食品发酵工艺第六章-有机酸

Chapter6FermentedFoodProductsProductsfromMicroorganisms

2FoodandfoodrelatedproductsWholecellsproductsCheeseandyogurtFermentedfruitsandvegetablesOrganicacidsAlcoholicbeveragesFlavoringagents:aminoacidsandnucleotides3Non-foodproductsEnzymeVitaminsAntibioticsBiotechdrugs

Lacticacid-ANaturalProductItismadebyfermentationofdifferentsugars(glucose,sucrose,orlactose)bymeansofthegeneralactobacillus,streptococcus

andpediococcus.OrganicAcid1.LacticacidfermentationLactobacillusbulgaricusStreptococcusthermophilusLactobacteriaceae•Grampositive,rodsorcocci•Obligateanaerobes(norespiratorychain)•Catalasenegative(oftenaerotolerant)Homolacticfermentation

(homofermentation)

•GlucosedegradedviaEMPpathway,withlacticacidastheonlyendproductglucose+2ADP+2Pi➞2lacticacid+2ATP•Importantindairyindustry(yogurt,cheese)homofermentationHeterolacticfermentation

(heterofermentation)•Glucosedegradedviaphosphoketolasepathway(PK)•Inadditiontolacticacid,alsoethanolandCO2producedglucose+ADP+Pi➞lacticacid+ethanol+CO2+ATPphosphoketolasepathway(PK)

G→→

xylulose5-phosphate

acetylphosphate+glyceraldehyde3-phosphatephosphoketolaseethanolpyruvatelacticacid

C6H12O6＋ADP+Pi→CH3CHOHCOOH＋CH3CH2OH＋CO2+ATPTypesPath.ProductsEnergyInversionrateHomoEMP2

Lacticacid2ATPhighHeteroPK1Lacticacid1alcohol1CO21ATPlowHomofermentation

vs.heterofermentationHowtorecognizeheterofermentationstraininlab?（1）ProductionofC02（2）Gramstaining

(√)(×)LacticacidinFoodLacticacidisnaturallypresentinmanyfoodstuffs,suchascheese,yogurt,soysauce,fermentedmeatandpickledvegetables,etc.Itservesaseitheraflavoringagent,pHregulatororapreservative.Lacticacidproductionprocess19WhatisYogurtAsemi-solidcaseingelformedbytheactionofspecificlacticacidbacteriaonmilkFermentedmilkMicrobesusedinYoghurtInvolvedLactobacillusbulgaricusand/oracidophilusStreptococcusthermophilusTheyworkbettertogetherthantheydoseparately

because….AcidproductionrateismuchhigherFormationoftypicalyogurtflavourandtextureIngredientsandFunctionLactoseispartialconvertedtolacticacid,whichmakesdigestioneasierforlactose-intolerantpeople.Containinghigheraminoacidthanmilk.Lacticacidcausesthemilkproteins(casein)tocoagulateintoasemisolidcurdandalsorestrictsspoilagebacteria.Freshlypreparedyogurtcontains10,000,000,000(109)bactriapergram.

MainFamiliesofLacticBacteriaFig1:Lactobacilli(SmallIntestine)Fig2:Bifidobacteria(LargeIntestine)SmallIntestineLargeIntestineYogurtProductionMilkSelectionCoolingto42-45℃DryMatterStandardizationHomogenizationHeatTreatmentInoculationDeaerationSterilizationDenaturingproteinReducingthefatcontentincreasingthetotalsolidsTomixallingredientsthoroughlyandimproveyogurtconsistencyYogurtvariations1.Setyogurt

：pouringtheinoculatedmilkintopotsandfermentingit,normallyconsumedbyuseofaspoonorsoldintocustomers’containers.2.Stirredyogurt:

fermentedinbulk,stirredandthendispensedintopots.TwotypesofyogurtInoculationFlavoringFillRetailContainerFermentFermentCool/StoreBreakStir/CoolFillSetyogurt

Stirredyogurt

ConeBottomProcessorCHEESECHEESEBasicCheese-makingSteps1.Collect/delivermilk2.Pasteurizemilk3.Addstarterculture4.AddrennetandCaCl25.CutthecurdandHeat6.Separatecurdfromwhey7.Saltthecurd(drysalt)8.Packageandripencheese

Rennin,anacidproteasefromcalves’stomach,thatpartiallyhydrolysesthemilkprotein(casein)andleadstocoagulation

inthepresenceofCa2+toform“curds.”Theliquidportionofthemilkatthistimeiscalled“whey.”Pasteurization

SeparatethecurdfromthewheySaltingPackage,CoatCheeseand

Ripening

Q:What’sthedifferencebetweenyogurtmakingandcheesemaking?

Citricacidisaweakorganicacidfoundincitrusfruits(lemon).Itisagood,naturalpreservativeandisalsousedtoaddanacidic(sour)tastetofoodsandsoftdrinks.CitricacidAspergillusnigerWell-knownproductionorganismofcitricacidandotherorganicacids.Alsoawell-knownover-producerofenzymes,inparticularstarch-degradingenzymesandplantcell-walldegradingenzymes.PhosphofructokinaseQ:Citrateisoneofthebest-knowninhibitorsofglycolysis,whyA.nigercouldoverproducecitratebyanactiveglycolyticpathway?

1.Biochemistryofcitricacidformation

EMP

acetyl-CoA

Gulcose

pyruvate

HMP

oxaloaceticacid

decarboxylationCO2

fixationcondensationcitricacid

2.

MetabolicregulationofcitricacidproductionbyA.niger（1）Phosphofructokinase(PFK)

inhibitedbyahighinternalconcentrationofATP（2）α-keto-glutaratedehydrogenaseinhibitedbyglucoseandammonium(NH4+)

Threeexcessandthreelimiting

ExcessiveconcentrationsGlucose

Ammonium(NH4+)

Dissolvedoxygen-AnalternativerespiratorypathwaywithouttheformationofATP-SuddeninterruptionsinaerationcauseanirreversibleimpairmentofcitricacidproductionPhosphatelimitationMn2+

deficiency

ResultsinahighintracellularammoniumconcentrationLowpHCitratedegradingenzyme(e.g.aconitaseorisocitratedehydrogenases)withintheTCAcyclearepHsensitiveSuboptimalconcentrations幻灯片49Fermentationconditions

SolidcultureorliquidcultureRawmaterials:sweetpotatostarch

With

ChinesecharacteristicsPurificationofCitricAcid

1.Brothpre-treatment：heat2.Filtration3.Neutralize

CaCO3+CitricAcid→CO2+CalciumCitrate4.Acidifying

CalciumCitrate＋H2SO4

→CitricAcid＋CaSO45.ConcentrationReactcitricacid