruitandvegetablesreducesproductstoragequalityandmarketability(Hodgesetal.,2004).LOXisconsideredtobepartlyresponsiblefortheformationofsuper-oxide(O2−)andsingletoxygen(Gardner,1995).SODandCATareimportantactivefree-radicalscav-engingenzymes,andsuper-oxidecanbeconvertedintohydrogenperoxidebySOD,andhydrogenperoxidecanbeconvertedintowaterbyCAT(Scandalios,1993).Oxidativestress,decreaseofSODandCATactivities,combinedwiththeincreaseofLOXactivity,mightcontributetothedevel-opmentofchillinginjuryinpeachfruit,andtheeffectivenessofCAwith5%O2+5%CO2indelayingtheoccurrenceofchillinginjurymaybeduetodelayingthereductionofantiox-idantenzymesduringstoragetime(Wangetal.,2005).Inthisexperiment,LOXactivityincontrolfruitincreasedonday6,buttheactivityofSODandCATdidnotchangesignifi-cantlyatthistime(Fig.5),sotheremightbemarkedoxidativestressinloquatfruiton6d.Comparedwithcontrolfruit,thedegreeofoxidativestressinMAPandCAtreatmentsmightbelessseriousfortheLOXactivitydidnotchangeorchangedslightlyduringstoragetime,andtheactivitiesofSODandCATincreasedduringmostofstorageperiods.TheoxidativestressmightbelessseriousinCAtreatmentsthaninMAPforthehigherSODactivitiesinCA.ReducingoxidativestressinloquatfruitmightbeoneofthereasonsCAconditionswereeffectiveinmaintainingfruitresistanceandreducing.Mean-while,lowertemperaturewasmorebeneficialforinhibitingdiseasedevelopmentwhenfruitwerestoredinthesamecon-ditions(Fig.1).

Inconclusion,thepresentstudyshowedthatCAwith10%O2+1%CO2wasmoreeffectiveinreducingthedecayofloquatfruitthanMAPandcontrol,andthemainreasonmightbereducingtheactivitiesofPPOandoxidativestress.

Acknowledgments

ThisworkwassupportedbyMinistryofScienceandTech-nologyofChina(2001BA501A09)andtheNationalNaturalScienceFoundationofChina(30430480).

References

Assis,J.S.,Maldonado,R.,Munoz,T.,Escribano,M.I.,Merodio,C.,

2001.EffectofhighcarbondioxideconcentrationonPALactivityandphenoliccontentsinripeningcherimoyafruit.PostharvestBiol.Technol.23,33–39.

Beaudry,R.M.,1999.EffectofO2andCO2partialpressureonselected

phenomenaaffectingfruitandvegetablequality.PostharvestBiol.Technol.15,293–303.

Brecht,J.K.,Chau,K.V.,Fonseca,S.C.,Oliveira,F.A.R.,Silva,

F.M.,Nunes,M.C.N,Bender,R.J.,2003.Maintainingoptimalatmosphereconditionsforfruitandvegetablesthroughoutthepostharvesthandlingchain.PostharvestBiol.Technol.27,87–101.

Cheng,G.W.,Crisosto,C.H.,1995.Browningpotential,phenoliccom-position,andpolyphenoloxidaseactivityofbufferextractsofpeachandnectarineskintissue.J.Am.Soc.Hortic.Sci.120,835–838.

Ding,C.K.,Chachin,K.,Hamauzu,Y.,Ueda,Y.,Imahori,Y.,1998.

Effectsofstoragetemperaturesonphysiologyandqualityofloquatfruit.PostharvestBiol.Technol.14,309–315.

Ding,C.K.,Chachin,K.,Ueda,Y.,Imahori,Y.,Wang,C.Y.,2002.Mod-ifiedatmospherepackagingmaintainspostharvestqualityofloquatfruit.PostharvestBiol.Technol.24,341–348.Escalona,V.H.,Aguayo,E.,G´omez,P.,Art´es,F.,2004.Modifiedatmo-spherepackaginginhibitsbrowninginfennel.Lebensm.-Wiss.u.-Technol.37,115–121.

