各类农产品贮藏技术.ppt

第六章各类农产品贮藏技术,第一节粮食贮藏（储藏）第二节果品贮藏第三节蔬菜贮藏,Section1GrainStorage,Grainharvesting,threshingandcleaningDryingmethodsThebiodeteriorationofgrainandtheriskofmycotoxinsStorage,1、Grainharvesting,threshingandcleaning,(i)HarvestingmethodsSometimes,itisdesirabletohastenthetimeofcropharvesting.Afteragraincropreachesphysiologicalmaturity,anydelayinharvestingmaycausedeteriorationinqualityandyieldreduction.Anumberofdirectandmethodsmaybeadoptedbycropproducerstohastenthetimeofcropharvesting.,Physiologicalmaturity,definedasmaximumkerneldryweight,moisturepercentagerangesfromabout20to40%（2530%）.determinesthereadinessofthecropforharvest.Thisstageofcropdevelopmentisreachedpriortothecropbeingreadyforcombiningasthekernelisrelativelysoft(easilydentedwithfingernail)andkernelmoisturepercentageisrelativelyhigh.Onceaplanthasattainedphysiologicalmaturity,itcannotaccumulateanymoredrymatter.,Harvesting,Harvestingmethodsdifferaccordingtothepartoftheplanttobeused.Asregardsforagecrops,thewholeplantiscut,butforundergroundcrops(eg,groundnuts,rootsandtubers),thecropisliftedwhilethesoilstickingtoitisremoved.Withcereals,thecropisfirstcuteitherasawholeorpartially(ears),andthenthreshedandcleanedtoseparatethegrainfromtheearsandstraw.Inthelattercasetwomainalternativesexist:separateharvestingandthreshing,orcombinedharvestingandthreshing.,Harvesting,HarvestingmethodsManualharvestingMechanizedharvestingDIRECTMETHODSDefoliationandDesiccationLeavingitinthefieldlongerpredisposesittoweathering.Sometimes,inclementweatherthreatensthequalityoftheharvest,therebycompellingtheproducertomakeadjustmentsintheharvestingschedule.Suchadjustmentsinclude“inducing”earlyharvestmaturitybyapplyingadefoliantordesiccant.,Harvesting,Adefoliantcausesleaf-drop,whileadesiccantcausestheplanttodryoutinthefieldanddie.Incottonproduction,greenleavestendtostainthefibers.Defoliationofcottonpriortomechanizedharvestingreducesnotonlytheamountofundesirableplantdebrisintheharvestedfiberbutalsothechanceoftaintingitwithplantpigments.,Harvesting,INDIRECTMETHODSGenerally,cropsareharvestedwhentheconditionsoftheeconomicproductaresuchthattheproductcanbestoredforareasonableperiodoftimewithoutdeterioration.However,iftheproducthasafacilityfordrying,thecropmaybeharvestedsoonerthannormalharvestmaturitythendriedtostorablemoisturecontentatalaterdate.,Harvesting,(ii)Threshingmethods,TraditionalthreshingMechanizedthreshing,Combinedharvestingandthreshingmethods,(iii)Cleaning,2、Dryingmethods,Thereisanessentialneedtodrygrainquicklyandeffectivelyafterharvestandbeforestoragetoretainmaximumquality,toattainamoisturecontentsufficientlylowtominimiseinfestationbyinsectsandmicroorganisms(bacteria,fungi,etc.),andtopreventgermination.,Naturalmethodsofdryingmakeuseofexposureofthewetgraintothesunandwind.Artificialdryersemploytheapplicationofheatfromcombustionoffossilfuelsandbiomassresources,directlyorindirectly,andinbothnaturalandforcedconvectionsystems.Mechanicaldryers,longusedindevelopedcountries,arefindingincreasedapplicationasfarmingandgrainhandlingsystemsdevelop.,Drying,Naturalandsolardrying,Thetraditionalpracticeofgraindryingistospreadcropontheground,thusexposingittotheeffectsofsun,windandrain.Thelogicofthisisinescapable;thesunsuppliesanappreciableandinexhaustiblesourceofheattoevaporatemoisturefromthegrain,andthevelocityofthewindtoremovetheevaporatedmoistureis,inmanylocations,atleasttheequivalentoftheairflowproducedinamechanicaldryer.,Drying,Drying,Mechanicaldryers,Batch-in-BinDryersThesmallcapacityversionofthebatch-in-bindryer,otherwiseknownastheflat-beddryer,hasbeendevelopedforfarm-orvillage-leveluse.Itscapacityisoftheorderof1-3tonnes/daywithdryingtimesof6-12hours.,Drying,Re-circulatingBatchDryers,Thedryerisaself-containedunitwithanannulardryingchamber,500mmthick,aroundacentralplenumchamber,afanandheater,andacentralaugerfortransportingthegrainfromthebottomtothetop.Whendryingiscompletethegrainisdischargedfromthetop.Mostdryersofthistypeareportableandcanbemovedrelativelyeasilyfromfarmtofarm.,Drying,Continuous-flowDryersContinuous-flowdryerscanbeconsideredasanextensionofre-circulatingbatchdryers.However,ratherthanthegrainre-circulatingfrombottomtotop,asinthelatter,thegrainisremovedfromthebottom,insomesystems,cooled,andthenconveyedtotemperingorstoragebins.,Drying,Drying,3、Thebiodeteriorationofgrainandtheriskofmycotoxins,Theconditionofstoredgrainisdeterminedbyacomplexinteractionbetweenthegrain,themacro-andmicro-environmentandavarietyoforganisms(includingmicroorganisms,insects,mites,rodentsandbirds)whichmayattackit.,ecosystem,Grainprovidesanabundantsourceofnutrients,andthenaturalconsequenceofthetypeofstableecosystemdescribedabovewillnormallybespoilage(biodeterioration)ofthegrain,causedbytheorganisms.,Theorganismsthatareintroducedintothestoragefacilityfromthefieldortheairincludebacteriaandfungi,especiallyAspergillusspp.(e.g.,A.glaucus,A.flavus,andA.candidus)andPenicillium,Helminthosporium,andFusarium.Theseorganismscreatemoldinessinstoredgrain.SomeliketheA.flavus,producedeadlytoxins(e.g.,themycotoxinaflatoxiningrainssuchascornandcropssuchaspeanuts).,3.1microorganisms,Fungimayinfectgraininthefield,themajorspeciesbeingAlternaria链格孢属,Cladosporium枝孢属,Helminthosporium长蠕孢属,andFusarium镰孢属.Theirroleinqualitydeteriorationinstorageisminimal.StoragefungiofimportanceareAspergillus曲霉,Penicillium青霉,andtoalesserextentSporendonema丝内霉.,moulds,Theextentofcontaminationbymouldsislargelydeterminedbythetemperatureofthegrainandtheavailabilityofwaterandoxygen.Mouldscangrowoverawiderangeoftemperatures,frombelowfreezingtotemperaturesinexcessof50C.Ingeneral,foragivensubstrate,therateofmouldgrowthwilldecreasewithdecreasingtemperatureandwateravailability.,moulds,Theintergranularwaterconcentrationisdescribedeitherintermsoftheequilibriumrelativehumidity(RH,%)orwateractivity(aw).Typicalwateractivitieswhicharenecessaryformouldgrowthrangefrom0.70to0.90.,moulds,Theinteractionbetweengraintemperatureandmoisturecontentalsoaffectstheextentofmouldcolonisation.Thepassageofwaterfromthegrainintothevapourphaseisencouragedbyanincreaseintemperature.Maize,forexample,canberelativelysafelystoredforoneyearatamoisturelevelof15percentandatemperatureof15C.However,thesamemaizestoredat30Cwillbesubstantiallydamagedbymouldswithinthreemonths.,moulds,Insectsandmites(arthropods)can,ofcourse,makeasignificantcontributiontowardsthebiodeteriorationofgrain,throughthephysicaldamageandnutrientlossescausedbytheiractivity.Theyarealsoimportant,however,becauseoftheircomplexinteractionwithmouldsand,consequently,theirinfluenceonmouldcolonisation.,moulds,insectsIngeneral,grainisnotinfestedbyinsectsbelowatemperatureof17Cwhereasmiteinfestationscanoccurbetween3and30Candabove12percentmoisturecontent.Themetabolicactivityofinsectsandmitescausesanincreaseinboththemoisturecontentandtemperatureoftheinfestedgrain.Arthropodsalsoactascarriersofmouldsporesandtheirfaecalmaterialcanbeutilisedasafoodsourcebymoulds.Furthermore,mouldscanprovidefoodforinsectsandmitesbut,insomecases,mayalsoactaspathogens.,moulds,BrokenkernelsAnotherimportantfactorthatcanaffectmouldgrowthistheproportionofbrokenkernelsinaconsignmentofgrain.Brokenkernels,causedbygeneralhandlingand/orinsectdamage