天津科技大学生物工程专业英语部分电子版

天津科技大学生物工程专业英语部分电子版Chapter1Introduction1.1ThenatureofbiotechnologyBiotechnologyisanareaofappliedbioscienceandtechnologywhichinvolvesthepracticalapplicationofbiologicalorganisms,ortheirsubcellularcomponentstomanufacturingandserviceindustriesandtoenvironmentalmanagement?.Biotechnology5utilizesbacteria,yeasts,fungi,algae,plantcellsorculturedmammaliancellsasconstituentsofindustrialprocesses.Successfulapplicationofbiotechnologywillresultonly?fromtheintegrationofamultiplicityofscientificdisciplinesandtechnologies,includingmicrobiology,biochemistry,genetics,molecularbiology,chemistryandchemicalandprocessengineering.toBiotechnologicalprocesseswillnormallyinvolvetheproductionofcellsorbiomass,andtheachievementofdesiredchemicaltransformations.Thelattermaybefurthersubdividedinto:(a)formationofadesiredendproduct(e.g.enzymes,,organicacids,steroids);.15(b)decompositionofagivenstartingmaterial(e.g.sewagedisposal,,destructionofindustrialwastesoroilspillages).Thereactionsofbiotechnologicalprocessescanbecatabolic,inwhichcomplexcompoundsarebrokendowntosimplerones(glucosetoethanol),oranabolicorbiosynthetic,wherebysimplemoleculesarebuiltupintomorecomplexones(antibiotic20synthesis).Catabolicreactionsareusuallyexergonicwhereasanabolicreactionsarenormallyendergonic.Biotechnologyincludesfermentationprocesses(rangingfrombeersandwinestobread,cheese,antibioticsandvaccines)waterandwastetreatment,partsoffoodtechnology,andanincreasingrangeofnovelapplicationsrangingfrombiomedicalto25metalrecoveryfromlowgradeores.Becauseofitsversatility,biotechnologywillexertamajorimpactinmanyindustrialprocessesandintheoryalmostallorganicmaterialscouldbeproducedbybiotechnologicalmethods.Predictionsoffutureworldwidemarketpotentialforbiotechnologicalproductsintheyear2000havebeenestimatedatnearlyUS$G5bn(Table1.1).However,itmustalsobeappreciatedthatmanyimportantnew30bio-productswillstillbesynthesizedchemicallyfrommodelsderivedfromexistingbiologicalmolecules,e.g.,newdrugsbasedontheinterferons?.Thustheinterfacebetweenbioscienceandchemistryanditsrelationshiptobiotechnologymustbebroadlyinterpreted.6Summary...Biotechnologycanbeconsideredtobetheapplicationofbiologicalorganismsandprocessestomanufacturingindustries.Biotechnologyencompassesawiderangeofdisciplinesandsubjects.Althoughpresentdayactivitiesarehighlysophisticatedandnovelmanyoftheprocesseshavetheirrootsinthedawnofhistory.Thespecificprocessesarecatalysedbymicroorganisms,plantoranimalcells,or5productsderivedfromthemsuchasenzymes.Theorganismsofbiotechnologycanbeharvestedforbiomass,canbeusedto•performchemicalconversionsandmaybethesourceofactivemolecules,includingenzymesandmonoclonalantibodies.Genemanipulationtechniqueshavebroughtanewdimensiontoappliedgeneticsandhavecreatedthepotentialforcompletelynovelindustrialprocesses,forexamplehuman10interferonproducedbybacterialcells.Significantdevelopmentsarealsooccurringinprocessandcontrolengineeringandfermentationtechnologywhichwillfurtheradvancethedevelopmentofbiologically-basedindustrialactivity.Biotechnologyappearstobeanareaofexpansionandopportunityinvolvingmanysectorsofindustry,includingagriculture,foodandfeedstuffs,pharmaceutical,energyand15waterindustries.ItwillplayamajOrroleintheproductionofnewdrugs,hormones,vaccinesandantibiotics,cheaperandmorereliablesuppliesofenergyand(inthelongerterm)chemicalfeedstuffs,improvedenvironmentalcontrolandwastemanagement.Biotechnologywillbelargelybasedonrenewableandrecyclablematerialsthusbeingbetterfittedtotheneedsofaworldwhereenergywillbecomeincreasinglymore20expensiveandinshortsupply.IChapter2BiochemistryofGrowthandMetabolism1IntroductionThepurposeofamicroorganismistomakeanothermicroorganism1Insomecasesthebiotechno1ogist,whoseekstoexploitthemicroorganism,maywishthistohappenasfrequentlyandasquicklyaspossible.Inothercases,wheretheproductisnottheorganismitself,thebiotechnologistmustmanipulateitinsuchawaythattheprimarygoalofthemicrobeisdiverted.Asthemicroorganismthenstrivestoovercometheserestraintsonitsreproductivecapacity,itproducestheproductwhichthedesires.Thegrowthoftheorganismanditsvariousproductsarethereforeintimatelylinkedbyvirtueofitsmetabolism.Metabolismisamatrixoftwocloselyinterlinkedbutdivergentactivities.Anabolicprocessesareconcernedwiththebuildingupofcellmaterials,notonlythemajorcellconstituents(proteins,nucleicacids,lipids,carbohydrates.etc.)butalsotheirintermediateprecursors—aminoacids,purineandpyrimidines,fattyacicls,varioussugarsandsugarphosphates.Anabolicprocessesdonotoccurspontaneously:theymustbedrivenbyanenergyflowthatformostmicroorganismsisprovidedbyaseriesof‘energy-yielding’catabolicprocesses.ThedegradationofcarbohydratestoCO2andwateristhemostcommonofthesecatabolicprocesses,butafarwiderrangeofreducedcarboncompoundscanbeutilizedbymicroorganismsinthisway.Thecouplingofcatabolicandanabolicprocessesisthebasisofallmicrobialbiochemistry,andcanbediscussedeitherintermsoftheoverallbalanceorintermsofindividualprocesses,ashere.Inpracticewecanveryusefullydistinguishbetweenorganismswhichcarryouttheirmetabolismaerobically,usingoxygenfromtheair,andthosethatareabletodothisanaerobically,thatis,withoutoxygen.Theoverallreactionofreducedcarboncompoundswithoxygen,togivewaterandCO2,isahighlyexothermicprocess;anaerobicorganismcanthereforebalancearelativelysmalleruseofitssubstratesforcatabolismtosustainagivenlevelofanabolism,thatis,ofgrowth.Substratetransformationsforanaerobicorganismsareessentiallydisproportionations,witharelativelylow‘energyyield‘,sothatalargerproportionofthesubstratehastobeusedcatabolicallytosustainagivenlevelofanabolism.Thedifferenceisveryclearlyillustratedinanorganismsuchasyeast,whichisafacultativeanaerobethatis,itcanexisteitheraerobicallyoranaerobically.Transformingsugaratthesamerate,aerobicyeastgivesCO2,water,andarelativelyhighyieldofnewyeast,whereasyeastgrownanaerobicallyhasarelativelyslowgrowthwhichisnowcoupledtoahighconversionofsugarintoethanolandCO2.Chapter3AppliedGeneticsTheinitialstepindevelopingabiotechnologicalprocessisgenerallyasearchforasuit-ableorganism.Suchorganismswillbeexpectedtocreateaproductorservicethatwillgenerateafinancialreturntothatindustry.Inpractice,thegeneticisthastoselectanor-ganismthatproducesthedesiredproduct.Onceasuitableorganismisfound,convention-5albreedingandmutagenesismethodsareusedwherepossibletoinducegeneticchangesthatmayproduceevenmoreofthedesiredproduct.Sanismsistediousandtimedemandingandmostofthemethodsavailabletothegeneticistsupuntilrecentlyhaveinvolvedtrialanderror.However,newgenetictechnologies,toplastfusionandtheuseofrecombinantDNAtechniques,areallowingnewapproachesby10whichusefulgenetictraitscanbeinserteddirectlyintothechosenorganism.Thus,totallynewcapabilitiescanbeengineeredandmicroorganismsinparticularandplantandanimalcellstoalesserextentmaybemadetoproducesubstancesbeyondtheirnaturallyendowedgeneticcapabilities.Increasedproductivityisnottheonlygoaloftheappliedgeneticistwhenmanipulat-15ingapotentialindustrialorganism.,resistancetoviralinfectionandincreasedgeneticstabilitymaybeincorporatedintoorganismsthatlackthem,theformationofharm-fulby-productscanbereducedoreliminatedandobjectionableodours,coloursorslimeproductscanberemoved.Asuccessfulindustrialcultureshàuldultimatelyexhibitmostorallofthefollowing20characteristics:itshouldbeapureculture;begeneticallystable;beeasilypropagated;exhibitrapidgrowthcharacteristics;havegoodrateofproductformation;befreeoftoxicbyproducts;andbeamenabletogeneticmanipulation.Culturesthatareusedindustriallygenerallyhaveariseninthreestages(1)asare--searchculturestudiedtoseekausefulproduct;(2)asadevelopmentculturea25researchculturewhichhasgainedameasureofimportance;and(3)asaproductionculturearesearchculturethatisnowactuallyusedforindustrialproduction.Thefinalculturemaybethesameastheoriginalresearchculturebutmoreoftenitwillhavebeensubjectedtoanarrayoftreatmentstomaximizeproductivity.Thisfinalindustrialorganismwillhavebeengeneticallyprogrammedtoperformametabolicfunc—30tionfarinexcessofthatofthewildtype.Thiswillonlybeachievedbymaximumcon-trolofthegrowthoftheorganismduringproduction.Thedevelopmentoftheindustrialorganismfromawildtypewillhaverequiredchangesinitsgeneticinformationthateliminateundesirablepropertiesorevenintroduceentirelynewones.Findingthedesiredorganism.andimprovingitscapabilitiesisnowafundamental35aspectofmostbiotechnologicalprocesses(Fig.3.1)1SelectionandscreeningInallaspectsofbiotechnologymajoreffortsaredirectedtoscreeningprogrammestogenerateneworganisms,eitherfromsomenaturalsourceorfromestablishedculturesbywayofmutationorbyhybridizationprogrammes,includinggeneticengineering.Theseorganismsmustbescreenedforusefulproductsandgrownuponalargeenoughscaletoproduceandextractthedesiredproductandthentosubjecttheproducttocriticalevaluation.Screeningcanbedefinedastheuseofhighlyselectiveprocedurestoallowthedetectionandisolationofonlythosemicroorganismsormetabolitesofinterestfromlargepopulation.Thefurtheradvancementofanisolatewillinvolveimprovement.andpreser20vationoftheculture.Howevermajorhindrancetothefullexploitationofthiscapacityistheavailabilityofsuitablescreeningprocedureswhichcanidentifythenecessaryprod-uct,especiallyinthepresenceofculturemediumconstituents.Themajorgroupoforganismspresentlyusedinbiotechnologyaremicroorganisms.Thescreeningmethodologiestobedescribedwillconcentratelargelyonthisgroup.Inthesearchfornewmicroorganismsfromtheenvironmentforbiotechnologicalprocessestherearenormallythreetypesofoptionavailable;theseinvolvethechoiceofhabitatforsampling,thephysicalseparationproceduresforseparatingoutthedesiredmicroorganismandthechoiceofmethodtoachieveselectionwhichinmostcasesin-volvedenrichmentcultures(Table3.1)Althoughmanynewproduqermicroorganismsarewild-typesandhavebeenisolatedfromnaturalenvironmenrs,majoreffortsarealsodirectedtogeneratingnewgenomesfromexistinggenomesbylaboratorymanipulation.Organismscanbemodifiedbymutation,recombinadontransformation,transductionandgenecloningeitherbysinglepro-cessesorincombinations(Table3.1).Withnaturalselectionand,moreparticularly,withgeneticmanipulation,allindus—triallyimportantmicroorganismswillhavebeensubjectedtosomeformofscreen-ing.Thedesignofthescreeningprogrammeisofmajorimportancetoachievemaximumrecognitionofnewgenotypes.Screenscanbedividedintotwobasicforms:(1)non-selectiverandomscreenswithalltheisolatesbeingtestedindividuallyforthedesiredqualities;and.rationalscreensinwhichthereissomeaspectofpreselection.253.2Culturemaintenance.Havinggeneratedanovelmicroorganismeitherbynaturalselectionorbygeneticmanipulation,theneworganismmustbestoredorpreservedwithminimumdegenerationofitsgeneticcapabilities.Maintenance,preparationandpropagationoftheorganismmustachievespecificstandardsofreproducibility.ThemaintenanceprocessofanindustrialmicroorganismisanintergralfeatureoftheinfrastructureofbiotechnologyTherearenomethodscommontoallindustries.Specificmaintenancetechniquesforindustrialmicroorganismsareusuallywellkeptindustrialsecrets.Inpracticemostindustrialmicroorganismswillbepreservedbyanyoneofthefollowingprocedures:(1)onagarmediumwithregularsubeulturing;(2)byreducedmetabolism-mineraloilcoverage,refrigeration,orstorageinadeepfreeze;.drying-drysand,silicagel,soilorfilterpaper;freezedrying-widelypractisedbecauseofconvenienceandgreaterstabilitythanpreviousmethods;cryopreservationatultralowtemperatures(70to196‘Ccostlymethodbutsuitableforawiderangeoforganismsandonethatgiveshighsurvivalrates)Culturecollectionsthroughouttheworldareplayinganincreasinglyimportantroleinbiotechnologyinprovidingacomprehensiverangeofpure,verifiedorganismsthatareofpast,presentorpotentialinterest.Importantoperatingstrainsmustberetainedinaviableandproductivecondition.Inparticular,manynewgeneticallymanipulatedorgan-ismsexhibitsomedegreeofinstabilityandpreservationmustaimatachievingminimalstraindrift.Theremainingpartofthischapterwillexamineinsomedetailthevarioustech-niquesthatarenowavailabletotheappliedgeneticistformodifyingthegenomeofin-dustriallyimportantorganisms.3.6RecombinantDNAtechnologyTheanalysisandmanipulationofgeneticmaterialhasbeenrevolutionizedbythedevelopmentofinvitrogenec1oningtechniqueswhichhaveallowedtheisolation,purificationandselectiveamplificationinsuitablebiologicalsystemsofalmostanydiscretesegmentofDNAfromalmostanyorganism.Duetodeletion.ofDNAcontainingrelevantgenes,genecloningenablesthemethodsforanalysisandmanipulationtobetargetedprimarilyonthegeneregionofinterest,thusvastlyincreasingtheefficiencyofthemethodusedandsimplifyingtheidentificationandcharacterizationofthenewmodifiedderivativesIncontrasttoprotoplastfusionwherelargepartsorentiregenomesaremixedandthecharacteristicsofinterestarecontrolledgenerallybyalargenumberofgenes(forexample,antibiotics),recombinantDNAtechnologyisprimarilyconcernedwithsmallnumbersofindividualgenescontrollingknowngeneproducts(forexample,proteins,peptides,etc.).基因操作:theformationofnewcombinationsofheritablematerialbytheisolationofnucleicacidmolecules,producedbywhatevermeansoutsidethecell,intoanyvirus,bacterialplasmid,orothervectorsystemsoastoallowtheirincorporationintoahostorganisminwhichtheydonotnaturallyoccurbutinwhichtheyarecapableofcontinuedpropagation.ThebasicrequirementsforinvitrotransferandexpressionforeignDNAinahostbacterialcellareoutlinedinFigs3.6and3.7andcansummarizedasfollows:(I)TheisolationofcircularplasmidDNAmoleculeswhichmustcontainonesitewheretheintegrationofforeignDNAwillnotdestroyessentialfunctions.(2)ThegenerationofDNAfragmentsthataresuitableforcloningbywayofrestrictionendonucleases.Theinsertmaybeachromosomalfragmentfroman-othermicroorganism(prokaryoteoreukaryote),fromananimalorplant,orfromachemically-synthesizedDNAsequence.AmethodofsplicingtheforeignDNAintothevector.IncorporationofthehybridDNArecombinantsintothehostcell.Expressionofthetransformantswhichhavetherecombinantplasmids.8SummaryAppliedgeneticsisconcernedwithderivingnewandimprovedstrainsoforganismsthatcanbeutilizedforthebenefitofmankind.Inbiotechnologythiswillinvolvetheselectionoforganismsfromnaturalsources,fromculturecollectionsandotherorganizations,orbyfurtherexploitationof‘inhouse’strains.Awidevarietyoftechniquesisavailabletomodify,deleteoraddtothegeneticcomplementoforganisms.Selectionandscreeningactivitiesoccupyamajorpartofbiotechnologicalprogrammes.Screeningistheuseofprocedurestoallowthedetectionandisolationofonlythoseorganismsormetabolitesofinterestamongalargepopulation.Screensmaybenon-selectiverandomscreensinwhichalltheisolatesaretreatedasindividualsfortherequisitequalitiesortheymayberatio-nalscreensinvolvingsomeaspectofpreselection..Producerorganismsmustbepreservedwithminimumdegenerationofgeneticcapabilities.Preservationcanbeonagarmedium,byreducedmetabolism,drying,freezedry-ingorbyultra-lowtemperature.Organismgenomescanbemodifiedbymutagenesisorbyvariousformsofby-bridization.Mutationalprogrammesareprimarilyaimedatstrainimprovementandmu-tagensavailableincludeUVandionizingradiation,thynñnestarvationandawideselectionofchemicalmutagens.Themutationrateinanorganismisgeneticallycontrolledandcanbealteredbymutatororanti-rnutatorgenes.Hybridizationisessentiallyamethodthatfacilitatestherecombinationofgeneticmaterialbetweenorganismsandcanbeexpressedbysexualorparasexualmechanisms.Sexualhybridizationoccursbetweenhaploidnucleiandwillinvolvekaryogamy,nuclear*fiandfinallymeiosis.Recombinationofthegeneticcharacteristicswillarisebecausedfrearrangementandreorganizationofthechromosomes.Parasexualprocessesusevariouscellularmechanismstobringtogethergeneticma-terialfromdifferentgeneticsources.Themainmethodspractisedindustriallyinvolveconjugation,transduction,transformationandmitoticrecombination.Protoplastfusiontechniquesarewidelypractisedwithmanymicrobialcellsaswellaswithplantandanimalcells.Fusionrateshavebeengreatlyincreasedbymeansofthefusogenpolyethylglycol.RecombinantDNAtechnologiesallowtheisolation,purificationandselectiveamplificationinspecifichostcellsofdiscreteDNAfragmentsorgenesfromalmostanyorgan-ismbThebasicrequirementsofthistechnologyarerestrictionendonucleaseenzymeswhichcancleavedouble-strandedDNAatspecificsitesgeneratingDNAfragmentsofdefinedsizes.ThesefragmentscanthenbeinsertedintocarriervehiclessuchasplasmidsorphageandbecovalentlybondedbyDNAligaseenzymes.TransformationisthemainmethodusedfortheinsertionofthesechimericDNAmoleculesintohostcells.ThetypesofhostcellaretypicallybutnotexclusivelyspecificmutantcellsofE.coil,B.subtilisorS.cerevisiae.Transformedcellsareidentifiedbyseveralmeansincludingcomplementa-Honandresistancemarkershybridization,immunologicalmethodsrestrictionen-donucleaseanalysis.Chapter4FermentationTechnology1ThenatureoffermentationTheoriginsoffermentationtechnologywerelargelywiththeuseofmicroorganismsfortheproductionoffoodsandbeveragessuchascheeses,yoghurts,alcoholicbeverages,vinegar,sauerkraut,fermentedpicklesandsausages,soyasauceandtheproductsofmanyotherOrientalfermentations(Table4.1)Thepresent-daylargescaleproductionprocessesoftheseproductsareessentiallyscaledupversionsofformerdomesticarts.Parallelingthisdevelopmentofproductformationwastherecognitionoftherolemicroorganismscouldplayinremovingunpleasantwastesandthishasresultedinmas—siveworld-wideserviceindustriesinvolvedinwaterpurification,effluenttreatmentandwastemanagement.Newdimensionsinfermentationtechnologyhavemadeuseoftheabilityofmicroorganisms(1)tooverproducespecificessentialprimarymetabolitessuchasglycerol,aceticacid,lacticacid,acetone,butylalcohol,butanediol,organicacids,aminoacids,vitamins,polysaccharidesandxanthans;(2)toproduceusefulsecondarymetabolites(groupsofmetabolitesthatdonotseemtopLayanimmediaterecognizableroleinthelifeofthemicroorganismproducingthem)suchaspenicillin,streptomycin,oxytetracyclinecephalosporin,giberellins,alkaloids,actinomycin;and(3)toproduceenzymesasthedesiredindustrialproductsuchastheexocellularenzymesamylases,proteases,pectinasesorintracellularenzymessuchasinvertase,asparaginase,uricoxidase,restrictionendonucleasesandDNAligaseMorerecently,fermentationtechnologyhasbeguntousecellsderivedfromhigherplantsandanimalsunderconditionsknownascellortissueculture.Plantcellcultureisdirectedtowardssecondaryproductformationsuchasalkaloids,perfumesandflavourswhileanimalcellculturehasinitiallybeenmainlyconcernedwiththeformationofproteinmoleculessuchasinterferons,mono-clonalantibodiesandmanyothers.Therearethreemainoperatingtypesofbioreactorsforbiotechnologicalprocessestogetherwithtwoformsofbiocataysts.Bioreactorscanbeoperatedonabatch,semi-continuous(fed-batch)orcontinuousbasis.Reactionscanoccurinstaticoragitatedcultures,inthepresenceorabsenceoxygen,andinaqueousorlowmoistureconditions(solidsubstratefermentations).Thebiologicalcatalystscanbefreeorcanbeattachedtosurfacesbyimmobilizationorbynaturaladherence.Thebiocatalystscanbecellsinagrowingornon-growingstateorisolatedenzymesusedassolubleorimmobilizedcatalysts.Ingeneral,thereactionsoccurringinabioreactorareconductedundermoderateconditionsofpH(nearneutrality)andtemperature(20to65t).Inmostbioreactorstheprocessesoccurinanaqueousphaseandproductstreamswillberelativelydilute.10SummaryGrowthistheincreaseofcellmaterialexpressedintermsofmassorcellnumber.Thedoublingtimeofanorganismpopulationisthetimerequiredforthedoublinginbiomasswhilegenerationtimerelatestotheperiodnecessaryforthedoublingofcellnumbers.Mathematicalequationshavebeendevelopeddescribingtheessentialfeaturesof.microbialgrowthinbioreactors.Inbatchcultivation,thereisacontinuouslychangingnutrientenvironmentwhichisreflectedinthephysiologicalstateoftheculture.Incon-trast,incontinuousculture,withcontrolledadditionandremovalofmedium,asteadystateofpopulationcharacteristicscanbeachieved.Infermentationtechnology,largenumbersofcellsaregrownunderdefinedcon-trolledconditionsfarbiomassorproductformation.Ingeneraltheprocessesarecarriedoutinacontainmentsystemorbioreactor,themainfunctionofwhichistominimizethecostofproducingaproductservice.Processescanbeconsideredasconversioncost-in-tensiveorrecoverycost-intensive.Bioreactorscanoperateonabatch,fçd-batchorcon-tinuousbasis.Thebiocatalysts(microorganisms,plantoranimalcellsorenzymes)canfunctioninafreeformorbeimmobilized.Optimizationofabioreactorprocesswillin-volveminimizingrawmaterialsandenergyuseandmaximizingproductformation.Bioreactordesignwilldependonthenatureofthçprocess.ThecontinuousstirredtanksystemWSTR)isthemostwidelyusedbioreactorandcanbeoperatedforaerobicprocessesaswellasforanaerobicprocesses.MixinginaCSTRbioreactorisachievedbyamechanicallyoperatedcentralshaftequippedwithbladesorimpellers.Incontrast,tow-erbioreactorsdonothavemechanicalagitationandmixingofcontentsisachievedbytherisingairbubbles.Mediumisformulatedtomeetthenutritionaldemandsoftheproducerorganisms,theobjectivesoftheprocessandthescaleoftheoperationCostofmediumisacritiàalfactorindeterminingtheeconomicsofafermentationprocess,andformostindustrialprocessesrelatively•complexmixturesofcheapnaturalproductsareused.Instrumentationofbioreactorsinvolvesmeasuringspecificparametersrecordingthem.andthenusingthisinformationtoimproveandoptimizethepro-cess.Measurementscanbemadeon—lineoroff-line.Thereisalackofefficienton-linesensorsforbioreactorprocesses.Off-linedeterminationsareslowandunsuitableforcomputersystems.Thereisanincreasinginvolvementofcomputercontroloffermentationprocesses.Massandenergytransferprocessesareamajorpartofallfermentationprocess-es.Mixingmechanismsaimtooptimizebothaxialandradialdispersiontoensurecorn-pletedispersionofmediumcomponentsthroughoutthebioreactor,thusencouraginggoodmasstransferratesandhighbiologicalproductivity.Solidsubstratefermentationsareconcernedwiththegrowthormicroorganismsonsolidmaterialsinthe.absenceornearabsenceoffreewatertThesefermentationscanuseindigenousmicroorganisms,puresingleculturesandpuremixedcultures.lnter-particlemasstransferandintra-particlediffusionarethetwomainconditionslimitingsolidsubstratefermentations.Chapter5EnzymeandImmobilizedCellTechnology5ImmobIlizedenzymesThemostimportantdrawbacksintheuseofisolatedenzymesarethattheyarenotsufficientlystableunderoperationalconditionsandaswater-solublefreemolecules,theyaredifficulttoseparatefromsubstrateandproductsandtoreuserepeatedly.5.6PropertiesofimmobilizedenzymesImmobilizationofanenzymecanresultinsignificantchangesinitsproperties.Thesea1-terationscanbeattributedto(1)chemicaland/orconformationalchangesintheenzymestructure,(2)theheterogeneousnatureofcatalysisbyimmobilizedenzymes,and(3)thephysicalandchemicalnatureofthecarrierused.8SummaryEnzymesarehighlyspecificbiocatalysts,functioningathighconversionratesundermildphysiologicalconditionsinaqueoussolutions.Theyoccurnaturallyinsidealllivingor—ganismsbutcanalsooccurinnatureasextracellularenzymessecretedbyorganismsintotheenvironment.Over2000enzymeshavebeenisolatedbutonlyabout20havegainedsignificantcommercialimportanceandmostofthesearehydrolases,forexampleamy-lases,proteases,pectinasesandcellulases.Otherenzymesofimportanceareglucoseiso-meraseandglucoseoxidase.Mostimportantcommercialenzymesareproducedfromalimitednumberofmicroorganismswhichhavealonghistoryofacceptabilityasfoodbeverageproducers.Safetyregulationsimposeseverelimitationstonovelenzymeproducts.Extracellularandintracellularmicrobialenzymesareproducedindustriallybysub-,deeptank,andsolidsubstratefermentationtechn