Acetic acid fermentation[1]

ABOUT Acetic acid fermentation

1. ACETIC ACID FERMENTATION

2. AceticAcid(Vinegar)
Aceticacidisproducedindustriallybothsyntheticallyand
bybacterialfermentation.About75%ofaceticacidmade
foruseinthechemicalindustryismadebythe
carbonylationofmethanol.Inthisprocess,methanoland
carbonmonoxidereacttoproduceaceticacidaccordingto
theequation:CH
3OH+CO→CH
3COOH
Previously,thisacidwasproducedbyoxidationof
acetaldehyde.Thisremainsthesecond-most-important
manufacturingmethod,2CH
3CHO+O
2→2CH
3COOH
Thefermentationaccountsforonlyabout10%ofworld
production,butitremainsimportantfortheproductionof
vinegar,asmanyfoodpuritylawsstipulatethatvinegar
usedinfoodsmustbeofbiologicalorigin.

3. ProducedbyGreeksandRomansaslongas10000yrs.
Usedasrefreshingdrink.
Vinegaristypically4-18%aceticacidbymass.
Vinegarisuseddirectlyasacondiment,andinthe
picklingofvegetablesandotherfoods.Tablevinegartends
tobemorediluted(4%to8%aceticacid)
Producedinflatopenvatsthroughsurfacegrowthof
bacteria
Comparetoslowsurfacemethod19
th
centuryTrickling
generatorprocessandsubmergedfermentationprocess(H
FringscompanyofGermany)weredeveloped.

4. StrainsUsedinfermentation:
Gluconobacteroxydans:convertethanolto
aceticacid
Acetobacter aceti, Acetobacter
pasteurianus,Acetobacterperoxidans:
Convertethanoltoaceticacidandfurther
intoCO2andH2O
Theyaregramnegative,rodshape,acid
tolerantbacteria.
Productionstrainslosetheirhighyielding
characteristic,ifgrownonagar,so
transportedtonewvinegarplantinsmall
fermentersornewbatchisinoculatedwith

5. BiosynthesisofAceticAcidProduction
Oxidationofethanoltoacetaldehydeandthentoaceticacid
Reductionof2NADorNADPandproductionof6ATP
Enzymesinvolvedarealcoholdehydrogenaseand
acetaldehydedehydrogenase
1moleethanolconvertedto1moleaceticacid
Strictaerobicprocess.
Inpresenceof5%aceticacidandethanolifaeration
interruptedfor2min,kills34%population
Inpresenceof12%aceticacidandethanolifaeration
interruptedfor10to20seconlycankills34%population
Bothaceticacidandethanolrequiredforoptimalgrowthof
Acetobacter
0.2%ethanolisminimumrequirementandhighestshould
notexceedthan5%
Highyieldingstrainsproduce13to14%aceticacid

7. Production
•Givensufficientoxygen,thesebacteriacanproducevinegar
fromavarietyofalcoholicfoodstuffs.Commonlyusedfeeds
includeapplecider,wine,andfermentedgrain,malt,rice,or
potatomashesanddonotrequireadditionofanyother
nutritionalcomponents.Butgrainalcoholotechnicalalcohol
needstobeaddedwiththesame.
C
2
H
5
OH+O
2
→CH
3
COOH+H
2
O
Insubmergedfermentationsnutrientsmustbe5timeshigher
thanotherprocesses.
•AdilutealcoholsolutioninoculatedwithAcetobacterand
keptinawarm,airyplacewillbecomevinegaroverthe
courseofafewmonths.Industrialvinegar-makingmethods
acceleratethisprocessbyimprovingthesupplyofoxygento
thebacteria.

