Study On Propionic Acid Production By Propionibacterium Acidipropionici Using Low-cost Biomass In A Fibrous Bed Bioreactor

Propionic acid is one of the short-chain fatty acids with many applications in foodstaff,chemical and pharmaceutical industries. Currently, propionic acid is mainly produced viapetrochemical process. However, concerns on the sustainability of the curde oil supply havegenerated interest in investigating microbial fermentation to produce propionic acid. In thepresent study, attempts to improve propionic acid fermentation in terms of final productconcentration were conducted by Propionibacterium acidipropionici immobilized in a fibrousbed bioreactor with economic biomass as the substrate.The basic growth character （temperature, initial pH, speed of incubator, inoculumconcentration, inoculum volume） of Propionibacterium acidipropinici, the utilizable carbonand nitrogen source and the inhibition caused by the end product were studied. The resultshowed that it grew best at32℃, and initial pH6.5, with incubator150r/min and theinoculums volume5%（24h cultured broth ml/fresh medium ml）. The utilizable carbonsources were extensive but the only organic nitrogen sources was good for its growth; noevident substrate inhibition phenomenon was observed when cultured in different initialglucose concentrations; it couldn’t grow well at the propionate concentration of2g/L.Jerusalem artichoke powder hydrolysis with dilute H2SO4produced58.7%（w/w）sugar. Comparison of the kinetics of immobilized-cell fermentation using the FBB with thoseof fed-batch free-cell fermentation showed that immobilized cell fermentation gave a muchhigher propionic acid concentration （68.5g/L vs.40.6g/L）, propionic acid yield （0.434g/gvs.0.379g/g） and propionic acid productivity （1.55g/L/h vs.0.190g/L/h） at pH6.5.Furthermore, repeated-batch fermentation, carried out to evaluate the stability of the FBBsystem, showed that long-term operation with a high average propionic acid yield of0.483g/g,high productivity of3.69g/L/h and propionic acid concentration of26.2g/L were achieved inall eight repeated batches during fermentation for more than200h.Batch fermentations at various glucose concentration and pump flow rates wereinvestigated in the FBB system. No obvious glucose inhibition was observed. When theoptimal pump flow rate was80ml/min and initial concentration of glucose was60g/L,propionic acid yield and propionic productivity was up to0.511g/g and4.31g/L/h respectively. In the FBB, the fed-batch fermentation using cassava starch hydrolysate as the sole carbonsource gave a maximum propionic acid production of50.1g/L with a yield of0.433g/gcassava starch. To improve propionic acid productivity, two fibrous bed bioreactors wereapplied.41.5g/L of propionic acid was obtained in batch fermentation, with propionic acidyield0.466g/g cassava starch and propionic acid productivity2.68g/L/h.Through adaptation in the free-cell repeated fed-batch fermentation, a high propionicacid concentration of60.46g/L was obtained with glucose as the substrate and throughadaptation in the FBB repeated fed-batch fermentation, a high propionic acid concentration of80.86g/L was obtained with glucose as the substrate. With the two adapted strain as theinoculum, the kinetics of free-cell and immobilized-cell propionic acid fermentation wasinvestigated.