发酵工艺

FermentationTechnologyBTY323Lectures10,11TheessentialcomponentsofafermentorOutletportSteamgenerator/RefrigerationunitStirrermotorpHprobeTemperatureprobeFoambreakerMixingflangeStirrerpaddleSterileairsupply0.5mfilterunitFilling/inoculationportGlass(10L)orsteelvesselHeatexchangeelementAiroutlet(tocondenser)Fermentorcontrols•TemperaturecontrolCriticalforoptimumgrowth•AerationRelatedtoflowrateandstirrerspeedDependentontemperature•MixingDependsonfermentordimensions,paddledesignandflangingControlaerationrateMaycausecelldamage(shear)•pHcontrolImportantforculturestability/survival•FoamingcontrolTemperaturecontrol•Heatsuppliedbydirectheatingprobesorbyheatexchange•Microbialgrowthisverysensitivetotemperaturechanges-accuratetemperaturefeed-backcontrolisrequired•Fermentationsareexothermic–coolingmayberequiredAeration•Filteredairissuppliedbyforcedairflowatthebaseofthefermentor•Thesizeofairbubblesisdictatedbytheair-supplytubeholediameter•Thetimetakenforairbubblestorisetothesurface(residencetime)isdependentonbubblesizeandstirrerrate.•Therateofoxygendissolutionisdependentonsurfacearea(bubblesize)andresidencetime•ThedO2(dissolvedoxygenconcentration)isdependentonthedissolutionrateandthemicrobialuptakerate.•TomaintainconstantdO2,anO2electrodeisusedtogivefeed-backinformationtotheair-supplypumpTypicaldO2profileinbatchfermentorwithoutoxygenmonitoringFermentationtimeCellgrowth[oxygen]RapidoxygendepletionLow[oxygen]limitsmaximumculturegrowthCulturedeathMixing•Efficientmixingiscriticalfor:HomogeneousdistributionofnutrientsEventemperaturedistributionRapidpHadjustmentRetentionofairbubbles•Differentdesignsofstirrerbladesgivedifferentcirculationpatterns•Mixingisassistedbythepresenceofflangesonthefermentorwalls•Stirrertipspeeddictatesthedegreeofshearstress•Somecellstypesareverysusceptibletoshearstress•ExcessivestirringcanpromotefoamingpHcontrol•MostcultureshavenarrowpHgrowthranges•Thebufferinginculturemediaisgenerallylow•MostculturescausethepHofthemediumtoriseduringfermentation•pHiscontrolledbyusingapHprobe,linkedviacomputertoNaOHandHClinputpumps.pHGrowth2-3pHunitspH6.58.5UncontrolledControlledFoaming•FoamingiscausedwhenMicrobialculturesexcretehighlevelsofproteinsand/oremulsifiersHighaerationratesareused•Excessfoamingcauseslossofculturevolumeandmayresultinculturecontamination•Foamingiscontrolledbyuseofafoam-breakerand/ortheadditionofanti-foamingagents(silicon-basedreagents)Sterilisation•Thefermentorandalladditions(medium,air)mustbecompletelysterile•Sterilisationisperformedby:Smallfermentors(10L);autoclavingLargefermentors;•Vessel:steamsterilisation;gas(ethyleneoxide)•Medium:autoclavingorultrafiltration•Air:ultrafiltrationFermentationSystems•StirredBatch•FedBatch•Continuous•AirliftBatchFermentor1.Mediumadded2.Fermentorsterilised3.Inoculumadded4.Fermentationfollowedtocompletion5.CultureharvestedGlucoseCellbiomassTimeProductCharacteristicsofaBatchFermentationSystem•Simplestfermentoroperation•Sterilisationcanbeperformedinthereactor•Allnutrientsareaddedbeforeinoculation•MaximumlevelsofCandNarelimitedbyinhibitionofcellgrowth•BiomassproductionlimitedbyC/Nloadandproductionoftoxicwasteproducts•CellsareharvestedwhenbiomasslevelsorproductlevelsstarttodeclineFed-BatchFermentorsFeedstockvessel(sterile)PumpCharacteristicsofFedBatchFermentors•Initialmediumconcentrationisrelativelylow(noinhibitionofculturegrowth)•Mediumconstituents(concentratedCand/orNfeeds)areaddedcontinuouslyorinincrements•Controlledfeedresultsinhigherbiomassandproductyields•FermentationisstilllimitedbyaccumulationoftoxicendproductsGlucoseBiomassProductBiomassProductGlucoseBATCHFED-BATCHContinuousFermentorFeedstockvessel(sterile)Pump1CollectionvesselPump2Flowrate1=Flowrate2CharacteristicsofContinuous(Chemostat)Fermentors•Inputrate=outputrate(volume=const.)•Flowrateisselectedtogivesteadystategrowth(growthrate=dilutionrate)DilutionrateGrowthrateculturewashesoutDilutionrateGrowthratecultureovergrowsDilutionrate=Growthratesteadystateculture•Productisharvestedfromtheoutflowstream•Stablechemostatculturescanoperatecontinuouslyforweeksormonths.