8. The‘slow’Process
Vinegarusedtobeproducedbykeepingwineinopen,
partiallyfilledcontainers.Additionofsomevinegarspeeded
upthereaction.Thisconceptwasalreadyincorporatedinto
theprocessknownasthe‘Orleansprocess’,the‘French
method’orthe‘slowprocess’.
Inthisprocess,woodenbarrelsarepartiallyfilledwithgood
qualityvinegarwhichactsasasourceofinoculumandwine
isaddedatweeklyintervalsforfourweeks.
Afterfiveweeks,aportionofvinegariswithdrawnandthe
sameamountofwineisintroducedandtheprocessis
repeatedresultinginaveryslowcontinuousprocess.

9. The ‘slow’ Process

10. The‘quick’Process/SurfaceProcess
Theideathatvinegarcanbeproducedrapidlybytrickling
winethroughpackedpumice(greystone)wasdiscovered.
Itisthebasisformodernmethodsofmanufactureof
vinegarusingagenerator.
Thegeneratorconsistsofawoodenormetal-coatedtank
upto60m
3
packedwithbeechwoodshavingsonwhich
cellsareallowedtogrow.
Thefeedtricklesfromthetopthroughthewoodshavings.A
largevolumeofairisspargedintothetankthrough
perforationsinthebottom.
Employing12%(v/v)alcohol,88%to90%conversioninto
aceticacidisattainedin5daysbythisprocess.Restofthe
ethanolusedinprimarymetabolism.Ethanolpumpedback
tothetopuntillcompleteconversion.

11. Diagram of Trickling Generator for Vinegar

12. TheSubmergedCultureProcess
Lowalcoholicwinesandmasheswereinitiallyusedforlow
yieldingprocesses,butnowadayshighyieldingstrains
needtobeprovidedwithregulatedaerationandfermenter
sizeupto50m
3
.
fermentersaremadeupofSS,stirredfrombottomand
aeratedfromtopthroughsuctionrotor.
Heatexchangerscontrolstemperature.
Householdvinegar(13%)isproducedinasemi
continuous,fullyautomaticprocess,beginningwitha
startingmaterialthatcontains7to10gaceticacid/100ml
and5%ethanol.
Theethanolconc.Ismeasuredcontinuouslyduringthe
processandwhentheconc.sinksto0.05to0.3%(35hr),
50to60%ofthesolutionisremovedandreplacedwitha
newmashcontaining0to2gaceticacid/100mland10to
15%ethanol.

14. Theadvantagesofsubmergedcultivationoverthe
tricklinggeneratorare:
1.Thesubmergedcultivationpermits30timesfaster
oxidationofalcohol
2.Asmallerreactorvolumeisneeded(about16%ofthe
tricklinggenerator)toproduceanequivalentamountof
vinegar
3.Greaterefficiencyisachieved;yieldsare5-8%higherand
morethan90%ofthetheoreticalyieldisobtained
4.Theprocesscanbehighlyautomated
5.Lowercapitalinvestmentperproductionamount
6.Lessplantarearequired
7.Lowpersonnelcostduetoautomaticcotrol

15. Anaerobic Fermentation
The genus Clostridiumor Acetobacteriumcan convert sugars
to acetic acid directly, without using ethanol as an intermediate.
C
6
H
12
O
6
→ 3 CH
3
COOH
These acetogenic bacteriaproduce acetic acid from one-
carbon compounds, including methanol, carbon monoxide, or a
mixture of carbon dioxideand hydrogen:
2 CO
2
+ 4 H
2
→ CH
3
COOH + 2 H
2
O
Clostridiumbacteria are less acid-tolerantthan Acetobacter.
But at present, it remains more cost-effectiveto produce
vinegar using Acetobacterthan to produce it using Clostridium.
As a result, although acetogenic bacteria have been known
since 1940, their industrial use remains confined to a few niche
applications.

16. Recovery
The physical methods of separation of acetic acid from
water include :
i. Fractional distillation
ii. Azeotropic dehydration distillation
iii. Solvent extraction
iv. Extractive distillation
v. Caron adsorption
Acetic acid produced here is turbid one so clarified using
plate filtes and filterate is treated with K
4Fe(CN)
6 to
decolorize the final product if desirable