Although nowell-adjustedmodelcouldbeelaboratedfromthe
the experimentaldatatomathematicallyexplainthemechanism
of theiturinAproduction,usingtheDOEtechniquedidleadtoa
positiveconclusiononthetechnicalfeasibilityoftheproposed
processbysuccessfulidentification ofoperatingconditionsthat
resultedinhighproductivitybystudyingdifferentconditionsof
operatingparameterswithastatisticallycontrolledvariation.
These conditionswerefoundforthecombinationoflevels 1
(0.46 L/min)ofair flow rateand 1 (22.9%w/w)ofricehusk.At
the lowerlevelconditions,lessoxygenisavailabletotheferment
due toboththelowerair flowrateandthereducedporosityofthe
packed bedasaresultofthelowerratioofricehuskcomparedto
soybeanmealandwheatbran.Accordingto Phae andShoda,1991
a loweraerationratefavorsahigherproductionofiturinAand
Khan etal.(2012) also foundthatasmallbutsteadysupplyof
oxygenimprovestheproductionofiturin,since Bacillus is a
facultativeaerobicmicroorganism.Ontheotherhand,thebulking
agentwasimportantoperationallytoreducethepressuredrop
and allowair flow distributionacrossthepackedbed.