,arepredisposedtomouldinvasionoftheexposedendosperm.Ithasbeenestimated,forexample,thatincreasingtheproportionofbrokengrainsbyfivepercentwillreducethestorage-lifeofthatconsignmentbyapproximatelyoneorderofmagnitude;thatisfrom,say,150to15days.,moulds,Mouldgrowthisalsoregulatedbytheproportionsofoxygen,nitrogenandcarbondioxideintheintergranularatmosphere.Manymouldswillgrowatverylowoxygenconcentrations;ahalvingoflineargrowth,forexample,willonlybeachievediftheoxygencontentisreducedtolessthan0.14percent.Interactionsbetweenthegasesandtheprevailingwateractivityalsoinfluencemouldgrowth.,Incertaingrains,suchaswheatthatiscultivatedprincipallyforflour,thecharacteristicelasticpropertiescausedbytheproteinglutenislost,reduced,orcompletelydestroyedbypestseatingit.Suchgrainisnolongerfitformakingbreadflour.,3.2Insects,3.2Insects,Themostcommonstoragepeststhatdamagestoredgrainincludethericeweevil(Sitophilusoryzae),granaryweevil(Sitophilusgranatius).Angoumoisgrainmoth(Sitotrogacerealella),Australianwheatweevil(Rhizoperhadominica),andthelessergrainborerfoundinelevators.OthersarePloidiainterpunctella,whichdamagecorninparticular;cadelle(Tenebroidesmauritanicus);khaprabeetle(Trogodermagranarium);saw-toothgrainbeetle(Oryzaephilussurinamensis);andconfusedflourbeetle(Triboliumconfusum).常见的贮粮害虫有米黑虫、黄粉虫、玉米象、豌豆象、蚕豆象、绿豆象、麦蛾、谷蠹、螨类等,3.3Temperatureandmoisture,Notwithstandingthestoragefacility,twofactorsarecriticaltotheretentionofgrainqualityforalongperiodoftime:thetemperatureandmoisturecontentofgrain.Seedsinasingleheaddonotripenuniformlybutoveraperiodofabout3to10days.Atthisstage,theaveragemoisturecontentoftheseedisabout25to30%.Thismoistureistoohighforbinstorage.,Forstorageinwinter,thegrainmoistureshouldbemorethan14%inmostcase.IntheCoastalPlainsandGulfCoast,alowermoisturecontentof11to12%isrecommended.Lowerpercentofmoisture(1%lowerontheaverage)isrequiredinthesummermonths.,Acombinationofhighmoisture(13%orgreater)andhightemperature(70,or21.1)promotesinfestationbymicroorganismsandinsectsthatleadstospoilage.Undersuchconditions,thegrainrespires,producingheat,carbondioxide,andwater.Thisadditionalwaterfurtherincreasesgrainmoisturecontent.,Therespiratoryactivitiesoftheorganismraisetheheatinthegrainbin,sometimesto90to160.Theintenseheatisresponsibleforthebrowningofgrain(callbinburn（Thebrowndiscolorationofgraininstoragecausedbyintenseheatgeneratedfromtherespirationoforganismsintheenclosedstoragebin.）)andevenacharredappearanceandoff-taste.Attemperaturesabove130(54.4),heatsterilizationoccursinthebin,killinginsectsandinactivatingmicrobes.,fermentationUnderconditionsofhighmoisture(greaterthan14%)andlowoxygen,fermentationoccursinthebin.Thisismoreofaproblemwhendeepbins(suchasthoseusedinterminalelevators)areusedforgrainstorage.Itisimportanttoaeratethesebinstoavoidcondensationofmoisture.,Thishappensbyconvectionalcurrent(warmairatthebottomofthebinrisingthroughthegrainandbeingreplacedbycoldair).Therisingwarmairmaycondensenearthetopofthebinwherethecoolgrainis.Toavoidthiscondition,anexhaustfanisinstalledtodrawupthewarmupthewarmairatthebottomofthebinthroughametalpipe.Thispipehasperforationsneatthebottomandisinstalledinthecenterofthebintodrawupthewarmairatthebottomofthebin.,4、Storage,THEGOALSOFGRAINSTORAGE,Theproductshouldhavehighpurity.Itshouldbeingoodphysicalcondition(shape,size,color).Thereshouldbeminimalmechanicaldamage(breakage,cracks,andsplits).Theseedshouldhavehighviability.Thereshouldbenodamagefrominsects(holes,devouredcontents).Thereshouldbenomoldsordiseaseinfection.Thereshouldbenocontaminationfromrodentdroppings.Thereshouldbenopesticideresidue.Thereshouldbenotoxicmicrobialmetabolites.Thereshouldbenolossofflavor.Thereshouldbenofoulodor.Thereshouldbeadequatemoistureintheproduct,Therearefourgeneralwaysinwhichseedcanbestoredforvaryinglengthsoftime.Themethodchosendependsonthedurationoverwhichitisdesiredforseedtomaintainitsquality,amongotherfactors.Seedqualitycannotbeimprovedduringstorage,sincequalitydeclineswithtime.,(1)CONDITIONEDSTORAGESeedsaremaintainedinadryandcoolenvironment.Formostgraincropssuchascorn,wheat,andbarley,seedmoistureatstorageshouldbeabout12to13%andthetemperature20(68)orless.Theseconditionscanholdseedqualityforabout1year.Manycommercialseedcompaniesoperatesuchafacility.,(2)CRYOGENICSTORAGECryogenicstorageofseedisusedwhenseedtobestoredforaverylongperiod.Suchseedsareheldinliquidnitrogenat-196(-295).Thepracticaluseofthismethodofstorageislimitedbythesmallsizeofthecryogenictank.Itiswidelyusedbygermplasmbanksforlong-termstorage.,(3)HERMETICSTORAGESeedsunderthistypeofstoragearesealedinmoisture-resistantcontainers.Metalcontainersareusedwhenverylongstorageperiodsaredesired.Beforethecontainerissealed,theambientairinsidemaybereplacedwithaninertgas(e.g.,argonornitrogen)forbestresults.,(4)CONTAINERIZEDSEEDSTORAGEIncontainerizedseedstorage,seed(usuallyhigh-valuegermplasm)aremaintainedinspeciallyconstructedrooms,equippedwithdehumidifiersandotherenvironmentalcontrolsystems.Sometime,adesiccantisusedtocontrolthelevelofhumidityoftheenvironment.,SUMMARY,Thebesttimeofharvestingdependsontheeconomicpartoftheplant,utilization,andthemethodofstorage.Impropertimingofharvestingcausesyieldreduction,reductioninproductquality,andlossofeconomicvalue.Topreventspoilageinstorage,thegrainshouldbeinproperconditionpriortobeingplacedinstorage(e.g.,rightmoisturecontentofmaterial).Thestorageconditionsshouldbeappropriate(temperatureandmoisture).Saprophyticfungiarethemostimportantmicrobesinqualitydeteriorationofstoredgrain.,review,EcosystemtreatmentbeforestoragephysiologicalmaturityBiodeteriorationtypeofstorageCONDITIONEDSTORAGECRYOGENICSTORAGEHERMETICSTORAGECONTAINERIZEDSEEDSTORAGE,WHEATSTORAGE,WHEATSTORAGE,Preharvest,Thefirststepingoodstoredgrainmanagementistothoroughlycleanbinsandhandlingequipmentthreetofourweeksbeforeharvest.Sinceoldgrainandfinesunderperforatedfloors,inaerationducts,ingrainhandlingequipment,andinsideandoutsidegrainbinsarelikelytobecontaminatedwithinsects,removethismaterialtoavoidimmediateinfestationofthenewcrop.Considerfumigatinganyareasthatcantbecleaned.Afterthebinandequipmentarecleaned,considersprayingthebinwithanapproved,residual-typeinsecticide.,MakeSureGrainisDryEnough,Insectsandmoldsarelessactiveindrygrain,somakesurewheatis14%moistureorlessfor9monthsstorageand13%moistureorlessformorethan9monthsstorage.Barleyshouldbeabout0.5percentagepointsdrierthanthesevalues.,InsecticideTreatment,Ifgrainwillbestoredintonextsummerorifyouoftenhaveproblemswithinsects,considerapplyingagrainprotectantasthecropismovedintostorage.Contactyourcountyextensionofficeforthelatestinformationonapprovedprotectants.Contactpotentialbuyerstoseeiftheywillaccepttreatedgrainsomewillnot.,RustyGrainBeetleonWheat,RedFlourBeetleonWheat,MitesonWheat,Aspergillus,ManageFines,Finestendtocongregateinpocketsinstoragebins,theyrestrictairflow,andtheyaremoresusceptibletoattackbymoldsandinsects.Trytolimittheamountoffinesinstoragebysettingcombinesforminimumgraindamageandmaximumcleaning,operategrainaugersslowlyandfullofgraintoreducekernelbreakage,andconsidercleaninggrainbeforestoragetoremovefines.Eitheruseagrainspreadertofillbinsanddistributefinesuniformlythroughoutthegrainmass,ordon