Gardner,H.W.,1995.Biologicalrolesandbiochemistryoflipoxygenasepathway.HortScience30,197–205.G´omez,P.A.,Art´es,F.,2004.Controlledatmospheresenhancepostharvestgreenceleryquality.PostharvestBiol.Technol.34,203–209.

Hodges,D.M.,Lester,G.E.,Munro,K.D.,Toivonen,P.T.A.,2004.

Oxidativestress:importanceforpostharvestquality.HortScience39,924–929.

Kader,A.A.,Ben-Yehoshua,S.,2000.Effectsofsuperatmosphericoxy-genlevelsonpostharvestphysiologyandqualityoffreshfruitandvegetables.PostharvestBiol.Technol.20,1–13.

Klaustermeyer,J.A.,Morris,L.L.,1975.Theeffectsofethyleneandcar-bonmonoxideontheinductionofrussetspottingoncrispheadlettuce.PlantPhysiol.56,63(Abstract).

Lin,L.,Tian,S.P.,Wan,Y.K.,Xu,Y.,Yao,H.J.,2004.Effectsoftem-peratureandatmospherecomponentonqualityofstoredjujubefruit.ActaBot.Sin.46,928–934.

Lin,S.,Sharpe,R.H.,Janick,J.,1999.In:Jules,J.(Ed.),Loquat:Botany

andHorticulture,HorticulturalReviews,23.Wiley,NewYork,pp.234–276.

Liu,Q.,Yu,B.G.,Wang,X.X.,1994.Theeffectsofstorageconditions

onthequalityandphysiologicalchangesinloquat.J.NanjingAgric.Univ.17,27–31(inChinesewithEnglishabstract).

Qiu,W.L.,Zhang,H.Z.,1996.FruitTreeofChinaLonganandLoquat.

ChinaForestryPublishingHouse,Beijing,pp91–103(inChinese).Scandalios,J.G.,1993.Oxygenstressandsuperoxidedismutase.Plant

Physiol.107,7–12.

Shaw,P.E.,1980.Loquat.In:Nagy,S.,Shaw,P.E.(Eds.),Tropicaland

SubtropicalFruit.AVIWestport,CT,pp.480–481.

Tian,S.P.,Jiang,A.L.,Xu,Y.,Wang,Y.S.,2004.Responsesofphysiology

andqualityofsweetcherryfruittodifferentatmospheresinstorage.FoodChem.87,43–49.

Tian,S.P.,Li,B.Q.,Xu,Y.,2005.EffectsofO2andCO2concentrationonphysiologyandqualityoflitchifruitinstorage.FoodChem.91,659–663.

Tian,S.P.,Xu,Y.,Jiang,A.L.,Gong,Q.Q.,2002.Physiologicaland

qualityresponsesoflonganfruittohighO2orhighCO2atmospheresinstorage.PostharvestBiol.Technol.24,335–340.

Wang,Y.S.,Tian,S.P.,Xu,Y.,2005.Effectsofhighoxygenconcentration

onpro-andanti-oxidantenzymesinpeachfruitduringpostharvestperiods.FoodChem.91,99–104.

150Z.Dingetal./PostharvestBiologyandTechnology41(2006)143–150

Zhou,H.W.,Lurie,S.,Lers,A.,Khatchitski,A.,Sonego,L.,Arie,

R.B.,2000.Delayedstorageandcontrolledatmospherestorageofnectarines:twostrategiestopreventwoolliness.PostharvestBiol.Technol.18,133–141.

Whitaker,J.R.,Lee,C.Y.,1995.Recentadvancesinchemistryofenzy-maticbrowning.In:Lee,C.Y.,Whitaker,J.R.(Eds.),SymposiumonEnzymaticBrowninganditsPrevention,vol.600.Washington,DC,USA,pp.2–7.

Zheng,Y.H.,Li,S.Y.,Xi,Y.F.,2000.Changesofcellwallsubstances

inrelationtofleshwoodinessincold-storedloquatfruit.ActaPhyto-physiol.Sin.26,306–310(inChinesewithEnglishabstract).