第六章 各类农产品贮藏技术

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Section1GrainStorage1.Grainharvesting,threshingandcleaning2.Dryingmethods3.Thebiodeteriorationofgrainandtheriskofmycotoxins4.Storage1、Grainharvesting,threshingandcleaning(i)HarvestingmethodsSometimes,itisdesirabletohastenthetimeofcropharvesting.Afteragraincropreachesphysiologicalmaturity,anydelayinharvestingmaycausedeteriorationinqualityandyieldreduction.Anumberofdirectandmethodsmaybeadoptedbycropproducerstohastenthetimeofcropharvesting.Physiologicalmaturitydefinedasmaximumkerneldryweight,moisturepercentagerangesfromabout20to40%（25~30%）.determinesthereadinessofthecropforharvest.Thisstageofcropdevelopmentisreachedpriortothecropbeingreadyforcombiningasthekernelisrelativelysoft(easilydentedwithfingernail)andkernelmoisturepercentageisrelativelyhigh.Onceaplanthasattainedphysiologicalmaturity,itcannotaccumulateanymoredrymatter.HarvestingHarvestingmethodsdifferaccordingtothepartoftheplanttobeused.Asregardsforagecrops,thewholeplantiscut,butforundergroundcrops(eg,groundnuts,rootsandtubers),thecropisliftedwhilethesoilstickingtoitisremoved.Withcereals,thecropisfirstcuteitherasawholeorpartially(ears),andthenthreshedandcleanedtoseparatethegrainfromtheearsandstraw.Inthelattercasetwomainalternativesexist:separateharvestingandthreshing,orcombinedharvestingandthreshing.HarvestingHarvestingmethodsManualharvestingMechanizedharvestingDIRECTMETHODSDefoliationandDesiccationLeavingitinthefieldlongerpredisposesittoweathering.Sometimes,inclementweatherthreatensthequalityoftheharvest,therebycompellingtheproducertomakeadjustmentsintheharvestingschedule.Suchadjustmentsinclude“inducing”earlyharvestmaturitybyapplyingadefoliantordesiccant.HarvestingAdefoliantcausesleaf-drop,whileadesiccantcausestheplanttodryoutinthefieldanddie.Incottonproduction,greenleavestendtostainthefibers.Defoliationofcottonpriortomechanizedharvestingreducesnotonlytheamountofundesirableplantdebrisintheharvestedfiberbutalsothechanceoftaintingitwithplantpigments.HarvestingINDIRECTMETHODSGenerally,cropsareharvestedwhentheconditionsoftheeconomicproductaresuchthattheproductcanbestoredforareasonableperiodoftimewithoutdeterioration.However,iftheproducthasafacilityfordrying,thecropmaybeharvestedsoonerthannormalharvestmaturitythendriedtostorablemoisturecontentatalaterdate.Harvesting(ii)ThreshingmethodsTraditionalthreshingMechanizedthreshingCombinedharvestingandthreshingmethods(iii)Cleaning2、DryingmethodsThereisanessentialneedtodrygrainquicklyandeffectivelyafterharvestandbeforestoragetoretainmaximumquality,toattainamoisturecontentsufficientlylowtominimiseinfestationbyinsectsandmicroorganisms(bacteria,fungi,etc.),andtopreventgermination.Naturalmethodsofdryingmakeuseofexposureofthewetgraintothesunandwind.Artificialdryersemploytheapplicationofheatfromcombustionoffossilfuelsandbiomassresources,directlyorindirectly,andinbothnaturalandforcedconvectionsystems.Mechanicaldryers,longusedindevelopedcountries,arefindingincreasedapplicationasfarmingandgrainhandlingsystemsdevelop.DryingNaturalandsolardryingThetraditionalpracticeofgraindryingistospreadcropontheground,thusexposingittotheeffectsofsun,windandrain.Thelogicofthisisinescapable;thesunsuppliesanappreciableandinexhaustiblesourceofheattoevaporatemoisturefromthegrain,andthevelocityofthewindtoremovetheevaporatedmoistureis,inmanylocations,atleasttheequivalentoftheairflowproducedinamechanicaldryer.DryingDryingMechanicaldryersBatch-in-BinDryersThesmallcapacityversionofthebatch-in-bindryer,otherwiseknownastheflat-beddryer,hasbeendevelopedforfarm-orvillage-leveluse.Itscapacityisoftheorderof1-3tonnes/daywithdryingtimesof6-12hours.DryingRe-circulatingBatchDryersThedryerisaself-containedunitwithanannulardryingchamber,500mmthick,aroundacentralplenumchamber,afanandheater,andacentralaugerfortransportingthegrainfromthebottomtothetop.Whendryingiscompletethegrainisdischargedfromthetop.Mostdryersofthistypeareportableandcanbemovedrelativelyeasilyfromfarmtofarm.DryingContinuous-flowDryersContinuous-flowdryerscanbeconsideredasanextensionofre-circulatingbatchdryers.However,ratherthanthegrainre-circulatingfrombottomtotop,asinthelatter,thegrainisremovedfromthebottom,insomesystems,cooled,andthenconveyedtotemperingorstoragebins.DryingDrying3、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.,themycotoxinaflatoxiningrainssuchasc